©RgANIC 6ke»ISt^ W. H. Penkin EStanleyKipping OIIGANIC CH E MISTRY PART I. BY AY H. BIRKIN, Jun., Ph.D., F.R.S. PROFESSOR OF ORGANIC CHEMISTRY IN THE OWENS COLLEGE AND F. STANLEY KIPPING, Ph.D., D.Sc. (Lond.) LECTURER AND ASSISTANT IN THE CHEMICAL RESEARCH LABORATORY, CENTRAL TECHNICAL COLLEGE, CITY AND GUILDS OF LONDON INSTITUTE ; P II I L A 1) E L PIIIA J. B. L T P P I N C O T T COMP A N Y 1 8 9 5 PREFACE. Our original intention was to write a small text-book on Organic Chemistry, based on the syllabus drawn up by the Science and Art Department, in the hope that it would be useful to students attending the elementary or advanced classes in the subject, and not without value to teachers as a handy book of reference. As, however, it soon became apparent that, by making comparatively few additions, the subject- matter might be made to include the facts usually dealt with in a course of about sixty lectures, the scope of the work was enlarged to this extent, so as at the same time to make it more useful to general students as an introduction to Organic Chemistry. Part I., which deals with the fatty compounds, contains, in the first place, a general account of the methods most fre- quently employed in the separation, purification, and analysis of organic compounds, and in the determination of molecular weight. The preparation and properties of typical com- pounds are then described, attention being directed to those changes which come under the heading of general reactions rather than to isolated facts regarding particular substances. Questions of constitution are also discussed at some length, and in the case of most of the typical compounds, the facts on which the given constitutional formula is based are specific- ally mentioned. This course was adopted, not only in order 4 PREFACE. to avoid the introduction of a long chapter on structure at an earlier stage, but also because, in our opinion, a constant use of constitutional formulae, accompanied by a clear con- ception of their meaning, is one of the greatest helps, even to a beginner, in committing the facts to memory. A considerable proportion of the text, dealing as a rule either with matters of less importance or of a more advanced nature, is printed in small type, and should be left out of consideration until the rest of the subject-matter has been mastered, or, at any rate, studied. The consideration of the ' summary and extension ' at the conclusion of some of the more important chapters, should also be postponed until the student has acquired some knowledge of the subject, as the method here adopted is not well suited to the requirements of a beginner. One of the principal objects throughout has been to treat the subject from a practical point of view (as far as this could be done in a text-book on theoretical chemistry), because, un- less a thorough course of practical work accompanies the theoretical, no really satisfactory progress can be made. The student should himself perform many of the simple exercises involved in the purification and analysis of organic compounds, and should prepare typical substances in order to become prac- tically acquainted with their properties. Such general opera- tions as oxidation, reduction, hydrolysis, nitration, sulphon- ation, &c., and the more important general reactions for the identification of the several classes of compounds, should also be included in the practical course. In many respects we have made free use of the excellent text-books of V. Meyer and Jacobson and von Richter, of Beilstein's Handbuch, and of Ost's Lehrbuch der technischen Chemie. We are also much indebted to Dr A. Harden for help in revising the proof-sheets and in preparing the index. CONTENTS. Page Chapter I.-Composition, purification, and analysis of ORGANIC COMPOUNDS 9 Origin and Present Meaning of the Tenn ' Organic ' 9 Composition of Organic Compounds 11 General Principles of Organic Analysis 11 Separation and Purification of Organic Compounds 12 Tests of Purity 19 Qualitative Elementary Analysis 21 Quantitative Elementary Analysis 25 Estimation of Carbon and Hydrogen 25 Quantitative Determination of Nitrogen 29 Quantitative Determination of Chlorine, Bromine, and Iodine 33 Chapter II.-Deduction of a formula from the results of analysis and determination of molecular WEIGHT 36 Chapter III.-Constitution or structure of organic compounds 51 Chapter IV.-The paraffins, or hydrocarbons of the METHANE SERIES 55 Methane, or Marsh-gas 55 Ethane 59 Propane 61 Butanes 62 Pentanes 65 Isomerism 65 Homologous Series 67 General Formulm 68 Chapter V.-Unsaturated hydrocarbons-the olefines, OR HYDROCARBONS OF THE ETHYLENE SERIES 72 Ethylene 72 Propylene 78 Hydrocarbons of the Acetylene Series-Acetylene 81 Allylene-Allene 86 Chapter VL-The monohydric alcohols 88 6 Contents. Page Methyl Alcohol 88 Ethyl Alcohol 92 Production of Wines and Beers; Alcoholic Fermentation.... 97 Homologues of Ethyl Alcohol 102 Propyl Alcohol-Isopropyl Alcohol.. 104 Butyl Alcohols-Amyl Alcohols 105 Chapter VII.-The ethers 109 Methyl Ether 109 Ethyl Ether 110 Radicles 114 Chapter VIII.-Aldehydes and ketones 116 Formaldehyde 117 Acetaldehyde 120 Polymerisation of Acetaldehyde 124 Acetal- Chloral 125 Homologues of Acetaldehyde 127 Heptaldehyde, or (Enanthol 127 Ketones 127 Acetone 128 Homologues of Acetone 132 Hydroximes and Hydrazones 132 Chapter IX.-The fatty acids 142 Formic Acid 142 Acetic Acid 147 Homologues of Acetic Acid 154 Propionic Acid 155 Normal Butyric Acid 156 Isobutyric Acid-Isovaleric Acid 157 Active Valeric Acid 157 Normal Heptylic Acid 158 Palmitic Acid-Stearic Acid 158 Derivatives of the Fatty Acids-Acid Chlorides 158 Anhydrides 160 Acetic Anhydride 161 Amides 161 Acetamide 162 Substitution Products of Acetic Acid 162 Chlor-, Dichlor-, and Trichlor acetic Acid 163 Fats, Oils, Soap, Stearin, and Butter 166 Composition of Fats and Oils 166 Soaps 168 Stearin and Glycerol 169 Butter and Margarine 170 CONTENTS. 7 Page Chapter X.-Ethereal salts 171 Halogen Ethereal Salts and Halogen Derivatives of the Paraffins-Methyl Chloride 171 Methylene Dichloride-Chloroform 172 Carbon Tetrachloride 174 Iodoform-Ethyl Chloride 175 Ethyl Bromide 176 Ethyl Iodide 177 Ethereal Salts of Nitric Acid-Ethyl Nitrate 179 Ethereal Salts of Nitrous Acid-Ethyl Nitrite 180 Nitro-paraffins 181 Ethereal Salts of Sulphuric Acid „ 181 Ethyl Hydrogen Sulphate 182 Mercaptans and Sulphides 183 Ethyl Mercaptan-Ethyl Sulphide 184 Ethereal Salts of Organic Acids-Ethyl Acetate 185 Chapter XL-Synthesis of ketones and fatty acids WITH THE AID OF ETHYL ACETOACETATE AND ETHYL MALONATE 189 Ethyl Acetoacetate 189 Ketonic Acids 195 Ethyl Malonate 196 Chapter XII.-Alkyl compounds of nitrogen, phos- phorus, ARSENIC, SILICON, ZINC, MERCURY, AND OTHER ELEMENTS 199 Ethylamine 200 Diethylamine 203 Triethylamine . 204 Tetrethylammonium hydroxide 205 Phosphines 208 Arsines 210 Triethylarsine-Tetrethylarsonium iodide 211 Dimethylarsine oxide 212 Organic Silicon Compounds-Silicon Tetramethyl 213 Silicon Tetrethyl 214 Organo-metallic Compounds 214 Zinc Ethyl 215 Zinc Methyl 216 Mercuric Ethyl 217 Chapter XIII.-The glycols and their oxidation pro ducts 218 Ethylene Glycol 219 Oxidation Products of the Glycols-Glyoxal 223 8 CONTENTS. Paoe Hydroxy carboxy lie Acids- GlycoIlic Acid 223 Lactic Acid 225 Hydracry lie Acid 227 Dicarboxylic Acids-Oxalic Acid 229 Oxamide 233 Malonic Acid-Succinic Acid 234 Succinic Anhydride 236 Hydroxydicarboxylic Acids-Malic Acid 239 Tartaric Acid 241 Hydroxy tricarboxylic Acids-Citric Acid 245 Chapter XIV.-Trihydric and polyhydric alcohols 248 Glycerol 248 Cl i lorohyd rins 251 Nitro-glycerin 252 Unsaturated Compounds related to Glycerol 254 Allyl Alcohol 254 Allyl Iodide-Allyl Bromide 255 Allyl Sulphide 256 Acrolein 256 Acrylic Acid 257 Polyhydric Alcohols-Erythritol-Mannitol 258 Chapter XV.-The carbohydrates 259 The Sugars-Cane-sugar 260 Dextrose 262 Levulose 265 Action of Phenylhydrazine on Dextrose and Levulose 267 Maltose-Milk-sugar 269 Galactose 270 Starch 271 Gluten-Dextrin 272 Cellulose 273 Chapter XVI.-Cyanogen compounds 276 Cyanogen 277 Hydrocyanic Acid 278 Potassium Ferrocyanide 283 Potassium Ferricyanide 284 Nitriles 284 Cyanic Acid 286 Cyanuric Acid-Thiocyanic Acid 287 Allyl Isothiocyanate-Urea 289 Uric Acid 291 Glycine 292 Index 294 ORGANIC CHEMISTRY. PART I. CHAPTER I. COMPOSITION, PURIFICATION, AND ANALYSIS OF ORGANIC COMPOUNDS. Origin and Present Meaning of the Term 'Organic.'- Although spirits of wine, sugar, fats, and other substances obtained directly or indirectly from animals or plants have always claimed a large share of attention from chemists, their investigation met with only slight success until towards the close of the last century, when the composition of many of these natural products was established by the French chemist Lavoisier (1743-94). Lavoisier it was who first showed that vegetable substances are generally composed of carbon, hydrogen, and oxygen, whilst animal substances, although consisting for the most part of the same three elements, frequently contain nitrogen, and sometimes phosphorus and sulphur. The peculiar composition of these natural products, and the fact that they behaved differently from mineral compounds, led to the belief that all animal and vegetable substances wrere produced under the influence of some peculiar vital force, and that their formation was regulated by laws quite different from those which governed the formation of mineral 10 COMPOSITION, PURIFICATION, AND ANALYSIS substances; consequently, it was thought impossible to prepare any animal or vegetable product artificially or synthetically in the laboratory. For these reasons compounds obtained from animals and plants-that is to say, directly or indirectly from living onjanisms-were called organic, and were classed separately from inorganic or mineral substances. This distinction between organic and inorganic compounds appears to have been generally accepted until 1828, when Wohler succeeded in obtaining urea, an excretion of certain animal organisms, from ammonium cyanate, a substance which was at the time considered to be inorganic or mineral, because it could be produced in the laboratory; this synthesis showed conclusively that the influence of a living organism was not necessary for the production of the ' organic ' substance urea. After this important discovery it was soon found that many other so-called ' organic ' substances could be prepared in the laboratory from 'inorganic' materials without the help of a vital force, and ultimately it came to be generally acknowledged that the formation of 1 organic ' and ' inorganic ' substances is governed by precisely the same laws. The supposed difference between the two classes of com- pounds having been shown to be purely an imaginary one, the terms ' organic ' and ' inorganic ' lost their original meaning; they are, nevertheless, still made use of in the classification of chemical compounds. The atoms of carbon are distinguished from those of all other elements by their extraordinary capability of combining with one another and with hydrogen to form compounds, such as CH4, C6H6, C10H8, &c., the molecules of which are often composed of a very large number of atoms; the atoms of other elements, however, rarely combine with hydrogen to form more than one or two compounds, and have only to a very limited extent the power of combining with one another. In consequence of the pro- perties just mentioned, carbon forms a larger number of OF ORGANIC COMPOUNDS. 11 compounds than any other element, and, speaking generally, these compounds are related to one another, but widely different to those of other elements. For these reasons it is convenient to consider the carbon compounds separately, and to distinguish them by the term organic, which recalls the fact that carbon is a most important constituent of all animal and vegetable substances; organic chemistry, therefore, is the chemistry of the carbon compounds. Some of the simpler compounds of carbon, such as carbon dioxide, carbon monoxide, carbon bisulphide, &c., which are of general importance, are always described in works on inorganic chemistry for the sake of convenience ; they are, nevertheless, organic compounds, because they contain carbon. Composition of Organic Compounds.-In spite of their great number, organic compounds are almost always com- paratively simple in composition, being made up, as a rule, of not more than four or five elements. Organic substances, such as sugar, starch, and tartaric acid, which occur in the vegetable kingdom, almost invariably consist of carbon, hydrogen, and oxygen, although a few- morphine and strychnine, for example-contain nitrogen as well. Those occurring in the animal kingdom generally contain nitrogen as well as carbon, hydrogen, and oxygen : urea and uric acid, for instance, are composed of these four elements ; a few animal substances also contain sulphur and phosphorus. Artificially prepared organic compounds may contain any element. Some-benzene, for example-are composed of carbon and hydrogen only, but the majority contain oxygen as well; nitrogen and the halogens are very often present in carbon compounds produced in the laboratory; so also are the metals calcium, sodium, silver, &c., which form salts with organic, just as they do with inorganic acids. General Principles of Organic Analysis.-The qualitative analysis of organic compounds is carried out by methods quite 12 COMPOSITION, PURIFICATION, ANO ANALYSIS different from those employed in the case of inorganic sub- stances. Most organic compounds are insoluble in water and in acids, and could not be examined by the ordinary wet methods of analysis : even those which are soluble do not show, except in rare cases, a sufficiently characteristic behav- iour to enable them to be identified by their reactions. There is, again, this wide difference between inorganic and organic analysis, that, whereas a mixture of inorganic compounds may be directly submitted first to qualitative and then to quanti- tative examination, in the case of a mixture of carbon com- pounds it is usually necessary to separate and purify each constituent before its composition can be determined. * For these reasons organic analysis usually consists of several processes : Firstly, the substance is submitted to a preliminary qualitative examination, the object of which is to find out how many distinct compounds are present, and to separate and purify each of them. The nature of each constituent is then determined ; this may sometimes be done by proving it to be identical with some known compound by methods to be described later. If this be impossible, a further qualitative examination is made to ascertain what elements the substance contains; the pure compound is then submitted to quantitative or elementary analysis, from the results of which its percentage composition is obtained. Separation and Purification of Organic Compounds.-The separation of a pure organic compound from a mixture of any kind is often a matter of considerable difficulty, and it is usually necessary to employ different processes for different mixtures. Although, therefore, it is impossible to give a method which would be applicable in every case, the more important steps in the general examination and purification of organic substances may be briefly indicated. In the case of any substance of unknown composition, a small portion is ignited on platinum foil, in order to ascertain * Generally speaking, portions of the text which are printed in smaller type are intended only for those who have already acquired an elementary knowledge of organic chemistry. OF ORGANIC COMPOUNDS. 13 whether it contains inorganic matter; if it leaves a non- combustible residue, it is probably a salt of some organic acid, or it contains inorganic compounds as impurity. The separation of an organic from an inorganic substance can usually be accomplished by shaking or boiling the substance with some solvent, such as alcohol, ether, benzene, chloroform, petroleum, &c. Most organic compounds are soluble in one or other of these liquids, whereas the majority of inorganic compounds are insoluble, or nearly so. Water or dilute acids may often be employed for the same purpose, since many inorganic substances are soluble, many organic substances insoluble, in these liquids. The separation of two or more organic substances may sometimes be effected in a similar manner. In the case of a mixture of cane-sugar, tartaric acid, and benzoic acid, for example, the last-named compound only can be dissolved out with ether, the tartaric acid being- then separated from the sugar by treating with alcohol, in which it is much more readily soluble than sugar. Solid or liquid organic substances in aqueous solution, or suspended in water in a fine state of division, may often be isolated by agitating the solution or mixture with some solvent, such as ether, benzene, chloroform, &c., which does not mix with water. For this purpose a separating funnel (fig. 1) is employed, and after being shaken vigorously, the mixture is allowed to stand until it forms two layers ; the two solutions are now separ- ated by turning the stopcock (a, a') and running off that which is underneath, the extraction being repeated, if neces- Fig. 1. 14 COMPOSITION, PURIFICATION, AND ANALYSIS sary, with a fresh quantity of the organic solvent. The com- bined extracts are then dried (p. 17), and the solvent distilled or slowly evaporated. The process of crystallisation is one of the simplest and best methods of separating and purifying organic substances, but before it can be successfully employed, a suitable solvent must be found. About a centigram of the substance is boiled for a short time in a test tube with 1-2 c.c. of some solvent (such as water, ether, alcohol, carbon bisulphide, benzene, light petroleum, &c.), and, if necessary, the hot liquid is filtered from any insoluble matter; if, on cooling, the substance be deposited in crystals, the rest of the material is treated in the same way, the insoluble portion, if any, being examined separately. Should no separation of crystals take place on cooling, the solution is concentrated by evapor- ation, and then allowed to cool; if, again, crystals be not deposited, some other solvent is tried. The crystals ulti- mately obtained are collected on a filter, washed with a small quantity of the solvent, and further purified by recrystallisa- tion. If only one constituent of a mixture be dissolved by the liquid employed, this particular substance is obtained in a state of purity without difficulty, because the others are easily got rid of by filtration; when, however, two or more of the constituents are soluble, their further separation can usually be effected by fractional crystallisation. In this process, advantage is taken of the difference in solubility of the substances. On slowly cooling the hot solution, the more sparingly soluble substance is first deposited, and can be separated by filtration from the more readily soluble compound, which does not crystallise until the solution is further cooled or concentrated; the two crops of crystals are then separately redissolved, and the process repeated until each substance is obtained in a pure state, as shown by a determination of its melting-point (p. 20). Another method extensively used in the separation and OF ORGANIC COMPOUNDS. 15 purification of organic substances, both solid and liquid, is distillation in a current of steam. The substance and a little water are placed in a flask (A, fig. 2) which is connected with a condenser, and heated on a water- or sand-bath ; a rapid current of steam, generated in a separate vessel (I>), is then passed through the mixture. The distillate, which contains Fig. 2. the volatile organic substance in solution, or in suspension, is afterwards extracted with ether, or filtered, or treated in some other way according to circumstances. In this simple manner it is often possible to isolate a compound when all other methods fail; it is, however, only applicable in the case of the comparatively few organic substances which are volatile in steam. Many compounds which cannot be distilled in the ordinary way because they undergo decomposition, are volatile in steam, and pass over unchanged, even when their boiling- points are much higher than that of water. Organic substances which boil without decomposition can be purified by distillation. The substance is placed in a 16 COMPOSITION, PURIFICATION, AND ANALYSIS distilling flask (A, fig. 3), which is connected with a con- denser, the neck of the flask being closed with a cork, through which a thermometer passes; the bulb of the thermometer is placed just below the opening of the side-tube (B), and a few scraps of unglazed porcelain or platinum are put in the distilling flask, to prevent 'bumping' or sudden ebullition. In the case of liquids which boil at temperatures above 130° or so, a long Fig. 3. glass tube (C) without a water-jacket is used instead of a Liebig's condenser, which is apt to crack. If the compound to be purified contain only a small quantity of non-volatile impurities, the thermometer rises very rapidly as soon as the liquid begins to boil, but then remains practically stationary until almost the whole has distilled. Towards the end of the operation, however, it begins to rise again, and distillation is then stopped, the impurities remaining in the distilling flask. If the distillate be now transferred to a clean flask, and OF ORGANIC COMPOUNDS. 17 redistilled, it will boil at a constant temperature, which is the boiling-point* of the liquid. All pure substances which boil without decomposition have a definite boiling-point (b.p.), which is dependent on the pressure. As the pressure diminishes, the boiling-point is lowered, so that, by carrying out the process under reduced pressure, it is often possible to distil a substance which would undergo decomposition under ordinary atmospheric pressure, because in the latter case it is heated more strongly. The boiling-point is one of the most important physical constants of a substance, and affords a valuable means of identifying it. An observation of the boiling-point should always be made with an apparatus similar to that shown above, and a considerable quantity of the liquid should be distilled, in order to make sure that it has a constant boiling- point ; if not, it is impure. Before distilling a substance, it should be carefully dried ; in the case of liquids, this is done by shaking them with a few small pieces of fused calcium chloride, potassium carbonate, or other dehydrating agent, and then decanting or filtering. When a mixture of two (or more) volatile substances is distilled in the manner described above, it begins to boil at some temperature lying between the boiling-points of the constituents. As distillation proceeds, the boiling-point rises, and towards the end of the operation, it usually becomes nearly the same as that of the liquid which boils at the higher temperature. In the case of a mixture of alcohol (b.p. 78-3°) and water (b.p. 100°), for example, the ther- mometer at first registers some temperature between 78-3 and 100° according to the proportion of the two substances, and the first portions of the distillate contain a larger pro- portion of alcohol than the original mixture. During dis- tillation, the thermometer slowly and continuously rises, and at last registers 99-100°, the portions passing over at this temperature consisting of practically pure water, The change * See foot-note, p. 21. 18 COMPOSITION, PURIFICATION, AND ANALYSIS in boiling-point is due to a change in the composition of the mixture; the alcohol, being more volatile, passes off more quickly than the water. It is possible, therefore, to partially separate a mixture of liquids by collecting the distillate in portions or fractions at intervals of 5 or 10°, the operation being termed fractional distillation. By redistilling each fraction separately, a further separation is effected, and, after a sufficient number of operations, the constituents of the mixture are obtained in a practically pure condition, boiling at a constant temperature. Such a separation, however, can only be satisfactorily effected provided that there is a differ- ence of at least 20-30° between the boiling-points of the liquids; in many cases, even when there is a greater difference than this, a complete separation cannot be accomplished. As an illustration of the process of fractional distillation, the case of a mixture of 50 c.c. of benzene (b.p. 81°) and 50 c.c. of xylene (b.p. 140°) may be taken. The mixture begins to boil at about 87°, the thermometer rising gradually to 140'; if the receiver be changed every 10°, the following fractions are obtained : 87-100° 33 c.c. (1) 100-110' 16 c.c. (2) 110-120° 8'5 c.c. (3) 120-130° 8 c.c. (4) 130-140° 33 c.c. (5) The first and last are larger than the others, because the tempera- tures at which they are collected are approximately the boiling- points of the constituents. If, now, the fractions 1 and 5 be separ- ately redistilled, they will yield a large fraction boiling at 81-85° and at 135-140° respectively, as well as small intermediate fractions, which are collected separately. By repeating these operations with the fractions 2, 3, and 4, a large proportion of the mixture is ultimately separated into two fractions, from which benzene and xylene respectively can be obtained in an almost pure condition by further fractional distillation. The process of fractional distillation is greatly facilitated by employing a flask with a long neck, or by causing the mixed vapours to pass through a long vertical tube before they enter the condenser. By this means the vapour of the liquid of higher boiling-point is partially condensed, and OF ORGANIC COMPOUNDS. 19 runs back into the distilling flask instead of passing over with the more volatile liquid. Fractional distillation is frequently carried out under reduced pressure for the reasons already stated in the case of ordinary distillation. A simple apparatus for this purpose is easily made by inserting the side-tube of one distilling flask (A, fig. 4) into the neck of a second flask (B), and connecting the side-tube (of B) with a water-pump. The liquid to be Fig. 4. distilled is placed in A; the air is then exhausted, and the distillation carried out in the usual manner, the process being interrupted when the receiver is being changed. Tests of Purity.-Before attempting to determine the composition of an organic substance, its purity must be established. It would be useless to test for chlorine, for example, in an impure organic compound, since, even if a distinct indication were obtained, this element might be 20 COMPOSITION, PURIFICATION, AND ANALYSIS present (as a chloride) in the form of impurity. In the case of a compound, liquid or solid, which distils unchanged, its purity can generally be established by observing if its boiling- point is constant. A solid substance should be examined under the microscope in order to see whether it is homo- geneous, and an observation of its melting-point should be made. Pure substances which melt or liquefy without decom- position do so at a definite temperature, which is called the melting-point of the compound ; when, however, the substance is impure, not only is the melt- ing-point lowered, but it is also rendered indefinite, the mixture becoming soft and pasty at a certain temperature, and not melting completely until heated considerably above this point. The determination of the melt- ing-point affords, therefore, a valuable test of purity, and also serves as a means of identifying a compound. The apparatus generally em- ployed for determining the melt- ing-point consists of a small beaker (a, fig. 5) of about 50 c.c. capacity, containing concen- trated sulphuric acid, and fitted with a glass stirrer (5). A minute quantity of the sub- stance is placed in a capillary tube (c), closed below, which is attached to a thermometer (7) by means of a small india-rubber ring, or simply caused to adhere to it by capillary attraction. The acid is slowly heated, being constantly stirred, and the temperature at Fig. 5. OF ORGANIC COMPOUNDS. 21 which the substance liquefies-that is to say, its melting- point (m.p.) *-is noted. QUALITATIVE ELEMENTARY ANALYSIS. A pure compound having been obtained, it is often possible, by noting its appearance, smell, crystalline form, solubility in various solvents, and by determining its melting- or boiling-point, to prove that it is identical with some substance the composition of which is known : when, however, this cannot be done, the next step is to ascertain of what elements the substance is composed. In order, in the first place, to ascertain whether the sub- stance contains carbon-that is to say, whether it really is an organic compound-a small quantity is heated on platinum foil. If it inflames and burns aw'ay, or swells up, giving a black mass, which on strongly heating entirely disappears, the substance is in all probability organic. The salts of organic acids usually char when treated in this way, and, on further heating, the carbonaceous matter burns away, leaving a residue which may be dissolved in water or acids and examined by the usual methods of inorganic analysis; sodium acetate, for example, yields sodium carbonate, silver acetate gives metallic silver, and copper acetate the oxide of the metal. If a halogen, or sulphur, be present in the acid, it is generally found in the residue in combination with the metal. The behaviour of a substance when heated with concentrated sulphuric acid often affords an indication of the presence of carbon, as many organic substances blacken under these conditions owing to the separation of carbonaceous matter. If neither of these tests give a decisive result, the compound is mixed with about ten times its weight of pure copper oxide, and the mixture heated to redness in a narrow tube of hard glass sealed at one end, the escaping gases being led into * The observed melting- or boiling-point of a substance is usually rather lower than the true value, because, as a rule, the column of mercury is not wholly immersed in the heating liquid or vapour. 22 COMPOSITION, PURIFICATION, AND ANALYSIS lime-water; under these conditions all organic substances* are decomposed, yielding carbon dioxide, the formation of which is proved by the lime-water becoming turbid. The presence of hydrogen may sometimes be detected by heating the substance in a dry test tube and noticing whether any water is formed as the result of decomposition: as, how- ever, many organic compounds do not yield water under these conditions, but simply distil unchanged, and as the detec- tion of water itself in such small quantities is not a very simple matter, the only reliable test for hydrogen is to heat the substance with dry copper oxide in a stream of dry air or oxygen (see pp. 26-28); if hydrogen be present, it will be oxidised to water, the formation of which may be proved by passing the products of combustion through a weighed calcium chloride tube. The presence of chlorine, bromine, or iodine in organic compounds cannot, as a rule, be detected by the methods employed in the examination of inorganic substances, as for example, by means of silver nitrate, or by heating -with manganese dioxide and sulphuric acid; chloroform, for instance, contains a very large proportion of chlorine, but when pure it gives no precipitate with silver nitrate, and simply boils away when heated with manganese dioxide and sulphuric acid. A simple but not quite conclusive test for the halogens is to take a piece of copper wire, and heat one end of it in the oxidising zone of the Bunsen flame until it is quite black and ceases to colour the flame green. A small quantity of the substance is then heated on the end of the wire in the flame, when, if a halogen be present, a green colouration is usually observed, due to the formation of a volatile halogen compound of copper. As, however, this test sometimes fails, and as, moreover, it does not give any information as to which of the halogens is present, one of the following methods is almost invariably adopted. * Except the stable carbonates and cyanides of the alkalies and alkaline earths. OF ORGANIC COMPOUNDS. 23 (a) A small quantity of the substance is placed in a narrow test tube, together with a bright piece of sodium (or potassium) about the size of a pea, and gently heated, care being taken, especially in the case of volatile compounds, that the metal is brought into contact with the substance and thoroughly chars it. The mixture is then heated more strongly, finally at a red heat, and after allowing to cool a little, the tube is broken by introducing the hot end into about 10 c.c. of water contained in an evaporating basin. The alkaline solution is filtered from carbonaceous matter, the filtrate acidified with pure nitric acid and a portion tested with silver nitrate; if a precipitate be formed, the presence of halogen in the original substance is proved, and its nature may be deter- mined by submitting the rest of the solution, or the pre- cipitate, to the usual examination. This test depends on the fact that when any organic substance containing chlorine, bromine, or iodine is heated with sodium, the halogen combines with the metal to form chloride, bromide, or iodide of sodium, which can then be tested for in the usual manner. (6) A small quantity of the substance is heated with pure lime in a tube of hard glass, as described later (p. 35). The mixture is allowed to cool, carefully shaken into distilled water, the solution acidified with nitric acid, filtered from carbonaceous matter, and tested with silver nitrate. If the substance contained a halogen-chlorine, for instance-heat- ing it with calcium oxide causes the formation of calcium chloride. The presence of nitrogen in an organic substance is frequently indicated by the peculiar, unpleasant smell, like that of burning feathers, which is observed on heating the substance on platinum foil. A better test is to strongly heat a fairly large quantity of the substance with soda-lime * in a hard glass tube, when, if ammonia is evolved, the presence of * Soda-lime is prepared by intimately mixing quicklime and caustic soda, and strongly heating the mixture until it is quite dry. 24 COMPOSITION, PURIFICATION, AND ANALYSIS nitrogen is proved. As, however, certain organic compounds containing nitrogen do not yield ammonia when heated with soda-lime, the following test must be applied before the absence of nitrogen may be considered as satisfactorily proved. The substance is carefully heated with a bright piece of sodium or potassium exactly as described in testing for the halogens; the alkaline solution is filtered from carbonaceous matter, a few drops of ferrous sulphate added to the filtrate, the mixture warmed for a short time, acidified with pure hydrochloric acid, and tested with a drop of ferric chloride, when, if nitrogen were present in the original substance, a deep bluish-green coloration, or a precipitate of Prussian blue, is produced. This test depends on the fact that the nitrogen and some of the carbon in the organic compound combine with the sodium to form sodium cyanide ; when the alkaline solution of sodium cyanide is warmed with ferrous sulphate, ferrous hydrate is precipitated and sodium ferrocyanide is formed, 6NaCN + Fe(OH)2 = Na4Fe(CN)6 + 2NaOH, so that on afterwards adding a ferric salt* to the acidified solution, Prussian blue is produced. Sulphur and phosphorus may be detected by gradually adding a small quantity of the substance to a fused mixture of potassium carbonate and nitre, heated on a piece of platinum foil; under these conditions the sulphur is oxidised to sul- phuric acid, the phosphorus to phosphoric acid. The residue, which should be colourless, the carbon having been burned to carbon dioxide, is dissolved in water, and the solution of potassium salts tested for the above-mentioned acids in the usual way. Another method, similar in principle, consists in oxidising the substance with nitric acid in a sealed tube, as described later (pp. 33-35). * During the operation some of the ferrous hydrate generally becomes oxidised to ferric hydrate, which, on acidifying with hydrochloric acid, is converted into ferric chloride ; a precipitate of Prussian blue is thus at once produced. OF ORGANIC COMPOUNDS. 25 Sulphur may also be detected by heating the substance with sodium or potassium in the manner described above, and bringing a portion of the alkaline solution into contact with a bright silver coin; if the original substance contained sulphur, an alkaline sulphide will have been produced, the presence of which will be at once recognised by the formation of a black stain on the silver coin. QUANTITATIVE ELEMENTARY ANALYSIS.* When the qualitative examination has been completed, the quantitative analysis may be proceeded with, but not before : the reason of this is, that the presence of certain elements necessitates a slight change in the methods to be employed, as will be shown below. Estimation of Carbon and Hydrogen.-All organic com- pounds f are decomposed when brought into contact with red- hot copper oxide, or with any substance which readily gives up oxygen, the carbon being con- verted into carbon dioxide, the hydrogen into water; by em- ploying a known weight of substance, and collecting and weighing these products of combustion, the percentage of carbon and hydrogen may be readily determined. The appar- atus generally used for this purpose is shown in the accompany- ing figures. The calcium chloride or drying tube (fig. 6) is filled with granulated anhydrous calcium chloride, or with fragments of pumice moistened with concentrated sulphuric acid, and serves Fig. 6. * The following account of the methods most commonly adopted in the quantitative analysis of organic compounds is only intended to indicate the nature of the processes; the details of manipulation, upon which success depends, can only be learned by practice in the laboratory. + With the exceptions already mentioned in the foot-note, p. 22. 26 COMPOSITION, PURIFICATION, AND ANALYSIS to absorb the water; the potash bulbs (fig. 7) are partly filled, as shown, with strong potash (sp. gr. about 1-28), the small tube (a), which contains anhydrous calcium chloride, serving to retain the aqueous vapour which .is taken up in the passage of the gases through the potash. The calcium chloride tube and the potash bulbs are carefully weighed before and after the combus- tion, the caps (b, V) with which they are closed being removed in both cases; the gain in weight of the former corre- sponds with the amount of water produced, that of the latter representing the amount of carbon dioxide absorbed. The combustion is carried out in a piece of hard glass com- bustion tube (a, b, fig. 8), which is usually about 90 cm. long, and open at both ends; part of the tube (/to/) is filled with a layer of granulated copper oxide kept in its place by loose asbestos plugs (e, e). Before commencing the analysis the tube is heated in a combustion furnace (k), at a dull red heat, a current of air, carefully freed from carbon dioxide and mois- ture-by passing first through potash contained in the wash bottle (</), and then through the two towers (h, j)* containing pumice moistened with concentrated sulphuric acid-being led through it in order that any moisture or traces of organic matter may be removed; the empty section of the tube (a, f) is then allowed to cool. The drying tube (Z) having been fitted into the end (b) through an india-rubber cork, and the potash bulbs (???) attached by means of a short piece of india-rubber tubing, 0-15 to 0-2 gram of the substance, accurately weighed out in a narrow porcelain or platinum boat (d), is introduced into the tube; a roll of platinum foil (c) is then placed behind Fig. 7. * In practice, two such sets of drying apparatus are usually employed,, one for the air, the other for the oxygen. OF ORGANIC COM POUNDS. 27 the boat in order to prevent as far as possible any backward diffusion of the products of combustion. When a volatile liquid is to be analysed, the substance is weighed out in a thin glass bulb (shown on a larger scale at n), which is afterwards placed in the boat (at cP). A slow stream of air care- fully freed from moisture and carbon dioxide, as before, is now passed through the tube, the combustion of the sub- stance being started and regu- lated by turning on the gas taps (beginning at c). As soon as the whole of the tube has been gradually raised to a dull red heat, the current of air is turned off, and a stream of pure oxygen is passed, in order to burn any remaining organic matter, and to oxidise the copper which has been formed by the reduction of some of the copper oxide; finally, air is again passed until the oxy- gen is expelled from the ap- paratus. The whole operation occupies from 11 to 3 hours, according to the nature of the substance. The calcium chloride tube and the potash bulbs are then disconnected, their ends closed with the india-rubber caps, and allowed Fig. 8. 28 COMPOSITION, PURIFICATION, AND ANALYSIS to stand for one or two hours, when they are again weighed. Now, since the gain in weight of the potash bulbs is due to the absorption of carbon dioxide, which has been formed during the combustion, ^jths or T3Tths (C/CO2) of this gain in weight represents the quantity of carbon in the amount of substance taken; as also the gain in weight of the calcium chloride tube corresponds with the amount of water formed, j^ths or |th (H2/H2O) of this increase represents the amount of hydrogen. The percentage of carbon and hydrogen may therefore be calculated. Example.-0-1582 gram of substance gave on combustion 0-0614 gram of H2O and 0-3620 gram of CO2; therefore, 0-1582 gram of substance contains 0-0614 x = 0-0068 gram 3 9 of hydrogen, and 0-3620 x = 0-0987 gram of carbon, n x inn x x xr v x x • 0-0068 X 100 so that 100 parts of the substance contain = 0-1582 . oi x f r j j 0-0987 x 100 , 4-31 parts of hydrogen, and -Q~jgg2 = ®^-40 parts of carbon. If the substance consist of carbon, hydrogen, and oxygen only, the difference between the sum of the above numbers and 100 must represent the quantity of oxygen; the per- centage composition of the substance is therefore C 62-40 per cent. II 4-31 O 33-29 ii (by difference). The percentage of oxygen is always obtained by difference, there being no satisfactory method by which this element may be directly estimated. The following points remain to be noticed in connection with the determination of carbon and hydrogen. If the substance contain nitrogen, it is necessary to insert a roll of bright copper gauze, about four inches long, into the front part (5) of the tube; this is kept red hot during the combustion, OF ORGANIC COMPOUNDS. 29 and serves to decompose any oxides of nitrogen* produced during the operation, which would otherwise be absorbed by the water in the calcium chloride tube and by the potash, and thus lead to erroneous results. When the sub- stance contains a halogen, a roll of silver gauze must be used in order to prevent any halogen or halogen compound of copper from passing into the absorption apparatus; usually, in analysing a substance containing halogens, sulphur, or phosphorus, the space / to f (fig. 8) is filled with lumps of fused lead chromate instead of copper oxide. Lead chromate, like copper oxide, is a powerful oxidising agent at high temperatures, its action being probably represented by the equation 4PbCrO4 = 4Pb + 2Cr2O3 + 10 0. Any sulphur dioxide, phosphorus pentoxide, or halogen pro- duced during the combustion is completely retained by the lead chromate, as PbSO4, PbCl2, &c., and thus its passage into the absorption apparatus is prevented. Quantitative Determination of Nitrogen.-Nitrogen may be estimated in two ways, either volumetrically by Dumas' method, or gravimetrically, as ammonia, by Will and Varren- trap's process. 1. Volumetric Estimation by Dumas' Method.-This process is based on the fact that when ignited with copper oxide, nitrogenous organic substances are entirely decomposed into carbon dioxide, water, and nitrogen. If the gaseous products of combustion be collected over potash, the carbon dioxide is absorbed, and the residual gas consists of practically pure nitrogen ; by measuring the volume of the gas obtained * 2NO2 + 4Cu = N2 + 4CuO; N2O3 + 3Cu = N2 + 3CuO. In order to render the roll of gauze as efficient as possible, it is heated in a blow- pipe flame until thoroughly oxidised, and, while red hot, dropped into a little pure methyl alcohol contained in a test tube; the methyl alcohol reduces the copper oxide, giving a very bright surface of copper. The roll is then completely freed from methyl alcohol by heating at 160-180° for half an hour, just before commencing the combustion. 30 COMPOSITION, PURIFICATION, AND ANALYSIS from a known weight of substance, the percentage of nitrogen can be readily ascertained. The analysis is carried out in a combustion tube similar to that used in the determination of carbon and hydrogen (fig. 8), but containing in the front end (0 a roll of copper gauze, which serves to decompose any oxides of nitrogen formed during the combustion (see foot-note, p. 29). Instead, however, of placing the sub- stance in a boat, the weighed quantity is intimately mixed with finely-powdered copper oxide, this mixture occupying the space c to e. Before com- mencing to heat the sub- stance, a stream of carbon dioxide is passed through the tube until the air has been expelled, which is the case when the bubbles are almost entirely absorbed* in passing through the potash; at the same time the roll of copper gauze and the front part of the tube are raised to dull redness. The combustion is then started by gradually heating the mixture of substance and copper oxide, the escaping gases being either collected over mercury in a eudiometer containing potash, or more conveni- ently in the apparatus shown in fig. 9. As soon as the whole of the tube has been raised to a dull or cherry-red heat, and gases cease to be evolved, a current Fig. 9. * The bubbles are never completely absorbed, as it 's impossible to drive out the last traces of air. OF ORGANIC COMPOUNDS. 31 of carbon dioxide is led through the combustion tube until the rest of the nitrogen has been expelled. The eudiometer is then closed with the thumb, inverted in a cylinder of water, and the thumb removed so that the mercury may fall out and the strong potash mix with the water. After about half an hour's time, the tube is held vertically in such a position that the level of the water inside and outside is the same, and the volume (p) of the nitrogen is observed, the temperature (Z°) of the gas-that is, of the water surrounding the tube-and the height (P) of the barometer being also noted. The apparatus (Schiff's nitrometer) shown in fig. 9, which is now very generally used in nitrogen determinations, con- sists of a graduated tube (uc), provided with a stopcock (a) and a reservoir (tZ), by means of which the tube may be filled with potash (sp. gr. 1-3), and which also serves for regulating the pressure in the apparatus; the lower part of the tube (cb) is filled with mercury, which forms a seal and prevents the passage of the potash into the combustion tube (e). After carbon dioxide has been passed through the combustion tube for a considerable time, the tube (&) is connected, and the reservoir (d) lowered. If the bubbles are almost completely absorbed as they ascend through the potash, the combustion is proceeded with, the nitrogen remaining in the tube at the end of the operation being swept into the apparatus by means of carbon dioxide, as described above. The apparatus is now placed aside for about an hour to cool; the reservoir (d) is then raised until the potash in it and in the tube («c) is at the same level, and the volume of nitrogen (w) is read off, the temperature (t°) and the barometric pressure (P) being noted. The weight of nitrogen in the quantity of substance taken is readily ascertained when its volume (in cubic centimetres) has been determined by either of the methods described. Since the volume v is measured at f° under a pressure P - w, where w = the tension of aqueous vapour in mm. of 32 COMPOSITION, PURIFICATION, AND ANALYSIS mercury* at the temperature f, the volume V at 0° and 760 ,, , P - w 273 . . „ mm. would be v x x ^0. As, now, 1 c.c. of nitrogen weighs 0-001256 gram at N.T.P.,+ the weight of V c.c. will be V x 0-001256 gram. Example.-10-2248 gram of substance gave 7-1 c.c. of nitro- gen measured at 16°; P = 753-5 mm., w = 13-5 mm. The weight of the gas, therefore, is 7-1 x x x 0-001256 I OU 2oV n noons + * •+ 0-00805 x 100 = 0-0080o gram, and the percentage of nitrogen ■ 0* 2248 = 3-58. 2. The Gravimetric Estimation of Nitrogen as Ammonia, by Will and Varrentrap's method, depends on the fact already stated, that many nitrogenous organic substances, when heated with caustic alkalies, are decomposed in such a way that the whole of their nitrogen is converted into ammonia: by estimating the amount of ammonia produced by the decom- position of a known weight of the substance, the percentage of nitrogen can be determined. The apparatus (fig. 10) employed for this purpose consists of a piece of hard glass tube (ad), about 35 cm. long, drawn out and sealed at one end (a); an asbestos wad is loosely fitted into the end (a), and the space a to 5 is filled with coarsely powdered soda-lime; the part 1) to c contains a mixture of the weighed substance and finely powdered soda- lime, the remainder of the tube (c to d) being filled with coarsely powdered soda-lime only, the whole being kept in position by an asbestos wad (at d). * Some of the values of w which are most frequently required are the following: t = 10° 12° 14° 16° 18° 20° w = 9 14 10-43 11-88 13-51 15-33 17-36 mm. When the apparatus shown in fig. 9 is employed, the vapour tension of the strong potash is much less than that of pure water; if the potash has a sp. gr. =1-3 it is usual, in practice, to deduct from P half the tension of aqueous vapour at the temperature t. t Normal temperature and pressure-that is, 0° and 760 mm. OF ORGANIC COMPOUNDS. 33 The absorption apparatus (e) contains dilute hydrochloric acid, and serves to absorb the ammonia; it is fitted into the open end of the tube by means of an india-rubber cork. The tube is gradually heated in a combustion furnace, as in determining nitrogen volumetrically (commencing at tZ), and when the whole has been raised to a red heat, the ammonia remaining in the tube is drawn into the absorption bulb by- breaking off the sealed end and aspirating air through the apparatus. The amount of ammonia which has been produced may be determined gravimetrically by precipitation with platinic chloride, or, if a known volume of standard hydrochloric acid has been introduced into the bulbs, the quantity- neutralised by the ammonia may be estimated volumetrically by titration with standard alkali. The soda-lime method is not altogether satisfactory, because, owing to the decomposition of some of the ammonia formed during the operation, the results are usually too low. This decomposition may, to some extent, be prevented by adding a little sugar to the mixture of the substance and soda-lime. Furthermore, the method is not of universal application, as many nitrogenous organic substances, especially those belonging to the aromatic group, do not yield the whole of their nitrogen in the form of ammonia when heated with soda-lime. Quantitative Determination of Chlorine, Bromine, and Iodine.-The halogens in an organic compound are very readily estimated by the method devised by Carius, which consists in oxidising the substance with nitric acid at a high Fig. 10. 34 COMPOSITION, PURIFICATION, AND ANALYSIS temperature in presence of silver nitrate. Under these con- ditions the carbon is completely oxidised to carbon dioxide, and the hydrogen to water, the halogen combining with the silver ; the chloride, bromide, or iodide of silver thus produced is collected and weighed in the ordinary way. The decom- position is carried out in a strong glass tube (ah, fig. 11), about 40 cm. long, sealed at one end (a); the substance is Fig. 11. weighed out in a small glass receptacle, which is placed in the tube together with a few crystals of silver nitrate. Pure concentrated nitric acid having been added in quantity sufficient to fill |th to |d of the tube, the open end is drawn out and sealed, as shown at b. The tube is then placed in an iron case, and heated in a specially constructed apparatus (fig. 11) at a temperature necessary to ensure complete decomposition, usually at about 180°, for four hours; in the case of very stable substances, a much higher temperature and prolonged heating are required, and fuming nitric acid must be used. When quite cold the tube is opened,* the * Very great care must always be taken in working with sealed tubes, as they frequently explode, and serious accidents may occur. The tube is wrapped in a cloth as it is being removed from the iron case; after the pressure has been released by holding the capillary point in a flame, the tube is cut with a file in the usual way. OF ORGANIC COMPOUNDS. 35 contents poured into distilled water, and the halogen silver salt treated in the usual way. Another method of estimating the halogens, especially useful in the case of substances which are difficult to de- compose, consists in heating the compound with pure, freshly ignited quicklime (prepared by calcining marble) in a narrow piece of combustion tube, about 50 cm. long, and closed at one end. In charging the tube a little lime is first introduced, and then the mixture of the substance with about ten times its weight of quicklime, the remainder of the tube being nearly filled with quicklime. After tapping gently to form a small channel for the passage of the gases, the tube is heated in a combustion furnace, the front part being raised to a bright red heat before the decomposition of the substance is proceeded with. When quite cold, the contents of the tube are cautiously shaken into excess of dilute nitric acid, the acid solution filtered from carbonaceous matter, and the halogen precipitated by the addition of silver nitrate. Sulphur and Phosphorus may be estimated by heating the substance in a sealed tube with nitric acid, as described above, but without the addition of silver nitrate. The whole of the sulphur is oxidised to sulphuric acid, the phosphorus to phosphoric acid, which may then be estimated by the ordinary methods of analysis. Another method for determining sulphur and phosphorus (applicable only in the case of organic acids and some non- volatile neutral compounds), consists in heating the substance with a mixture of potassium carbonate and nitre in a platinum crucible, until the product is colourless. Here, again, the sub- stance is completely oxidised, and the sulphate or phosphate produced may be estimated in the solution of the residue. 36 DEDUCTION OF A FORMULA. CHAPTER II. DEDUCTION OF A FORMULA FROM THE RESULTS OF ANALYSIS AND DETERMINATION OF MOLECULAR WEIGHT. The quantitative analysis of an organic compound is usually made with one of two objects: either to prove that a particular compound is what it is supposed to be, or to ascertain the percentage composition of some pure substance, the nature of which is quite unknown. In the first case, the results of the analysis are compared with the calculated percentage composition, and if the two series of values agree within the limits of experimental error, the fact is taken as evidence that the substance in question is what it was believed to be. Example.-A substance obtained by oxidising a fat with nitric acid is suspected to be succinic acid, C4H6O4, and, on analysis, it gives the following results : C = 40-56, H = 5-12, 0 = 54-32 (by difference) per cent. Since the percentage composition of succinic acid, calculated from its formula, is C = 40-68, H = 5-08, 0 = 54-24 per cent., the analysis affords strong confirmation of the conclusion previously arrived at. In the second case, the nature of the substance being entirely unknown, it is necessary to deduce a formula from the analytical results-that is to say, to find the relative number of the atoms in the molecule of the compound. Example.-The percentage composition of a substance is found to be C = 84-0, H = 16-0; deduce its formula. Since an atom of carbon ■weighs twelve times as much as an atom of hydrogen, the ratio between the number of atoms of carbon and the number of atoms of hydrogen is or 7 :16 ; the formula Crll]6 may therefore be given to the substance, this formula having been obtained by dividing the DEDUCTION OF A FORMULA. 37 percentage of each element by the atomic weight of that element. Example.-The percentage composition of a substance is C = 39-95, H = 6-69, 0 = 53-36; deduce its formula. Pro- ceeding as before, the ratio between the number of atoms is found to be 3-33 : 6-69 : 3-33, r 39-95 „ „„ „ 6-69 „ n 53-36 „ „„ C = = 3-33, 11 = --- = 6-b9, (J = , „ = 3-33 ; 12 1 16 dividing now each term by 3-33 to simplify, and allowing for experimental errors, the ratio of the atoms C : H : O = 1:2:1; the formula obtained in this way is therefore CH2O. In order, then, to calculate a formula from the percentage composition, the quantity of each element is divided by the atomic weight of that element, and the ratio is then expressed in whole numbers by dividing each term by the smallest, or by some simple fraction of the smallest term. Example.-The percentage composition of a substance is C = 19-88, H = 6-88, N = 46-86, O = 26-38; deduce its formula. C = = 1.657 - 1-649 = 1 H = = 6-880 4- 1-649 = 4 N = = 3-347 4- 1-649 = 2 14 O = -= 1-649 - 1-649 = 1 16 The formula, therefore, is CH4bT2O; the ratio of the atoms determined experimentally is, of course, not exactly 1 : 4 : 2 :1, owing to unavoidable errors. The formula calculated from the results of analysis is the simplest expression of the ratio of the atoms, and is termed an empirical formula; such a formula may, or may not, show how many atoms of each element the molecule of the 38 DEDUCTION OF A FORMULA. substance contains, because substances such as formaldehyde, CH2O, acetic acid, C2H4O2, and lactic acid, C3H6O3, have the same percentage composition, and would all be found, on analysis, to have the same empirical formula, CH2O. Determination of Molecular Weight. Further investigation is necessary in order to deduce the molecular formula of a compound, by which is meant a formula expressing not only the ratio, but also the actual number of the atoms in the molecule; in other words, the molecular weight of the compound must be determined. If, for example, it can be proved that a compound of the empirical formula CH2O has a molecular weight = GO, this fact shows that the molecular formula is C21I4O2 (C2 = 24, H4 = 4, O2 = 32; total 60), and not CH2O or C3116O3; that is to say, the molecule consists of two atoms of carbon, four of hydrogen, and two of oxygen. The determination of the molecular weight of a substance is therefore of great importance, and for this purpose certain physical methods, described later, are adopted whenever possible; no purely chemical methods are known by which the molecular weight can be established with certainty, although such methods often afford some indication of the probable molecular weight, as will be seen from the following examples. Chemical Methods.-In the case of organic acids, the analysis of a salt of the acid is often of value; the silver salt is generally employed for this purpose, a weighed quantity being ignited in a porcelain crucible, when complete decom- position ensues, and a residue of pure silver is obtained. Example.-The percentage composition of an organic acid is C = 39-95, H - 6-69, 0 = 53-36; its empirical formula is therefore CH2O. Its silver salt was prepared; 0-2960 gram of the pure salt gave on ignition 0-1620 gram of silver, so that . 0-1620 x 100 the percentage of silver in the salt is = 54-73. u • jybu DEDUCTION OF A FORMULA. 39 Now, since 54-73 parts of silver are contained in 100 parts of the salt, 107-7 parts of silver will be contained in - OO54 jg = 196-78 parts of salt; but 107-7 is the atomic weight of silver, so that if the salt contain one atom of silver, its molecular weight must be 196-78, and, as the salt is formed from the acid by displacing 1 part of hydrogen by 107-7 parts of silver, the molecular weight of the acid must be 196-78 - 107-7 + 1 = 90-08. Since, however, the acid is composed of carbon, hydrogen, and oxygen, the atomic weights of which are all taken as whole numbers, the molecular weight of the acid must also be a whole number-that is to say, 90-the value found experimentally being not quite correct, owing to errors in the analysis. The molecular weight of the acid being 90, its molecular formula is not CH2O (= 30) or C2H4O2 (= 60), but C3H6O3 (= 90), that of tlie silver salt being CoH.OoAg (= 196-7). This conclusion is based on the assumption that the silver salt contains only 1 atom of silver-that is to say, that the acid is monobasic; until this assumption is proved to be correct, the analysis of the silver salt does not establish the molecular formula of the acid. If the acid had the molecular formula C6H12O6, and contained two atoms of displaceable hydrogen-that is to say, were dibasic-the silver salt C6H10O6Ag2 would contain, as before, 54-75 per cent, of silver, and the molecular weight, calculated as above, would again appear to be 90. But if the acid were dibasic, it would probably be possible to displace only one atom of hydrogen, and obtain an acid salt, C6H11O6Ag, the analysis of which would point to the molecular formula C6H12O6. If this were found impossible, the fact would be taken as evidence against this molecular formula, and the conclusion would be drawn that the probable molecular formula is C3H6O3. Most organic bases combine with hydrochloric acid to form salts which, like ammonium chloride, form double salts with platinic chloride and with auric chloride. These double salts 40 DEDUCTION OF A FORMULA. usually have the composition B'^^PtCJg, and B',HAuC14, where B' represents one molecule of a monacid base, such as methylamine CH5N, ethylamine C2H7N, &c. When these salts are ignited in a porcelain crucible, pure finely divided platinum, or gold, remains ; so that the percentage of metal in the salt is very easily determined. Assuming that one molecule of the salt contains 1 atom of platinum or gold, and that the salt has the above composition, the molecular weight of the base can be calculated. Example.-The platinum double salt (platinocldoride) of an organic base gave on ignition 37-2 per cent, of platinum; what is its probable molecular weight ? Since 37-2 parts of platinum are contained in 100 parts of the salt, 197 parts of the , . . 100 x 197 metal are contained in - = ^29-4 parts of salt, and, as 197 is the atomic weight of platinum, the mole- cular weight of the salt is 529-4. The molecular weight of , , ™ , n B',H9PtCL - HgPtCL the base (C3H9N) is therefore ---- or 529-4 - (2 + 197 + 212-4) _ 529-4-411-4 ~Q 2 2 As in the case of acids, so in that of bases, the molecular weight calculated from the analytical results may be incorrect, because it is not known whether the compound is a monacid base or not. Some bases are diacid, and form platinochlorides of the composition B",H2PtCl6, so that a diacid base of the molecular weight 118 would yield a platinochloride containing the same percentage of platinum as the salt of a monacid base of the molecular weight 59. It will be seen from the above examples, that, assuming that there is only one atom of any particular element in the molecule of the compound, the probable molecular weight may be calculated from the results of analysis. This being the case, the probable molecular formula of a compound may often be determined by preparing and analys- ing some simple derivative. DEDUCTION OF A FORMULA. 41 Example.-A liquid hydrocarbon has the percentage com- position C = 92-31, H = 7-69; its empirical formula is therefore CH. On treating this hydrocarbon with bromine, it yields hydrogen bromide and a bromo-derivative consisting of C = 45-86, H = 3-18, Br = 50-96 per cent. The empir- ical formula of this derivative is C = I5- = 3-82 - 0-637 = 6' 12 H = = 3-18 - 0-637 = 5 Br = = 0-637 - 0-637 = 1, 80 C6H5Br. Now since, from experience, there are strong grounds for supposing that the number of atoms of carbon in the molecule is not changed on treating with bromine, the probable mole- cular formula of the hydrocarbon is C6H6; it cannot be less than this, but it may be greater. A hydrocarbon C12H12, for example, might give a bromo-derivative C12H10Br2, and these compounds would have the same percentage composi- tion as C6II6 and C6H5Br respectively. The probable molecular weight may often be deduced with tolerable certainty by studying the methods of formation, and the chemical and physical properties of a substance. When, for example, acetone is distilled with concentrated sulphuric acid, it is converted into a hydrocarbon which, on analysis, is found to have the empirical formula C3H4. The fact that this hydrocarbon boils at 163° affords very strong evidence that the molecular formula is not C3H4, or C6H8, but probably C9H12, because other hydrocarbons which contain only 3 or 6 atoms of carbon boil at a temperature much below 163°, and an increase in molecular weight is generally accompanied by a rise in boiling-point. Physical Methods.-One of the most important physical methods by which the molecular weight of a compound can be ascertained is by determining its vapour density. This 42 DEDUCTION OF A FORMULA. method is based on the hypothesis that equal volumes of all gases measured under the same conditions of temperature and pressure, contain the same number of molecules (Avogadro's Law). If, therefore, the weights of equal volumes of various gases be determined under the same conditions, these weights must be in the same proportion as the weights of the mole- cules of the gases. In other words, the molecular weight of a substance can be determined by ascertaining the weight of a given volume of the vapour of the substance, compared with the weight of the same volume of hydrogen measured under the same conditions. The former divided by the latter is the specific gravity or vapour density (V.D.) of the gas compared with hydrogen as unity. Now, since the vapour density is a number expressing how many times a given volume of the gas is heavier than the same volume of hydrogen, it also expresses how many times one molecule of the substance is heavier than one molecule of hydrogen ( = 2), because equal volumes contain an equal number of molecules. The molecular weight, on the other hand, is a number expressing how many times one molecule of the substance is heavier than one atom of hydrogen ( = 1); therefore the molecular weight is double the vapour density, because the standard with which it is compared is half as great: M.W. = V.D. x 2. Sometimes air is taken as unit weight in stating the specific gravity or vapour density cf a gas; since air is 14-43 times heavier than hydrogen, the sp. gr. compared with air is of the value when compared with hydrogen; so that, in order to obtain the molecular weight, the sp. gr. is in such cases multiplied by 28-86 = 2 x 14-43. Determination of Vapour Density. The vapour density of a substance is ascertained experi- mentally, (a) by measuring the volume occupied by the vapour of a known weight of the substance at known temperature DEDUCTION OF A FORMULA. 43 and pressure, or (5) by ascertaining tire weight of a known volume of the vapour of the substance at known temperature and pressure. The observed volume of the vapour is then reduced to 0° and 760 mm., and the weight of a volume of hydrogen at 0° and 7 60 mm. equal to the corrected volume of the vapour is calculated; the weight oi the vapour divided by that of the hydrogen is the vapour density. Example.-An organic liquid has the empirical formula C4H10O; 0-062 gram of the liquid gave 23-2 c.c. of vapour at 50° and 720 mm., what is its molecular formula? The volume at 0° and 760 = 23-2 x - x -273- = 18 57 c.c. 760 273 + 50 and 1 c.c. of hydrogen at N.T.P. weighs 0-0000896 gram; therefore 18-57 c.c. weigh 0-00164 gram. The weight of the vapour _ 0-062 37 7 - VD The weight of the hydrogen 0-00164 The molecular weight = V.D. x 2 or 37-7 x 2 = 75-4. Since the molecular weight of a compound of the empirical formula C4H10O is calculated to be 74, the determination of the vapour density proves that the molecular formula of the liquid is C4H10O, so that in this case the empirical is iden- tical with the molecular formula. The molecular weight determined experimentally from the vapour density frequently differs from the theoretical value by several units, owing to experimental errors; this, however, is of little importance, since all that is required in most cases is to decide between multiples of the empirical formula, in the above example, between C4II10O = 74, C8H20O2 = 148, &c. The determination of the vapour density is only possible when a substance can be converted into vapour without decomposition under the conditions of the experiment. In many cases, however, a non-volatile compound, or a com- pound which cannot be vaporised without decomposition, can be converted into some simple derivative which is volatile, so that, by determining the vapour density of the latter, 44 DEDUCTION OF A FORMULA. the molecular weight of the parent substance can be ascer- tained. The following are some of the methods employed in deter- mining vapour density : Gay-Lussac's or Hof- mann's Method.-A gradu- ated barometer tube (ab, fig. 12), about 85 cm. long, and 35 mm. wide, filled with and then inverted in mer- cury, is surrounded by a wider tube (c), through which the vapour of some liquid boiling at a known and constant temperature is passed. For this purpose the upper end of the outer tube (c) is connected with a vessel (A), usually made of cop- per, containing the heating liquid, which is kept in rapid ebullition. The liquids most commonly employed are water (b.p. 100°), xylene (b.p. 140°), aniline (b.p. 183°), and ethyl benzoate (b.p. 213°). The condensed liquid escapes through the side-tube (/), and is collected for subsequent use. As soon as the barometer tube is at a constant temperature, a weighed quantity (about 0-05 gram) of the substance con- tained in a small stoppered vessel (d), which it fills completely, is introduced into the open end (6). The vessel immediately rises to the surface of the mercury in the tube, the substance vaporises into the Torricellian vacuum, and the mercury is forced downwards; as soon as the level remains stationary, Fig. 12. DEDUCTION OF A FORMULA. 45 the volume of the vapour is noted. The temperature of the vapour is the boiling-point of the liquid employed to heat the barometer tube. The pressure is determined by sub- tracting the height of the column of mercury in the inner tube (ab), above the level in the trough, from the height of the barometer, both readings having been first reduced to 0°.* The weight of the vapour is that of the substance taken. The great advantage of this method lies in the fact that it affords a means of determining the vapour density of sub- stances under greatly reduced pressures, and therefore at temperatures very much below their ordinary boiling-points, so that it can often be employed with success in the case of substances which are only volatile without decomposition under reduced pressure. Dumas' Method.-A globe-shaped vessel of about 200 c.c. capacity (a, fig. 13), the neck of which is drawn out to a fine tube, is carefully weighed, the tem- perature (f°) and pressure (Pz) being noted. A fairly large quantity of the substance (about 8-10 grams) is now introduced by gently heating the globe and quickly dipping the tube into the liquid. The vessel is then immersed in an oil-bath (shown in section in fig. 13) containing a thermometer (b\ and heated at a constant temperature, at least 20° above the boiling-point of the com- pound. The air in the apparatus is quickly expelled by the rapid vaporisation of the substance, and the vessel is filled with the vapour of the liquid. As soon as the whole of the liquid has been vaporised, which is known by the fact that gas ceases to issue from the fine tube, the point of the latter is sealed before the blowpipe, the temperature of the oil-bath (^°) and the height of the barometer Fig. 13. * By correcting for the expansion of the mercury. 46 DEDUCTION OF A FORMULA. (P) being noted. The globe is allowed to cool, and is then cleaned, dried, and weighed. The point of the tube is now broken under water (or mer- cury), which rushes in and fills the globe completely, except for the minute quantity of liquid produced by the condensa- tion of the vapour in the globe; the globe is again weighed, and its capacity or volume (v) calculated from the weight of the water contained in it, the weight in grams being equivalent to the volume in c.c. The volume may also be measured directly by transferring the liquid from the globe to a graduated vessel. When the globe is weighed the first time it is full of air, but at the second weighing it is full of vapour; if, therefore, the first weight be subtracted from the second, the difference, W, is the weight of the volume, v, of vapour less the weight of the volume, v, of air.* The weight of the air is calculated by reducing the volume, v, at t'° and P' to N.T.P., and multiplying by 0-001293, the weight of 1 c.c. of air at N.T.P.; this weight added to W gives the weight of the volume, v, of vapour at t° and P. The volume, v, of vapour at t° and P is then reduced to N.T.P., the weight of an equal volume of hydrogen at N.T.P. calculated, and divided into the weight of the vapour. Victor Meyer's Method.-Owing to its simplicity, and the rapidity with which the determination may be made, this method is now used whenever possible; the apparatus is represented in fig. 14. The bulb tube («6) is closed (at a) by means of an india-rubber stopper, and heated by the vapour of some constant boiling liquid f contained in the outer vessel (c) ; as the air expands it escapes through the narrow tube (cZ), which dips under the water in the vessel (e). As soon as the * Changes in the temperature of the air, height of the barometer, and volume of the globe occurring during the experiment may be neglected. + See page 44; in determining the vapour density of substances of high boiling-point, diphenylamine (b.p. 310°) or sulphur (b.p. 448°) may be used, or the bulb tube (ab) may be heated at a constant temperature in a metal bath. DEDUCTION OF A FORMULA. 47 temperature of the bulb tube (ab) becomes constant-that is to say, when bubbles of air cease to escape (from d)-the graduated tube (y) is filled with water and inverted over the end of d; the stopper (a) is now removed, and a small bottle or bulb (d, fig. 12) completely filled with a weighed quantity (about 0-1 gram) of the liquid dropped into the apparatus,* the stopper being replaced as quickly as possible. The sub- stance immediately va- porises, and the vapour forces the air out of the apparatus into the grad- uated vessel (g). When air ceases to issue (from d), the stopper (a) is at once taken out to pre- vent the water (in e) from passing into the apparatus. The volume of the vapour is ascertained by measuring the volume (y) of the air in the graduated tube, its teynperature (t°) and the barometric pres- sure (P) being noted. The volume of the air (in g) is not the same as that actually occupied by the hot vapour (in ah'), because the air displaced has been cooled, and is measured under a different pressure. Its volume now is equal to that which the given weight of vapour would Fig. 14. * In order to prevent fracture, a little mercury or sand is usually placed in b. 48 DEDUCTION OF A FORMULA. occupy under the same conditions of temperature and pres- sure. The temperature of the volume, v, of air being t°, and the height of the barometer P, the volume at N.T.P. ,, , 273 P - w would be v x x , w being the tension of aqueous vapour at t° (foot-note, p. 32). The weight of an equal volume of hydrogen at N.T.P. is then calculated and divided into the weight of the substance taken; the vapour density is thus obtained. Determination of Molecular Weight from the depression of the freezing-point of a solvent.-When sugar is dissolved in water, the solution freezes at a lower temperature than pure water, and the extent to which the freezing-point is lowered or depressed is, within certain limits of concentration, directly proportional to the weight of sugar in solution; 1 part of sugar, for example, dissolved in 100 parts of water depresses the freezing-point about 0-058°-that is to say, the solution freezes at - 0-058° instead of at 0°, the freezing-point of pure water; 2 parts of sugar dissolved in 100 parts of water lower the freezing-point 0-116°, 3 parts 0-174°, and so on. Solutions of other organic compounds in other solvents, such as acetic acid, benzene, &c., behave in a similar manner, and, in sufficiently dilute solutions, the depression of the freez- ing-point is (approximately) proportional to the number of molecules of the dissolved substance in a given weight of the solvent, and independent of the nature of the substance. If, then, molecular proportions of various substances be separately dissolved in a given (and sufficiently large) quantity of the same solvent, the depression of the freezing-point is the same in all the solutions, but different with different solvents. In other words, if the molecular weight in grams of any substance be dissolved in 100 grams of a given solvent, the depression of the freezing-point is a constant quantity, K, which is termed the molecular depression of that solvent. DEDUCTION OF A FORMULA. 49 When, therefore, this constant has been determined for any solvent, the molecular weight, M, of a substance can be ascertained by observing the depression of the freezing- point of a sufficiently dilute solution, containing a known quantity of the substance. If 1 gram of the substance were dissolved in 100 grams of the solvent, the observed depression, D, would be K x because K is the depression produced by the molecular weight in grams-that is to say, by M grams-and the depression varies directly with the weight of dissolved substance. If, again, P grams of the substance -were dissolved in 100 grams of the solvent, the depression, D = P K x P K x - : hence the molecular weight M = ---, so that K M ° D and P being known, if the depression be ascertained experi- mentally, the molecular weight, M, can be calculated. This method of determining the molecular weight of organic compounds was first applied by Raoult, and is usually known as Raoult's or the cryoscopic method. The observation is usually made with the aid of the apparatus devised by Beckmann (fig. 15) in the following manner : A large tube (A), about one inch in diameter, and provided with a side-tube (B), is closed with a cork (C), through which pass a stirrer (a) and a thermometer (6) graduated to T^°. A weighed quantity (about 25 grams) of the solvent is placed in the tube, which is then fitted into a wider tube (D), which serves as an air- jacket and prevents a too rapid change in temperature. The apparatus is now introduced through a hole in the metal plate (E) into a vessel which is partly filled with a liquid, the temperature of which is about 5° lower than the freezing- point of the solvent. The solvent (in A) is now constantly stirred, when the thermometer rapidly falls and sinks below the freezing-point of the solvent, until the latter begins to freeze; the thermometer now rises again, but soon becomes stationary at a temperature which is the freezing-point of the solvent. A weighed quantity of the substance is now intro- 50 DEDUCTION OF A FORMULA. duced through the side-tube (B), and after first allowing the solvent to melt completely, the freezing-point of the solution is ascertained as before. The difference between the two freez- ing-points is the depression (D); the molecular weight of the sub- stance is then calculated with the aid of the above formula. Example.-4-9818 grams of cane-sugar (C12H22O11) dissolved in 96-94 grams of water caused a depression in the freezing-point of 0-295° (D). Since 96-94 grams of the solvent contain 4-9818 grams of substance P, the quantity in 100 grams = 5-139 grams. The constant, K, for water is 19; hence the molecular weight, M, of cane- . . , , , 19 x 5-139 sugar is found to be - u • jy d = 331, the true value being 342. As in the determination of molecular weight from the vapour density, the experi- mental and theoretical values frequently differ by several units, this is of little import- ance for the reasons already stated. The constants, K, for the sol- vents most frequently used are : acetic acid, 39 ; benzene, 49 ; water, 19. Fig. 15. CONSTITUTION OF ORGANIC COMPOUNDS. 51 CHAPTER III. CONSTITUTION OR STRUCTURE OF ORGANIC COMPOUNDS. Even when the molecular formula of an organic compound has been established by the methods described in the fore- going pages, the most difficult and important steps in the investigation of the substance have still to be taken. Many cases are known in which two or more compounds have the same molecular formula, and yet are different in chemical and physical properties; there are, for example, two compounds of the molecular formula C2H4O2, three of the molecular formula C5H12, and so on. Now, if the properties of a compound depended simply on the nature and number of the atoms of which it is composed, there could not be two or more different substances having the same molecular formula. The only possible conclusion to be drawn from the proved existence of such compounds is, therefore, that the difference between them is a difference in constitution; in other words, that the atoms of which their molecules are composed are differently arranged. There is nothing at all improbable in this conclusion : in the case of simple inorganic compounds, the behaviour of any particular atom depends on the nature of the other atoms or groups of atoms with which it is united. The hydrogen atoms in ammonia, NH3, for example, are not, but the hydrogen atoms in sulphuric acid, H2SO4, are displaceable by zinc, and the only difference between them is a difference in their state of combination. It is just the same in the case of organic compounds; the state of combination determines the behaviour of the atoms, and therefore the properties of the compound depend on the state of combination of all the atoms of which its molecule is composed. Now, although the actual arrangement or structure of the 52 CONSTITUTION OF ORGANIC COMPOUNDS. molecule cannot "be directly determined, it is possible to obtain some idea of the state of combination of the atoms by studying the chemical behaviour of the compound. Methyl alcohol, CH4O, for example, is readily acted on by sodium, yielding a compound of the composition CH3NaO, which is formed by the displacement of one hydrogen atom (a) by one atom of the metal; the other three hydrogen atoms in methyl alcohol cannot be displaced, no matter how large a quantity of sodium be employed. Again, when methyl alcohol is treated with hydrogen chloride under certain conditions, one atom of hydrogen and one atom of oxygen are displaced by one atom of chlorine, a compound of the composition CH3C1 being formed, CH4O + HC1 = CH3C1 + H2O. When this compound is heated with water, it is transformed into methyl alcohol, one atom of chlorine being displaced by one atom of oxygen and one atom of hydrogen ; the change is, in fact, the reverse of that represented above. From these and other experiments it is concluded that methyl alcohol contains one atom of hydrogen (a) combined differently from the other three; also that one atom of hydrogen is closely associated with the oxygen atom, because the two are constantly displaced and replaced together; as, further, the compound CH3C1 does not contain a hydrogen atom which can be displaced by sodium, it is concluded that the particular hydrogen atom (a) in methyl alcohol which is dis- placeable by sodium is the same as that which is closely associated with the oxygen atom. These conclusions may be expressed by the formula CH3(OH). Now any compound, such as ethyl alcohol, C2H6O, propyl alcohol, C3H8O, &c., which behaves like methyl alcohol under the same conditions, may be assumed to contain one atom of hydrogen and one atom of oxygen in the same state of combination as in methyl alcohol, and may be represented by formulae such as C2H5(OH), C3Hr(OH), &c.; in other words, the constitution of any compound may be ascertained by CONSTITUTION OF ORGANIC COMPOUNDS. 53 comparing its behaviour under various conditions with that of some compound of known constitution. Atoms or groups of atoms which are found to show the same behaviour are considered to be in a similar state of combination. In this way it is possible to determine the state of combination of many or of all the atoms of which the molecule is composed, and then, by using suitable formulae, not only the state of combination or constitution, but also the chemical behaviour, of the substance may be expressed. Formulae employed for this purpose are called rational or constitutional formulae. Another way of representing compounds is by means of graphic formulae, the object of which is to express still more fully and clearly the constitution and chemical behaviour of the substance. Before giving examples of the use of graphic formulae, it will be necessary to consider the molecular formulae of some of the simpler organic compounds. For this purpose attention may be directed in the first place to compounds such as (a) CII4 and CHC13; (b) CO2 and COS; (c) COC12; and (d) HCN, which contain only one atom of carbon in the molecule. In all these compounds the atom of carbon is combined with (a) 4 monovalent or monad atoms, (b) 2 dyad atoms, (c) 1 dyad and 2 monad atoms, or (d) 1 triad and 1 monad atom-that is to say, with four monad atoms or their valency equivalent. With the doubtful exception of carbon monoxide, CO,* no compound containing only one carbon atom is known, in which the carbon atom is combined with more or less than four monad elements or their valency equivalent; carbon, therefore, is tetravalent, and this fact may be expressed by writing its symbol, C= or =C= or - C- or in any other way, four lines being drawn simply to express its tetravalent character. For similar reasons the monovalent hydrogen atom may be * Oxygen may be assumed to be a tetrad in CO. 54 consTitution of organic compounds. represented by H-, divalent oxygen by 0= or -0-, tri- valent nitrogen by N= or , and so on, the number of lines serving to recall the valency of the atom. If, now, in the case of substances such as CH4, CH3C1, CHC13, in which the carbon atom is united with four monad atoms, each of the latter be placed at the extremity of one of the four lines which represent the valency of carbon, the following formulae are obtained : H H H H-C-H H-C-H Cl-C-Cl H Cl Cl If in the case of substances such as C02, COC12, COS, each of the dyad atoms be given two lines, the compounds will be represented by the formulae 0=C=0 c}/C=O C^g Similarly, HCN may be expressed by the formula H-C=N. Formulae of this kind are termed graphic formula. They are intended to express in a purely diagrammatic manner the constitution of the several compounds-that is to say, the state of combination and the valency of each of the atoms in the molecule. In all such formulae, therefore, the number of lines running to or from any given symbol must be the same as the number of monad atoms with which the element represented by that symbol is known to combine. The constitution of carbon bisulphide, for example, cannot be /S expressed by the formula C\ | , or that of carbon dioxide by \s a formula such as 0-C-0, because the valency of the elements is not correctly indicated by the number of lines. These lines are sometimes called valencies, more frequently bonds or linkings; in the graphic formula H- C=N, the CONSTITUTION OF ORGANIC COMPOUNDS. 55 hydrogen atom is said to be combined with carbon by one bond or linking, the nitrogen atom by three. The hydrogen and nitrogen atoms are not directly combined, but are both united with carbon. It must not be supposed, however, that these lines are intended to represent the actual force or attraction which causes the atoms to combine. They are simply expressions of valency or combining capacity, and may be shortened or lengthened at will without altering their significance : as a rule, they are shortened, as in the formulae H-C:N and 0 : C : S, or brackets are employed instead, as in CH3(OH), H which signifies the same as CH3-OH and H-C-0-H. All H these, except the last, would be termed constitutional rather than graphic formulae, but there is no sharp difference between them. All such formulae are based on considerations of valency and on a study of the chemical behaviour of the compounds which they represent; they express, in fact, in a concise and simple manner the most important chemical properties of the compound. CHAPTER IV. THE PARAFFINS, OR HYDROCARBONS OF THE METHANE SERIES. It has already been noted that carbon differs from all other elements in forming an extraordinarily large number of compounds with hydrogen; these compounds, composed of hydrogen and carbon only, are called hydrocarbons. Methane, or Marsh-gas, CH4, is the simplest hydrocarbon. It is met with, as its name implies, in marshes and other places in which the decomposition or decay of vegetable matter is taking place under water. On stirring a marshy 56 HYDROCARBONS OF THE METHANE SERIES. pond or swamp, bubbles consisting of marsh-gas, carbon dioxide, and other gases, frequently rise. It is one of the principal constituents of the gas which streams out of the earth in the petroleum districts of America and Russia; it also occurs in coal-mines, the gas (fire-damp) which issues from the fissures in the coal sometimes containing as much as 80-90 per cent, of methane, to the presence of which, mixed with air, explosions in coal-mines are due. Ordinary coal-gas usually contains about 40 per cent, of methane. Methane is formed* when zinc methylt (p. 216) is decom- posed with water, Zn(CH3)2 + 2H2O = 2CH4 + Zn(0H)2. It is also obtained when sulphuretted hydrogen or steam, together with the vapour of carbon bisulphide, is passed over heated copper, CS2 + 2H2S + 8Cu = CH4 + 4Cu2S CS2 + 2H2O + 6Cu = CH4 + 2Cu2S + 2CuO; and by reducing carbon tetrachloride with sodium amalgam (p. 93), CC14 + 4H2 = CH4 + 4HC1. Since carbon bisulphide and hydrogen sulphide may be pro- duced by the direct union of their constituent elements, and carbon tetrachloride is formed on treating carbon bisulphide with chlorine, these reactions are of considerable theoretical importance, as they afford a means of synthesising methane from its elements. They are often quoted as examples of the synthesis of an organic compound from inorganic materials, but such a view is rather misleading, because carbon and carbon bisulphide are just as truly ' organic ' as methane. * The words formed, obtained, and. produced are used when the method is of theoretical importance, and not suitable for the actual preparation of the compound. + Compounds, such as zinc methyl, are often unavoidably introduced long before their properties are described; in such cases references are given. The groups of atoms, CH3-,C2Hg-, C3H7-, and C4H9-, are termed methyl, ethyl, propyl, and butyl respectively. HYDROCARBONS OF THE At ETHANE SERIES. 57 Methane is prepared by heating one part of anhydrous sodium or potassium acetate with four parts of soda-lime in a hard glass tube or retort, and collecting the gas over water, C2H3O2Na + NaOH = CH4 + Na2CO3. The gas obtained in this way contains small quantities of hydrogen, ethylene (p. 72), and other impurities. Pure methane is prepared by slowly running methyl iodide from a dropping funnel into a flask containing a zinc- copper couple* covered with dilute alcohol, to which a few drops of sulphuric acid have been added. The methyl iodide is reduced by the nascent hydrogen formed by the action of the dilute acid on the zinc-copper couple, and a constant stream of methane is obtained without application of heat, CH3I + 2H = CH4 + HI. In a similar manner, all halogen derivatives of marsh-gas (p. 171) are converted into marsh-gas on treatment with nascent hydrogen, generated from zinc and hydrochloric acid, from sodium amalgam and water, or in any other suitable manner (p. 93). Methane is a colourless, tasteless gas; it condenses to a liquid at - 11° under a pressure of 180 atmospheres. It burns with a pale-blue, non-luminous flame, and forms a highly explosive mixture with certain proportions of air or oxygen, CH4 + 2O2 = CO2 + 2H2O 2 vols. + 4 vols. = 2 vols. + 4 vols. It is almost insoluble in water, but rather more soluble in alcohol. It is very stable ; when passed through bromine, potash, nitric acid, sulphuric acid, solution of potassium per- manganate, and solution of chromic acid, it is not absorbed or changed in any way. When mixed with chlorine in the dark, no action takes place; but if a mixture of 1 vol. of * Granulated zinc coated with a thin layer of copper by immersion in a dilute solution of copper sulphate and subsequent drying. 58 HYDROCARBONS OF THE METHANE SERIES. methane and 2 vols. of chlorine be exposed to direct sunlight, explosion ensues, and carbon is deposited, CH4 + 2C12 = C + 4HC1. In diffused sunlight there is no explosion, but after some time a mixture of hydrochloric acid and four other compounds is produced, the proportion of each depending on the quantity of chlorine present, and on the conditions of the experiment. CH4 + C12 = CH3C1 + HC1. Methyl Chloride. CH4 + 2C12 = CH2C12 + 2HC1. Methylene Chloride. CH4 + 3C12 = CHC13 + 3HC1. Chloroform. CH4 + 4C12 = CC14 + 4HC1. Carbon Tetrachloride. All these compounds are formed by the displacement of one or more hydrogen atoms by an equivalent quantity of chlorine. The carbon atom cannot combine with more than four monad atoms, so that hydrogen must be displaced if any action at all take place. Now it may be supposed that in the formation of methyl chloride, CH3C1, for example, one of the hydrogen atoms is drawn away from the carbon by the superior attraction of the chlorine, and that one atom of chlorine takes up the vacant place in the molecule without the other atoms being disturbed or their state of combination altered ; this change may then be represented graphically thus : H\ >H Cl Hx /Cl H + I = + | If/ ^11 Cl Hz XH Cl In the formation of methylene chloride, CH2C12, it may be supposed that a repetition of this process occurs, and so also in the case of the other products; in other words, it may be assumed that in all the above examples the action of the chlorine is not such that the molecule of marsh-gas is completely broken up into atoms, which then, by combination with chlorine, form totally new molecules, but that cei tain atoms simply change places. To such changes as these, in which certain atoms are simply displaced by an HYDROCARBONS OF THE METHANE SERIES. 59 equivalent quantity of other atoms, without the state of com- bination of the rest of the molecule being altered, the term substitution is applied, and the compounds formed as the result of the change are called substitution products. The four compounds mentioned above are substitution products of methane and of one another: methyl chloride, CH3C1, is a mono-substitution product, methylene chloride, CH2C12, a di-substitution product of marsh-gas, and so on; chloroform, CHC13, is a tri-substitution product of methane, a di-substitution product of methyl chloride. If, by treat- ment with nascent hydrogen in the manner described above, any of these substitution products be reconverted into marsh- gas or into one another, the change would be termed inverse substitution. The only way in which it is possible to produce a change in marsh-gas, or in any of its chloro-substitution products, is by a process of direct or inverse substitution. The atom of carbon already holds in combination the maximum number of atoms, and some of them must be displaced if any other atom enter the molecule. Compounds such as these, in which the maximum combining capacity of all the carbon atoms is exerted, and which can only yield derivatives by substitution, are termed saturated. Ethane, ethyl hydride, or dimethyl, C2H6, like methane occurs in the gas which issues from the earth in the petroleum districts. It is formed when methyl chloride or methyl iodide, CH3I, is treated with sodium, 2CH3I + 2Na = C2H6 + 2NaI; this reaction affords a means of preparing ethane from its elements, because methane can be formed from its elements, as already described, and then converted into methyl chloride by treatment with chlorine. Ethane is also formed when zinc ethyl (p. 215) is decom- posed with water, Zn(C2H5)2 + 2H2O = 2C2H6 + Zn(OH)2; 60 HYDROCARBONS OF THE METHANE SERIES. when ethylene (p. 72) is treated with nascent hydrogen, C2H4 + 2H = C2H6; and when methyl iodide is treated with zinc methyl, 2CH3I + Zn(CH3)2 = 2C2H6 + Znl2. Ethane is prepared by reducing ethyl iodide with the zinc- copper couple, exactly as described in the preparation of pure methane, C2H5I + 2H = C2H6 + HI, or by the electrolysis of dilute acetic acid, or of a con- centrated aqueous solution of potassium acetate (Kolbe). When acetic acid is used, ethane and carbon dioxide are evolved at tlie positive, hydrogen at the negative pole, CH3.CO2H = q H + 2CO' + H2; CH3-CO2H 2 6 2 2 when potassium acetate is employed, the following decom- positions occur: CH3.CO2K = q H + 2CO.' + 2K CH3.CO2K 2 6 2 and 2K + 2H2O = 2K0H + H2, so that the same gases are evolved as before. Ethane is a colourless, tasteless gas, which liquefies at 4° under a pressure of 46 atmospheres; it is practically insoluble in water, slightly soluble in alcohol. It is in- flammable, burns with a feebly luminous flame, and can be exploded with air or oxygen. 2C2H6 + 7O2 = 4CO2 + 6H2O 4 vols. + 14 vols. = 8 vols. +12 vols. It is very stable, and is not acted on by alkalies, nitric acid, sulphuric acid, bromine, or oxidising agents at ordinary temperatures. When mixed with chlorine and exposed to diffused sunlight, it gives various substitution products, 1, 2, 3, 4, 5, or 6 atoms of hydrogen being displaced by an equivalent quantity of chlorine. HYDROCARBONS OF THE METHANE SERIES. 61 C2H6 + C12 = C2H5C1 + HC1 Ethyl Chloride. C2H6 + 2C12=C2H4C12 + 2HC1 Ethylene Chloride. C2H6 + 6C12 = .C2C16 + 6HC1. Perchlorethane. Ethane, like methane, cannot combine directly with chlorine or with any element; it is a saturated compound. The constitution of ethane may be deduced theoretically in the following manner: the two atoms of carbon must be directly united, because hydrogen, being monovalent, cannot link the two carbon atoms together; as, moreover, carbon is tetravalent, one of the six hydrogen atoms must be placed at the end of each of the remaining six lines; in this way H H the graphic formula H-C-C-H is obtained. This view, H H based entirely on considerations of valency, is confirmed by a study of the methods of formation and properties of ethane. When methyl iodide is treated with sodium or with zinc methyl, the metal combines with the halogen, and a group of atoms, CH3-, is left; as, however, carbon is H tetravalent, this group H-C-, like the atom of hydrogen H H-, cannot exist alone, and immediately combines with a similar group forming ethane, CH3-CH3, or dimethyl, which is a saturated compound, because all the carbon atoms in the molecule are exerting their maximum valency or combining capacity. Propane, propyl hydride, or methyl-ethyl, C3H8, occurs in petroleum, and can be obtained by reducing propyl iodide or isopropyl iodide (p. 178) with zinc and hydrochloric acid, or with the zinc-copper couple, C3H7I + 2H = C3H8 + HL 62 HYDROCARBONS OF THE METHANE SERIES. It is also obtained by treating a mixture of ethyl and methyl iodides with sodium, C2HJ + CHoI + 2Na = CJI8 + 2NaI, Z O O O O 7 and by treating zinc ethyl with methyl iodide, Zn(CeH5)„ + 2CHJ = 2CoHfi + ZnL. \ w U/ aa o o o z Propane is a gas, and closely resembles methane and ethane in chemical properties. It condenses to a colourless liquid at temperatures below - 17° under ordinary atmospheric pressure. It burns with a more luminous flame than ethane. When treated with chlorine in diffused sunlight, it yields propyl chloride and other substitution products, one or more hydro- gen atoms being displaced, C8H8 + Cl2 = C8H7C1 + HC1. O O 0 4 Constitution.-Since propane is produced by the action of sodium on a mixture of methyl and ethyl iodides, and also by the action of zinc ethyl on methyl iodide, it is concluded H that propane is formed by the combination of -C-H and I H H H H-C-; its constitution is therefore represented by the H A H H H formula H-C-C-H, or CH3« CH2- CH3, and it may be ini regarded as derived from ethane, just as ethane may be considered as derived from methane, by substituting the mono- valent group of atoms CH3- for one atom of hydrogen. Butanes, C4H10.-Two hydrocarbons of the molecular formula C4H10 are known. One of them, butane, diethyl or methyl-propyl, occurs in petroleum, and can be obtained by treating ethyl iodide with sodium, 2C2H5I + 2Na = C4H10 + 2NaI. HYDROCARBONS OF THE METHANE SERIES. 63 The other, isobutane, or trimethylmethane, is formed when tertiary butyl iodide (p. 178) is treated with nascent hydrogen, C4H9I + 2H = C4H10 + HI. These two hydrocarbons have been proved to have the same molecular formula, but to be different in properties. Although they are both gases under ordinary conditions, butane liquefies at about 0°, isobutane not until about - 17° under atmospheric pressure, so that they are certainly distinct substances. In chemical properties they closely resemble propane and one another. They give substitution products with chlorine, but the compounds obtained from butane are not identical with those produced from isobutane, although they have the same molecular formula. Constitution of the two Butanes.-The production of butane from ethyl iodide in the above-mentioned manner indicates that this hydrocarbon is di-ethyl. It is therefore represented by the formula H H H H H-C-C-i-i-H, or C2H5 - C2H5, or CHo • CH2 • CH2 • CH3, ll H H i B"m' which not only brings to mind the method of formation of the hydrocarbon, but also indicates its relation to propane. Butane, in fact, may be regarded as propane in ■which one atom of hydrogen has been displaced by the monovalent CH3- group. When, however, the graphic formula of propane is carefully considered, it will be seen that the eight atoms of hydrogen are not all in the same state of combin- ation relatively to the rest of the molecule, but that two of them (a), {a) H H H I I I H-C-C-C-H, or CH3-CH2-CH3, or CH2(CH3)2 H H H (a) (a) («) 64 HYDROCARBONS OF THE METHANE SERIES. are united with a carbon atom which is itself combined with two carbon atoms, whereas each of the other six atoms of hydrogen is combined with a carbon atom which is united with only one other. If, then, one of the (a) hydrogen atoms be displaced by a CII3- group, the constitution of the product would be represented by the formula H H H 1 J । H -C C C-H, A A H-C-H I H or CII3-CH-CH3, or CH(CH3)3 CH3 Isobutane. (nJ whereas, if one of the other hydrogen atoms were displaced, a hydrocarbon of the constitution represented by formula i. would be formed. As in these two cases the atoms would not all be in the same state of combination, the properties of the compounds represented by these formulae would be different. It is next important to note that the above two are the only formulae which can be constructed with four atoms of carbon and ten atoms of hydrogen, if it be assumed that carbon is tetravalent and hydrogen monovalent. All formulae such as H H I \ /H H-C\ H\ I \ H H (X XH H \l I H/\ /H or )C-C-H CZ /H H / I Hx C-H | / H HZ H-CZ A will, on examination, be found to be identical with i. or n., as they express the same state of combination. Since, then, formula i. represents the constitution of butane, that of iso- butane or trimethylmethane is expressed by formula n. This HYDROCARBONS OF THE METHANE SERIES. 65 conclusion is confirmed by a study of the methods of formation and chemical behaviour of isobutane. Pentanes.-Three hydrocarbons of the molecular formula C5H1Q are known ; two of them-namely pentane (b.p. 37°), and isopentane (b.p. 30°)-occur in petroleum, and are colour- less mobile liquids. The third, tetramethylmethane (b.p. 9-5°), can be obtained by treating tertiary butyl iodide with zinc methyl, 2(CH3)3CI + Zn(CH3)2 = 2(CH3)3C-CH3 + Znl2. For reasons similar to those stated in the case of the simpler hydrocarbons, the constitutions of the three pentanes are repre- sented by the formulae H H H H । /H । । r zc h H-C-C-C< I I \r/H 11 H | \h H Isopentane. H H-C-H i H | H H-C-C-C-H H | H H-C-H H Tetramethylmethane. H H H H H H-C-C-A-A-A-H I I I I I H H H H H Pentane. They may all be regarded as derived from the butanes (pen- tane and isopentane from normal butane, tetramethylmethane from isobutane) by the substitution of a CH3- group for one atom of hydrogen. Isomerism.-Compounds, such as the two hydrocarbons C4H10, and the three hydrocarbons C5H12, which have respec- tively the same molecular formula, but different properties, are said to be isomeric. The phenomenon is spoken of as isomerism, and the compounds themselves are called isomers or isomerides. Isomerism is due to a difference in con- stitution or arrangement of the atoms. When graphic formulae are employed to represent the con- stitutions of the hydrocarbons, it will be found possible to construct as many different formulae as there are isomerides. It is possible, for example, to construct three different graphic 66 HYDROCARBONS OF THE METHANE SERIES. formulae for a substance of the molecular formula C5H]Q, and three isomerides only are known; more could not be repre- sented by graphic formulae, assuming always that carbon is tetravalent. This agreement between theoretical conclusions and observed facts is strong evidence of the tetravalent character of carbon. Ethane may be regarded as derived from methane, propane from ethane, and the butanes from the propanes by substitut- ing the monovalent group of atoms CH3- for one atom of hydrogen, and, theoretically, this process can be continued without limit. If one hydrogen atom in each of the three pentanes be displaced by a CH.- group, a number of iso- meric hydrocarbons, C6H14, would be obtained, from each of which, by a repetition of the same process, at least one hydro- carbon, C»H16, might be formed, and so on. It is evident then, that, theoretically, a great number of hydrocarbons may exist, and, as a matter of fact, very many have actually been isolated from petroleum (p. 70). As the number of carbon atoms in the molecule increases, the number of possible isomerides rapidly becomes larger; 7 isomerides of the molecular formula C-H16, 18 of the formula C8H18, and no less than 802 of the formula C13II28 could, theoretically, be formed. In many cases, all the possible isomerides have not been prepared, but there can be little doubt that they could be obtained by suitable reactions. The several isomerides are usually distinguished by the terms normal or primary, iso- or secondary, and tertiary. A normal or primary hydrocarbon is one in which no carbon atom is directly combined with more than two others, as, for example, CH3-CH2.CH2.CH3 Normal Butane. ch3- ch2 • ch2 • ch2 - ch2 • ch3. Normal Hexane. A secondary or iso-hydrocarbon contains at least one carbon atom directly united with three others, ch»-c<h: Isobutane or Trimethylmethane. CH^ ^ch3 Di-isopropyl. HYDROCARBONS OF THE METHANE SERIES. 67 A tertiary hydrocarbon contains at least one carbon atom directly combined with four others, ch3 i ch3 - c - ch3 I CH3 Tertiary Pentane (or Tetramethylmethane). CH3 ch3 - c - ch2 - ch3 I ch3 Tertiary Hexane (or Trimethylethylmethane). In the case of iso- and tertiary hydrocarbons, it is convenient to use a name which readily expresses the constitution of the compound ; examples of such names are given above in brackets. The hydrocarbons methane, ethane, propane, &c., are not only all produced by similar reactions, but they also show very great similarity in chemical properties; for these reasons they are classed together as the paraffins, or hydrocarbons of the methane series. The class, or generic name ' paraffin,' was assigned to this group because paraffin-wax consists principally of the higher members of the methane series. Paraffin-wax is a remarkably inert and stable substance, and is not acted on by strong acids or alkalies; the name paraffin, from the Latin parum aftn^ (small or slight affinity), was given to it for this reason. Homologous Series.-When the paraffins are arranged in order of molecular weight, they form a series, each member of which contains one atom of carbon and two atoms of hydrogen more than the preceding member. Methane, CH4 Ethane, C2H6 Propane, C3H8 Butane, C4H10 Pentane, C5H12 difference CH2 n CH2 h CH2 u CH2. The members of this series are similar in constitution and in chemical properties; but, as the molecular weight increases, the physical properties undergo a gradual and regular variation. Such a series is termed homologous, and the several members are spoken of as homologues of one another; there are many homologous series of organic compounds. 68 HYDROCARBONS OF THE METHANE SERIES. General Formulae.-The molecular composition of all the members of a homologous series can be expressed by a general formula. In the case of the paraffin series the general formula is CTOH2;l + 2, which means, that in any member containing n atoms of carbon in the molecule, there are 2n + 2 atoms of hydrogen; in propane, C3H8, for example, n = 3; 2n + 2 = 8. That this is so can be readily seen by writing the graphic formulae of some of the paraffins in the following manner : H HH HHH H C H H CC H H CCC H H HH HHH when it is at once obvious that for every atom of carbon there are two atoms of hydrogen, the molecule containing, in addi- tion, two extra hydrogen atoms. Since the members of a homologous series can, as a rule, be obtained by similar or general methods, if these be given it is usually unnecessary to describe the preparation of each member separately. In viewr, also, of the great similarity in chemical properties, a detailed account of each compound may be omitted if the general properties of the members of the series be described; the physical properties may also be treated in a general manner, since they undergo a regular and gradual variation as the molecular weight increases. The following is a summary of the principal facts relating to the paraffins treated in this way; it will be found advan- tageous to omit this and other summaries until some know- ledge of other series has been acquired. SUMMARY AND EXTENSION. The Paraffin or Methane Series.-Saturated hydrocarbons of the general formula Callan + a- The more important members of the series are the following, the number of possible isomers being indicated by the figures in brackets : Methane (1), CH4 Ethane (1), C2H6 Propane (1), C3H8 Butane (2), C4Hlfl Pentane (3), C5H12 Hexane (5), CfiH14 Heptane (9), C7H16 Octane (18), C8HI8 Nonane (35), CgH^ Decane (75), C^H^ HYDROCARBONS OF THE METHANE SERIES. 69 Nomenclature.-The names of all the hydrocarbons of this series have the distinctive termination ane, those of the higher members having prefixes which denote the number of carbon atoms in the molecule. Occurrence.-The paraffins are found in nature in enormous quantities as petroleum or mineral naphtha, in smaller quantities as natural gas, and as earth-wax, or ozokerite. Methods of Preparation.-(1) By the dry distillation of an alkali salt of a fatty acid (p. 142) with potash, soda, or soda-lime, CH3-COONa + NaOH = CH4 + Na2CO3 C3H7-COOK + KOH = C3H8 + K2CO3. (2) By the action of nascent hydrogen on the alkyl* halogen compounds, CH3C1 + 2H = CH4 + HC1 C2H5I + 2H = C2H6 + HI. (3) By the action of sodium or zinc on the alkyl halogen com- pounds (Frankland), 2C.,H5I + 2Na = C2H5 -C„H3 + 2NaI 2CH3I + 2Na = CH3-CH3 + 2Nal. (4) By decomposing the zinc alkyl compounds (p. 215) with water, Zn(CH3)2 + 2H.,0 = 2CH4 + Zn(OH)2 Zn(C3H7)2 + 2H2O = 2C3H3 + Zn(OH)2. (5) By the action of the alkyl halogen compounds on the zinc alkyl derivatives, 2CH3I + Zn(CH3)2 = 2CH3CH3 + Znl2 2CH3I + Zn(C2H5)2 = 2CH3C2H5 + Znl2. Tertiary hydrocarbons, such as tetramethylmethane, may be similarly prepared by acting with the zinc alkyl compounds on certain dihalogen derivatives of the paraffins (p. 139), gg|>CCl2 + Zn(CH3)2 = cS|>C<CH3 + ZnC1* (6) By the electrolysis of aqueous solutions of the sodium or potassium salts of the fatty acids, 2CH3.COOK + 2H2O = CH3-CH3 + 2KHCO3 + H2. (7) By the destructive distillation of coal, cannel, turf, shale, and other products of vegetable origin. Physical Properties.-The first four members of the series are colourless gases under ordinary conditions, but on the application of pressure at a low temperature they condense to liquids, and the * The meaning of the word alkyl is given on p. 115. 70 HYDROCARBONS OF THE METHANE SERIES. more readily the greater the number of carbon atoms in the molecule. Methane liquefies at - 11° under a pressure of 180 atmospheres, ethane at 4° under 46 atmospheres, butane at 0° under ordinary atmospheric pressure. The hydrocarbons containing from 4 to about 16 atoms of carbon are colourless liquids under ordinary conditions, the boiling-point rising as the series is ascended. Normal pentane boils at 37°, normal hexane at 69°, and normal heptane at 98°, the difference between the boiling-points of con- secutive normal hydrocarbons being about 30°. The higher members of the series, from about C16H34 (m.p. 18°), are colourless solids, the melting-point rising with increasing molecular weight. The specific gravity of the hydrocarbons from butane, C4H10, to octane, C8H18, varies from 0-600 to about 0-718; from octane upwards the sp. gr. increases until the solid hydrocarbons are reached, when it becomes almost constant at 0-775 - 0-780, this value being determined at the melting-point. The paraffins are insoluble, or nearly so, in water, but soluble in alcohol, ether, and other organic liquids. Chemical Properties.-The paraffins are all characterised by great stability. At ordinary temperatures they are not acted on by nitric acid, fuming sulphuric acid, alkalies, or such powerful oxidising agents as chromic acid and potassium permanganate, and even at higher temperatures only a very slow action occurs. They are, however, attacked by chlorine and, less readily, by bromine in sunlight with formation of substitution products. Iodine has no action on the paraffins. The paraffins are saturated compounds, and cannot combine directly with any element. Paraffins of Commercial Importance.-In Pennsylvania, North America, in Baku, South-east Russia, and in other parts of the world, a gas escapes from the earth under considerable pressure. This natural gas is variable in composition, but usually contains a large proportion of methane and hydrogen, small quantities of other gaseous paraffins, and other hydrocarbons. It is employed as a fuel at Pittsburgh in Pennsylvania for a variety of industrial purposes. In the localities already mentioned, enormous quantities of petroleum or mineral naphtha are also obtained, either from natural springs or from artificial borings. The origin of natural gas and petroleum is unknown, but it is supposed that they are produced by the destructive distillation in the lower layers of the earth's crust of the fatty remains of (sea) animals. Crude petroleum is specifically lighter than water, and varies HYDROCARBONS OF THE METHANE SERIES. 71 greatly in consistency and colour, being generally a thick yellow or brown liquid with a greenish colour when viewed by reflected light. It consists almost entirely of a mixture of hydrocarbons, that obtained from Pennsylvania being composed chiefly of paraffins, that from Baku of hydrocarbons belonging to a different (naphthene) series. Petroleum is not only, next to coal-gas, one of the most important illuminating agents of the present day, but is also the source of a number of substances of considerable commercial value. The crude oil is not directly employed for illuminating purposes, owing partly to the fact that it contains very volatile hydrocarbons which render it too inflammable. In order to obtain the various substances in a condition suitable to the purposes for which they are required, the crude oil is distilled from large iron vessels and the distillate collected in fractions. American petroleum, treated in this way, yields: Petroleum ether (b.p. 40-70°), gasoline (b.p. 70-90°), and ligroin or light petroleum (b.p. 80-120°), colourless mobile liquids used as solvents for resins, oils, caoutchouc, &c.; cleaning oil (b.p. 120-170°), employed for cleaning purposes, and as a substitute for oil of turpentine in the preparation of varnishes ; refined petroleum, kerosene, or burning oil (b.p. 150-300°), used for illuminating pur- poses ; the portions collected above 300° are employed as lubricating oils. The residue consists of heavy lubricating oils, vaseline, and tarry matter. Russian petroleum also yields a variety of products, such as benzine, kerosene, Vulcan oil, vaseline, and tarry matter, which, though slightly different in composition, are similar in pro- perties and uses to those obtained from American oil. Ordinary paraffin-wax is obtained from the tar which is produced by the destructive distillation of cannel-coal or shale. When this tar is fractionally distilled, it yields several liquid products similar to those obtained from petroleum-such as photogene and solar oil, which are used as solvents and for illuminating purposes-and solid paraffins, or paraffin-wax, which is purified by treatment with con- centrated sulphuric acid and redistillation. Paraffin-wax is a colourless, semi-crystalline, waxy substance, soluble in ether, &c., but insoluble in water ; its melting-point ranges from about 45-65°, according to its composition ; its principal use is for the preparation of candles (p. 170). Ozokerite is a naturally occurring solid paraffin or earth-wax which is found in Galicia and Roumania; it is purified by treat- ment with concentrated sulphuric acid and distillation. 72 HYDROCARBONS OF THE ETHYLENE SERIES. CHAPTER V. UNSATURATED HYDROCARBONS- THE OLEFINES, OR HYDROCARBONS OF THE ETHYLENE SERIES. When the halogen mono-substitution products of the paraffins, such as ethyl bromide (p. 176), propyl chloride, &c., are heated with an alcoholic solution of potash, they are con- verted into hydrocarbons, C2H5Br + KOH = C2H4 + KBr + H.,0 C3H7C1 + KOH . C3H6 + KC1 + H2O. The compounds obtained in this way, and by other methods to be described later, contain two atoms of hydrogen less than the corresponding paraffins, and form a homologous series of the general formula CnH.,w; their names are derived from those of the corresponding paraffins by changing the termination ane into ylene, Methane, CH4 ; Ethane, C2H6; Propane, C3H8; Butane, C4H10. Ethylene, C2H4; Propylene, C3H6; Butylene, C4II8. The simplest member of the series is ethylene; the hydro- carbon CH2 (methylene), which would correspond with methane, is unknown, and all attempts to prepare it have been unsuccessful. The word ' olefine ' is derived from ' olefiant ' or ' oil- making ' gas, a name originally given to ethylene on account of its property of forming an oily liquid (ethylene dichloride or Dutch liquid) with chlorine; the generic or class name ' olefine ' is now applied to all the hydrocarbons of the series. Ethylene, ethene, or olefiant gas, C2H4, is formed during the destructive distillation of many organic substances, and occurs in coal-gas, of which it forms about 6 per cent, by volume; the luminosity of the burning gas is to a great extent due to ethylene. HYDROCARBONS OF THE ETHYLENE SERIES. 73 It is formed when acetylene (p. 81) is reduced with zinc dust and ammonia, C2H2 + 2H = C2H4, and when methylene iodide is heated with copper, 2CH2I2 + 4Cu = C9H4 + 2Cu2I2, a reaction which is very similar to the formation of ethane by the action of sodium on methyl iodide (p. 59); also when ethyl bromide is heated with alcoholic potash, C9H5Br + KOH = C9H4 + KBr + H9O, Z «J Z tx z * and when a solution of potassium succinate (p. 235) is sub- mitted to electrolysis, C2H4(COOK)2 = C2H4 + 2CO2 + 2K. In the latter case, a mixture of ethylene and carbon dioxide is obtained at the positive pole, the alkali metal which separ- ates at the negative pole acting on the water with liberation of hydrogen. This interesting method of formation of ethylene is similar to the production of ethane by the electrolysis of potassium acetate (p. 60). Ethylene is prepared by heating a mixture of 1 vol. of ethyl alcohol and 6 vols. of concentrated sulphuric acid in a capa- cious flask (fig. 16), the gas thus produced being passed through wash-bottles containing potash, to free it from sulphur dioxide and carbon dioxide, and then collected over water; when the evolution of gas slackens, a further supply may be obtained by dropping a mixture of 1 vol. of alcohol and 2 vols. of sulphuric acid through the funnel. The reaction may be expressed by the equation c2h5.oh = c2h4 + h2o, but in reality it is not quite so simple (p. 183). Ethylene is a colourless gas, has a peculiar sweet but not unpleasant smell, and liquefies at 10° under a pressure of 60 atmospheres; it is only sparingly soluble in water, more readily in alcohol and ether. It burns with a luminous 74 HYDROCARBONS OF THE ETHYLENE SERIES. flame, and forms a highly explosive mixture with air or oxygen, C2H4 + 3O2 = 2CO2 + 2H2O 2 vols. + 6 vols. = 4 vols. + 4 vols. Its chemical behaviour is totally different from that of the paraffins. It combines directly with hydrogen at high Fig. 16. temperatures (in presence of spongy platinum at ordinary temperatures) forming ethane, c2h4 + H2 = C2H6. Although it is not acted on by hydrochloric acid, it combines directly with concentrated hydrobromic and hydriodic acids at 100°, forming ethyl bromide and ethyl iodide respec- tively, C2H4 + HBr = C2H6Br C2H4 + HI = C2H6L It is absorbed by, and combines with, fuming sulphuric acid, HYDROCARBONS OF THE ETHYLENE SERIES. 75 and, more slowly, with ordinary sulphuric acid, yielding ethyl hydrogen sulphate (p. 182), from which ethyl alcohol is produced on boiling with water, C2H4 + H9S04 = C9H5-HSO4 c2h5-hso4 + H2O = C2H5-OH + H2SO4. It combines directly with chlorine and bromine, and also with iodine in alcoholic solution, C2H4 + X2 = C2H4X2 (X = Cl,Br,I). Constitution of Ethylene.-Ethylene is formed when ethyl bromide, a mono-substitution product of ethane, is heated with alcoholic potash, which simply takes away one atom of hydrogen and one atom of bromine (C2H5Br = C2H4 + HBr); since, there- fore, the constitution of ethyl bromide is represented by the formula H H H H I Ha) II H-C-C-H, that of ethylene would be H-C-C (i.), (b) | I I H Br H assuming that one of the (a) hydrogen atoms were taken away, H H H-C-C-H (n.) if one of the (&) hydrogen atoms were removed. But if ethylene have the constitution (i.), ethylene di- bromide C2H4Br2 (p. 78), the compound formed by the direct combination of ethylene with bromine, must be represented by H H I I the formula (nr.), H-C-C-Br, because, from the behaviour H Br of the paraffins, it is known that the carbon atom in the CH3- group cannot combine with bromine except by substitution. As, however, a substance C2H4Br2 (ethylidene dibromide, p. 78), whose constitution must be represented by the formula (in.), is known, and is not identical with ethylene dibromide, 76 HYDROCARBONS OF THE ETHYLENE SERIES. the latter cannot have the same constitution, but must be H H represented by the only alternative formula H-C-H. Br Br This being the case, the constitution of ethylene might be expressed by formula (il). But such a formula does not indicate that carbon is tetravalent, nor does it recall the fact that ethylene combines directly with Cl2, Br2, HBr, &c. These deficiencies might be remedied by writing ethylene H H H-C-C-H to show that the carbon atoms are tetravalent, I I but that their combining capacity is not fully exercised ; this formula would express the fact that each of the carbon atoms has still the power of combining with one monad atom or group. It is usual, however, to represent the constitution of H H ethylene by the formula H-C=C-H or CH2 = CH.,or CH2:CH2, the two carbon atoms being joined by two lines, bonds, or linkings; this formula is not quite the same as that just given, because it indicates that the particular portion of the com- bining power of each of the carbon atoms, which before was represented as doing nothing, or free, is in some way exerted in ' satisfying,' or combining with, the other carbon atom. There are at least two very good reasons for writing the formula in this way and not with unoccupied lines, or free bonds; firstly, because it has been found impossible to H H prepare hydrocarbons such as H-C-, -C-, or - C-H, a fact I I I H H which indicates that no carbon compound, in which the maximum combining capacity of the carbon atom or atoms is not exerted in some way, can exist; secondly, because when- HYDROCARBONS OF THE ETHYLENE SERIES. 77 ever a compound contains one carbon atom which is not combined with the maximum quantity of four monad atoms or their valency equivalent, the carbon atom directly united with it is in the same ' unsatisfied ' condition. One has never been found to exist without the other, and so it is assumed that they have some action on one another. The above view of the constitution of ethylene receives support from the formation of the gas by the electrolysis of succinic acid, as is clearly seen if the decomposition be represented thus : ch2cooh ch2- co2 h- ch2 h I = I + + = II + 2CO2 + I ; ch2-cooh ch2- co2 h- ch2 h again, the formation of ethylene by the action of copper on methylene iodide can only be explained on the assumption that ethylene has this constitution, ch.l^; ch2 + 4Gu = || + 20u2I2. CH2 k _ CH2 All organic compounds, which, like ethylene, contain carbon atoms having the power of combining directly with other atoms or groups, are said to be unsaturated. In the graphic formulae of all such substances, these particular carbon atoms are represented as joined by a double bond or double linking. When an unsaturated compound enters into direct combination, the double bond is said to be broken, and the two carbon atoms, which before were written with two lines between them, are now joined by only one; the combination of ethylene with bromine, for example, is expressed graphically, H H H H C=i + Br-Br = Br-C-C-Br, II II H H H H to show that ethylene dibromide, like the paraffins, is a saturated substance, and cannot combine except by sub- stitution. The substances formed by the direct union of unsaturated 78 HYDROCARBONS OF THE ETHYLENE SERIES. compounds with atoms or groups of atoms are called additive products, in contradistinction to substitution products. Un- saturated compounds always combine with 2, 4, 6, &c. monovalent atoms or groups, because they always contain an even number of unsaturated carbon atoms. Derivatives of Ethylene.-Ethylene dichloride, C2H4C12, or CH2C1-CH2C1, was originally called Dutch liquid, or oil of Dutch chemists, by whom it was discovered. It is obtained by the direct combination of ethylene and chlorine, and is a colourless liquid of sp. gr. 1-28 at 0°, boiling at 85°. It is isomeric with ethylidene chloride, CH3-CHC12 (p. 139). Ethylene dibromide, C2H4Br2, or CH2BrCH2Br, is prepared by passing ethylene into bromine until the colour of the latter disappears; the product is purified by fractional distillation. It is a colourless crystalline substance, melts at 9-5°, and boils at 131°; its sp. gr. is 2-21 at 0°. It is isomeric with ethylidene bromide, CH3-CIIBr2. Substitution products of ethylene, such as chlorethylene or vinyl chloride, CH2:CHC1, bromethylene or vinyl bromide, CH2:CHBr, cannot be obtained by treating ethylene with a halogen, because additive products are produced in this way. They are prepared by heating the halogen additive products of ethylene with alcoholic potash, CH2Br.CH2Br + KOH = CH2:CHBr + KBr + H2O. Vinyl chloride is a gas, vinyl bromide a colourless liquid, boiling at 16°; they are unsaturated compounds, and combine directly with Br2, HBr, &c. Propylene or methyl-ethylene, C3II6, or CH3-CH:CH2, is formed by the dehydrating action of phosphorus pentoxide on propyl alcohol (p. 104), CH3.CH2.CH2.OH = CH3.CH:CH2 + H2O. It is prepared by boiling either propyl or isopropyl bromide with alcoholic potash, Propyl bromide, CH»-CH2-CH„Br ~TT ~TT _rT TT_, Isopropyl bromide, CH^CHBr-CH, = CH>'CH :CH' + HBr' HYDROCARBONS OF THE ETHYLENE SERIES. 79 It is a gas very similar to ethylene in properties; it liquefies at ordinary temperatures under a pressure of 7-8 atmospheres, and being an unsaturated compound, combines readily with bromine, forming propylene dibromide, CH3-CHBr-CH2Br, an oily liquid boiling at 141°. The higher members of the olefine series are obtained by methods similar to those employed in the case of propylene. Three isomeric butylenes of the molecular formula C4H8 are known, namely, CH^ 2' Iso- or y-butylene. CH3-CH2-CH:CH2 Normal or a-butylene. CH3-CH:CH-CH3 /3-Butylene. They are all colourless gases, and combine directly with chlorine, bromine, hydrobromic acid, &c. Five isomeric amylenes or pentylenes, C5II10, are known, the most important being trimethylethylene or ff iso-amylene, ^>C:CH-CH3, which is obtained by treating fusel oil (pp. 99, 104-5) with zinc chloride; it is a colourless liquid, and boils at 32°. SUMMARY AND EXTENSION. The Olefine or Ethylene Series.-Unsaturated hydrocarbons of the general formula CnH2n. The following are the more important members of this series, the number of possible isomerides being given in brackets : Ethylene (1), C.2H4 Propylene (1), C3HS Butylene (3), C4H8 Amylene (5), C5H10 Hexylene (13), C6H12. Methods of Preparation.-By the action of dehydrating agents, such as H2SO4, ZnCl2, P2O5, &c-> on the alcohols (p. 88), CH3.CH2.OH = CH2:CH2 + h2o. By the action of alcoholic potash on the alkyl halogen compounds (P- 171), CH3-CH2Br + KOH = CH,: CH, + KBr + H2O CH3-CHBr-CH3 + KOH = CH3-CH :CH2 + KBr + H2O. By the electrolysis of certain dibasic acids (p. 229), or, better, of their potassium salts, 80 HYDROCARBONS OF THE ETHYLENE SERIES. ch2cooh ch2 = II + 2CO2 + H2. ch2cooh ch2 Physical Properties.-The first four members of the series are gases; the following fourteen or so, liquids ; the higher members, solids at ordinary temperatures : the boiling-point and the melting- point rise on passing up the series, as in the case of the paraffins. They are insoluble, or nearly so, in water, but more readily soluble in alcohol. Chemical Properties.-The olefines burn with a luminous smoky flame, and can be exploded with oxygen or air. They are unsatu- rated hydrocarbons, and difl'er very considerably in chemical pro- perties from the saturated hydrocarbons of the paraffin series; whereas the latter are either not acted on, or form substitution products when treated with Cl2, Br2, HC1, HBr, HC10, H2SO4, &c., the olefines, as a rule, readily enter into direct combination with all these substances, forming saturated additive products. The olefines are converted into paraffins on treatment with nascent hydrogen, + 2 H = CHH2n + 2. They combine with chlorine and bromine, sometimes with iodine, forming saturated compounds which may be regarded as di-sub- stitution products of the paraffins, CH3CH :CH2 + Cl2 = CHsCHC1CH2C1. They combine with hydrobromic and hydriodic acids, but not, as a rule, with hydrochloric acid, yielding alkyl halogen compounds, CH2:CH2+ HBr = C2H5Br CH3CH :CH2 + HI = CH8.CHICHS, combination generally taking place in such a manner that the halogen atom unites with that carbon atom which is combined with the smallest number of hydrogen atoms ; propylene, for example, yields with hydrobromic acid isopropyl bromide, CH3-CHBrCH3, and not propyl bromide, CH3-CH2-CH2Br; normal butylene, CH3 CH2-CH:CH2, with hydriodic acid, gives secondary butyl iodide, CH3 CH2 CHI CH3, and so on. Fuming sulphuric acid, in some cases ordinary sulphuric acid, readily absorbs the olefines, forming alkyl hydrogen sulphates, CH2:CH2 + H2SO4 = C2H5HSO4. Hypochlorous acid, in aqueous solution, converts the olefines into chlorohydrins (p. 222), CH2:CH2 + H0C1 = CH2C1CH2OH. Unlike the paraffins, the olefines are readily oxidised by chromic HYDROCARBONS OF THE ETHYLENE SERIES. 81 acid and potassium permanganate. When oxidation is carried out carefully under suitable conditions, products containing the same number of carbon atoms as the original olefine are obtained; ethylene, for example, giving ethylene glycol (p. 219); butylene, the corresponding butylene glycol, CH2:CH2 + O + H2O = CH.,(OH)CH2OH CH3.CH2CH:CH2 + O + H2O = CH3-CH2CH(OH)-CH2-OH. Generally speaking, when a substance contains the group -CH = CH-, this group, on oxidation, is in the first place converted into the group -CH(OH)-CH(OH)-. The compounds thus formed readily undergo further oxidation in such a way that the originally unsaturated carbon atoms are forced asunder. Propylene, on vigor- ous oxidation, yields acetic and formic acids; a-butylene gives propionic and formic acids, CH3CH:CH2 + 40 = CH3.COOH + H-COOH CH3-CH2-CH:CH2 + 2O2 = CH3-CH2-COOH + H-COOH. HYDROCARBONS OF THE ACETYLENE SERIES. The relation between the hydrocarbons of the acetylene series and those of the olefine series is the same as that between the olefines and the paraffins; in other words, the members of the acetylene series contain two atoms of hydrogen less than the corresponding olefines, and the general formula of the series is C„H2m _ 2. Paraffins, CwH2n + 2 Olefines, Acetylenes, CnH2u _ 2 Methane, CH4 Ethane, C2H6 Ethylene, C2H4 Acetylene, C2H2 Propane, C3H8 Propylene, C3H6 Allylene, C3H4 Acetylene, C2H2, the simplest member of the series, occurs in small quantities (about 0-06 per cent, by vol.) in coal-gas. It is produced during the incomplete combustion of methane, ethyl alcohol, coal-gas, and other substances; also when the vapour of such substances is passed through a red-hot tube. It is formed when hydrogen is led through a globe in which the electric arc is passing between carbon poles, c2 + h2 = c2h2. This synthesis of acetylene from its elements is of great 82 HYDROCARBONS OF THE ACETYLENE SERIES. interest, because ethylene can be produced from acetylene by the action of nascent hydrogen, and ethylene is readily converted into ethyl alcohol by treating with sulphuric acid and water consecutively (p. 75). As, moreover, a large number of organic substances can be produced from ethyl alcohol, it is possible to prepare all these compounds, starting with carbon and hydrogen. Acetylene is also produced by the electrolysis of a solution of the potassium salt of fumaric or maleic acid (p. 241), hydrogen being evolved at the negative pole (as the result of the action of the liberated potassium on the water) a mixture of acetylene and carbon dioxide at the positive pole, C2H2(COOK)2 = C2H2 + 2CO2 + 2K. Acetylene is prepared by heating ethylene dibromide with excess of alcoholic potash, CQH4Br2 + 2K0H = C2H2 + 2KBr + 2H2O. In the first place, the potash takes away one molecule of hydrogen bromide (C2H4Br2 + KOH = C2HgBr + KBr + H2O), and the vinyl bromide thus produced is then further acted on (C2H3Br + KOH = C2H2 + KBr + H2O). A more convenient method of preparation is to burn coal-gas with a supply of oxygen insufficient for complete combustion, the products being aspirated through an ammoniacal solution of cuprous chloride, when the red copper derivative of acetylene is precipitated. When this compound is decomposed with hydrochloric acid, acetylene is evolved. Acetylene is a colourless gas, which liquefies at 1° under a pressure of 48 atmospheres. It has a characteristic smell, resembling that of garlic, and quite different from that which is noticed when a Bunsen is burning below, although the latter is often erroneously ascribed to the presence of acetylene. It is slightly soluble in water, much more readily in alcohol. It burns with a luminous, very smoky flame, this behaviour being shown by all hydrocarbons which contain a very large percentage of carbon. HYDROCARBONS OF THE ACETYLENE SERIES. 83 Copper acetylene, the brownish-red amorphous compound which is precipitated when acetylene is passed into a solution of cuprous chloride in ammonia, has probably the composition C2H2Cu2O, and its formation serves as a delicate test for acetylene. The dry substance explodes when struck on an anvil or when heated at about 120°. It is decomposed by hydrochloric acid with formation of acetylene and traces of vinyl chloride, but when warmed with a solution of potassium cyanide, it yields pure acetylene. Silver acetylene, CQH2Ag2O, is a colourless amorphous compound obtained on passing acetylene into an ammoniacal solution of silver nitrate. It is more explosive than the copper compound. When acetylene is passed over heated sodium or potassium, hydrogen is evolved, and a metallic substitution product formed, 2C2H2 + 2Na = 2C2HNa + H2. Acetylene combines directly with nascent hydrogen, being converted first into ethylene, then into ethane, CJI9 + 2H = C9H4 C2H2 + 4H = C„H6. Li Lt Lt Li Lt V It combines directly with chlorine, forming dichlorethylene and tetrachlorethane, C2H2 + Cl2 = C2H2C19 C2H2 + 2C12 = C2H.,C14, with bromine, forming dibromethylene and tetrabromethane, and with halogen acids under certain conditions, giving in the first place substitution products of ethylene. Thus, when the copper compound of acetylene is decomposed with hydrochloric acid, small quantities of vinyl chloride or chlorethylene are produced. Sulphuric acid absorbs acetylene. When the solution is diluted with H.,O, and then distilled, acetaldehyde (p. 120) passes over, c2h2 + h2o = C2H4O. Acetaldehyde is also formed when acetylene is passed through an aqueous solution of mercuric bromide. This remarkable reaction-that is, the addition of the elements of 84 HYDROCARBONS OF' THE ACETYLENE SERIES. water to the group HC=CH, by treatment with sulphuric acid or with halogen mercuric salts-appears to be a general one, and is frequently employed as a method of synthesis in organic investiga- tions. When acetylene is heated at a dull red heat, it is converted into benzene (part ii.), 3C2H2 = C6H6. Constitution of Acetylene.-The formation of acetylene from ethylene dibromide may be expressed by the equation H H H-i-i-H = C9H9 + 2HBr, II 2 Br Br so that the constitution of the hydrocarbon might be repre- sented by one of the formulae H H H i-C 01 H-c, which, in order to recall the fact that carbon is tetravalent, and that acetylene combines directly with four monad atoms, must then be written H H H -i-i- or H-C-C-. II II I. n. Since, however, as stated in discussing the constitution of ethylene, one unsaturated carbon atom is never found to exist alone, but requires the presence of another, it must be assumed that the particular portion of the combining capacity of each of the carbon atoms which is not exerted in uniting with hydrogen, is in some way exerted in combining with or satis- fying the other carbon atom. For these reasons, formula i. is written H H I I C=C or CH : CH. But it is impossible to write formula n. in any such manner, HYDROCARBONS OF THE ACETYLENE SERIES. 85 and at the same time to represent both carbon atoms as actively tetravalent. For these and other reasons the con- stitution of acetylene is expressed by the formula CH • CH, which recalls the fact that it contains doubly unsaturated carbon atoms, and is capable of combining directly with two pairs of monad groups or atoms to form additive compounds. This view of the constitution of acetylene accords well with its whole chemical behaviour. The formation of acetylene by the electrolysis of fumaric acid affords support to this view, as will be readily understood if the decomposition be represented thus : CH-COOH CH- CO2 H- CH II = II + + = III + 2CO2 + H2. CH-COOH CH- CO2 H- CH Fumaric Acid. When the hydrocarbon combines with two monovalent atoms, such as 2H, Cl2, Br2, HBr, &c., it loses part of its unsaturated character, and the two carbon atoms, which before were represented as joined by three lines, or by a treble binding or treble linking, are now represented as joined by two only, as in the olefines, CH • CH + 2H = CH2:CH2 CH = CH + Br2 = CHBr:CHBr. If, now, these compounds, which are still unsaturated, again combine with 2H,Br2, &c., they are converted into saturated compounds, CH2:CH2 + 2H = CH3-CH3 CHBr:CHBr + Br2 = CHBr2-CHBr2. Acetylene can also combine with the valency equivalent of four monad atoms, with one atom of oxygen and two atoms of hydrogen, for example, CH H H CH, III + V = I CH O HC:O Homologues of Acetylene.-Two hydrocarbons of the mole- cular formula C3H4 are known; they may be represented by the formulae 86 HYDROCARBONS OF THE ACETYLENE SERIES. CH3.CiCH and CH2:C:CH2. Allylene or Methylacetylene. Allene. Allylene, like acetylene, contains two doubly unsaturated carbon atoms, whereas allene resembles rather ethylene in constitution, and may be considered as containing two pairs of (singly) unsaturated carbon atoms, CH2:C:CH2. This ex- ample shows that isomerism in the acetylene series may be due to a difference in the position of the unsaturated carbon atoms in the molecule, as well as to a difference in the extent of unsaturation, and consequently the number of isomerides in any given case is, theoretically, even greater than in the olefine series. Allylene is prepared by heating propylene dibromide (di- bromopropane) with alcoholic potash, CHyCHBr-CH2Br + 2KOH = CH3-C : CH +2KBr + 2H2O. It is a gas, very similar to acetylene in properties, and gives characteristic copper and silver compounds. Allene is said to be produced in small quantities by heating allyl bromide (p. 255) with alcoholic potash, CH2:CHCH2Br + KOH = CH2:C:CH2 + KBr + H2O. It is also a gas, but it differs from allylene in not forming metallic derivatives. Only those hydrocarbons which contain the group -C: CH yield metallic compounds with ammon- iacal solutions of cuprous chloride and silver nitrate. The higher homologues of acetylene have been compara- tively little investigated. SUMMARY AND EXTENSION. The Acetylene Series: Unsaturated hydrocarbons of the general formula CwH2h_2. The most important members of this series are acetylene, CH;CH, allylene, CH3-C;CH, and its isomeride allene, CH2:C:CH2, and crotonylene, CH3-C:C-CHS. Methods o f Preparation.-By treating the monohalogen substitu- tion products of the olefines, or the dihalogen substitution products of the paraffins, with alcoholic potash, HYDROCARBONS OF THE ACETYLENE SERIES. 87 CH,:CHBr + KOH = CH; CH + KBr + H,0 CH3-CHBr-CH2Br + 2K0H = CH3C;CH + 2KBr + 2H3O. By the electrolysis of the alkali salts of unsaturated dibasic acids, CHCOOH CH II = HI + 2CO2 + H2. CHCOOH CH Physical and Chemical Properties.-The members of the acetylene series up to C^H^ are gases or volatile liquids having a peculiar odour. They are sparingly soluble in water, more readily in alcohol, and burn with a luminous, very smoky flame. The hydro- carbons, CwH2w_2 may be classed in two groups : (1) The true acetylene series, consisting of those compounds which, like acetylene, contain the group-C;C-; and (2) the di-olefines, or hydrocarbons, such as allene, CH2:C:CH2, and diallyl, CH2:CH-CH2-CH2-C.H:CH2, which resemble the olefines in con- stitution. The former behave on the whole like acetylene, whereas the latter are similar to the olefines. Those hydrocarbons of the true acetylene series which contain the group -C;CH form metallic compounds such as copper acetylene, C2H2Cu2O, and silver acetylene, C2H2Ag2O, when treated with ammoniacal solutions of cuprous chloride and silver nitrate. The copper compounds are red, the silver compounds white, and both classes are explosive, the latter more so than the former. These compounds are decomposed by hydrochloric acid, and by warm potassium cyanide solution, the acetylenes being regenerated. The di-olefines, and those members of the true acetylene series, such as CH3-C:CCH3, which do not contain the group -C-CH, do not form these metallic derivatives. The hydrocarbons of the true acetylene series may be caused to combine with the elements of water either by dissolving them in strong sulphuric acid, and then adding water and warming ; or by shaking them with a concentrated aqueous solution of mercuric chloride or bromide, and then decomposing the precipitate which is formed with a dilute mineral acid, CH; CH + H2O = CH3 CHO CH3-C• CH + H2O = CH3 CO CH3. In the case of all the higher members, combination takes place in such a way that the oxygen atom becomes united with the carbon atom which is not combined with hydrogen ; allylene, for example, yields acetone, as shown above, and not propaldehyde, CH3 CH. CHO. All the hydrocarbons of the.CnH2n_2 series combine directly with 88 HYDROCARBONS OF THE ACETYLENE SERIES. two molecules of chlorine, bromine, halogen acids, and with nascent hydrogen, &c., the action taking place in two stages, C2H2 + 2H = C2H4 C2H2 + 4H = C2H6 CH3C;CH + Br2 = CH3CBr:CHBr CH3CBr:CHBr + Br2 = CH3CBr2CHBr2. Like the olefines, they are readily oxidised and converted into compounds containing a smaller number of carbon atoms in the molecule. CHAPTER VI. THE MONOHYDRIC ALCOHOLS. The monohydric alcohols form a homologous series of the general formula CnH2nfl-OH, or CwH2n+2O. They may be regarded as derived from the paraffins by the substitution of the monovalent hydroxyl-group HO- for one atom of hydrogen. Methyl alcohol, CH3-OH, derived from methane, CH3-H Ethyl it C2H5OH, h ethane, C2H5-H Propyl it C3H7-OH, h propane, C3H7-H, &c. Methyl alcohol, wood spirit, or carbinol, CH3-OH, occurs in nature in several substances, amongst others in combination with salicylic acid, as methyl salicylate, in oil of winter- green (Gaultheria procumbens). When this oil is distilled with dilute potash, an aqueous solution of pure methyl alcohol collects in the receiver. Methyl alcohol may be obtained from methane, by first converting the hydrocarbon into methyl chloride, and then heating the latter with dilute aqueous potash in closed vessels, CH3C1 + KOH = CH3-OH + KC1. Methyl alcohol is prepared from the products of the destructive distillation of wood. When wood is heated in iron retorts out of contact with air, gases are evolved, water, tar, and other products collect in the receiver, and wood-coke THE MONOHYDRIO ALCOHOLS. 89 or charcoal remains. After allowing the distillate to settle, the brown aqueous layer, which contains methyl alcohol, acetic acid, acetone, and other substances, is drawn off from the wood-tar and distilled from a copper vessel, the vapours being passed through hot milk of lime, to free them from acetic acid, and then collected in a receiver; this distillate is diluted with water to precipitate oily impurities, and then submitted to careful fractional distillation over quick- lime. The liquid obtained in this way contains 98-99 per cent, of methyl alcohol. In order to free it from acetone and other impurities, it is mixed with powdered calcium chloride, with which the methyl alcohol combines, forming a crystalline compound of the composition CaCl2 + 4CH4O. This substance is freed from acetone by pressure between cloths, and then decomposed by distilling with water; the aqueous methyl alcohol is finally dehydrated by repeated distillation with quicklime, but it still contains traces of acetone and other impurities. Pure methyl alcohol can be prepared by warming the impure product with oxalic acid, when methyl oxalate is produced (p. 233), 2CH>-0H + C9O4H„ = C9O4(CH.,)2 + 2HoO; this crystalline substance is decomposed by distilling with potash, and the aqueous solution of pure methyl alcohol dehydrated with caustic lime as before. Methyl alcohol is a colourless, mobile liquid of sp. gr. 0-796 at 20°; it boils at 66°, has an agreeable vinous or wine- like odour, and a burning taste. It mixes with water in all proportions, a slight contraction in volume taking place, and heat being developed; it burns with a pale, non-luminous flame, and its vapour forms an explosive mixture with air or oxygen, 2CH3-OH + 3O2 = 2CO2 + 4H2O. It is largely used in the manufacture of organic dyes and var- nishes, and for the preparation of methylated spirit (p. 100). 90 THE MONOHYDRIC ALCOHOLS. Sodium and potassium dissolve readily in methyl alcohol with evolution of hydrogen and formation of metallic compounds called methylates or methoxides, 2CH3-OH + 2Na = 2CH3-ONa + II2, a reaction which is similar to the decomposition of water by sodium. Sodium methoxide is readily soluble in methyl alcohol, but can be obtained in a solid condition by evaporating the solution in a stream of hydrogen; it is a colourless, crystalline, very deliquescent compound, which rapidly absorbs carbon dioxide from the air, and is immediately decomposed by water with regeneration of methyl alcohol, CH3ONa + H2O = CH3OH + NaOH. Potassium methoxide has similar properties. Although neutral to test-paper, methyl alcohol acts like a weak base, and combines with acids to form salts; when saturated with hydrogen chloride, it yields methyl chloride, corresponding with potassium chloride, CH3OH + HC1 = CH3C1 + H.?O KOH + HC1 = KC1 + H.,O, and when warmed with sulphuric acid, it gives methyl hydrogen sulphate, corresponding with potassium hydrogen sulphate, and methyl sulphate, corresponding with potassium sulphate, CH3-OH + HoSO4 = CH3-HSO4 + H2O 2CH„-0H + H"SO, = (CH.,)2SO4 + 2H„O. When phosphorus pentachloride, trichloride, or oxychloride is added to methyl alcohol, a considerable development of heat occurs, and methyl chloride is formed, CH3-OH + PC15 = CH3C1 + HC1 + POC13 3CH3-OH + PC13 = 3CH3C1 + H3PO3 3CH3-OH + POC13 = 3CH3C1 + H3PO4. The corresponding bromides of phosphorus act in a similar manner. THE MONOHYDRIC ALCOHOLS. 91 Methyl alcohol is readily oxidised,* being first converted into formaldehyde and then into formic acid, CH3-OH + 0 = CH,0 + H2O CH2O + 0 = CH2O2. Formaldehyde. Formic Acid. Constitution of Methyl Alcohol.-Since only one of the four hydrogen atoms in methyl alcohol, CH4O, is displaceable by potassium or sodium, it must be concluded that this particular hydrogen atom is in a different state of combination from the other three; but methyl alcohol is formed by the action of dilute alkalies on methyl chloride, CH3C1 + KOH = CH3OH + KC1, * The substances most frequently used in oxidising organic compounds are: Chlorine water, bromine water, nitric acid, chromic acid, manganese dioxide and sulphuric acid, and potassium permanganate. Chlorine and bromine, in presence of water, act as oxidising agents by liberating oxygen, Cl2 + H20 = 2HC1 + 0. Nitric acid gives up some of its oxygen and is reduced to an oxide of nitrogen, the nature of which depends on that of the substance undergoing oxidation, and on the conditions of the experiment, 2HN0.} = H20 + N203 + 20 2HNO3=H2O + 2NO2 + O, &c. Chromic acid in the presence of sulphuric or acetic acid gives oxygen and a chromic salt, 2CrO3 = Cr2O3 + 30, or 2CrO3 + 3H2SO4 = Cr2(SO4)3 + 3H2O + 30. A mixture of potassium dichromate and sulphuric acid, which is very often used instead of chromic acid, yields oxygen and a mixture of chromic sulphate and potassium sulphate, which frequently crystallises out in dark purple octahedra of chrome-alum, K2SO4, Cr2(SO4)3 + 24HaO, K2Cr207 + 4H2S04 = K2SO4 + Cr2(SO4)3 + 4H20 + 30. Potassium permanganate, in alkaline solution, is decomposed, yielding a precipitate of hydrated manganese dioxide, 2KMnO4 + H20 = 2Mn02 + 2K0H + 30; but in acid solution the same quantity of permanganate gives five instead of three atoms of oxygen, 2KMnO4 + 3H2S04 = K2SO4 + 2MnSO4 + 3H2O + 50, because manganese dioxide and sulphuric acid yield oxygen, 2Mn0a + H2SO4 = MnS04 + H20 + 0. 92 THE MONOHYDRIC ALCOHOLS. and the three hydrogen atoms in methyl chloride, which are known to be combined with carbon, are not displaceable by metals. It is evident, therefore, that the displaceable hydrogen atom in methyl alcohol is not combined with carbon; the only other possibility is that it is combined with oxygen, and that methyl alcohol has the constitution H H-C-0-H, which is usually written CH3-OI1. When H represented in this way, the whole chemical behaviour of methyl alcohol is summarised in its graphic formula; the fact that the oxygen atom cannot be taken away without one of the hydrogen atoms accompanying it-as, for example, when the alcohol is treated with HC1, PC15, PBr5, tec.-is recalled by the two atoms being represented as directly united. The similarity between methyl alcohol and the metallic hydroxides is also accounted for; the alcohol may be regarded as derived from water, H-O-H, by substituting the monovalent CH3- group for one atom of hydrogen, just as sodium hydroxide, Na-OH, is obtained by the substitution of one atom of sodium. Methyl alcohol, in fact, is methyl hydroxide, and, like other hydroxides, it forms salts and water when treated with acids, CH3OH + HC1 = CH3C1 + H2O Na-OH + HC1 = NaCl + H2O." Like water and certain metallic hydroxides, it contains dis- placeable hydrogen, 2CH3-OH + 2Na = 2CH3-ONa + Ho Zn(OH)2 + 2K0H = Zn(OK)2 + 2H2O. It may also be considered as a hydroxy-substitution product of the paraffin, methane ; it is termed a monohydric alcohol because it contains one hydroxyl-group. Ethyl alcohol, spirits of wine, alcohol, or methyl carbinol, C2H6-OH, has been known from the earliest times, as it is 93 contained in all wines prepared by the fermentation (p. 97) of grape juice. It may be obtained from ethane by converting the hydro- carbon into ethyl chloride and heating the latter with dilute alkalies under pressure, C2H5C1 + KOH = C2H5-OH + KC1, and by passing ethylene into fuming sulphuric acid, and then boiling the solution with water, a reaction of considerable theoretical importance, C9H4 + H9S04 = C9H5-HSO4 C2H5-HSO4 + H2O = C2H5.OH + H2SO4; also by reducing* acetaldehyde in aqueous solution with sodium amalgam, C2H4O + 2H = C2H6O. Alcohol may be prepared by placing a weak aqueous * The substances most frequently used in reducing organic compounds are, sodium, zinc, tin, iron, sodium amalgam, hydrogen iodide, sulphuretted hydrogen, and sulphur dioxide in aqueous, acid, alkaline or alcoholic solution. Sodium, acting on the alcoholic or moist ethereal solution of the substance, is one of the most powerful reducing agents known, 2Na + 2C2H5.OH = 2C2H5-ONa + 2H 2Na + 2H2O = 2NaOH + 2H. Sodium Amalgam, an alloy of sodium and mercury, acts on aqueous or dilute alcoholic solutions in the same way as metallic sodium, the action being, however, greatly moderated by the presence of the mercury. Zinc and hydrochloric or sulphuric acid, or zinc dust and acetic acid, are perhaps the most commonly employed reducing agents; in some cases the action is much accelerated by coating the zinc with copper in the form of the zinc-copper couple (p. 57). Zinc dust is sometimes employed in alkaline solution, as, for instance, in the presence of potash, soda, or ammonia, Zn + 2K0H = Zn(OK)2 + 2H. Substances which are reduced only with great difficulty are frequently mixed with zinc dust and heated at a high temperature. Tin and hydrochloric acid act as reducing agents, stannous chloride being first produced, Sn + 2HC1 = SnCl2 + 2H. Stannous chloride is not acted on by hydrochloric acid alone, but, in THE MONOHYDRIC ALCOHOLS. 94 solution of cane- or grape-sugar in a capacious flask, adding a small quantity of brewer's yeast, and keeping the mixture in a warm place (at about 20°). After some time it begins to froth and ferment (p. 97), and, if the flask be fitted with a cork and delivery tube, it can be proved that carbon dioxide is being evolved by passing the gas into lime-water. After about 24 hours' time the yeast is filtered oft', and the solution distilled from a flask or retort connected with a condenser, the process being stopped when about one-third has passed over. In this way the more volatile alcohol is partially separated from the water (fractional distillation). The dis- tillate has an unpleasant vinous smell, and consists of an aqueous solution of slightly impure alcohol. It is poured into a retort or flask connected with a condenser, and a con- siderable quantity of freshly-burnt lime in the form of small lumps is then slowly added; after some hours, the alcohol is distilled by heating on a water-bath. By repeating this process several times, employing fresh caustic lime in sufficient quantity, alcohol containing only about 0-2 per cent, of water is obtained, but it is impossible to free it completely from water by distillation over lime. When the alcohol con- tains less than about 0-5 per cent, of water, it is known commercially as absolute alcohol. Wines, beers, and spirits contain alcohol, and its prepara- tion from these liquids is very simple. The liquid is distilled, and the alcohol, thus freed from colouring matter and other presence of reducible substances, it is a very powerful reducing agent, being converted into stannic chloride, SnCl2 + 2HC1 = SnCl4 +211. Hydriodic Acid, in concentrated aqueous solution, is a very powerful reducing agent at high temperatures, the hydrogen iodide being decomposed into hydrogen and iodine. Sulphuretted Hydrogen, being readily decomposed into sulphur and hydrogen, is frequently used as a mild reducing agent, generally in the form of ammonium sulphide. Sulphur Dioxide has only a limited use ; in presence of water and reduc- ible substances, it is converted into sulphuric acid, SO2 + 2H2O = H2SO4 + 2H. THE MONOHYDRIC ALCOHOLS. 95 solid substances, is then dehydrated by distillation with caustic lime. Alcohol is a colourless, mobile liquid of sp. gr. 0-8062 at 0°; it has a pleasant vinous odour and a burning taste; it boils at 78°, but does not solidify until about - 130° (hence its use in alcohol thermometers). It burns with a pale, non- luminous flame, and its vapour forms an explosive mixture with air or oxygen, C2H5-OH + 3O2 = 2CO2 + 3H2O. It mixes with water in all proportions with develop- ment of heat and diminution of volume; 52 vols. of alcohol and 48 vols. of water give a mixture occupying only 96-3 vols. Ethyl alcohol closely resembles methyl alcohol in chemi- cal properties. It quickly dissolves sodium and potassium with evolution of hydrogen and formation of ethylates or ethoxides, 2C2H5-OH + 2Na = 2C2H5-ONa + H2. These compounds are readily soluble in alcohol, but may be obtained in a solid condition by evaporating the solution in a stream of hydrogen. They are colourless, hygroscopic sub- stances, rapidly absorb carbon dioxide from the air, and are immediately decomposed by water with regeneration of alcohol, C2H5-OK + H2O = C2H5-OH + KOH. Although it has a neutral reaction, alcohol acts like a weak base, and when treated with acids, is converted into salts with formation of water, C2H5-OH + HI = C2H5I + H2O. When treated with the chlorides or bromides of phosphorus, it is converted into ethyl chloride or ethyl bromide, an energetic action taking place, C2H5-OH + PBr5 = C2H5Br + HBr + POBr3. Alcohol is readily oxidised by chromic acid, yielding acetalde- THE MONOHYDRIC ALCOHOLS. 96 THE MONOHYDRIC ALCOHOLS. hyde, which on further oxidation is converted into acetic acid, C2H5-OH + 0 = C2H4O + H2O C2H4O + 0 = C2H4O2. Acetaldehyde. Acetic Acid. By the action of the ferment, mycoderma aceti, it is, under certain conditions (p. 148), oxidised to acetic acid at ordinary temperatures by the oxygen of the air. The presence of alcohol in aqueous solution may be detected by Lieben's iodoform reaction (p. 175). A small quantity of iodine is placed in the solution, and then caustic potash is added drop by drop until the colour of the iodine disappears. If alcohol be present in considerable quantity, a yellow pre- cipitate of iodoform is produced almost immediately. In very dilute solutions of alcohol only a very slight precipi- tate is formed even after some time, but it may be recognised as iodoform by its odour, and by the characteristic appear- ance of its six-sided crystals when viewed under the micro- scope. By means of this reaction it is possible to detect 1 part of alcohol in 2000 parts of water. It is especially valuable as affording a means of distinguishing between ethyl and methyl alcohols, as the latter does not give the iodoform reaction, although many other substances, such as acetone, aldehyde, &c., do so. The presence of water in alcohol can be detected by adding a little anhydrous copper sulphate. If water be present, the colourless powder turns blue, owing to the formation of the hydrated salt, but this test is not very delicate. Constitution.-The formation of alcohol from ethyl chloride, the fact that only one of its six atoms of hydrogen is displace- able by metals, and its close resemblance to methyl alcohol in chemical properties, lead to the conclusion that it is a hydroxide H H of the constitution H-C-O-H, or C2H5-OH. It may H H be regarded as a mono-hydroxy-substitution product of ethane. THE MONOHYDRIC ALCOHOLS. 97 Production of Wines and, Beers ; Alcoholic Fermentation. When the juice of grapes is kept for a few days at ordinary temperatures, it changes into wine; the sugars, dextrose and levulose (p. 262), present in the juice being decomposed into alcohol and carbon dioxide. This change is brought about by a small vegetable organism; the process is called fermentation, and the active agent which causes the change is termed a ferment. All wines, beers, and spirits, and the whole of the alcohol of commerce are prepared by the process of fermentation. The ferment which brings about the conversion of grape- juice into wine is present on the grapes and stalks and in the air; it is a living organism, and during fermentation it rapidly grows and multiplies, feeding on the sugar, mineral salts, and nitrogenous substances contained in the juice. In order that fermentation may take place, the conditions must be favourable to the life and growth of the living ferment; sufficient food of a suitable kind must be at hand, and the temperature must be kept within certain limits. Beer is prepared from malt and hops. Malt is the grain of barley which has been caused to sprout or germinate by first soaking it in water and then keeping it in a moist atmosphere at a suitable temperature. During the process of germination a ferment, diastase, is formed in the grain. The malt is now heated at 50-100° in order to stop germina- tion and to cause the production of various substances which impart to it both colour and flavour, the character of the beer depending largely on the temperature and the duration of heating. It is then stirred up with water and kept at 60-65°, when fermentation sets in, the diastase converting the starch in the malt into dextrin and a sugar, maltose. This solution is now boiled in order to stop the diastatic fermentation, and then hops, the flower of the hop-plant, are added in order to impart a slight bitter taste, and also on account of the preservative properties of the hops. After 98 THE MONOHYDRIC ALCOHOLS. cooling to from 5° to 20°, yeast is added, when alcoholic fer- mentation sets in, the sugar maltose being gradually converted into alcohol and carbon dioxide. The beer is then run off and kept until ready for consumption. Beer usually contains 3-6 per cent, of alcohol, small quantities of dextrin, sugars, and colouring matters, and traces of succinic acid, glycerol, and other substances. It contains, moreover, carbon dioxide, to which it owes its refreshing taste, and small quantities of fusel oil, which help to give it a flavour. The production of beer involves two distinct fermentations. In the first place, the starch in the malt is converted into maltose and dextrin by the diastase, 3(C6H10O5) + H2O = C^H^On + C6IJ1UO5; Starch. Maltose. Dextrin. in the second place, the maltose is transformed into alcohol by the yeast, C^H^On + H2O = 4C2H6O + 4CO2. One of the ferments cannot do the work of the other; yeast cannot convert starch into maltose, nor can diastase set up the alcoholic fermentation of sugar. Diastase is an amorphous substance, without definite form or structure, and apparently lifeless. Such ferments are termed enzymes, in contradistinction to living organ- ised ferments of definite structure, of which yeast is an example. Yeast (saccharomyces) consists of rounded, almost trans- parent living cells, which are usually grouped together in chain-like clusters. When placed in solutions of certain sugars containing small quantities of mineral substances, &c., which the organism requires for food, the cells soon begin to bud and multiply, provided also that the temperature is kept between about 5° and 30°; if it exceeds these limits, the plant stops growing, and fermentation ceases. There are several sugars which can be fermented with yeast, the most important being dextrose or grape-sugar, CfiH]OOC), levulose or fruit-sugar, C6H12O0, and maltose, CloHooOir Cane-sugar, C]OHo.2On, does not ferment -with pure yeast, but does so with ordinary yeast, because the latter contains other THE MONOHYDRIC ALCOHOLS. 99 ferments which rapidly convert the cane-sugar into equal molecules of dextrose and levulose : C12H22OU + H2O = C6H12O6 + C6H12O6. Dextrose. Levulose. The alcoholic fermentation of these sugars is expressed approximately by the equation, C6H12O6 = 2C2H6O + 2CO2; but small quantities of succinic, acetic, lactic, and butyric acids, glycerol, fusel oil, and other substances are also formed. Fusel oil is a mixture of the higher homologues of ethyl alcohol; it is usually present in small quantities in beers and spirits. Manufacture of Alcohol and Spirits,-Alcohol is prepared on the large scale from potatoes, grain, rice, and other substances rich in starch. The raw material is reduced to a pulp or paste with water, mixed with a little malt, and the mixture kept at about 60° for 30-60 minutes, when diastatic fermentation takes place, and the starch is converted into dextrin and maltose. After cooling to about 15°, yeast is added, and the mixture kept until alcoholic fermentation is at an end. It is possible to obtain alcohol from starch without the use of malt, since starch is converted into dextrose when heated with dilute sulphuric acid, and, after neutralising with lime, the solution can be fermented with yeast. Alcohol is also prepared from beet-root, molasses (treacle), and other substances rich in sugar, by direct fermentation with yeast. The weak solution of alcohol obtained by any of these methods is submitted to fractional distillation in specially constructed apparatus. The distillate is known as ' raw spirit,' and contains from 80-95 per cent, of alcohol and a small quantity of fusel oil, which passes over in spite of the fact that its constituents boil at a higher temperature than alcohol or water. For the preparation of spirits, liqueurs, and other articles 100 THE MONOHYDRIC ALCOHOLS. of consumption, the raw spirit must be freed as much as possible from fusel oil, which is very injurious to health. For this purpose it is diluted with water and filtered through charcoal, which absorbs some of the fusel oil. Finally, the spirit is again fractionally distilled, the portions which pass over first (' first runnings ') and last (' last runnings ') being collected separately; the intermediate portions consist of ' refined ' or ' rectified spirit,' most of the fusel oil, which has not been removed, being present in the last runnings. For most other purposes the separation of the fusel oil is unnecessary, and if a stronger alcohol be required, the raw spirit is again fractionated, or distilled over lime. Alcohol is used in large quantities for the manufacture of ether, chloroform, &c., and in the purification of the alkaloids. It is employed as a solvent for gums, resins, and other sub- stances, in the preparation of tinctures, varnishes, perfumes, &c., and is also used in spirit-lamps. In this country a heavy excise duty has long been levied on spirits of wine, a fact which acted as a serious impediment to its extended use; but since 1856 the Government has permitted the manufacture and sale of methylated spirit free of duty. Methylated spirit contains about 90 per cent, of raw spirit (ethyl alcohol), about 10 per cent, of partially purified wood- spirit or methyl alcohol, and a small quantity of paraffin-oil, the addition of which renders the alcohol unfit for drinking purposes, without affecting its value as a solvent; methy- lated spirit is therefore used instead of alcohol whenever possible, as it is so much cheaper. Methylated spirit cannot be separated into its constituents by any commercial process, but the water and tarry and oily impurities can be got rid of almost completely by distilling with a little potash, and then dehydrating over lime; the purified spirit may be employed in most chemical experiments in the place of pure ethyl alcohol. Alcoholometry.-In order to ascertain the strength of a sample of alcohol-that is, the percentage of alcohol in pure THE MONOHYDRIC ALCOHOLS. 101 aqueous spirit, it is only necessary to determine its specific gravity at some particular temperature, and then to refer to published tables, in which the sp. gr. of all mixtures of alcohol and water is given. If, for example, the sp. gr. is found to be 0-8605 at 15-5°, reference to the tables would show that the sample contained 75 per cent, of alcohol by weight. For excise and general purposes the sp. gr. is determined with the aid of hydrometers graduated in such a manner that the percentage of alcohol can be read off directly on the scale. The standard referred to in this country is proof-spirit, which contains 49-3 per cent, by weight, or 57-1 per cent, by volume of alcohol: it is defined by act of parliament as being 'such a spirit as shall at a temperature of 51° F. weigh exactly y^ths of an equal measure of distilled water.' Spirits are termed under or over proof according as they are weaker or stronger than proof-spirit : thus 20° over proof means that 100 vols. of this spirit diluted with water -would yield 120 vols. of proof-spirit, whilst 20° under proof means that 100 vols. of the sample contain as much alcohol as 80 vols. of proof-spirit. The name proof-spirit owes its origin to the practice in vogue during the last century, of testing the strength of samples of alcohol by pouring them on to gunpowder and applying a light. If the sample contained much water, the alcohol burned away, and the water made the powder so damp that it did not ignite ; but if the spirit were strong enough, the gunpowder took fire. A sample which just succeeded in igniting the powder was called proof- spirit. For the determination of alcohol in beers, wines, and spirits, a measured quantity of the sample is distilled from a flask connected with a condenser until about |d has passed over. The distillate, which contains the whole of the alcohol, is then diluted with water to the volume of the sample taken, and its sp. gr. determined with a hydrometer; the percentage of alcohol is found by referring to the tables already mentioned. 102 THE MONOHYDRIC ALCOHOLS. Distillation is necessary because the sugary and other extractive matters contained in the sample influence the sp. gr. to such an extent that a direct observation would be of no value. The percentage of alcohol by weight in some of the best-known fermented liquors may be roughly taken as being as follows : Brandy 50 % Whisky 50 % Gin 40 % Port 20 % Sherry 16 % Claret 7 % Hock 8 % Burton Ale..5-5 % Lager-bier 3 % Homologues of Ethyl Alcohol.-The members of the series of monohydric alcohols may all be considered as derived from the paraffins by the substitution of the monovalent HO- group for one atom of hydrogen. Like the paraffins, they exist in isomeric forms, but, as two or more isomeric alcohols may be derived from one hydrocarbon, the number of iso- merides is greater in the alcohol than in the paraffin series. Propane, CH3-CH2-CH3, for example, exists in only one form, but two isomeric alcohols may be derived from it -namely, propyl alcohol, CH3-CH9-CH2-OH, and isopropyl alcohol, CH3-CH CH3, or CH3-CH(OH).CH3. OH In order to distinguish between the various isomerides, the alcohols may be considered as derivatives of methyl alcohol 1 II or carbinol, CH3-OH, or C< . Thus, propyl alcohol, (oh CH3-CH2-CH2-OH, may be termed ethyl-carbinol, because it may be considered as derived from carbinol by displacing one atom of hydrogen by the ethyl group C2H5-. Isopropyl alcohol, (CH3)2CH-OH, may be called dimethyl-carbinol, and regarded as derived from carbinol, by substituting two methyl or CH3- groups for two atoms of hydrogen. Such names as these serve to express the constitution of the substance, as will be seen by considering the case of the four isomeric butyl alcohols, C4H9-OH, THE MONOHYDRIC ALCOHOLS. CHo-CH2-CH3 H H OH Normal butyl alcohol, or propyl carbinol (primary). 103 CH3.CH2CH2CH2OH, or C gH<c£ H OH ^|>CHCH2OH, or C Isobutyl alcohol, or isopropyl carbinol (primary). 2I&>CH 0H, or C- C2H5 CH3 C2H5 H OH Methylethyl carbinol (secondary). CH3 ch3 CH3 OH CHX CHo^C-OH, or C CHf" Trimethyl carbinol (tertiary). The alcohols are divided into three classes, namely, normal or primary, iso- or secondary, and tertiary alcohols. Primary or normal alcohols (such as normal propyl alcohol, CH3>CH.,-CH2-OH), contain the group -CH2-OH, and may be considered as mono-substitution products of carbinol. On oxidation with chromic acid, &c., they are converted first into aldehydes (p. 116) and then into fatty acids, (p. 142), the group -CH2-OH being transformed first into -C^^, and then ■ + II into -O^q ch3.ch„.oh + 0 = CH3-CHO + H.,0 CHUCHO + 0 = CH3-COOH. These oxidation products contain the same number of carbon atoms in the molecule as the alcohols from which they are obtained. Secondary or iso-alcohols, such as isopropyl alcohol, CH3'CH(OH)-CH3, contain the group^>CH-OH, and may be regarded as di-substitution products of carbinol. On oxi- dation they are converted into ketones (p. 127) containing the same number of carbon atoms, the group^>CH-OH becoming >CO, CH3.CH(OH)-CH3 + 0 = ch3-co-ch3 + h2o. THE MONOHYDRIC ALCOHOLS. 104 Tertiary alcohols, such as tertiary butyl alcohol, chk CH3^.C(OH), contain the group -C-OH, and may be CH< regarded as tri-substitution products of carbinol. On oxida- tion they yield both ketones and fatty acids, which contain a smaller number of carbon atoms than the alcohol from which they are derived, the molecule of the latter being broken up. Tertiary butyl alcohol, or trimethyl carbinol, (CH3)3C-OH, for example, yields acetone, CH3-CO-CH3, acetic acid, CH3-CO-OH, carbon dioxide, and other products. It could not be converted by simple loss of hydrogen into a compound, CHx CH.^CO, containing the same number of carbon atoms-a ^ .3 change which would be analogous to that undergone by primary and secondary alcohols-because carbon is tetravalent and not pentavalent, as represented in this formula. Propyl alcohol (normal ethyl carbinol), CH3-CH2-CH2-OH, is one of the principal constituents of fusel oil, from which it is prepared by fractional distillation. It is formed when propyl iodide is heated with freshly precipitated silver hydroxide, C3H7I + Ag-OH = C3H7OH + Agl. It is a colourless liquid of sp. gr. 0-817 at 0°, boils at 97°, and is miscible with water in all proportions. On oxidation with chromic acid, it is converted first into propaldehyde and then into propionic acid, CH3-CH2CH2-OH + 0 = CH3-CH2-CHO + H2O Propaldehyde. CH3.CH2.CH2OH + 20 = ch3.ch2-co-oh + h2o. Propionic Acid. Isopropyl alcohol, or dimethyl carbinol, (CH3)2CH-OH, is best prepared by the reduction of acetone in aqueous solution with sodium amalgam, CH3-CO-CH3 + 2H = CH3.CH(OH).CH3. THE MONOHYDRIC ALCOHOLS. 105 It is a colourless liquid of sp. gr. 0-789 at 0°, and boils at 81°, or about 16° lower than normal propyl alcohol. On oxidation it yields acetone, CH3-CH(OH)-CH3 + O = CH3-CO-CH3 + h2o. There are four isomeric butyl alcohols, C4H9-OH. Normal butyl alcohol, or propyl carbinol, CH3-CH2-CH2-CH2-OH, may be prepared by the reduction of butaldehyde, CH3-CH2-CH2-CHO, and is produced during the fermenta- tion of glycerol by certain bacteria. It boils at 117°. Isobutyl alcohol, or isopropyl carbinol, (CH3)2-CH-CH-2OII, is contained in large quantities in fusel oil. It boils at 107°. Methylethyl carbinol, (CH3)-CH(OH)-C2H5, is obtained by the reduction of methyl ethyl ketone, CH3-CO-C2H5 (p. 136), by means of sodium amalgam. It boils at 100°. Trimethyl carbinol, (CH3)3C-OH, may be prepared by the action of zinc methyl, Zn(CH3)2, on acetyl chloride, CH3-COC1, a reaction which is described below (p. 107). It may also be obtained from isobutyl alcohol, as explained later (p. 108). Trimethyl carbinol is one of the few alcohols which are solid at ordinary temperatures. It melts at 28°, and boils at 83-84°. Amyl alcohols, CjH^-OH.-Of the eight isomerides theo- retically capable of existing, the following two occur in fusel oil: Isobutyl carbinol, ^3>CH-CH2-CH2-OH. B.p. 131°. (Isoamyl alcohol.) Secondary butyl carbinol, R B ?o (Active amyl alcohol.) * 1 These alcohols always occur in commercial amyl alcohol, and their boiling-points lie so close together that they cannot be separated by fractional distillation. A separation may, however, be accomplished by treating the mixture with sulphuric acid, and thus converting both alcohols into the alkyl hydrogen sulphates, C5HirOH + H2SO4 = C5H11-HSO1 + H2O. By neutralising these acid salts with barium hydrate, the barium salts, (C5Hn-SO4).2Ba, are obtained; and, as the barium salt of iso- butyl carbinol is more sparingly soluble than that of active amyl alcohol, the two may be separated by fractional crystallisation. 106 THE MONOHYDRIC ALCOHOLS. From the pure salts the respective alcohols are then obtained in a pure condition by distillation with dilute mineral acids, C5Hu-HSO4 + 1I2O = C6Hu-0H + H2SO4. Commercial amyl alcohol is prepared from fusel oil by fraction- ation, and is a mixture of about 87 per cent, of isobutyl carbinol and about 13 per cent, of active amyl alcohol. It has a pungent, unpleasant smell, boils at about 131°, and is used as a solvent, and in the preparation of essences and perfumes (p. 189). SUMMARY AND EXTENSION. The Monohydric Alcohols.-Hydroxy-derivatives of the paraf- fins of the general formula CnH2n+1-0H. The more important members of the series are the following. The letters p., s., t., in brackets, denote primary, secondary, and tertiary. Name and composition. B.p. Sp. gr. Methyl alcohol (p.) CH3-OH, 66° 0-812 at 0° Ethyl alcohol (p.) C2H5-OH, 78° 0-806 „ Propyl alcohol (p.) \c,H,.OH, Isopropyl alcohol (s.) J 97° 0-817 83° 0-816 „ Butyl alcohol, (p.) 117° 0-823 „ Isobutyl alcohol (p.) 1 p „ on Tertiary butyl alcohol (t.) 4 9 ' 108° 0-816 „ 83° 0-786 at 20° Methylethyl carbinol (s.)/ 99° 0-827 Active amyl alcohol (p.).. 128° - If Isoamyl alcohol (p.) g 0U Six other isomerides of " 5 11 little importance _ 132° 0-825 „ Methods of Preparation.-Methyl alcohol is prepared from the products of the dry distillation of wood. Ethyl alcohol is obtained by the alcoholic fermentation of sugar by means of yeast; the fusel oil produced at the same time contains propyl, isobutyl, active amyl, and isoamyl alcohols. The alcohols are formed when the halogen substitution products of the paraffins are heated with water, dilute aqueous alkalies, or freshly precipitated silver hydroxide, CH3Br+KOH=CH3 OH + KBr C3H7I +Ag-OH=CSH7OH + Agl; more readily by heating these halogen derivatives with silver or potassium acetate, and decomposing the products with potash, C2H5I + C2H3O2Ag = C2H#.C2H3O2 + Agl Silver Acetate. Ethyl Acetate. C2H5C2H3O2 + KOH = C2H6OH + C2H3O2K. THE MONOHYDRIC ALCOHOLS. 107 This method gives very good results, and is much used in the preparation of the higher alcohols, because the halogen derivatives of the higher paraffins (such as hexyl chloride, C6H13C1), when treated directly with alkalies, are mainly converted into olefines, CH3.CH2-CH2CH2.CH2.CH2C1 + KOH = CH3.CH2-CH2CH2.CH:CH2 + KC1 + H2O, so that the yield of alcohol is small. Alcohols are also formed when the hydrocarbons of the olefine series are dissolved in sulphuric acid, and the solutions boiled with water, C3H6 + H.,SO4 = C3H7HSO4 c3h7hso"4 + h2o = c3h7.oh + H28O4, and when aldehydes and ketones are reduced with nascent hydro- gen, aldehydes giving primary, ketones secondary alcohols, CH3CH2CHO + 2H = ch3.ch2ch2oh CH3COCHs + 2H = CH3-CH(OH)-CH3. Tertiary alcohols are, as a rule, more difficult to obtain than the primary or secondary compounds; they are usually prepared by gradually adding the chloride of a fatty acid to excess of a zinc alkyl derivative. Thus acetyl chloride, CH3-COC1, acts on zinc methyl, Zn(CH3)2, forming a compound which, when treated with water, yields trimethyl carbinol, (CH3)3C-OH. In this reaction the zinc methyl and acetyl chloride form a crystalline compound zO /O-ZnCH3 CH3-C< + Zn(CH3)2 - CH3-C^-CH3 \C1 XC1 ' which is then very slowly acted on by a further quantity of zinc methyl, /O-Zn-CH3 /O-ZmCH3 CH3-C^CH3 + Zn(CH3)2 = CH8C^CH3 + CH3Zn.Cl. This product is decomposed by water, when trimethyl carbinol, methane, and zinc hydroxide are obtained, /O-Zn-CH3 /OH CH3.C^CH3 + 2H2O - CH3.C^CH3 + Zn(OH)o + CH4. \ch3 \ch3 Other tertiary alcohols may be prepared by employing other zinc alkyl compounds and other acid chlorides. Conversion of Primary into Secondary and Tertiary Alcohols.- A secondary alcohol may be prepared from the corresponding 108 THE MONOHYDRIC ALCOHOLS. primary compound by first converting the latter into an olefine by treating with dehydrating agents such as H2SO4, ZnCl2, and P2OS, CH3CH2CH2OH = CHs-CH:CH2 + h2o. The olefine is then dissolved in fuming sulphuric acid, when an alkyl hydrogen sulphate is formed, the SO4H- group uniting with that carbon atom which is combined with the least number of hydrogen atoms, ch3ch:Ch2 + h2so4 = ^|>chso4h. The alkyl hydrogen sulphate is finally converted into a secondary alcohol by boiling with water, ^hP=ch-so4h + h2o = ch^ch-oh + H2SO4. In a similar manner, a primary alcohol, such as isobutyl alcohol, may be converted into the tertiary alcohol, trimethyl carbinol, gH>CH.CH2.0H^gHr>C:0Hj _ CH^p^CH3 >CH.rC ()H Physical Properties.-No gaseous alcohols are known. The members up to CJ2H2fiO are, with few exceptions, neutral, colourless liquids, possessing a characteristic odour and a burning taste. Trimethyl carbinol and all the higher alcohols, such as cetyl alcohol, ClfiH33-OH, which occurs in spermaceti in combination with palmitic acid, and melissyl alcohol, C3nHfi)-OH, which is found in beeswax, also in combination with palmitic acid, are solids. Methyl, ethyl, and the propyl alcohols are miscible with water, but as the series is ascended, the solubility in water rapidly decreases, the amyl alcohols, for example, being only sparingly soluble. The alcohols are miscible in all proportions with most organic liquids. The sp. gr. gradually increases, and the boiling-point rises on passing up the series ; moreover, the primary alcohols boil at a higher temperature than the secondary, and the latter at a higher temperature than the tertiary isomerides, as shown in the table (p. 106). Chemical Properties.-The fact that the alcohols interact with other compounds so much more readily than the paraffins is due to the presence of the hydroxyl group, the rest of the molecule remaining unchanged, except under exceptional circumstances. In many reactions the alcohols behave as alkyl substitution pro- ducts of water; in others, their similarity to metallic hydroxides is more marked. THE MONOHYDRIC ALCOHOLS. 109 They dissolve sodium and potassium with evolution of hydrogen, 2C3H7OH + 2Na = 2C3H7ONa + H2. They interact with acids, forming neutral or acid ethereal salts, such as CH3C1, C2H6Br, (C2H5)2SO4, C3H7-HSO4. They are converted into halogen derivatives of the paraffins, when treated with PC15, PC13, POC13, or with the corresponding bromo-derivatives, PC15 + C3H7OH = C3H7C1 + POC13 + HC1. They are converted into olefines by dehydrating agents, such as H2SO4, and ZnCl2, CH3CH2OH = CH2:CH2 + H2O. The action of oxidising agents varies with the nature of the alcohol. Primary alcohols are converted into aldehydes, and then into fatty acids, secondary alcohols into ketones, and in both cases the oxidation products contain the same number of carbon atoms in the molecule as the alcohol from which they are formed, CH3.CH.,CH.,OH + O = CH3CH2-CHO + H2O CH3-CH(OH)CH3 + o = ch3.coch8 + h2o. Tertiary alcohols do not yield oxidation products containing the same number of carbon atoms as the alcohol, but are decomposed, giving simpler acids or ketones. CHAPTER VII. THE ETHERS. The ethers, such as methyl ether, -CH3-O-CH3, methyl ethyl ether, CH3-O-C9H5, &c., are substances which contain an oxygen atom united to two hydrocarbon groups, such as CH.,-, C0Hk-, and CoH7-. They are related to the metallic oxides in the same way as the alcohols to the metallic hydroxides. CH3-OH corresponds to K-OH CH3-O-CH3 u .. KO-K. Methyl ether, CH3-O-CH3, may be prepared by the action of sulphuric acid or other suitable dehydrating agent on methyl alcohol, 2CH3-OH = CH3.O-CH3 + H2O. 110 THE ETHERS. It is a gas which liquefies at -23°, and dissolves readily in water (1 vol. of water dissolves 37 vols. of methyl ether). Ethyl ether, ether, or sulphuric ether, C4H10O or C2H6O-C2H6, is formed, together with sodium iodide, when sodium ethoxide is warmed with ethyl iodide, CJL-ONa + C2H5I = C2H5-Q.C2H5 + Nai. It is also produced when ethyl alcohol is heated with sulphuric acid, zinc chloride, or other dehydrating agent, 2C2HrOH = C2H5.O-C2H6 + H2O. Ethyl ether is prepared by the following method : A mixture of five parts of 90 per cent, alcohol and nine parts of concentrated sulphuric acid is heated in a flask fitted with a tap funnel and thermometer, and connected with a condenser (fig. 17). As soon as the temperature rises to 140° Fig. 17. THE ETHERS. 111 the mixture begins to boil, and ether distils over. Alcohol is now slowly run in from the tap funnel, the temperature being kept at 140-145°, and the process continued until a consider- able quantity of ether has collected. The crude product in the receiver is a mixture of ether, alcohol, and water, and contains sulphur dioxide. It is shaken with dilute soda in a separat- ing funnel; the layer of ether which collects on the surface is then separated, dried over calcium chloride or quicklime, and purified by redistillation from a water-bath. The ether still contains traces of water and alcohol, which may be got rid of by adding pieces of bright sodium, allowing to stand for some time, and again distilling. Sodium ethoxide and sodium hydroxide remain, and pure ether passes over. The formation of ether from alcohol takes place in two stages. When alcohol is heated with sulphuric acid, it is converted into ethyl hydrogen sulphate (p. 182), C2H5-OH + H2SO4 = C2H5-HSO4 + H2O; this compound then interacts with alcohol, yielding ether and sulphuric acid, C2H5-HSO4 + CJL-OH = C2H5-O.C2H5 + H2SO4. That this is the true explanation of the formation of ether, is shown by the fact that ether is formed when pure ethyl hydrogen sulphate is heated with alcohol. Now, since the sulphuric acid necessary for the conversion of the alcohol into ethyl hydrogen sulphate is regenerated when the latter is heated with alcohol, a given quantity of the acid might, theoretically, convert an unlimited quantity of alcohol into ether. As a matter of fact, a small quantity of sulphuric acid can transform a very large quantity of alcohol into ether, but the process has a limit, because the acid becomes diluted by the water formed in the first stage of the reaction, and part of it is reduced by the alcohol with formation of sulphur dioxide. This method of preparing ether, by the continuous addition of alcohol to a solution of alcohol in sulphuric acid, is termed the continuous process. 112 THE ETHERS. Ether is a colourless, mobile, neutral, pleasant-smelling liquid of sp. gr. 0'736 at 0°. It boils at 35°, and does not solidify at - 80°. It is very volatile, and highly inflammable, its vapour forming an explosive mixture with air or oxygen, C4H10O + 6O2 = 4CO2 + 5H2O, so that all experiments in which ether is used should be conducted at a considerable distance from all flames or hot objects. Ether is soluble in about ten times its own volume of water, and is miscible with alcohol and other organic liquids in all proportions. Compared with alcohol, ether is a very indifferent sub- stance. It is not acted on by sodium or potassium, by alkalies or weak acids, or by phosphorus pentachloride in the cold. Concentrated acids, however, decompose ether, with formation of ethereal salts (p. 171), (C2H5)2O + 2HQSO4 = 2C9H5-HSO4 + H2O (C2H5)2O + 2HI = 2C2H5I + H2O. Ether is used in considerable quantities in surgery as an anaesthetic, since, like chloroform, it causes insensibility when inhaled; it is also very largely employed as a solvent for resins, fats, oils, alkaloids, &c. Constitution of Ether.-Since ether is produced by the action of ethyl iodide, C2H5I, on sodium ethoxide, C2H5-ONa, it may be concluded that it is formed by the substitution of the monovalent C9H5- group for the sodium atom, and its constitution may be expressed by the formula C9H5-O-C2H5. The same conclusion is arrived at from the fact that ether is formed when 1 mol. of H90 is taken away from 2 mols. of alcohol by the action of dehydrating agents, CJlJ OH H i OC2H5 = C2H5-OC9H5 + H.,O. When represented by this formula, several facts concerning the behaviour of ether are brought to mind. Ether, unlike alcohol, contains no HO- group, and therefore it is not acted on by sodium or potassium, or by phosphorus penta- THE ETHERS. 113 chloride; and, not being a hydroxide, it does not interact with acids to form an ethereal salt and water. Ether may be regarded as the anhydride of alcohol, as it is formed from alcohol (2 mols.) by the removal of the elements of water, just in the same way as nitric anhydride is formed from nitric acid, 2C2H5.OH = (C2H5)2O + H2O 2NO2OH = (NO2)2O + H2O. Ether may also be compared with the metallic oxides and regarded as ethyl oxide, since it is related to alcohol or ethyl hydroxide in the same way as the metallic oxides to the metallic hydroxides, C2H5-OH C2H5.O.C2H5 or (C2H5)2O K OH K-O-K or K2O. " Finally, it may be regarded as a di-substitution product of water, the mono-substitution product being the corresponding alcohol, H-OH C2H5.O-H C2H5-O-C2H5. The homologues of ether are very similar to ethyl ether in properties. SUMMARY AND EXTENSION. Some of the more important higher ethers are the following : Dipropyl ether (CH3-CH2CH2)2O B.p. 90-7° Di-isopropyl ether (cH^CbQoO „ 69° Diisobutyl ether n 122° Di-isoamyl ether (C5Hn)2O n 170-175° General Methods of Formation.-The ethers may be obtained by treating the sodium compounds of the alcohols with the alkyl halogen compounds, CH3-ONa +CH3I = CH3 O CH3 + Nai; but they are usually prepared by heating the alcohols with sulphuric acid. If a mixture of two alcohols be treated with sulphuric acid, three ethers are formed. A mixture of methyl and ethyl alcohols, for example, yields methyl ether, ethyl ether, and methyl ethyl ether, The formation of the two first- named compounds will be understood from the equations given 114 THE ETHERS. above in the case of ethyl ether. Methyl ethyl ether is produced by the interaction (a) of methyl hydrogen sulphate, and ethyl alcohol, (b) of ethyl hydrogen sulphate and methyl alcohol, CH3HSO4 + C2H5OH = CH3-O-C.,H5 + H2SO4 c2h6hso4 + ch3oh = C2H5OCH3 + H2SO4. All ethers, such as methyl ethyl ether, CH3-O-C2HS, which contain two different hydrocarbon groups, are termed mixed ethers, to distin- guish them from simple ethers, such as ethyl ether, C2H5-O-C2H5, and those given in the above table, which contain two identical groups. Mixed ethers can also be obtained by treating the sodium compounds of the alcohols with alkyl halogen compounds, CH3ONa + C3H7I = CH3OC3H7 + Nai. General Properties.-With the exception of methyl ether, which is a gas, the ethers are mobile, volatile, inflammable liquids, speci- fically lighter than water ; they all boil at a much lower temper- ature than the corresponding alcohols. In chemical properties they closely resemble ethyl ether. They are not acted on by alkalies or alkali metals, and do not combine with dilute acids; but they are decomposed when heated with strong acids, yielding ethereal salts, (C2H5)2O + 2H2SO4 = 2C2H5-HSO4 + H2O CHsOC2H6 + 2HBr = CH3Br + C2H6Br + H2O. Chlorine and bromine act on ethers, forming substitution products such as CH2C1O CH3, CH2BrOCH2Br, C2H5OC2H4C1, &c. Metamerism.-The ethers exist in isomeric forms. There are, for example, three compounds of the formula C4H10O, CH3.(J.CH2.CH2.CH3 Methyl Propyl Ether. CH,.OCH<gg3 Methyl Isopropyl Ether. CH3.CH8-OCH2CH,. Ethyl Ether. . Substances such as these, which have the same molecular formula, but in which all the carbon atoms in the molecule are not directly united, are called metameric ; the phenomenon is called metamerism, and the several compounds, metamers. Metamerism is simply a particular form of isomerism, and there is no real distinction between the two, the different terms being used purely for the sake of convenience. RADICLES. On studying the equations which represent the interactions of alcohols, ethers, &c., it is evident that certain groups of RADICLES. 115 atoms often remain unchanged during a whole series of double decompositions. Ethyl chloride, for example, may be converted into ethyl alcohol, the latter may be transformed into ethyl iodide, and this again may be converted into butane, but during all these interactions the group C2H5- remains unchanged, and behaves, in fact, as if it were a single atom, C2H5-C1 + HOH = C2H5.OH + HC1 C2H5-OH + HI = C2H5I + H2O 2C2H5-I + 2Na = C2H5-C2H5 + 2NaI. Numerous examples of a similar kind might be quoted; amongst others, the changes by which the five compounds, CH3.C1, CH3-OH CH3.O-CH3, CH3 I, and CH3-CH3, may be successively transformed one into the other. Groups of atoms, such as C2H5- and CH3-, which act like single atoms, and which enter unchanged into a number of compounds, are termed radicles, or sometimes compound radicles. Radicles may be monovalent, divalent, &c., according as they act like monad, dyad, &c., atoms; the radicles C.,H5- and CH3-, for example, are monad radicles, because they combine with one atom of hydrogen or its valency equivalent, as shown in the above equations. The name alkyl or alcohol radicle is given to all the mono- valent groups of atoms which are, theoretically, obtained on taking away one atom of hydrogen from the paraffins, methane, ethane, propane, butane, &c.; the distinctive names of these radicles are derived from those of the hydrocarbons by changing ane into yl, thus: methyl, CH3-; ethyl, C9H5- or CH3.CH2-; propyi, C3H7- or CH3-CH2-CH2-; isopropyl, C3H7-or (CH3)2CH-; butyl, C4H9- or CH3.CH9-CH2-CH2-; isobutyl, C4H9- or (CH3)2CH-CH2- &c. The compounds formed by the combination of these hypo- thetical alkyl radicles with hydrogen, as, for example, CH3-H, C2H5«H, C JE-H, are named collectively the alkyl hydrides, and are identical with the paraffins; the corresponding 116 RADICLES. chlorine compounds, such as CH3-C1, C.,H5-C1, C3H7-C1, are termed the alkyl chlorides, and so on. The letter R is frequently employed to represent an alkyl radicle, as, for example, in the formulae R-OH (alcohols) and R-OR (simple ethers). The name alkylene is given to the divalent radicles, which (except methylene) may be actually obtained by taking away two atoms of hydrogen from the paraffins. The alkylenes are methylene, CH2 = ; ethylene, C2H4 = ; propylene, C3Hfi = ; buty- lene, C4H8 =, &c.; and the compounds which they form, with chlorine, for example, such as CH.,:C1O, C2H4:C12, are termed collectively the alkylene chlorides, &c. Tri valent hydrocarbon radicles, such as glyceryl, C3H5=, are seldom met with, and will be mentioned later. Other radicles frequently met with are : hydroxyl, - OH ; carbonyl, = CO; carboxyl, - CO-OH ; cyanogen, - CN ; acetyl, -CO CH3, &c. The true significance of the term radicle will be more easily understood when a greater number of organic compounds has been considered. CHAPTER VIII, ALDEHYDES AND KETONES. The aldehydes form a homologous series of the general formula CwH2nO, or CnH2n + 1-CHO; they are derived from the primary alcohols C„H2n + rCH2-OH by the removal of two atoms of hydrogen from the -CH2-OH group, Paraffins. hch3 ch3.ch3 c2h5.ch3 Alcohols. HCH.,OH CH3-CH,OH c„h5.cho.oh Aldehydes. HCHO CH3CHO c2h5cho. The word aldehyde is a contraction of aZcohol <7eZ///<Zrogenatum, this name having been originally given to acetaldehyde, ALDEHYDES AND KETONES. 117 because it is formed when hydrogen is taken from alcohol by a process of oxidation. Formaldehyde, or methaldehyde, H-CHO, is said to occur in those plant cells which contain the green colouring matter, chlorophyll, and is possibly an intermediate product in that wonderful process-the formation of starch and sugars from the carbon dioxide which the plant absorbs from the air. Formaldehyde is produced when calcium formate is sub- jected to dry distillation, (H-COO)2Ca = H-CHO + CaCO3, and is prepared by passing a stream of air, saturated with the vapour of methyl alcohol, through a tube containing a copper spiral, or platinised asbestos, heated to dull redness ;* the change is a process of oxidation, CH3-OH + 0 = H-CHO + H2O. The pungent-smelling liquid which collects in the receiver may contain, under favourable conditions, as much as 30-40 per cent, of formaldehyde, together with methyl alcohol and water. On evaporating the solution on a water-bath or even at ordinary temperatures, the formaldehyde gradually under- goes change (polymerisation), and is converted into para- formaldehyde, which remains as a white solid. The formation of formaldehyde may be readily demon- strated by heating a spiral of platinum wire to dull redness and quickly suspending it over methyl alcohol contained in a beaker; the spiral begins to glow, and irritating vapours are rapidly evolved, a slight but harmless explosion usually taking place. Formaldehyde is only known in dilute solution and in the state of a gas at high temperatures (see below). That it would probably be a gas at ordinary temperatures may be inferred by considering the boiling-points of the next higher members of the series. Since the difference between the boiling-points of two consecutive aldehydes such as * Unless special precautions be taken, explosions frequently occur. 118 ALDEHYDES AND KETONES. propaldehyde, C.2H5-CHO (49°), and acetaldehyde, CH3-CHO (20o,8), is about 28°, formaldehyde would probably boil at about - 7°, or 28° lower than acetaldehyde.* Aqueous solutions of formaldehyde have a very penetrating, suffoca- ting odour and a neutral reaction; they have also a powerful reducing action, since formaldehyde readily undergoes oxi- dation, yielding formic acid, H-CHO + 0 = H-COOH. "When its aqueous solution is mixed with an ammoniacal solution of silver oxide, the latter is reduced, a silver mirror being obtained, H-CHO + Ag2O = H-COOH + 2Ag; mercuric chloride is also reduced, first to mercurous chloride, then to mercury. When formaldehyde is treated with reducing agents, it is converted into methyl alcohol, H-CHO + 2H = H-CH2-OH. When a concentrated aqueous solution of formaldehyde is mixed with a saturated solution of sodium hydrogen sulphite, direct com- bination takes place, a compound of the constitution OH-CH2-SO3Na being formed. Formaldehyde interacts with hydroxylamine in aqueous solution, yielding formaldoxime, H-CHO + NH2-OH = H-CH: NOH + H2O, a substance which is only known in solution since it very readily undergoes polymerisation. Constitution.-Since carbon is tetravalent, there is only one way of expressing graphically the constitution of formal- IT dehyde, CH.,0, namely, by the formula H-C^q. In the formation of formaldehyde by the oxidation of methyl alcohol, CHS-O-H, the hydrogen atom of the HO- group and one of the atoms combined directly with carbon are * As a rule, the lowest member of a homologous series shows a somewhat abnormal behaviour, and its properties cannot be foretold with as much certainty as in the case of the higher members. ALDEHYDES AND KETONES. 119 taken away. The carbon and oxygen atoms in formaldehyde are therefore represented in a state of combination different from that existing in methyl alcohol-namely, as joined by two lines instead of one. Formaldehyde behaves in some ways like an unsaturated compound, capable of forming additive products, because, under certain conditions, it may act as if it had the constitution In aqueous solution I it probably exists to some extent as the hydrate CH2(OH)2. Paraformaldehyde, (CH.,O)n, is formed, as stated above, when an aqueous solution of formaldehyde is evaporated; it is a colourless, amorphous substance, sublimes readily, and melts at 171°. When strongly heated, it is completely decomposed into pure, gaseous formaldehyde, CH2O, as is proved by vapour density determinations; but as the gas cools, paraformaldehyde is again produced. When para- formaldehyde is heated with a large quantity of water, it is reconverted into formaldehyde. The relation between formaldehyde and paraformaldehyde is similar to that between yellow and red phosphorus, or between the allotropic modifications of elements in general. Just as yellow is converted into red phosphorus on heating, so formaldehyde is converted into paraformaldehyde; and just as red is changed into yellow phosphorus on heating more strongly, so paraformaldehyde is changed into formal- dehyde. Here, however, the similarity in behaviour ends, since the gaseous formaldehyde changes into paraformaldehyde on cooling. The different forms in which a definite compound may exist are termed polymeric forms or modifications, such forms being in many respects similar to the allotropic forms of the elements-that is to say, a polymeric form is simply an aggregate of the molecules of the original substance, and the change of the simple into a complex form is spoken of as polymerisation. Paraformaldehyde is a polymeric form or a polymeride or polymer of formaldehyde, and its molecule 120 ALDEHYDES AND KETONES. consists of two or more (n) molecules of formaldehyde united to form a complex molecule (CH2O)n. Formaldehyde forms several polymeric modifications, and the readiness with which it undergoes polymerisation is one of its most characteristic properties. When its aqueous solution is treated with lime-water or other weak alkali, formaldehyde undergoes polymerisation into formose, a mixture of sub- stances, some of which have the composition (CH2O)6 or C6H12O6, and belong to the sugar group. This reaction is of great interest, since it shows that complex vegetable sub- stances such as the sugars may be formed by very simple means. Methylal, CH2(OCH3)2, is an important derivative of formal- dehyde. It may be obtained by boiling aqueous formal- dehyde with methyl alcohol and a small quantity of sul- phuric acid, but is usually prepared by oxidising methyl alcohol with manganese dioxide and sulphuric acid, the formaldehyde first produced combining with the unchanged methyl alcohol, H-CHO + 2CH3-OH = HCH(OCH3)2 + H2O. Methylal, a pleasant-smelling liquid, which boils at 42° and is readily soluble in water, is used in medicine as a soporific. When distilled with dilute sulphuric acid, it is resolved into methyl alcohol and formaldehyde, a reaction which may be conveniently employed for preparing the latter. Acetaldehyde, or ethaldehyde, CH3-CHO, is contained in the ' first runnings ' obtained in the rectification of refined spirit (p. 100), having been formed by the oxidation of the alcohol during the process of filtration through charcoal; it is formed when a mixture of calcium acetate and calcium formate is submitted to dry distillation, (CH3-COO)2Ca + (H-COO)2Ca = 2CH3.CHO + 2CaCO3, and is prepared by oxidising alcohol with potassium bichrom- ate and sulphuric acid, CH3-CH2 OH + o = ch3-cho + h2o. ALDEHYDES AND KETONES. 121 Coarsely powdered potassium bichromate (3 parts) and water (12 parts) are placed in a capacious flask fitted with a tap- funnel and attached to a condenser, and a mixture of alcohol (3 parts) and concentrated sulphuric acid (4 parts) is then run in moderately rapidly, the flask being gently heated on a water-bath during the operation. A vigorous action sets in, and a liquid, which consists of aldehyde, alcohol, water, and small quantities of acetal (see below), collects in the receiver. This liquid is now distilled from a water-bath, the temperature of which is not allowed to rise above 50°, when the aldehyde, being very volatile, passes over, most of the impurities remaining in the flask; the distillate is then mixed with ether, and the mixture saturated with dry ammonia, when a crystalline precipitate of aldehyde ammonia (see below) is obtained. This substance is transferred to a filter, washed with ether, and then decomposed by distillation with dilute sulphuric acid at as low a temperature as possible; the aldehyde is finally dehydrated by distillation with coarsely powdered anhydrous calcium chloride, the receiver being well cooled with ice in this and in the previous operations. Acetaldehyde, or aldehyde, as it is usually called, is a colourless, mobile, very volatile liquid of sp. gr. 0-801 at 0°; it boils at 20-8°. It has a peculiar penetrating and suffocating odour, somewhat like that of sulphur dioxide, and when inhaled it produces cramp in the throat, and for some seconds takes away the power of respiration; it is very inflammable, and mixes with water, alcohol, and ether in all proportions. Aldehyde is slowly oxidised to acetic acid on exposure to the air, and, like formaldehyde, it has powerful reducing properties; it precipitates silver, in the form of a mirror, from ammoniacal solutions of silver oxide, being itself oxidised to acetic acid, CH3-CHO + Ag2O = CHg-COOH + 2Ag. On treatment with reducing agents, it is converted into alcohol, just as formaldehyde is reduced to methyl alcohol, 122 ALDEHYDES AND KETONES. CH3CHO + 2H = CH3.CH„.OH HCHO + 2H = H.CH2OH. Aldehyde interacts readily with hydroxylamine in aqueous solution, yielding a crystalline compound, acetaldoxime, CH3-CHO + NH2OH = CH3CH:NOH + h2o. When aldehyde is shaken with a concentrated solution of sodium hydrogen sulphite (sodium bisulphite), direct com- bination occurs, and a colourless substance of the compo- sition CH3-CHO,NaHSO3 separates in crystals. This com- pound is readily decomposed by acids, alkalies, and alkali carbonates, aldehyde being liberated. Aldehyde also com- bines directly with dry ammonia, yielding a colourless, crystalline substance, aldehyde ammonia, CH3-CHO,NH3, or CH3-CH\^h , which is decomposed by acids, aldehyde being regenerated. Aldehyde very readily undergoes polymerisation on treat- ment with acids, dehydrating agents, and other substances (see below). Its behaviour with alkalies is very characteristic; when it is warmed with potash or soda, a violent action sets in, and the aldehyde is converted into a brown substance called aldehyde resin. Aldehyde may be detected by its smell, by its reducing action on silver oxide, and by the ' magenta ' or ' rosaniline test ' (Schiff's reaction), which is carried out as follows: Sulphurous acid is added to a dilute solution of rosaniline hydrochloride until the pink colour is just discharged; the solution to be tested is now added, when, if it contain a trace of aldehyde, a violet or pink colour immediately appears. This behaviour is not characteristic of acetaldehyde, as, with very few exceptions, all aldehydes give this reaction. Constitution.-Aldehyde is formed by the oxidation of ethyl alcohol, just as formaldehyde is produced by the oxidation of methyl alcohol, two atoms of hydrogen being removed in both cases. Now, as regards formaldehyde, it ALDEHYDES AND KETONES. 123 must be assumed that the hydrogen atom of the HO- group takes part in the change; probably, therefore, this is also true in the case of acetaldehyde, because the two substances are so very similar in chemical properties that they must be similar in constitution. The two reactions may therefore be expressed in a similar manner, H ; H H-C-O-H + 0 = H-i = O + H2O H H H I = । CH3-C-O-H + o = ch3-c = o + h2o. H ' ' Judging from analogy, then, the constitution of aldehyde is expressed by the formula CH3-C^q; this view accords very well with the whole chemical behaviour of the compound. Aldehyde, unlike alcohol, does not contain a hydrogen atom displaceable by sodium or potassium, and does not form salts with acids; these facts are expressed by the above formula, which shows that aldehyde does not contain an HO- group. When aldehyde is treated with phosphorus pentachloride, one atom of oxygen is displaced by two atoms of chlorine, a change which is very different from that which occurs when alcohol is acted on, and which affords further evidence that aldehyde is not a hydroxy-compound. This point is rendered very clear if the behaviour of aldehyde and alcohol respec- tively with phosphorus pentachloride be represented side by side, CH3-CHO + PC15 = CH3.CHC12 + POC13 CH3.CH2OH 4- PC]5 = CH3-CH2C1 + POC13 + HC1. The fact that aldehyde has the power of combining directly with ammonia, sodium hydrogen sulphite, alcohol (see below), &c., is also indicated by the above constitutional formula. Under certain conditions the nature of the union between 124 ALDEHYDES AND KETONES. the carbon and oxygen atoms may undergo change, and the aldehyde may then act as if it had the constitution H CH3C-O-; in other words, it may behave like an unsaturated compound and combine directly with two monad atoms or groups, as in its reduction to ethyl alcohol, in its conversion into aldehyde ammonia, &c. It will be seen that both formaldehyde and acetaldehyde contain the monovalent group -C^q, which is usually written -CHO (not COH); it is the presence of this aldehyde group which determines their characteristic properties, and all aldehydes are assumed to contain a group of this kind. Polymerisation of Acetaldehyde.-Three well-defined poly- merides of aldehyde are known-namely, aldol, paraldehyde, and metaldehyde. Aldol, (C2H4O)2, or CH3-CH(OH).CH2.CHO, is produced by the action of dilute hydrochloric acid, or of zinc chloride, on aldehyde at ordinary temperatures. It is a colourless, inodorous liquid, miscible with water, and shows all the ordinary properties of an aldehyde. It can be distilled under reduced pressure without decomposition, but when distilled under ordinary pressure, or when treated with dehydrating agents, it is converted into crotonaldehyde (p. 256) and water, CH3.CH(OH).CH2CHO = CH3CH:CHCHO + h2o. Paraldehyde, (C2H4O)3, is readily produced by adding a drop of concentrated sulphuric acid to aldehyde, an almost explosive action taking place. It is a colourless, pleasant- smelling liquid, boils at 124°, and solidifies in the cold. It is soluble in water, its cold saturated solution becoming turbid on warming, as it is less soluble in hot than in cold water; when distilled with dilute sulphuric acid, it is con- ALDEHYDES AND KETONES. 125 verted into aldehyde. Paraldehyde is used in medicine as a soporific. Paraldehyde shows none of the ordinary properties of an alde- hyde, and probably, therefore, does not contain the aldehyde or -CHO group; in other words, it is not a true aldehyde, and its constitution is usually represented by the formula /O-CH^-CHo CH3-CH< )O 'O-CH-CH3. Metaldehyde, (C2H4O)n, is produced by the action of acids on aldehyde at low temperatures. It crystallises in colourless needles, and is insoluble in water; it can be sublimed with- out decomposition, but on prolonged heating, it is converted into aldehyde, a change which is also readily brought about by distilling it with dilute sulphuric acid. Metaldehyde is probably isomeric with paraldehyde. Derivatives of Aldehyde.-Acetal, CH3-CH(OC2H5)2, is produced when a mixture of aldehyde and alcohol is heated at 100°, or when alcohol is oxidised with manganese dioxide and sulphuric acid (compare methylal, p. 120), CH3-CHO + 2C2H5-OH = CH3.CH(OC2H5)2 + H2O. It is a colourless liquid, possessing an agreeable smell, and boiling at 104°; when distilled with dilute acids, it is decom- posed into alcohol and aldehyde, CH3-CH(OC2H5)2 + H2O = CHUCHO + 2C2H5-OH. Chloral, or trichloraldehyde, CC13'CHO, cannot be pre- pared by the direct action of chlorine on aldehyde; it is manufactured on a large scale by saturating alcohol with chlorine, first at ordinary temperatures, and then at the boiling-point, the operation taking some days. The crystalline product, which consists for the greater part of chloral alcoholate, CC13-CH\^^2^5, is distilled with concentrated sulphuric acid, and the oily distillate of crude chloral con- verted into chloral hydrate (see below). After purifying the 126 ALDEHYDES AND KETONES. hydrate by recrystallisation, from water, it is distilled with sulphuric acid, when pure chloral passes over. The formation of chloral alcoholate may be represented by the equations CH3.CH2.OH + o = ch3-cho + h2o CH3-CHO + C2H5-OH = CH3.CH(OH)-OC2H5 CH3.CH(OH)-OC2H5 + 3C12 = CC13-CH(OH).OC2H5 + 3HC1, the aldehyde first produced by the oxidising action of the chlorine (p. 91), combining with alcohol, and being finally converted into chloral alcoholate by substitution. It is, however, very doubtful whether the action is quite so simple. A more probable explanation is that acetal is first produced by the combination of the aldehyde with the unchanged alcohol, and then converted into trichloracetal, CC13-CH (OC2H5)2, by the further action of chlorine ; this substance is finally decomposed by the hydrogen chloride produced during the reaction, giving chloral alcoholate and ethyl chloride, CC13-CH(OC2H5)2 + HC1 = CC13-CH<J^H5 + C2HSC1. Chloral is an oily liquid of sp. gr. 1'512 at 20°, and boils at 97°. It has a penetrating and irritating smell, and in chemical properties closely resembles aldehyde, a fact which was only to be expected, since it is a simple substitution product of aldehyde, and contains the characteristic aldehyde group. It has reducing properties, combines directly with ammonia, sodium hydrogen sulphite, &c., and on oxidation it is converted into trichloracetic acid (p. 163), just as alde- hyde is converted into acetic acid, CC13.CHO + 0 = CClyCOOH. On the addition of small quantities of acids, it readily under- goes polymerisation, being transformed into a white amorphous modification called metachloral; the same change takes place when chloral is kept for a considerable time. One of the most interesting reactions of chloral is its behaviour with boiling potash, by which it is quickly decomposed, giving chloroform (p. 172) and potassium formate, ALDEHYDES AND KETONES. 127 CC13-CHO + KOH = CHC13 + H-COOK. Pure chloroform is often prepared in this way. Chloral Hydrate, CC13-CH(OH)2.-When chloral is poured into water, it sinks as an oil at first, but in a few seconds the oil changes to a mass of colourless crystals of chloral hydrate, a considerable rise in temperature taking place. Chloral hydrate melts at 57°, is readily soluble in water, and is decomposed on distillation with sulphuric acid, chloral passing over. In some respects it is a very stable substance; it does not polymerise, and does not give the rosaniline reaction of aldehydes. These facts point to the conclusion that chloral hydrate does not contain the aldehyde group, but that by combination with water the chloral has been converted into a substance of the constitution CCl3-CH\^jp Chloral hydrate is extensively used in medicine as a soporilic. Homologues of Acetaldehyde.-The higher members of the homologous series of aldehydes, such as propaldehyde, C2H5-CHO, butaldehyde, C3Hr-CHO, may be produced by the oxidation of the corresponding primary alcohols, or by the dry distillation of-the calcium salts of the corresponding fatty acids with calcium formate ; they resemble acetaldehyde in chemical properties. Heptaldehyde, or (Enanthol, C6H13-CHO, is of consider- able interest because it is one of the products of the dry distillation of castor-oil. It is a colourless oil, boils at 154°, and has a penetrating, disagreeable odour; on oxidation it yields normal heptylic acid, C6H13-COOH (p. 158). and on reduction, normal heptyl alcohol, C6H13-CH2-OH. KETONES. The ketones, of which the simplest, acetone, CH3-CO-CH3, may be taken as an example, are derived from the secondary alcohols, such as isopropyl alcohol, CH3-CH(OH)-CH3, by the removal of two atoms of hydrogen from the -CH(OH) 128 ALDEHYDES AND KETONES. group, the process being, in fact, strictly analogous to the formation of aldehydes from the primary alcohols. Ketones are characterised by containing the divalent group ^>C = 0 united with two alkyl radicles, as in CH3-CO-C.,H5, C2H5-CO-C2H5, and their composition may be expressed by the general formula CnH2nO; they are isomeric with the aldehydes: Propaldehyde, CH3-CHUCHO Dimethyl ketone, CH3-CO-CH3 c3h6o Butaldehyde, CH3CH2-CH2-CHO Ethylmethyl ketone, CH3-CH2-CO-CH3 C4H8O. Acetone, or dimethyl ketone, CH3-CO-CH3, occurs in small quantities in normal urine, and in cases of diabetes mellitus and acetonuria the quantity increases considerably. It also occurs in small quantities in the blood. Acetone is formed when isopropyl alcohol is oxidised with potassium bichromate and sulphuric acid, CH3-CH(OH).CH3 + 0 = CH3CO-CH3 + H2O, and is produced in considerable quantities during the dry dis- tillation of wood and many other organic compounds, such as sugar, gum, &c. Crude wood-spirit, which has been freed from acetic acid (p. 89), consists in the main of a mixture of acetone and methyl alcohol. These two substances may be roughly separated by the addition of calcium chloride, which combines with the methyl alcohol; on subsequent distillation, crude acetone passes over, and may be purified by conversion into the bisulphite compound (see below). Acetone is usually prepared by the dry distillation of crude calcium or barium acetate, (CH3.COO)2Ca = CH3COCH3 + CaCO3. The distillate is fractionated, and the portion boiling between 50 and 60° mixed with a strong solution of sodium bisulphite. The crystalline cake of 'acetone sodium bisul- phite,' which separates on standing, is well pressed, to free it from impurities, decomposed by distillation with dilute ALDEHYDES AND KETONES. 129 sodium carbonate, and the aqueous distillate of pure acetone dehydrated over calcium chloride. Acetone is a colourless, mobile liquid of sp. gr. 0-792 at 20°; it boils at 56-5°, has a peculiar, pleasant, ethereal odour, and is miscible with water, alcohol, and ether in all proportions. In chemical properties acetone resembles aldehyde in several important particulars. When shaken with a con- centrated aqueous solution of sodium bisulphite, direct combination takes place with considerable development of heat, and a colourless, crystalline substance, acetone sodium bisulphite, CH3-CO-CH3,NaHSO3, or (CH3)2C<^ separates. This compound is readily soluble in water, and is quickly decomposed by dilute acids and alkalies, acetone being regenerated. Acetone, like aldehyde, interacts with hydroxylamine in aqueous solution, forming acetoxime, (CH3)2CO + NH2-0H = (CH3)2C:NOH + H2O, a crystalline substance, melting at 59° When treated with phosphorus pentachloride, the oxygen atom in acetone is displaced by two atoms of chlorine, and ^-dichloropropane is formed, (CH3)2CO + PC15 = (CH3)2CC12 + POC13; on reduction, acetone is converted into secondary propyl alcohol, (CH3)2CO + 2H = (CH3)2CH-OH. At the same time acetone differs from aldehyde very widely in one or two important respects. It does not undergo polymerisation, and does not reduce ammoniacal solutions of silver oxide; it is oxidised only by moderately powerful agents, by which its molecule is broken up into acetic acid and carbon dioxide, CH3-CO-CH3 + 40 = CH3-C00H + CO2 + H2O. Acetone gives the iodoform reaction (p. 96), and is employed for the preparation of iodoform, chloroform, &c.; it is also used as a solvent. 130 ALDEHYDES AND KETONES. Constitution.-Acetone is formed when isopropyl alcohol, QH'^CH-OH (p. 104), loses two atoms of hydrogen by oxidation. It does not contain a hydroxyl-group, because, unlike the alcohols, it does not form salts with acids. That the oxygen atom is combined with carbon only-that is, that acetone contains a -CO- group, is shown by the behaviour of acetone with phosphorus pentachloride, which is similar to that of aldehyde. Furthermore, the -CO- group must be united with two methyl groups, as in the formula CH3-CO-CH3, because if it were not, acetone would be identical with propal- dehyde, CH3-CH2-Cxg. These facts, and many others which might be mentioned, show that acetone has the constitution O ii CH3-C-CH3, or (CH3)oCO ; its characteristic properties are determined by the presence of the divalent carbonyl or ketonic group^>C = 0, which is assumed to be contained in all ketones. The similarity in chemical behaviour between acetone and aldehyde is at once brought to mind on considering their graphic formulae; they both contain the carbonyl group, Acetone, qh^C = O Aldehyde, ch^C = O; and therefore those changes, in which only this group takes part, are common to both substances. Such changes are, for example, interaction with hydroxylamine, behaviour with phosphorus pentachloride, and direct combination with sodium bisulphite, hydrogen, &c.; in the last two reactions, acetone acts as if it had the constitution (CH3)2C\^-. As regards oxidation, the difference between the two compounds is also readily understood; acetone does not contain the readily oxidisable hydrogen atom of the aldehyde group, and does not combine with oxygen without the molecule being broken up; it is therefore less readily acted on than aldehyde, and does not reduce silver oxide or give the ALDEHYDES AND KETONES. 131 rosaniline test, since both these reactions are the result of oxidation. Condensation of Acetone.-When acetone is treated with certain dehydrating agents, it undergoes a peculiar change, two or more molecules combining together with elimination of one or more molecules of water, 2(CH3)2CO = C6H10O + H2O Mesityl Oxide. 3(CHA2CO = C9H14O +2H2O. Phorone. This, and similar changes, in which two or more molecules of the same or of different substances combine, with separation of water, are termed condensations, and the substances formed, condensation products; the process differs from polymerisation in this, that water is eliminated. Acetone yields three interesting condensation products. When it is saturated with dry hydrogen chloride, and the solution kept for some time, a mixture of mesityl oxide and phorone is formed, in accordance with the above equations; but when distilled with concen- trated sulphuric acid, acetone yields a hydrocarbon, mesitylene, (part ii.), a derivative of benzene, 3(CH3)2CO = C9H12 + 3H2O. Mesityl Oxide, C6H10O, is a colourless oil, boiling at 130°, and having a strong peppermint-like smell: when boiled with dilute sulphuric acid, it is decomposed with regeneration of acetone. Its con- stitution maybe represented by the formula CH3-CO-CH:C^Cqjj3. Phorone, C9H14O, crystallises in almost colourless prisms, melting at '28° ; it boils at 196°, has a pleasant aromatic odour, and is decomposed by boiling dilute sulphuric acid with formation of acetone. Substihction Products of Acetone.-Acetone is readily attacked by chlorine with formation of monochloracetone, CH3-CO-CH2C1 (b.p. 119J), and asymmetrical dichloracetone, CH3-CO-CHC12 (b.p. 120°). Symmetrical dichlor acetone, CH2C1-CO-CH2C1, is produced by the oxidation of dichlorisopropyl alcohol, or dichloro- hydrin (p. 252), CH2CbCH(OH)-CH2Cl; it is a colourless, crystalline solid (m.p. 45°; b.p. 172'5O). Higher substitution products of acetone have been obtained by indirect methods. The final product, hexachloracctone, or perchlor acetone, CC13-CO-CC13, 132 ALDEHYDES AND KETONES. is a colourless liquid, boiling at 204°. Corresponding bromo-sub- stitution products of acetone have also been prepared. These halogen substitution products are characterised by their exceedingly irritating action on the eyes, the presence of a mere trace of these substances in the air being sufficient to cause a copious flow of tears; when dropped on the skin, they produce very painful blisters. Homologues of Acetone may be obtained by the oxidation of the corresponding secondary alcohols and by the dry distillation of the calcium salts of the higher fatty acids; they resemble acetone in chemical properties. Methylnonyl Ketone, CH3-CO-C9H19, is the chief con- stituent of oil of rue, the essential oil obtained by distilling rue {Ruta graveolens) with steam. It is a colourless, crystalline substance, melts at 15°, boils at 224°, and possesses an odour resembling that of oranges. Hydroximes and Hydrazones.-Aldehydes and ketones interact readily with hydroxylamine, NH2-0H, and with phenylhydrazine, C6H5-NH-NH9 (part ii.), forming condensa- tion products. This property is not only highly characteristic of all aldehydes and ketones, with one or two exceptions, but is also of the greatest value in the isolation and identifi- cation of the compounds in question. The substances formed by the action of hydroxylamine on aldehydes are called aldoximes, those obtained from ketones, Ix-etoximes, the term oxime or hydroxime being applied to botli. Acetaldehyde, for example, yields acetaldoxime, CH3-CH0 + NH2-0H = CH3CH:N0H + H2O, acetone giving acetoxime or dimethyl ketoxime, (CH3)2CO + NH2-0H = (CH3)2C:N-OH + h2o, the interactions being expressed by the general equation >C;O + H2iN0H = >C:N0H + H2O. The oximes are usually prepared by mixing an aqueous or alcoholic solution of the aldehyde or ketone (2 mols.) with an aqueous solution of hydroxylamine hydrochloride, ALDEHYDES AND KETONES. 133 NH2-OH,HC1 (2 mols.), and then adding sodium carbonate (1 moL) in order to decompose the hydrochloride and set the base free, 2NH2.OH,HC1 + Na2CO3 = 2NH2-OH + 2NaCl + CO2 + H2O. The mixture is now heated gently, or kept at the ordinary temperature for some hours, and the oxime then extracted from the acidified solution by shaking with ether, or in some other suitable manner. The lower aldoximes are mostly colourless, volatile, solid compounds, which distil without decomposition under reduced pressure, and mix with water in all proportions; the higher members are only sparingly soluble in water. The ketoximes have similar properties. Most oximes are decomposed, on treatment with boiling moderately strong hydrochloric acid, with formation of hydroxylamine hydrochloride, and regenera- tion of the aldehyde or ketone, CH3-CH:N.OH + HC1 + H2O = CHUCHO + NH2-OH,HC1. They are usually readily soluble in caustic alkalies, with which they form compounds, such as CH„-CH:N.ONa and (CHXC:N-OK: but they are not decomposed by alkalies, even on boiling. One important dilference between aldoximes and ketoximes is, that the former are decomposed by acetyl chloride, yielding cyanides or nitriles (p. 284), CH3-CH:N-OH = CH3-CN + H2O, whereas the latter are converted into acetyl derivatives, (CH3)2C:N-OH + CH3-COC1 = (CH3)2C:N.O-CO-CH3 + HC1. The condensation products of aldehydes and ketones with phenylhydrazine are called phenylhydrazones, or simply hydrazones. They are formed according to the general equation, >C i 0 +H2: N.NH-C6H5 = >C:N«NHC6H5, as, for example, acetaldehyde hydrazone, CH3-CH:N-NH-C6H5, 134 ALDEHYDES AND KETONES. and acetone hydrazone, (CH3)2C:N-NH-C6H5. The hydra- zones are referred to later (part ii.), but it may be mentioned here that, like the hydroximes, they are usually decomposed by hot concentrated hydrochloric acid, with regeneration of the aldehyde or ketone. SUMMARY AND EXTENSION. The Aldehydes form a homologous series of the general formula CnHjn+j-CHO, or R-CHO, and are derived from the primary alcohols by the removal of two atoms of hydrogen from the -CH2-OH group. The more important members of the series are- B.p. Formaldehyde, CH2O H-CHO - Acetaldehyde, C2H4O CH3CHO 20-8° Propaldehyde, C3H6O CH3.CH2-CHO 49° Butaldehyde, 1 j'CHi-CH2-CH2-CHO 74° Isobutaldehyde, J G4H8°- \(CH3)2CH-CHO 63° Valeraldehyde, ) fCH3.CH2-CH2-CH2-CHO 102° Isovaleraldehyde, J \(CHS)2CHCH2CHO 92° Capraldehyde, C6HI2O CH3-CH2-CH2-CH2-CH2-CHO 128° Heptaldehyde,! CH 0 CH3 [CH2]5 CHO* 155° or CEnanthol, J 7 14 2 5 The Ketones are derived from the secondary alcohols by the removal of two atoms of hydrogen from the'>CH-OH group, and have the general formula R-CO-R', where R and R' may be the same or different radicles ; in the former case the substance is a simple ketone, but when R and R' are different, it is a mixed ketone (compare ethers, p. 114). The more important ketones are- Acetone, or dimethyl ketone (CH3)2CO B.p. 56-5° Propione, or diethyl ketone (C2I15)2CO n 103° Butyrone, or dipropyl ketone ) Isobutyrone, or di-isopropyl ketone J "" 3 7 2 tt 125° CEnanthone, or dihexyi ketone (C6H13)2CO M.p. 30-5' Laurone . (CnH^^CO it 69° Palmitone (C15.H31)2CO u 83° Stearone (C17H35)2CO it 88° When the less important mixed ketones are also considered, the ketones form a homologous series, c3h6o, c4h8o, c6h10o, c6h12o, &c., * [CHJj is a convenient way of writing -CH2-CH2-CH2-CH2-CH2-. ALDEHYDES AND KETONES. 135 in which numerous cases of isomerism occur. The first two members, acetone, CH3-CO-CH3, and methylethyl ketone, CH3-CO-CH2-CH3, exist in only one form, but there are three ketones of the composition C5H10O, namely, Diethyl Ketone, or Propione. Methylpropyl Ketone. Methylisopropyl Ketone. CH3.CH2.CO.CH2 CH3 CH8.CO CH2.CH2CH3 CH3-COCH<^3) and the number of possible isomerides rapidly increases on passing up the series. Both aldehydes and ketones maybe regarded as derived from the paraffins, by substituting one atom of oxygen for two atoms of hydrogen ; they are, therefore, isomeric. In the case of aldehydes, two atoms of hydrogen of one of the CH3- groups in the paraffin are displaced, CH3.CH2.CH2 CH3, giving CH3.CH2-CH2CHO; but in the case of ketones, the oxygen atom is substituted for two hydrogen atoms of a -CH2- group, CH3-CH2-CH2.CH3, giving CH3.CH2-CO-CH3. Nomenclature.-The aldehydes (from alcohol dehydrogenatuni) are conveniently named after the fatty acids which they yield on oxidation : Formaldehyde, HCHO, giving formic acid, H-COOH. Acetaldehyde, CH3-CHO, n acetic acid, CH3-COOH. Propaldehyde, C2H5-CHO, u propionic acid, C2H5-COOH. Simple ketones, having been first obtained by the dry distillation of a salt of a fatty acid, are usually named after that acid from which they are in this way obtained ; acetone, for example, from acetic acid, propione from propionic acid. Mixed ketones are named according to the alkyl groups which they contain, as exem- plified above in the case of the isomerides of the composition CsH10O. Ketones in general may also be named after the hydro- carbons from which they are theoretically derived, employing the prefix ' keto ' and a numeral, as, for example, 2-ketopropane, CH3-cb-CH3, and 3-ketohexane, CH3.CH2.CO CH2.CH2-CH3- Methods of Preparation.-Aldehydes are formed by the oxidation of primary alcohols, CH3-CH2-OH + 0 = CH3-CHO + H2O; whereas ketones are produced from secondary alcohols by similar treatment, CH8.CH(OH).CH3+ o = ch3.co-ch3 + h2o. 136 ALDEHYDES AND KETONES. Aldehydes may be prepared from the fatty acids by the dry distillation of their calcium salts with calcium formate : (CH3-COO).,Ca + (H-COO)2Ca = 2CH3CHO + 2CaCO3) (CH3-CH2-CH„-COO)2Ca + (H-COO)2Ca = 2CH3CH2CH2CHO + 2CaCO3. In its simplest form this reaction may be considered as being due to the removal of water and carbon dioxide from one molecule of the fatty acid and one molecule of formic acid ; thus, KCHro -OH = RCH0 + C°2 + h2o. Ketones may be prepared by the distillation of the calcium salts of the fatty acids alone, (CH3COO)2Ca = 2CH3CO-CH3 + CaCO3. If a mixture of the calcium salts of two fatty acids (other than formic acid) be employed, a mixed ketone is formed, (CH3-COO)2Ca + (C2H8.COO)2Ca = 2CH3COC2H8 + 2CaCO3; Calcium Acetate. Calcium Propionate. Methylethyl Ketone. at the same time two simple ketones (acetone and propione) are produced by the independent decomposition of the two salts. This method of formation is readily understood if, for the sake of simplicity, the free acids instead of their calcium salts be con- sidered, RCr'LcoJoh = RC0R' + C°2 + H2°- Ketones may, in fact, be prepared by heating the higher fatty acids with phosphoric anhydride at about 200°, 2CJ7H3S-COOH = C17H33COC17H33 + CO2 + H2O, Stearic Acid. Stearone. a method especially useful in the preparation of the higher ketones, such as laurone, palmitone, &c., which are obtained only with difficulty by any other method. A very important synthetical method for the preparation of ketones consists in treating the acid chlorides (1 mol.) with the zinc alkyl compounds (1 mol.l; in the first place, an additive product is formed, and this, on decomposition with water, yields the ketone, CaH#.C^ + Zn(C2H#)2 = C2H8.CCl<g^"CA /OZn-C2H5 C2H8.CC1< " + 2H.,0 XC2H8 = C2H6COC2H-, + C2H6 + Zn(0H)2 + HC1 ALDEHYDES AND KETONES. 137 (Compare formation of tertiary alcohols by the action of excess of the zinc alkyl compound, p. 107). Ketones may also be prepared by the hydrolysis of ethyl aceto- acetate and its derivatives, a synthetical method of great practical importance (p. 193). When hydrocarbons of the acetylene series are treated with 80 per- cent, sulphuric acid (or with a solution of mercuric chloride or bromide), they combine directly with the elements of water, an aldehyde or a ketone being formed according to the constitution of the hydrocarbon (p. 87). Physical Properties. - Excluding formaldehyde, the physical properties of which are unknown, the aldehydes and ketones up to about CuH22O are colourless, mobile, neutral, volatile liquids. Aldehydes have usually a disagreeable, irritating smell, and their sp. gr. (at 20°) varies from about 0'780 in the case of acetaldehyde, to 0'834 in the case of caprylic aldehyde, C7H15-CHO. Ketones have generally a not unpleasant odour, and their sp. gr. (at 20°) varies from 0'792 in the case of acetone, to 0'830 in the case of caprone, (C5Hu)2CO. The boiling-point rises fairly regularly on passing up both series. The lowest members of both classes of com- pounds are readily soluble in water, but the solubility rapidly decreases as the number of carbon atoms in the molecule in- creases. The higher aldehydes and ketones are usually colourless, waxy solids, insoluble or nearly so in water, but readily soluble in alcohol and ether. Chemical Properties.-Aldehydes and ketones have many chemical properties in common, because they are similar in constitution, both classes of substances containing the carbonyl group ^>CO. Owing to the presence of this group, they have the power of com- bining directly under certain conditions with two monad atoms or their valency equivalent All the lower aldehydes and many* of the lower ketones form crystalline additive compounds when shaken with a concentrated aqueous solution of sodium bisulphite. This property is of great value in purifying aldehydes and ketones, and especially in separating them from substances which do not form ' bisulphite compounds,' as illustrated in the preparation of acetone from crude wood-spirit (p. 128). These 'bisulphite compounds' are soluble in water, but usually insoluble or nearly so in alcohol and ether. They may be regarded as salts of hydroxy-sulphonic * With few exceptions, only those ketones containing the group CHSCO- combine readily with NaHSO3. 138 ALDEHYDES AND KETONES. acids* the compounds formed by aldehyde and acetone respec- tively being CH3.CH(OH)SO3Na Sodium Hydroxyethylsulphonate. C||*>C(OH).SO3Na. Sodium Hydroxyisopropylsulphonate. All these compounds are readily decomposed on warming with dilute alkalies or acids, the aldehydes or ketones being regenerated, CH3.CHj'CH(OH).SOsNa + HC1 = CH3.CHa.CHO + NaCl + H2O + SOy The characteristic behaviour of aldehydes and ketones with hydroxylamine and with phenylhydrazine has been described above. Aldehydes and ketones are readily acted on by reducing agents, such as sodium amalgam and water, zinc and hydrochloric acid, with formation of primary and secondary alcohols respectively, CH3.CH2.CH.,CHO + 2H = CH3CHsCH2CHaOH CH3COCH2CH3 + 2H = CH,CH(OH).CHj.CH3. A secondary alcohol is not the sole product of the reduction of ketones, but is usually accompanied by varying quantities of interesting substances belonging to the class of pinacones. Acetone, for example, yields not only isopropyl alcohol, CH3-CH(OH)-CH3, but also acetone pinacone, 2(CH3)2CO + 2H = (CH3)2C(OH)-C(OH)(CH3)2. The formation of a pinacone may be accounted for by assum- ing that the first product of reduction of a ketone is a sub- stance, produced by combination with one atom of hydrogen. This intermediate product may then combine with another atom of hydrogen to form a secondary alcohol, r^C^r^, or two molecules may unite to form a pinacone^ r /OHHO\ r^C ^^R' Similar products are formed in the reduc- tion of aldehydes, but in smaller quantities. Pinacone is decomposed on distillation with dilute sulphuric acid, yielding pinacoline, = ch3.co-c^ch3 + H2O, a very remarkable change, and one which has not been satisfac- torily accounted for. Pinacoline is a colourless liquid, boils at 106°, * A sulphonic acid is an organic acid containing the group -SO2 OH. ALDEHYDES AND KETONES. 139 and has a very strong odour of peppermint. That it has the con- stitution given above, is shown by the facts that on oxidation with chromic acid, it yields trim ethyl acetic acid and carbon dioxide, (CH3)3C-COCH3 + 40 = (CH3)3C-COOH + co2 + h2o, and that it is formed by the action of zinc methyl on trimethyl- acetyl chloride, (CH3)3-COC1. (Compare preparation of ketones, p. 136). Aldehydes and ketones are readily acted on by phosphorus penta- chloride with formation of dihalogen derivatives of the paraffins, the oxygen atom of the^>CO group being displaced by two atoms of chlorine. Aldehyde, for example, gives a dichlorethane, called ethyl- idene chloride (because it contains the ethylidene group CH3-CH =), CH3-CH0 + PC15 = CH3-CHC12 + POC13, and acetone gives ^-dichloropropane or acetone dichloride, (CH3)2CO + PC15 = (CH3)2CC12 + POC13. Aldehydes and ketones combine directly with hydrocyanic acid, forming additive products, termed hydroxycyanides. This reaction may be expressed by the general equation >C0 + HCN =>€<25, aldehyde, for example, giving hydroxyethyl cyanide, CH3-CH(0H)-CN, and acetone, hydroxyisopropyl cyanide, (CH3)2C(OH)-CN. These compounds are decomposed by hot concentrated alkalies and mineral acids, yielding hydroxycarboxylic acids, the -CN group being transformed into -C00H (compare p. 285), CH3-CH(0H)-CN + 2H2O = CH3.CH(0H)-C00H + NH3. Aldehydes differ from ketones in the following important respects : They usually undergo oxidation to a fatty acid on ex- posure to the air, and are readily oxidised by an ammoniacal solution of silver oxide, especially in presence of a little potash or soda, a silver mirror being formed. They also reduce alkaline solutions of copper (Fehling's solution, p. 263). Ketones, on the other hand, are only attacked by powerful oxidising agents, and the difference between their behaviour on oxidation and that of aldehydes is so characteristic that it may be made use of for deter- mining whether a substance of doubtful constitution be an aldehyde or a ketone. Aldehydes, on oxidation, are converted into fatty acids containing the same number of carbon atoms : 140 ALDEHYDES AND KETONES. ch3ch2cho + o = ch3-ch2cooh, Propaldehyde. Propionic Acid. CH3-[CH2]5-CHO + O = CH3-[CH2]5.COOH. Heptaldehyde. Heptylic Acid. Ketones, on oxidation, are decomposed with formation, usually, of a mixture of acids, each of which contains a smaller number of carbon atoms than the original ketone, CH3COCH3 + 40 = CH3C00H + C02 + II2O. CH3 CO- [CH2]4.CH3 + 3O = CH8 COOH + CH3 [CH2]3-COOH. In the case of mixed ketones, several acids may be formed. Methylamyl ketone, for example, might yield acetic acid, and valeric acid on oxidation, in which case the molecule would be decomposed as indicated by the dotted line in the above equation, or it might give carbon dioxide and caproic acid, the molecule being attacked in a different manner, CHj CO-[CHJrCH3 + 40 = CH3-[CH2]4-COOH + H20 + C02. It frequently happens, therefore, that, in oxidising mixed ketones, several products are formed, the nature of which may afford important evidence as to the constitution of the ketone. Generally speaking, the oxidation of a mixed ketone follows the rule (Popoff's law) that the ketonic group -CO- remains united with the smaller alkyl group, in which case the decomposition represented in the above example by the first equation would take place almost entirely. Later experiments have shown, however, that PopotTs rule does not hold good in all cases, and must be con- sidered as only approximately correct. Aldehydes differ from ketones in combining readily with am- monia, forming additive products, 4- NW - OH + WH3 - R^ .^ These compounds, of which aldehyde ammonia is an example, are usually crystalline, and very readily soluble in water. They are decomposed on distillation with dilute acids, with regeneration of the aldehyde, RCH<^ + HC1 = R-CHO + NH4C1. Aldehydes differ again from ketones in combining with alcohols with elimination of water, to form substances called acetals, H\co + H0-C2H, _ H_ O-C2H5 „ o R^U + H0.c jj5 - r<^^o.c2Hb + ALDEHYDES AND KETONES. 141 Aldehydes, especially the lower members of the series, very readily undergo polymerisation, a property which distinguishes them from ketones in a very striking manner. Polymerisation may take place spontaneously, as in the case of formaldehyde, but usually only on addition of a small quantity of some mineral acid or of some substance, such as ZnCl2, SO2, &c., which acts in a manner as yet unexplained. The most common form of polymeris- ation is the combination of three molecules of the aldehyde to form substances called paraldehydes, such as paraformaldehyde, (CH2O)3, and paracetaldehyde (C2H4O)3, the constitutions of which are usually represented by the formulae 0 : H-CH ."CH-H 4^ CH i H Paraformaldehyde. O CH^-CH y CH-CH, ■ ry CH . CH3 Paracetaldehyde, or Paraldehyde. The method of combination of the three molecules to form a paraldehyde will be readily understood with the aid of the dotted lines. The paraldehydes are decomposed into the original alde- hydes on distillation with dilute mineral acids. They do not show the characteristic reactions of aldehydes, consequently they are not true aldehydes, and do not contain the aldehyde group. Aldehydes are generally very unstable in presence of alkalies, by which they are converted into brown resins of unknown nature. Ketones, as mentioned above, are much more stable than alde- hydes ; they do not reduce alkaline solutions of silver, copper, &c., or combine directly with ammonia or with alcohols, and they do not polymerise like the aldehydes. When treated with dehydrating agents, both aldehydes and ketones readily undergo condensation, two or more molecules combining with loss of water, as illustrated in the case of aldehyde (p. 124) and acetone (p. 131). When condensations of this nature take place, the hydrogen atoms of one of the -CH2- or CH3- groups, which is in direct combination with the 2>CO group, are invariably eliminated, as shown in the following schemes, in which R, R' may be either hydrogen atoms or similar or different alkyl groups: 142 ALDEHYDES AND KETONES. RCiTIJCOR'' R' C-0 :-CH2-R RCCOR' = II R'.CCH2R (Type of Mesityl Oxide). K-C IL hCOR' R'-00 i-CH^R R-CH2-C:O R' R. CCOR' II = R'-C-CR II RCH2CR' (Type of Phorone). It is not necessary that the molecules undergoing condensation be identical; two different ketones, two different aldehydes, or an aldehyde and a ketone may condense together, always provided that the group -CH.,-CO- be present in the molecule of one at least of the substances. CHAPTER IX. THE PATTY ACIDS. The fatty acids form a homologous series of the general formula ChH2w + ^COOH, or CnH2nO2; they may be re- garded as derivatives of the paraffins, the alcohols, or the aldehydes. Paraffins. Alcohols. Aldehydes. Fatty Acids. HCH, HCH,OH HCHO H-CdoH ch3.ch3 CH3CHoOH CH.rCHO CHj-COOH c,h5.ch3 C2H5-CHoOH c2h5cho CoH5C00H. The term 1 fatty ' was given to the acids of this series because many of the higher members occur in natural fats, and resemble fats in physical properties. Formic Acid, CHQO2, or H'COOH, occurs in nature in nettles, ants (formicce), and other living organisms; the sting of ants and nettles owes part, at least, of its irritating effect to the presence of formic acid. When nettles or ants are macerated with water and the mixture distilled, weak aqueous formic acid collects in the receiver. Formic acid can be obtained from its elements by simple methods. When carbon monoxide is passed over moistened THE FATTY ACIDS. 143 potassium hydroxide heated at 100°, it is slowly ahsorbed, and potassium formate is produced, CO + KOH = H-COOK. When moist carbon dioxide is passed over potassium, formate and carbonate of potassium are formed, the carbon dioxide being reduced by the nascent hydrogen evolved during the interaction of the potassium and water, 2H2O + 2K = 2K0H + 2H, and CO2 + 2H + KOH = H-COOK + HoO, " or 3CO2 + 4K + H2O = 2H-C00K + K2CO3. The acid'may be obtained from the potassium salt by dis- tilling with dilute sulphuric acid. Formic acid can also be obtained by oxidising methyl alcohol or formaldehyde with platinum black (precipitated platinum), CH3-OH + 20 = H-COOH + H2O H-CHO + 0 = H-COOH, and by heating hydrocyanic acid with alkalies or mineral acids, HCN + 2H2O = H-COOH + NH3.* Formic acid is prepared by heating oxalic acid with glycerol (glycerin); it can be obtained by heating oxalic acid alone, C2O4H2 = H-COOH + CO2, but a large proportion of the acid sublimes without decom- position. Glycerol (about 50 c.c.) is placed in a retort con- nected with a condenser, crystallised oxalic acid (about 30 grams) added, and the mixture heated to about 100-110°; rather below this temperature, evolution of carbon dioxide commences, and dilute formic acid distils, but after keeping for some time at 100-110°, action ceases. A further quantity of oxalic acid is then added, and the heating continued, 'when carbon dioxide is again evolved, and a more concentrated solution of formic acid collects in the receiver. By adding * If an alkali be used, ammonia is liberated, and a salt of formic acid obtained; whereas when a mineral acid is employed, free formic acid and an ammonium salt are produced. 144 THE FATTY ACIDS. more oxalic acid from time to time, a large quantity of formic acid can. be obtained, the glycerol, like the sulphuric acid in the manufacture of ether, being able, theoretically, to con- vert an unlimited quantity of oxalic into formic acid. When crystallised oxalic acid, C2O4H2 + 2H2O, is heated with glycerol, it loses its water of crystallisation ; the anhydrous acid is then decomposed into carbon dioxide and formic acid ; part of the latter distils with the water, part combining with the hydroxide, glycerol, to form the salt, glycerol formate, or monoformin, C2O4H2,2H2O = HCOOH + CO2 + 2H2O C3H5(OH)3 + HCOOH = C3H5(OH)2-OCHO + H2O. On adding more crystallised oxalic acid, the monoformin is decom- posed by part of the water expelled from the oxalic acid crystals, yielding glycerol and formic acid, C3H5(OH)2-OCHO + H2O = C3H6(OH)3 + HCOOH. The regenerated glycerol and the anhydrous oxalic acid then interact as before, yielding monoformin, carbon dioxide, and water. In order to prepare anhydrous formic acid, the aqueous distillate is gently warmed and excess of litharge added in small quantities at a time, the solution being gradually heated to boiling ; as soon as the litharge ceases to be dissolved, the solution is filtered hot, and the filtrate evaporated to a small bulk, when colourless crystals of lead formate are obtained, 2H-C00H + PbO = (H-COO)2Pb + H2O. This salt is carefully dried, and about |$ths of it introduced in the form of coarse powder, between plugs of cotton wool, into the inner tube of an upright Liebig's condenser, which is connected above -with an apparatus for generating hydrogen sulphide, and below with a suitable receiver closed with a calcium chloride drying tube; the lead formate is heated by passing steam through the outer tube of the condenser, and carefully dried hydrogen sulphide is led over it, when anhydrous formic acid collects in the receiver, (II-COO)2Pb + SH2 = 2H-C00H + PbS. THE FATTY ACIDS. 145 The acid is now placed in a retort connected with a con- denser, the remainder of the dried lead salt added, and, after warming gently for a short time, the acid is distilled, care being taken to prevent absorption of moisture; this rectifica- tion or distillation over lead formate is necessary in order to free the acid from hydrogen sulphide. Formic acid is a colourless, mobile, hygroscopic liquid of sp. gr. 1-241 at 0°; it solidifies at low temperatures, melting again at 8°, and boiling at 101°. It has a pungent, irritating odour, recalling that of sulphur dioxide, and it blisters the skin like a nettle sting does; it is miscible with water and alcohol in all proportions. The anhydrous substance and its aqueous solution have an acid reaction, decompose carbonates, and dissolve certain metallic oxides; formic acid, in fact, behaves like a weak mineral acid. Like the aldehydes, it has reducing properties, and precipitates silver from warm solu- tions of ammoniacal silver nitrate, being itself oxidised to carbon dioxide, H-COOH + Ag2O = 2Ag + CO2 + H2O. When mixed with concentrated sulphuric acid, it is rapidly decomposed into carbon monoxide and water, H-COOH = CO + H2O, and when heated alone at 160° in closed vessels, it yields carbon dioxide and hydrogen, H-COOH = CO2 + H2. The Formates, or salts of formic acid, are prepared by neutralising the acid with alkalies, hydroxides, &c., or by double decomposition; they are all soluble in water, but some, such as the lead and silver salts, only moderately easily ; they are all decomposed by warm concentrated sulphuric acid, with evolution of carbon monoxide, and by dilute mineral acids, yielding formic acid. The sodium salt, H-COONa, and the potassium salt, H-COOK, are deliquescent; when heated at about 250°, they are converted into oxalates with evolution 146 THE FATTY ACIDS. of hydrogen, a reaction which may be made use of for the preparation of pure hydrogen, 2HC00Na = C2O4Na2 + H2. When ammonium formate is strongly heated, it is first con- verted into formamide (p. 162), then into hydrogen cyanide, water being eliminated in both stages, H-COONH4 = H-CO-NH, + H2O H-CONH2 = HCN + H2O. Silver formate, H-COOAg, is precipitated in colourless crystals on adding silver nitrate to a concentrated solution of an alkali formate, but it is unstable, and quickly darkens on exposure to light, very rapidly on boiling. In order to test for formic acid or a formate, the solution, if acid, is neutralised with soda, and a portion warmed with an ammoniacal solution of silver nitrate; if a black precipitate of silver be produced, the presence of formic acid is confirmed by evaporating the rest of the neutral solution to dryness, and then warming the residue very gently with concentrated sulphuric acid, when carbon monoxide is evolved, and may be ignited at the mouth of the test tube. Constitution.-Formic acid is produced from methyl alcohol, H H-C-0-H, by the substitution of one atom of oxygen for H two atoms of hydrogen, and must, therefore, have the con- stitution H H o=i-0-H or H-C-O, because these are the only formula? which can be constructed, assuming, as usual, that the atoms have the indicated valencies. But the second formula does not correctly indicate the be- haviour of formic acid ; it represents the two hydrogen atoms THE FATTY ACIDS. 147 as being in the same state of combination, which is very improbable, since one of them is, the other is not, readily displaced by metals; it does not recall the fact that formic acid behaves in some respects like an aldehyde, which is indicated in the first formula by the presence of the aldehyde H group l For these and other reasons, which will be O = C- seen more clearly after considering the case of acetic acid (p. 152), the constitution of formic acid is represented by the first formula, which is usually written H-CO-OH, or simply H-COOH. From analogy with methyl alcohol and other compounds, it may be assumed that it is the hydrogen atom of the HO- group, and not that directly combined with carbon, which is displaced when the acid forms salts. Acetic Acid, C2H4O2, or CH3-COOH, occurs in nature in combination with alcohols in the essences or odoriferous oils of many plants, and is formed during the decay of many organic substances. It can be produced by gently heating sodium methoxide in a stream of carbon monoxide, just as formic acid may be obtained from sodium or potassium hydroxide under the same conditions, CH3-ONa + CO = CH3-COONa; also by boiling methyl cyanide (p. 285) with alkalies or mineral acids, CH3-CN + 2H2O = CH3-COOH + NH3; and by exposing alcohol or aldehyde in contact with platinum black to the oxidising action of the air, C2H6O + 20 = C2H4O2 + H20 2C2H4O + 20 = 2C2H4O2. Acetic acid is manufactured on the large scale from the products of the dry distillation of wood. The brown aqueous portion of the distillate, obtained on heating wood in iron retorts (p. 89), contains a large quantity of acetic acid, and is called pyroligneous acid; it is first distilled with lime, as already described, to separate the methyl alcohol, acetone, and other volatile neutral substances, and the solution of 148 THE FATTY ACIDS. calcium acetate is then evaporated in iron pans, when tarry or ' empyreumatic ' matter rises as a scum and is skimmed off. The solution is finally evaporated to dryness, and the calcium salt distilled with concentrated hydrochloric acid from copper vessels, care being taken not to employ excess of acid, (C2H3O2)2Ca + 2HC1 = 2C2H4O2 + CaCl^ The concentrated aqueous acetic acid which collects in the receiver is now mixed with a little potassium permanganate or bichromate, and again distilled, by which means most of the impurities are oxidised, and commercial acetic acid is obtained. Vinegar.-When beer, or a weak wine such as claret, is left exposed to the air, it soon becomes sour, the alcohol which it contains being converted into acetic acid, C2H6O + O2 = C2H4O2 + H2O. This change is not a simple oxidation, as represented by the equation, but a process of fermentation brought about by a living ferment, mycoderma, aceti. This ferment, being in the atmosphere, soon finds its way into the solution, where it grows and multiplies and in some way causes the alcohol to combine with the oxygen of the air to form acetic acid. Strong wines, such as port and sherry, do not turn sour on exposure to the air, nor does an aqueous solution of pure alcohol, no matter how dilute, because the ferment is killed by strong alcohol, and cannot live in pure aqueous alcohol, since the latter does not contain nitrogenous substances, mineral salts, &c., which the ferment requires for food, and which are present in beers and wines. Vinegar is simply a dilute solution of acetic acid, contain- ing colouring matter and other substances, obtained by the acetous fermentation of poor wine or wine residues, of beer which has turned sour, and of other dilute alcoholic liquids; it is manufactured by one of the two following processes. THE FATTY ACIDS. 149 In the old French or Orleans process, a small quantity of wine is placed in large vats covered with perforated lids, the vats having been previously soaked inside with hot vinegar; the ferment soon gets into the wine, and vinegar is produced, the solution gradually becoming coated with a slimy film, known as ' mother-of-vinegar,' which is simply a mass of the living ferment. After some time more wine is added, the process being repeated at intervals until the vat is about half full; most of the vinegar is then drawn off, and the operations repeated with fresh quantities of wine. In the modern German or 1 quick vinegar process' large vats, provided with perforated sides, and fitted near the top and bottom with perforated discs, are employed, the space between the discs being filled with beech-wood shavings, which are first moistened with vinegar in order that they may become coated with a growth of the ferment; diluted 'raw-spirit,' containing 6-10 per cent, of alcohol, mixed with about 20 per cent, of vinegar, or with beer, or malt extract, to provide food for the ferment, is then poured in at the top, when it slowly trickles through the shavings in contact with the ferment, and provided with a free supply of air. The liquid which collects at the bottom is again poured over the shavings, the operations being continued until it is converted into vinegar-that is to say, until almost the whole of the alcohol has been oxidised to acetic acid. This process is much more rapid than the French method, since oxidation is hastened by the exposure of a large surface of the liquid; in both processes the fermenting liquid must be kept at a temperature of 25-40°. Vinegar produced by the French process contains 6-10 per cent, of acetic acid; whereas that produced by the German process from diluted raw-spirit contains only 4-6 per cent, of acetic acid. Vinegar is used for table purposes and in the manufacture of white-lead and verdigris (see below); it is too dilute to be economically employed for the preparation of commercial acetic acid. 150 THE FATTY ACIDS. Pure acetic acid is prepared by distilling anhydrous sodium acetate with concentrated sulphuric acid; this salt is obtained by neutralising the impure commercial acid with sodium carbonate, recrystallising, and then fusing to expel the water of crystallisation. The distillate from this process contains only a small quantity of water, and solidifies, when cooled, to a mass of colourless crystals; it is then termed glacial acetic acid in contradistinction to the weaker acid, which does not crystallise so readily. The small quantity of water in glacial acetic acid can be got rid of by separating the crystals from the more dilute mother-liquors by pressure, melting them, and then cooling again, repeating the processes if necessary. Anhydrous acetic acid is a colourless, crystalline, hygro- scopic solid, melts at 1G-50, boils at 118°, and has the sp. gr. 1-080 at 0°; it has a pungent, penetrating smell, a burning action on the skin, and a sharp sour taste; it is inflammable when near its boiling-point, burning with a feebly luminous flame. It is miscible with water, alcohol, and ether in all proportions, and is an excellent solvent for most organic compounds, and for many inorganic substances, such as sulphur, iodine, &c., which are insoluble in water. It is a fairly strong acid, dissolves certain metals, and acts readily on metallic hydroxides; unlike formic acid, it has not reducing properties. The pure acid does not decolourise potassium permanganate ; if impure, it will pro- bably do so. Acetic acid is largely used in medicine, in chemical labora- tories, and in the manufacture of organic dyes, as well as for the preparation of many acetates of considerable com- mercial importance; the uses of vinegar have been men- tioned. The Acetates, or salts of acetic acid, are prepared by neutralising the acid with carbonates, hydroxides, &c., or by double decomposition; they are crystalline compounds, sol- uble in water, and decomposed by mineral acids with libera- THE FATTY ACIDS. 151 tion of acetic acid. Sodium acetate, C2H3O2Na + 3H.,O, is extensively used in the laboratory; it melts in its water of crystallisation when heated, but as the water is expelled, it solidifies again. The anhydrous salt is hygroscopic, and is used as a dehydrating agent. Potassium acetate, C2H3O2K, is deliquescent. Ammonium acetate is gradually decomposed into acetamide (p. 162) and water on dry distillation, C9H„O9«NH, = CH.,-CO-NH9 4- H90. Silver acetate is pre- cipitated in colourless crystals on adding silver nitrate to a con- centrated neutral solution of an acetate; it is moderately sol- uble in cold water, and does not darken on exposure to light. Copper acetate, (C2H3O2)2Cu + H2O, is obtained by dissolving cupric oxide in acetic acid ; it is a dark, greenish-blue sub- stance. Verdigris is a blue, basic copper acetate, (C2H3O2)2Cu + Cu(OH)2, containing water of crystallisation, and is manu- factured by leaving sheet-copper in contact with vinegar, or with grape-skins, the sugars in which have undergone fermentation first into alcohol, then into acetic acid. When washed with water, part of the salt dissolves and green verdigris is obtained; both these basic acetates are used as pigments. Copper acetate and copper arsenite unite to form a beautiful emerald green, insoluble double salt, (C2H3O2)2Cu + (AsO3)2Cu3, known as Schweinfurth's green. This substance was formerly employed in large quantities in colouring wall-papers, carpets, blinds, &c.; but as its dust is poisonous, and as it is liable to decompose in presence of decaying starch or other organic matter, with evolution of hydrogen arsenide, its use is now almost abandoned. Lead acetate, or ' sugar of lead,' (C2H3O2)2Pb + 3H2O, prepared by dissolving litharge in com- mercial acetic acid, has a sweet (sugary) astringent taste, and is very poisonous; when its solution is boiled with litharge, a soluble basic lead acetate is formed. Feme acetate is prepared on the large scale by dissolving scrap iron in pyroligneous acid, the greenish ferrous salt first produced being rapidly oxidised in contact with the air and excess of acetic acid to the deep reddish-brown ferric salt; the 152 THE FATTY ACIDS. solution is known in commerce as ' iron liquor,' or ' black liquor.' AV hen a solution of ferric acetate containing traces of other salts is heated, an insoluble basic iron salt is pre- cipitated, the solution becoming clear; this property is made use of in separating the metals of the iron group, also in dyeing and ' printing ' cotton, for which purpose ' iron liquor' is used as a mordant. Aluminium acetate is pre- pared by precipitating a solution of aluminium sulphate with sugar of lead, or by dissolving precipitated aluminium hydroxide in acetic acid; its solution is known as ' red liquor,' and is used as a mordant, as, when heated, it loses acetic acid, an insoluble basic salt being formed. Chromic acetate is prepared by similar methods, and is also used as a mordant. If a solution is to be tested for acetic acid or an acetate, it is boiled with a few drops of strong sulphuric acid, when the characteristic smell of acetic acid is observed. A fresh portion of the solution is then neutralised with soda, if necessary, evaporated to dryness, and the residue warmed with a few drops of alcohol and a little strong sulphuric acid, when ethyl acetate (p. 185) is formed; this substance is recognised by its pleasant fruity odour (which should be compared with that of alcohol and of ether). Constitution.-The formation of acetic acid by the oxida- tion of ethyl alcohol is clearly a process similar to that by which formic acid is produced from methyl alcohol; if, therefore, the two changes be represented in a similar manner, H.CH2.OH + 20 = H-C00H + H,0 CH3CH2OH + 20 = CH3.C00H + H20, the constitution of acetic acid will be expressed by the H formula CH.yC0.0H, or H Again, formic acid is produced when hydrogen cyanide is THE FATTY ACIDS. 153 boiled with mineral acids (p. 143), whilst acetic acid is formed from methyl cyanide under the same conditions. Expressing these two changes in a similar manner, H-CN + 2H2O = H-CO-OH + NH3 CH3-CN + 2H2O = CH3-CO-OH + NH3, the constitution of acetic acid will be represented by the same formula as before. If now the properties of acetic acid be considered, it will be evident that the constitutional formula arrived at in this manner indicates the chemical behaviour of the acid, and accounts for its methods of formation, decompositions, and relations to other compounds better than any other formula. From the numerous arguments which might be advanced in support of this statement, the following only will be quoted : (1) Acetic acid contains an HO- group, because its behaviour with phosphorus pentachloride is similar to that of alcohols (p. 95). (2) It contains a methyl or CH3- group- that is to say, three of the four atoms of hydrogen in acetic acid are directly combined with carbon. This is shown by the fact that three of the four hydrogen atoms behave like those in CH4, C2H6, &c., and are displaceable by free chlorine (p. 162) ; also by the production of ethane by the electro- lysis of potassium acetate, a change which can be formulated in a simple manner, only by assuming the presence of a CH3- group, CH„-COOK CH3 CO2 3 = i 3 + 2 + 2K. ch3-cook ch3 co2 Since, then, judging by its chemical behaviour, acetic acid contains a CH3- and an HO- group, it must have the constitution CH3-C\Qjp which confirms the conclusion previously arrived at. The relation between formic and acetic acids, and their 154 THE FATTY ACIDS. similarity in certain chemical properties, are satisfactorily accounted for by the constitutional formulae and CH3-C\qjj, which thus confirm one another. The acids are both repre- sented as containing the monovalent group of atoms which has not been met with in any of the neutral compounds yet considered; it may be concluded, there- fore, that their characteristic acid properties are due to the presence of this group. As, moreover, aldehydes contain the group _C\^, but do not contain hydrogen displaceable by metals, it must be the hydrogen atom of the HO- group which is displaced when the acids form salts. The particular monovalent group of atoms common to formic and acetic acids is named the carioa^Z-group, and is usually written -CO-OH, or simply, for convenience, -COOH. Homologues of Acetic Acid.-As all the higher members of the series of fatty acids resemble formic and acetic acids in chemical properties, may be produced by similar methods, and undergo similar changes, it is assumed that they all con- tain a carboxy 1-group. With the exception of formic acid, they may, in fact, be regarded as derived from the paraffins, by the substitution of the monovalent carboxyl- group for one atom of hydrogen; acetic acid, CH3-COOH, from methane, CH4; propionic acid, C.,H5-COOH, from ethane; and so on. They form, therefore, a homologous series of the general formula CnH2w+ 1COOH, or CnH2MO2, and are all monobasic or monocarboxylic acids. As in other homologous series, the higher members exist in isomeric forms, the number of isomerides theoretically possible in any given case being the same as that of the corresponding primary alcohols. The two isomeric acids, butyric acid, THE FATTY ACIDS. 155 CH3-CH2 CH2.COOH, and isobutyric acid, ^3>CH-C00H, for example, correspond with the two primary alcohols, CH3-CH2.CH2.CH2.OH, and ^|>CH.CH2-OH, respectively. Those isomerides which are derived from the normal paraffins, by substituting -COOH for one atom of hydrogen in the CH3- group, are termed normal or primary acids, as normal butyric acid, CH3-CH2-CH2-COOH, normal heptylic acid, CH3.CH2.CH2-CH2-CH2-CH2 COOH; those which contain the group are usually termed CH\ Zsoacids, as, for example, isobutyric acid, ^^>>CH-COOH, pit. isovaleric acid, C^CH-CH^COOH, but the term is not used very systematically. With the exception of the normal acids and one or two well-known iso-acids, such as those just quoted, it is usual, to avoid confusion, to name the fatty acids as if they were derived from acetic acid, just as the alcohols are regarded as derivatives of carbinol; the four isomerides of the molecular formula C5H10O2, for example, are named as follows: C^>CH.CH2-COOH Isovaleric Acid (Isopropylacetic Acid). CH3.CH2-CH2-CH2.COOH Normal Valeric Acid (Propylacetic Acid). CHk CHo-^C-COOH. CH^ Trimethylacetic Acid. ^^CH-COOH Methylethylacetic Acid. Propionic acid, C3H6O2, or CH3-CH2-COOH, exists in only one form, and occurs in crude pyroligneous acid; it is formed when acrylic acid (p. 257) is reduced with sodium amalgam, C3H4O2 + 2H = C3H6O2, and when lactic acid (p. 225) is heated with concentrated 156 THE FATTY ACIDS. hydriodic acid, which, at a high temperature, is a powerful reducing agent,* CH3-CH(OH).COOH + 2HI = CH3CH2COOH + H2O + I2. It is prepared by oxidising propyl alcohol with chromic acid, ch3ch2-ch2.oh + 20 = CH3.CH2.COOH + h2o. Propionic acid is a colourless liquid, boils at 141°, and has a pungent sour smell; it is miscible with water in all propor- tions, but on adding a little calcium chloride to the solu- tion, part of the acid separates at the surface, forming an oily layer. This property is characteristic of all fatty acids, which are readily soluble in water, except formic and acetic acids. Propionic acid is a mono-carboxylic acid, and closely resembles acetic acid in chemical properties; its salts, the propionates, are soluble in water, and of little importance. There are two acids of the molecular formula C4H8O2. Normal butyric acid, CH3-CH2-CH2-COOH, occurs in the vegetable and animal kingdoms, both in the free state and in combination with glycerol; it is an important constituent of butter. It is formed during the decay of nitrogenous animal matter, and during the butyric fermentation of lactic acid. When milk is left exposed to the air, it turns sour, the milk sugar which it contains being converted into lactic acid by a minute organism, the lactic ferment, which is present in the air, and finds its way into the milk, C12H22OI1 + h20 = 4C3H6O3. Milk Sugar. Lactic Acid. The lactic ferment has the power of converting other sugars besides milk sugar (or lactose) into lactic acid. If now a little decaying cheese be added to the sour milk, and the solu- * In the reduction of lactic acid the following changes occur: CH3CH(OH)COOH + HI = CH3CHIC00H + H20 CH3.CHLCOOH 4- HI = CH3.CH2 COOH + I2. In such reductions it is usual to add a pinch of amorphous phosphorus to the mixture, in order that the iodine may be reconverted into hydriodic acid (31 + P + 3H2O = H3PO3 + 3HI). THE FATTY ACIDS. 157 tion be kept neutral by adding some chalk,* butyric fermenta- tion sets in, the lactic acid being converted into butyric acid by the action of another organism, the butyric ferment, which is present in the decomposing cheese, 2C3H6O3 = C4H8O2 + 2CO2 + 2^ Butyric acid is usually prepared by a combination of these two processes of fermentation. Butyric acid is a thick sour liquid, boiling at 163°. It has a very disagreeable odour, like that of rancid butter and stale perspiration, in which it occurs; it is miscible with water in all proportions, but separates on adding calcium chloride. The butyrates, or salts of butyric acid, are soluble in water; the calcium salt (C4H7O2)2Ca + H2O is more soluble in cold than in hot water, so that when a cold saturated solution is heated, part of the salt separates in crystals, and the solution becomes turbid. Isobutyric acid, or dimethylacetic acid, (CH3)2CH-COOH, may be prepared by the oxidation of isobutyl alcohol, (CH3)2CH-CH2-OH + 20 = (CH3)2CH-COOH + H20. It boils at 155°, and resembles the normal acid very closely, but is not miscible with water in all proportions, one part of the acid requiring about five parts of water for solution. Tiie calcium salt (C4H7O2)2Ca + 5H2O, unlike that of butyric acid, is more soluble in hot than in cold water. Of the four isomerides of the molecular formula C5H10O2, isovaleric acid, or isopropylacetic acid,(CH3)2CH-CH2-COOII, and active valeric acid, or methylethylacetic acid, g^>CH-C00H, are the most important. These acids occur together in the plant all-heal, or valerian, and in angelica root; the mixture of acids obtained by distilling the macerated plants with water is known as valeric or valerianic acid, and is an oily liquid, boiling at about 174°. A mixture of these two acids may * The ferment ceases to act if the solution become too strongly acid. 158 THE EATTY ACIDS. be prepared by oxidising commercial amyl alcohol (p. 105) with chromic acid. The hexylic acids, C6H12O2, are of little importance ; seven of the eight isomerides theoretically possible are known, including normal hexylic acid (caproic acid). Normal heptylic acid, C7H14O2, or C6H13-COOH, one of the seventeen theoretically possible isomerides, of which only nine are known, is prepared by oxidising castor-oil or cenanthaldehyde (p. 127) with nitric acid; it is an oily, rather unpleasant smelling liquid, sparingly soluble in water; it boils at 223°, and, like all the lower members of the series, is readily volatile in steam. Palmitic acid, C16H32O2, or C15H31-COOH, and stearic acid, C18H36O2, or Ci7H35-COOH, occur in large quantities in animal and vegetable fats and oils (p. 166), from which they are prepared on the large scale principally for the manufacture of stearin candles; they are colourless, waxy substances, melting at 62° and 69° respectively, and insoluble in water, but soluble in alcohol, ether, &c. Their sodium and potas- sium salts are soluble in pure water, and are the principal constituents of soaps (p. 168), but their calcium, magnesium, and other salts are insoluble. A mixture of these two acids was at one time thought to be a definite compound, and named margaric acid; this name is now given to an arti- ficially prepared acid, C17H34O2, or C16H33-COOH, which stands between palmitic and stearic acids in the series, and ■which seems not to occur in nature. Derivatives of the Fatty Acids. Acid Chlorides.-When phosphorus pentachloride is added to anhydrous acetic acid, an energetic action takes place, and acetyl chloride, CH3-C\^p is formed, with evolution of hydrogen chloride; this change is analogous to that which occurs when an alcohol is treated with phosphorus penta- chloride, THE FATTY ACIDS. 159 CH3-CO-OH + PC15 = ch3.coci + POC13 + HC1 CH3.CH9.OH + PCL = CHo-CHoCl + POCL + HC1. O Z U D A O Phosphorus trichloride and oxychloride also convert acetic acid into acetyl chloride. Acetyl chloride is best prepared by adding phosphorus trichloride, or oxychloride, from a tap funnel to anhydrous sodium or potassium acetate contained in a retort connected with a condenser, and then distilling from a water-bath; a phosphite, or a mixture of metaphosphate and chloride, is left in the retort, 3CH3.COONa + PC13 = 3CH3.COC1 + Na3PO3 2CH3-COOK + POC13 = 2CH3-COC1 + KPO3 + KCL It is a colourless, pungent-smelling liquid, boils at 55°, and fumes in moist air; when poured into water, it is rapidly decomposed, with formation of acetic acid, CH3-COC1 + H2O = CH3-COOH + HC1. Acetyl chloride bears the same relation to acetic acid as ethyl chloride to alcohol; it may, in fact, Be produced by passing hydrogen chloride into anhydrous acetic acid con- taining phosphorus pentoxide, which combines with the water formed, and thus prevents the reverse change (compare ethereal salts, p. 187), CH3-COOH + HC1 = CH3-COC1 + H2O. Acetyl chloride is not only quickly decomposed by alkalies and by water, but also, more or less rapidly, by all compounds containing one or more hydroxyl-groups; the interaction always takes place in such a way that hydrogen chloride is produced, the monovalent aw/yZ-group CHg-CC^ displacing the hydrogen of the hydroxyl-group, C9H5-OH + CH3-COC1 = C9H5-O-CO-CH3 + HC1 C3HrOH + CH3.COC1 = C3HrO-CO-CH3 + HC1. Acetyl chloride may therefore be employed as a reagent for determining the presence of a hydroxyl-group. All that is 160 THE FATTY ACIDS. necessary is to add the dry substance, in the state of a fine powder, if a solid, to excess of acetyl chloride, and then heat the mixture or solution for some time. The substance may be recovered unchanged, indicating that it is not a hydroxy- compound, or it may be converted into a new substance, an acetyl derivative, by the substitution of the acetyl-group for hydrogen; in the latter case, a combustion of the sub- stance is usually made, in order to ascertain its composition, from which the number of times the acetyl-group has dis- placed hydrogen is determined ;* or, since acetyl derivatives are decomposed by boiling acids and alkalies, the percentage of acetic acid obtained from the substance may be directly estimated, C2H5.OCOCH3 + KOH = C2H.OH + CH.-COOK. All the fatty acids except formic acid may be converted into acid chlorides, such as propionyl chloride, CH3-CH2-COC1, by the methods described above ; the products resemble acetyl chloride in chemical properties, and may be employed for the detection of hydroxy 1-gronps. Acid bromides, such as CH3-COBr, can be obtained in a similar manner. Anhydrides.-The hydrogen atom in a carboxyl-group -COOH is not, as a rule, displaced by the acetyl-group on treatment with acetyl chloride, but, when an alkali salt of a fatty acid is heated with acetyl chloride, an acetyl derivative of the acid is formed, CH3-COOK + CH3-COC1 = CH3.COO-CO.CH3 + KC1. The compound obtained from an acetate in this way may be regarded as acetyl oxide, (CH3-CO)2O, or as an anhydride of acetic acid, derived from 2 mols. of the acid by loss of 1 mol. of water, just as ethers are derived from alcohols, and inorganic anhydrides from the corresponding acids, * Except when the acetyl derivative has the same, or nearly the same percentage composition as the original substance, in which case the number of acetyl groups in the molecule is determined by boiling with standard alkali or acid, and then estimating by titration the amount of acetic acid which has been formed. THE EATTY ACIDS. 161 CH.COOH CHj-COx^ „ „ cocoon " m-.co '1 - Cft-OH _ C2H5\O h o no2-oh _ NO^ C2H5-OH " C2HfU + NO2-OH ~ N02^U + n2u- Acetic anhydride, (CH3-CO)2O, may be prepared by heat- ing the anhydrous alkali acetates (4 mols.) with phosphorus oxychloride (1 mol.); the salt is first acted on by the oxychloride yielding acetyl chloride (see above), which inter- acts with more salt, forming acetic anhydride, or, expressed in one equation, 4CH3-COONa + POC13 = 2(CH3-CO)2O + NaPO3 + 3NaCl. Acetic anhydride is a mobile liquid, boils at 137°, and has an unpleasant, irritating odour; it is decomposed by alkalies, by water, and by nearly all substances (except acids) which con- tain the hydroxyl-group, acetyl derivatives being formed, (CH3.C0).,0 + H2O = 2CH3-COOH (CH3-CO)2O + C2H5-OH = ch3.co-o-c2h5 + ch3.cooh. Acetic anhydride may therefore be employed in ascertaining whether a substance contains a hydroxyl-group just as well as acetyl chloride, the operations being carried out as already described. All the fatty acids, except formic acid, may be converted into anhydrides by treating the acid chloride with an alkali salt, or by heating excess of an alkali salt with phosphorus oxychloride. If an acid chloride be treated with a salt of a different acid, mixed anhydrides, corresponding with the mixed ethers, are obtained. All these anhydrides resemble acetic anhydride in chemical properties. Amides.-Acetyl chloride and acetic anhydride interact not only with compounds containing a hydroxyl-group, but also with anhydrous ammonia; the compound obtained in this way may be regarded as derived from ammonia by the substitution of the acetyl-group for one atom of hydrogen, and is named acetamide. 162 THE FATTY ACIDS. CH3-COC1 + 2NH3 = CH3CONH., + NH4C1 (CH.t-CO)2O + 2NHa = CH3CONHa + CH3COONH4. Acetamide, CH3-CONII2, may also be produced by heat- ing ethyl acetate (p. 185) with concentrated ammonia under pressure, CH3COOC2H5 + NH, = CIL.CONH2 + C2H5-OH, o ZD o o Z Z D ' but it is best prepared by slowly distilling ammonium acetate in a stream of dry ammonia, CH3 CO ONH4 - ch3 oo nh2 + h2o. As one distillation is not sufficient to insure complete decom- position, that portion of the distillate boiling above 140° is collected separately and redistilled, these operations being repeated three or four times. Acetamide crystallises in colourless needles, melts at 80-82°. and boils at 222°. When pure, it has only a faint odour, but as usually prepared, it has a strong smell of mice, owing to the presence of traces of impurity; it is readily soluble in water and alcohol. When heated with mineral acids or alkalies, it is decomposed into acetic acid and ammonia, or their salts (compare foot-note, p. 143), CH3-CO-NH2 + H2O = CH3.C00H + NH3; O Z Z O O' on distillation with phosphoric anhydride, it loses 1 mol. of water, and is converted into methyl cyanide or acetonitrile, CH3.CO.NH2 = ch3cn + h2o. Formic acid and all the higher fatty acids may be converted into amides by methods similar to those given above; formamide, H CO'NH2, for example, maybe prepared by distilling ammonium formate. These amides closely resemble acetamide in chemical and physical properties, but their solubility in water rapidly diminishes on passing up the series. It is a remarkable fact that the melting-points of the amides of the fatty acids lie very close together, most of them melting between 95° and 110°, and all within the limits of 79° and 129°. Substitution Products of Acetic Acid.-Since acetic acid, like methyl chloride, is a mono-substitution product of marsh- THE FATTY ACIDS. 163 gas, and contains three atoms of hydrogen combined with carbon, it might be expected to give halogen substitution pro- ducts, just as does methyl chloride. As a matter of fact, acetic acid yields three substitution products on treatment with chlorine in sunlight, CH3.COOH + Cl2 = CHoCLCOOH + HC1 CH3-COOH + 2C12 = CHC12-COOH + 2HC1 CH3-COOH + 3C12 = CC13-COOH + 3HCJ. If the constitutions of acetic acid and of these three com- pounds be correctly represented by these formulae, it would be expected that, as the chloro-substitution products still con- tain the carboxyl-group, they would behave like mono- carboxylic acids, and, like acetic acid, form salts, acid chlorides, anhydrides, &c. This again is the fact; the three substitu- tion products are monobasic acids, similar to acetic acid and to one another in chemical properties. The three chloracetic acids may be prepared by passing chlorine into boiling acetic acid, to which a little iodine has been added. When iodine is present, the process can be carried out in absence of sunlight, because the iodine is converted into iodine trichloride, which acts on the acetic acid even in the dark, CH3-COOH + IC13 = CH2CbCOOH + HC1 + ICL The iodine chloride is again converted into trichloride by direct combination with chlorine, and so the process con- tinues, a very small quantity of iodine being sufficient to insure chlorination. The iodine, or rather the iodine chloride, is spoken of as a chlorine carrier. Chloracetic acid, CH2C1-COOH, is a crystalline substance; it melts at 62°, and boils at 185-187°. Dichloracetic acid, CHC12-COOH, is a liquid, and boils at 190-191°; it is best prepared by treating chloral hydrate with potassium cyanide in aqueous solution, KCN + CC13.CH(OH)2 = CHC12-COOH + HCN + KC1. Trichloracetic acid, CC13-COOH, is best prepared by 164 THE FATTY ACIDS. oxidising the corresponding aldehyde, chloral, with concen- trated nitric acid, CC13-CHO + O = CC13-COOH. It melts at 52°, boils at 195°, and is decomposed by hot alkalies into chloroform and a carbonate, CC13-COOH 4- KOH = CHC13 4- KHCO3. The three bromacetic and iodacetic acids are similar in pro- perties. On treating any of these halogen substitution products with nascent hydrogen, they are reconverted into acetic acid by inverse substitution. The higher fatty acids may be converted into halogen substitution products, which, however, unlike those of acetic acid, exist in isomeric forms. Propionic acid, for example, gives two monochloro-propionic acids-namely, a-chloro propionic acid, CH3-CHC1-COOH, and /9-chloro-propionic acid, CH2C1-CH2-COOH. For the purpose of distinguishing between these substitution pro- ducts, the carbon atoms are lettered a, 7, 3, &c., commencing always with that which is combined with the carboxyl-group CH3.CH2 CH2 CH2 COOH ; 6 7 a the acid of the constitution cgVCBr-CH2-COOH, for example, is named /Lbromisopropylacetic acid. SUMMARY AND EXTENSION. The Fatty Acids.-Carboxy-derivatives of the paraffins of the general formula CnH2n+1-COOH, or CnH2MO2. The more im- portant members of this homologous series are the following, the number of known isomerides being given bv the figures in brackets : M.p. B.p. Sp. gr. Formic acid, H-COOH (1) 8-3° 101° 1-241 at 0 Acetic acid, CH3-COOH (1) 16-5° 118° 1-080 tt Propionic acid, C2H5-COOH (1) -24° 141° 1 -013 it -4° 163° 0-978 Butyric acid, C3H7-COOH (2)|Ir) 155° 0-965 <i Valeric acid, C4H9-COOH (4){^" al 186° 174° 0-957 0-947 it Heptylic acid, C6H]3-COOH (8) - 223° 0-945 it Lauric acid, CnH^-COOH (3) 43-6° - 0-875- Myristic acid, C^H^-COOH (2) 54° - 0-862 bl Palmitic acid, C15H31-COOH (2) 62° - 0-853 Stearic acid, C]7H3S-COOH (3) 69° - - 0-845 THE FATTY ACIDS. 165 Heptylic acid and all the higher members named in this table are normal acids ; they occur in nature in fats and oils, and contain an even number of carbon atoms. The higher normal acids containing an odd number of carbon atoms, C8H17-COOH, C10H21-COOH, &c., are known, but they do not occur in nature. Formic acid is prepared by heating oxalic acid with glycerol, acetic acid from pyroligneous acid, and by the acetous fermentation of alcohol, butyric acid by the butyric fermentation of lactic acid, and palmitic and stearic acids by the hydrolysis of glycerides occurring in fats and oils. Methods of Preparation.-By the oxidation of primary alcohols and of aldehydes, CoH3-CH.,-OH + 20 = C.,H5-COOH + H.,O c6h13.cho + 0= C6H13-COOH. By boiling alkyl cyanides with alkalies or mineral acids, C2H5-CN + 2H2O = C2H5COOH + NH3. By heating those dicarboxylic acids in which the two carboxyl groups are combined with one and the same carbon atom (p. 234), CH2(COOH)2 = ch3-cooh + co2. By the hydrolysis of derivatives of ethyl acetoacetate (p. 189), CH3-CO-CH(C3H7).COOC2H5 + 2K0H = C3H7.CH.,COOK + CH3-Cd0K + C2H5.OH. Physical Properties.-At ordinary temperatures, the lower mem- bers are colourless liquids (except acetic acid), miscible with water, alcohol, and ether in all proportions. On passing up the series, they become more oily in character, gradually lose their pungent smell, and become less readily soluble in water. The higher members, from C10H20O2, are solid, waxy, or fatty substances, have only a faint smell, and are insoluble in water, but soluble in alcohol and ether. They are all volatile in steam except the highest members, which, however, may be distilled in super-heated steam. The first three members are specifically heavier than water, but the sp. gr. decreases as the series is ascended (see table). With the exception of the highest members, they boil without decom- position under ordinary atmospheric pressure, the boiling-point rising about 19° for every addition of -CH2- to the molecule; the melting-point also rises, but not continuously, acids containing an odd number of carbon atoms melting at a lower temperature than the preceding members containing an even number of carbon atoms, C12H24O2 43-6° 40-5° c14h28o2 54° C15H3()O2 51° C'i6H-32O2 62° ^17^34^2* 60° 166 THE FATTY ACIDS. Chemical Properties.-The fatty acids are very stable, and are only with difficulty oxidised and broken up; nevertheless, owing to the presence of the carboxyl-group, they readily undergo a variety of double decompositions. They are all monobasic acids, but the acid character becomes less and less pronounced on passing up the series; whereas formic and acetic acids readily decompose carlxmates, and dissolve metals and metallic hydroxides, the higher members, such as palmitic and stearic acids, are with difficulty recognised as acids by ordinary tests. The metallic salts of the lower members are soluble in water; but on passing up the series, the solubility decreases, until, in the case of the higher acids, only the alkali salts (soaps) are soluble. Fatty acids interact with alcohols, especially in presence of dehydrating agents, forming ethereal salts and water, CH3-COOH + C2H5OH = CH3COOC2H5 + H2O. When treated with phosphorus pentachloride, &c., they are con- verted into acid chlorides, C2H5COOH + PCig = C2HgCOCl + POC18 + HC1. These acid chlorides interact readily with hydroxy-compounds, giving ethereal salts, C2H5-COC1 + CH3-OH = C2HSCOOCH3 + HC1; on distillation with an alkali salt of a fatty acid, they yield anhy- drides of the acids, C2H8-COC1 + C2H5COOK = (C2H5-CO)2O + KC1; and when treated with ammonia, they give amides, CH8COC1 + NHS = CH3-CONH2 + HCI. The fatty acids yield halogen substitution products under suitable conditions. From the alkali salts of the fatty acids, ketones, aldehydes, and paraffins can be prepared without difficulty, and, as the aldehydes and ketones are easily reduced to alcohols, which again are readily converted into ethers and olefines, all these com- pounds may be obtained from the fatty acids. Fats, Oils, Soaps, Stearin, and Butter. Composition of Fats and Oils.-When beef or mutton suet is kneaded in a muslin bag in a basin of hot water, the fat melts and passes out, leaving the membrane or tissue in the bag; the melted fat solidifies on cooling, and is known as tallow. The fat obtained from pigs, in a similar manner, is much softer, and is called lard THE EATTY ACIDS. 167 When tallow is heated with water in closed vessels at about 200°, or treated with superheated steam (steam which has been passed through tubes heated at about 200°), it is decomposed into glycerol (p. 248) and fatty acids; if the mixture be now distilled in superheated steam, these pro- ducts pass over, the distillate being an aqueous solution of glycerol, at the surface of which floats the mixture of fatty acids. A similar decomposition takes place when tallow is heated with dilute sulphuric acid, but in this case it is not necessary to heat so strongly. All animal fats, such as lard, goose-fat, bone-fat, butter, &c., and the fatty oils, such as olive-, linseed-, rape-, palm-, and cotton-seed oils, which are obtained by pressing the seeds or fruit of certain plants, behave in a similar manner, and when heated with dilute sulphuric acid, or with water under pressure, are decomposed into glycerol and a mixture of fatty acids. The occurrence of these acids in natural fats and oils, and the fact that the higher members of the series resemble fats in physical properties, led to the use of the term 'fatty acid,' which is now applied to all the members of the series. The chemical compounds of which these fats are com- posed are called glycerides; they are ethereal salts (p. 171), formed, together with water, by the combination of the fatty acids with the alcohol, glycerol, which acts as a hydroxide or weak base. Glycerol is a tri-acid base, and can combine with and neutralise three molecules of a monobasic or mono- carboxylic acid, forming neutral salts, just as can the tri- acid bismuth hydroxide, C3H5(OH)3 + 3CH3-COOH - C3H5(O.CO-CH3)3 + 3H2O ' Bi(OH)3 + 3HC1 - BiCl3 + 3H2O. These glycerides or salts are named after the acids from which they are formed. The salt formed from acetic acid is called triacetin; that from palmitic acid, tripalmitin ; and that from stearic acid, tristearin, and so on. 168 THE FATTY ACIDS. Now the chief constituents of fats and oils are tristearin and tripalmitin, which are solid at ordinary temperatures, and a liquid glyceride, triolein, which is formed by the combination of glycerol with oleic acid* When a fat con- tains a relatively large proportion of tristearin and tripalmitin, it is solid and comparatively hard (tallow) at ordinary tem- peratures ; when, however, it contains a relatively large pro- portion of triolein, it is soft and pasty (lard), or liquid (olive- oil). These glycerides, like other salts formed from weak acids and weak bases, are not very stable, and at moderately high temperatures they are decomposed by water and by dilute mineral acids, being converted into glycerol and an acid; in the case of tristearin, for example, CH.,O.CO-C17H35 ch2oh I I CHOCOC17H35 + 3H2O = CHOH + 3C17H35COOH. CH2OCOC17H35 ch2oh Glycerol. Stearic Acid. Since fats and oils are mixtures of glycerides, they yield mixtures of fatty acids. Soaps.-On treatment with alkalies the glycerides are de- composed much more readily than by water, yielding alkali salts, the weak base, glycerol, being liberated, just as ammonia or methyl alcohol is liberated from its salts on adding a stronger base. In manufacturing soaps, a fat or oil, such as tallow or cotton-seed oil, is heated in an iron pan with a small but sufficient quantity of caustic soda, when it is converted after some time into a thick, homogeneous, frothy solution, which contains glycerol and the sodium salts of the various acids which were present in the glycerides-that is to say, the sodium salts of stearic, palmitic, and oleic acids. Some common salt is now added, whereupon the sodium * Oleic acid, C17H33-COOH (p. 258), is a liquid at ordinary temperatures. It contains two atoms of hydrogen less than stearic acid, C17H35COOH, and is, therefore, an unsaturated acid, belonging to a different series; its lead salt is soluble in ether, a property very rarely met with in other lead salts. THE FATTY ACIDS. 169 salts separate from the solution of glycerol and salt as a curd, because they are insoluble in salt water. The curd, after having been drained off, and allowed to cool, slowly solidifies, and is then known as hard soap, which is simply a mixture of the sodium salts of palmitic, stearic, and oleic acids with water and alkali. When fats or oils are boiled with potash, instead of with soda, similar chemical changes take place, and the potassium salts of the acids are formed; if common salt be now added to the solution, the potassium are partially converted into sodium salts, and a hard soap is finally obtained ; if, however, without adding salt, the homo- geneous solution be allowed to cool, it sets to a jelly-like mass of soft soap, which is a mixture of the potassium salts of the above-named acids, containing glycerol and a large percentage of water. The decomposition of fats and oils in this way in the process of soap-making originally received the name saponifica- tion, and the fats and oils were said to be saponified. The term saponification was then applied generally to the analo- gous decomposition of other ethereal salts by alkalies, in spite of the fact that the products were not soaps, but the word hydrolysis has now to a great extent taken its place. Hydrolysis may be roughly defined as the decomposition of one compound into two or more, with fixation of the elements of water or of some hydroxide. The decomposition of glycerides by water, acids, and alkalies, and the changes expressed by the following equations, are examples of hydrolysis, C12H22On + H2O = C6H12O6 + CeH12O, C2H,O.-C2H. + H2O = C,H.O2 + C,H,-OH C2H5C1 + KOH = C2H5-OH + KC1. Stearin and Glycerol.-Stearin consists principally of a mixture of stearic and palmitic acids, and is manufactured by decomposing tallow with water, superheated steam, dilute sulphuric acid, or milk of lime under pressure 170 THE FATTY AGIOS. (see above). After distilling the products in a current of superheated steam - first acidifying with sulphuric acid, if lime has been used-the pasty mixture of fatty acids is separated from the aqueous solution of glycerol, and pressed, in order to squeeze out as much of the liquid oleic acid as possible. The pressed mass is then gently warmed, and pressed again between warm plates, when a further quantity of oleic acid is squeezed out, together with some palmitic and stearic acids. The hard mass that remains is called stearin; it is mixed with a little paraffin to make it less brittle, and employed in large quantities in the manufacture of stearin candles. The pasty mass of oleic, palmitic, and stearic acids, separated from the stearin, is known as oleo- margarine (from oleic and ' margaric ' acids), and is em- ployed for the preparation of artificial butter. Glycerol (p. 248) is obtained from the aqueous distillate, after separating the fatty acids; the solution is decolourised by filtration through charcoal, and evaporated to a syrup. Butter and Margarine.-Butter, prepared from cream, is a mixture of fat (about 87 per cent.), water (about 12 per cent.), and small quantities of casein, milk-sugar, and salts. Pure butter-fat contains about 92 per cent, of a mixture of tristearin, tripalmitin, and triolein, about 7'7 per cent, of tributyrin, and traces of other glycerides, and substances which impart flavour; it differs from all other fats and oils, in containing a large proportion of tributyrin, the glyceride of butyric acid. Artificial butter, or margarine, is prepared from oleomar- garine (see above), which has been carefully manufactured from the best ox-suet; the oleomargarine is flavoured and coloured by churning it with milk, sometimes also by the addition of artificial colouring and flavouring substances. When carefully prepared, it is a wholesome substitute for butter, and probably just as nutritious, although perhaps not quite so easily digested Ethereal salts. 171 CHAPTER X. ETHEREAL SALTS. It has been pointed out that the alcohols behave in some respects like metallic hydroxides, and combine with acids, forming salts and water, C2H5-OH + HC1 = C2H5C1 + H2O c2h5-oh + h2so4 = c2h5.hso4 + h2o Z U Z ZU 4 z CH-.OH + CH,-COOH = CH.,-GOOCH, + H2O. u u o u z These compounds are called ethereal salts or esters, in con- tradistinction to the metallic salts. Halogen Ethereal Salts and Halogen Derivatives of the Parafins. The ethereal salts of the halogen acids are identical with the halogen mono-substitution products of the parafins, and may be obtained either from the alcohols or from the par- affins ; they form homologous series of the general formula CmH2n, rX where X = Cl, Br, or I. Methyl chloride, CH3C1 Methyl bromide, CH3Br Methyl iodide, CH3I Ethyl „ C2H5C1 Ethyl „ C2H5Br Ethyl „ C2H5I Propyl H C3H7C1 Propyl ■■ C3H7Br Propyl n C3H7I The di-, tri-, &c. halogen substitution products of the par- affins, such as methylene dichloride, CH2C12, chloroform, CHC13, iodoform, CHI3, and carbon tetrachloride, CC14, can- not be regarded as ethereal salts, but, being closely related to the halogen ethereal salts, are conveniently considered in this chapter. Methyl chloride, or chloromethane, CH3C1, is one of the four substitution products obtained on treating methane with chlorine in sunlight, and is formed in small quantities when methyl alcohol is heated with concentrated hydrochloric acid, CH3-OH + HC1 = CH3C1 + H2O. 172 ETHEREAL SALTS. It is prepared by passing hydrogen chloride into methyl alcohol containing anhydrous zinc chloride (Groves' process), as described in the case of ethyl chloride (p. 175); also by heating methyl alcohol with sodium chloride and concentrated sulphuric acid. It is a colourless gas, and liquefies at very low temperatures, boiling at -24°; it burns with a green-edged flame, is moder- ately easily soluble in water, and when heated with water or dilute potash under pressure, it is converted into methyl alcohol, CH3C1 + H2O = CH3.OH + HC1. Methyl chloride is employed on the large scale in the preparation of organic dyes, the compressed gas being also used for the artificial production of a low temperature ; for these purposes it is manu- factured by heating trimethylamine hydrochloride (p. 207) with hydrochloric acid, N(CH3)3,HC1 + 3HC1 = 3CH3C1 + NH4C1. Methylene (or methene) dichloride, CH2C12, is prepared by reducing chloroform with zinc and hydrochloric acid in alcoholic solution, CHC13 + 2H = CH2C12 + HC1; it is a colourless, heavy liquid, boiling at 41°. Chloroform, or trichloromethane, CHC1.{, is formed when methane, methyl chloride, or methylene dichloride, is treated with chlorine in sunlight, and when many simple organic substances containing oxygen, such as ethyl alcohol, acetone, &c., are heated with bleaching powder, which acts as an oxidising as well as a chlorinating agent (see below). Chloroform may be prepared by distilling alcohol or acetone with bleaching powder : Some strong bleaching powder (about 450 grams) is made into a cream with about 1^ litres of water contained in a large flask, and alcohol, methylated spirit, or acetone (about 100 c.c.) is gradually added ; the flask is then connected with a condenser, and slowly heated on a water-bath, when a mixture of chloroform, water, and alcohol or acetone distils. If the operation has been success- ETHEREAL SALTS. 173 ful, the chloroform collects as a heavy oil at the bottom of the receiver; but if too much alcohol or acetone be present, the chloroform must be precipitated by adding water. It is then separated with the aid of a funnel, washed with water, shaken once or twice with a little concentrated sulphuric acid, which frees it from water, alcohol, &c., and redistilled from a water-bath. The chloroform prepared in this way is not quite pure; the pure substance is best prepared by distilling chloral or chloral hydrate (p. 125) with caustic soda, the product being separated in the manner just described, CC13-CHO + NaOH = CHC13 + H-COONa. The changes which occur in the preparation of chloroform from alcohol are complex; it is probable that aldehyde is first formed by oxidation, and then converted into chloral, which is decomposed by the calcium hydroxide which is always produced during the reaction, yielding chloroform and calcium formate. When acetone is employed, trichloracetone is probably formed in the first place ; this compound is then decomposed by the calcium hydroxide, giving chloroform and calcium acetate, 2CH3-CO-CC13 + Ca(OH)2 = 2CHC13 + (CH3-COO)2Ca. Chloroform is a heavy, pleasant-smelling liquid of sp. gr. L498 at 15°, and boils at 61°; when strongly heated, it burns with a green-edged flame, but it is not inflammable at ordinary temperatures. It is readily decomposed by warm alcoholic potash, yielding potassium formate and chloride, CHC13 + 4K0H = H-COOK + 3KC1 + 2H2O. If a drop of chloroform be added to a mixture of aniline (part ii.) and alcoholic potash, an intensely nauseous smell is observed on warming gently, owing to the formation of ph enylcarby!amine or phenylisocyanide* CHC13 + 3K0H + C6H5.NH9 = C6H5-NC + 3KC1 + 3H2O, or C6H5'NH2 + H-COOH = C6H5'NC + 2H2O. * The experiment should be performed in a test tube, only one drop of aniline being employed, and the contents of the test tube should afterwards be carefully poured into the sink-pipe, in a draught closet if possible. 174 ETHEREAL SALTS. This reaction affords a very delicate test for chloroform and for aniline, and is spoken of as the carbylamine reaction (p. 202). Chloroform is extensively employed in surgery as an anaes- thetic, its vapour when inhaled causing unconsciousness. For this purpose pure chloroform must be employed, as the impure substance is dangerous, and produces bad after-effects.* Pure chloroform gives no precipitate with silver nitrate, and does not darken when shaken with concentrated sulphuric acid or with strong potash. Carbon tetrachloride, or tetrachloromethane, CC14, the final product of the action of chlorine on CH4, CH3C1, CH2C12, and CHC13, is prepared by passing chlorine into boiling chloroform in sunlight, or by passing chlorine into carbon bisulphide in presence of antimony pentachloride, which acts as a chlorine carrier (p. 163), CS2 + 3SbCl5 = CC14 + S2C12 + 3SbCL, SbCl3 + Cl2 = SbCl5; in the latter case the sulphur dichloride is got rid of, after a preliminary distillation, by shaking the product with potash, the carbon tetrachloride being purified by redistillation. Car- bon tetrachloride is a very heavy, pleasant-smelling liquid, boiling at 76-77°; on treatment with nascent hydrogen, it is converted into CHC13, CH2C12, CH3C1, and CH4 successively, by inverse substitution. It is decomposed by hot alcoholic potash, CC14 + 4K0H = 4KC1 + CO2 + 2H2O. The halogen ethereal salts, methyl bromide, CH8Br (b.p. 4-5°), and methyl iodide, CH3I (b.p. 44°), are prepared by methods similar to those employed in the case of the corresponding * In the presence of air, chloroform gradually undergoes decomposition, especially under the influence of light, carbonyl chloride (phosgene gas, COC12) and hydrochloric acid being produced, CHC13 + O = COC12 + HC1. As carbonyl chloride is very poisonous, it is necessary to keep all chloroform required for anaesthetic purposes in the dark, the bottle being kept as full as possible, so as to exclude air. ETHEREAL SALTS. 175 ethyl salts (see below), which they closely resemble in chemical properties. Iodoform, or triiodomethane, CIII3, a halogen tri-substitu- tion product of methane, is closely related to chloroform, and may be considered here. It is formed when ethyl alcohol (but not methyl alcohol), acetone, aldehyde, and other simple organic substances containing oxygen united with a CII3-C= group are warmed with iodine and an alkali or alkali carbon- ate ; the changes which occur are doubtless similar to those which take place in the preparation of chloroform. Iodoform is prepared by gradually adding iodine to an aqueous solution of sodium carbonate containing a little alcohol and heated at 60-80°; the precipitated iodoform is separated by filtration, and purified by recrystallisation from dilute alcohol. It crystallises in lustrous, yellow, six-sided plates, melts at 119°, and has a peculiar, very characteristic odour; it sublimes readily, and is volatile in steam. It is used in medicine and surgery as an antiseptic. Ethyl chloride, or chlorethane, C2H5C1, is formed when ethane is treated with chlorine in sunlight, and when alcohol is heated with concentrated hydrochloric acid, or treated with phosphorus pentachloride, or trichloride, at ordinary temperatures, C2H5-0H + PCL = CJLC1 + POOL + HC1. Ethyl chloride is prepared by Groves' process: Hydrogen chloride, carefully dried with concentrated sulphuric acid, is passed into a flask containing absolute alcohol, to which about half its weight of coarsely powdered anhydrous zinc chloride has been added; the flask is connected with a reflux condenser (p. 186), and is provided with a safety tube. As soon as the solution is saturated with hydrogen chloride, it is gently warmed on the water-bath, when ethyl chloride and alcohol pass off; the alcohol vapour is cooled in passing through the condenser, the liquid running back into the flask. The gaseous ethyl chloride now passes through three 176 ETHEREAL SALTS. wash-bottles containing water, dilute potash, and concen- trated sulphuric acid respectively, by which means it is freed from hydrogen chloride, alcohol, and moisture; the pure ethyl chloride is then collected in a U-tube immersed in a freezing mixture. Zinc chloride is a powerful dehydrating agent, and com- bines with the water produced during the interaction, C2H5-OH + HC1 = C2H5C1 + H2O. Unless some dehydrating agent be present, very little ethyl chloride is formed, because it is decomposed by water, or rather its formation cannot take place in presence of much water. Ethyl chloride may also be prepared by warming a mixture of absolute alcohol, concentrated sulphuric acid, and sodium chloride, the gas being purified and condensed in the same way as before; the sulphuric acid not only interacts with the salt, forming hydrogen chloride, but also acts as a de- hydrating agent. Ethyl chloride is a colourless, very volatile liquid, boiling at 12-5°; it burns with a greenish, smoky flame, and is only sparingly soluble in water, but miscible with alcohol, ether, &c. When heated with water or potash under pressure, it yields ethyl alcohol, C2H5C1 + H2O = C2H5-OH + HC1; on treatment with chlorine in sunlight, it gives di-, tri-, &c. substitution products of ethane. It gives no immediate precipitate with aqueous silver nitrate, but when warmed with an alcoholic solution of silver nitrate, silver chloride is quickly precipitated, ethyl nitrate remaining in solution, C2H5C1 + AgNO3 = C2H5.NO3 + AgCl. Ethyl bromide, or bromethane, C2H5Br, is formed when alcohol is heated with concentrated hydrobromic acid, or treated with phosphorus tribromide or pentabromide, at ordinary temperatures, C2H5-OH + PBr5 = C2H5Br + POBr3 + HBr. ETHEREAL SALTS. 177 It is prepared by dropping bromine from a stoppered funnel into a mixture of alcohol (60 grams) and amorphous phos- phorus (10 grams) contained in a distilling-flask, connected with a condenser and immersed in cold water; after adding the whole of the bromine, the mixture is distilled. The distillate is shaken with dilute potash to free it from bromine, hydrobromic acid, and alcohol, and then washed by shaking with water; after drying with calcium chloride, the ethyl bromide is purified by fractional distillation, 3CJL-OH + P + 3Br = 3C2H,Br + H„P0„. It may also be prepared by distilling a mixture of alcohol, concentrated sulphuric acid, and potassium bromide. Ethyl bromide is a colourless, pleasant-smelling, heavy liquid, and boils at 39°; it resembles ethyl chloride in its behaviour with water, potash, and silver nitrate. Ethyl iodide, or iodethane, C2H5I, is formed when alcohol is heated with concentrated hydriodic acid; it is prepared by gradually adding iodine (100 grams), in small quantities at a time, to a mixture of alcohol (50 grams) and amorphous phosphorus (10 grams), and then distilling from a water- bath, the product being purified exactly as described in the case of ethyl bromide, 3C2H5-OH + P + 31 = 3C2H5I + H3PO3. Ethyl iodide is a colourless, pleasant-smelling, highly refrac- tive, very heavy liquid, boiling at 72°; on exposure to light, it turns yellowish-brown, owing to the separation of traces of iodine, this phenomenon being observed in the case of nearly all organic compounds containing iodine. In chemical properties it closely resembles ethyl chloride and ethyl bromide. Other halogen ethereal salts or halogen mono-substitution pro- ducts of the paraffins, such as propyl bromide, CsH7Br, butyl iodide, C4H9I, &c., may be prepared by methods similar to those given above; they are all colourless, neutral, pleasant-smelling liquids, as a rule specifically heavier than water, in which they are insoluble, or nearly so. They are slowly decomposed, or 178 ETHEREAL SALTS. hydrolysed (p. 188), by boiling water and by aqueous alkalies, yield- ing the alcohols, C3H7Br + KOH = C3H7-OH + KBr; when boiled with alcoholic potash, they are converted into olefines, C3H7I + KOH = C3H6 + KI + H2O. They do not give an immediate precipitate with silver nitrate in aqueous solution ; but in alcoholic solution, especially on warm- ing, a halogen silver salt is quickly precipitated, and an organic nitrate remains in solution, C2H5I + AgNO3 = C2H5-NO8 + AgL Although these compounds closely resemble one another in chemical properties, their physical properties depend to a considerable extent on the halogen which they contain, the sp. gr. and boiling-point rising on displacing chlorine by bromine, or bromine by iodine : Sp. gr. Sp. gr. at 0° B-P' at 0° Bp- Methyl chloride, CH3C1 - -22° Ethyl chloride, C2HBC10-921 12-5° Methyl bromide, CH3Br 1-73 + 4-5° Ethyl bromide, C2HBBrl-47 39° Methyl iodide, CH3I 2-33 45° Ethyl iodide, C2H8I 1-975 72° Although the monohalogen derivatives of methane and ethane exist in only one form, those of propane and the higher paraffins show isomerism. There are, for example, two compounds of the molecular formula, C3H7I, corresponding with the two alcohols, C3H7-OH, namely, normal propyl iodide, CH3-CH2-CH2I (b.p. 102°), and isopropyl iodide, CH3-CHI-CH3 (b.p. 89-9°). The mono- halogen derivatives of butane exist theoretically in four isomeric forms, two of which, CH3 CH2-CH2-CH2X, and CH3-CH2-CHX-CHS, pit are derived from normal butane; the other two, ^g^CH-CHjX, and -h3>CX.CH3, from isobutane. Tertiary butyl iodide, (CH3)3CI, has been previously mentioned. It may be obtained by treating isobutyl alcohol with zinc chloride or sulphuric acid, and then dissolving the isobutylene formed in this way in concentrated hydriodic acid, (CH3)2CH-CH2.OH = (CHs)2C: CH2 + H.,0 (CH8)2C: CH2 + HI = (CH3)2CI-CH8; also by heating trimethylcarbinol with hydriodic acid, (CH3)8C-OH + HI = (CH3)3T + H2O. It is a colourless oil, boils at 100° with slight decomposition, and is readily acted on by alkalies, being converted into isobutylene. ETHEREAL SALTS. 179 Ethereal Salts of Nitric Acid. The ethereal salts of nitric acid are formed when the halogen ethereal salts are warmed with silver nitrate in alcoholic solution, CH3I + AgNO3 = CH3-NO3 + Agl; they are also produced, together with nitrites (see below), when the alcohols are treated with concentrated nitric acid, C.,HrOH + HNCh = CJL.NO, + H9O. Of O O f O a Ethyl nitrate, C2H5-NO3, is formed when alcohol is treated with ordinary concentrated nitric acid, CJL.OH + HNO.» = CJL.NO, + H9O, AU O A O O A 7 but so much heat is developed that, unless care be taken, the reaction becomes almost explosive in violence ; even when the mixture is cooled, only a comparatively small quantity of ethyl nitrate is produced, owing to the acid oxidising some of the alcohol, and being itself reduced to nitrous acid, which then interacts with the alcohol, forming ethyl nitrite. If, however, the nitric acid be mixed with a little urea (p. 289), a substance which decomposes nitrous acid, CO(NH2)2 + 2N0-0H = C02 + 3H2O + 2N2, the reaction takes place with much less violence, and ethyl nitrate is the sole product. For these reasons ethyl nitrate is prepared by gradually adding alcohol (not more than 30 grains) to half its volume of nitric acid (sp. gr. 1-4), to which about 5 grams of urea have been added ; the mixture is then very slowly heated on a water-bath in a large retort provided with a condenser. The mixture of ethyl nitrate, alcohol, and acid which collects in the receiver is shaken with water in a separating funnel, the heavy oil dried with calcium chloride, and distilled from a water-bath. Ethyl nitrate is a colourless liquid of sp. gr. 141 at 20°, and boils at 87°; it has a pleasant fruity odour, and is almost insoluble in water, but readily soluble in alcohol, &c. It burns with a luminous flame, and when dropped on to a hot surface it sometimes explodes. It is slowly decomposed by 180 ETHEREAL SALTS. boiling water, quickly by hot alkalies, yielding alcohol and nitric acid or a nitrate, CJE-NO, + h.2o = c2h5-oh + hno3. On reduction with tin and hydrochloric acid it yields hydroxyl- amine, C2H6-NO3 + 6H = c2h5.oh + nh2-oh + h2o. Methyl nitrate, CH3-NO3 (b.p. 66°), and th.e higher homo- logues closely resemble ethyl nitrate in properties. Ethereal Salts of Nitrous Acid. The ethereal salts of nitrous acid are produced by the action of nitrous acid on the alcohols, C2H5-OH + HNO, = CoH5-NO2 + H2O. Z O Xi Xi X Xi They may be prepared by saturating the alcohols with the fumes evolved by the interaction of arsenic trioxide and nitric acid,* or by distilling alcohol with sodium nitrite and sulphuric acid, or with copper and nitric acid.t Ethyl nitrite, C2H5NO2, is usually prepared by slowly dropping concentrated nitric acid (3 c.c.) into a cold mixture of alcohol (20 c.c.) and concentrated sulphuric acid (2 c.c.), then adding copper turnings (about 4 grams), and distilling carefully from a water-bath. The distillate consists of a mixture of ethyl nitrite, alcohol, and its oxidation products ; when mixed with alcohol, it is employed in medicine as ' sweet spirits of nitre.' In order to prepare pure ethyl nitrite, the distillate is shaken with water, the oil dried over calcium chloride, and redistilled. Ethyl nitrite is a colourless liquid of sp. gr. 0-900 at 15-5°; it boils at 17°, and has a pleasant fruity odour like that of apples; it is insoluble in water, and is readily hydrolysed by boiling water or dilute alkalies, C9HVNO2 + KOH = CJL-OH + KN09. Z O X X O X * A s2O3 + 2H NO;! + 2 H2O = 2 H3AsO4 + N2O3. + 2Cu + 6HNO3 = 2Cu(NO3), + 2H2O + 2HNO2. ETHEREAL SALTS. 181 Methyl nitrite, CH3-NO2, is a gas; the higher homologues resemble ethyl nitrite. Nitro-paraffins.-When ethyl iodide is heated with silver nitrite, very interesting changes occur : part of the ethyl iodide interacts with the silver nitrite, yielding ethyl nitrite, the rest being con- verted into nitro-ethane, both changes being expressed by the equation C2H5I + AgNO2 = C2H5NO2 + Agl. Ethyl nitrite and nitro-ethane are isomeric ; the former is simply a salt of nitrous acid, HO-N:O, and has the constitution C2H5 O N:O, whereas the latter contains pentavalent nitrogen, and has the constitution C2H5 N^^. Compounds, similar to nitro-ethane in constitution and isomeric with the corresponding nitrites, may be obtained from other halogen ethereal salts in the above manner ; they are termed nitro- paraffins, because they are derived from the paraffins by the sub- stitution of the nitro group -for one atom of hydrogen. The nitro-paraffins are colourless, pleasant-smelling liquids, and distil without decomposition, but their boiling-points are much higher than those of the corresponding nitrites ; nitro-ethane, for example, boils at 114°, ethyl nitrite at 17°. They differ from the nitrites in certain important particulars: the nitro-paraffins are soluble in, but are not decomposed by caustic alkalies, whereas the nitrites, like all other ethereal salts, undergo hydrolysis, yielding an alcohol and a nitrite. The nitro-paraffins are converted into amines on reduction, C2H5NO2 + 6H = C2H5NH2 + 2H2O, whilst the nitrites yield hydroxylamine, or ammonia, and an alcohol, C5HnON:O + 6H = C5HnOH + NH3 + H2O. Ethereal Salts of Sulphuric Acid. Dibasic acids, such as sulphuric acid, form two classes of salts with alcohols-namely, acid salts, corresponding with the acid sulphates, and normal or neutral salts, corresponding with the neutral sulphates, Ethyl hydrogen sulphate, ^2^i>SO4 Ethyl sulphate, (C2H5)2SO4. Potassium hydrogen sulphate, j^>SO4 Potassium sulphate, K2SO4. 182 ETHEREAL SALTS. Ethyl hydrogen sulphate, ethylsulphuric acid, or sulpho- vinic acid (from sulphuric acid and spirits of wine), C2H5-HSO4, is formed when ethylene is passed into fuming sulphuric acid, or heated with ordinary sulphuric acid, C2H4 + H2SO4 = C2H5HSO4. It is prepared in the following manner : A mixture of equal volumes of alcohol and concentrated sulphuric acid is heated at 100° for about an hour, when part of the alcohol is converted into ethyl hydrogen sulphate, C2HB0H + H2SO4 = C2HsHSO4 + H2O. The solution is cooled, diluted with water, and treated with a slight excess of barium carbonate, when barium sulphate and barium ethylsulphate are formed, 2C2H5HSO4 + BaC03 = (C2H5-SO4)2Ba + CO2 + H2O. After filtering from the barium sulphate and excess of barium carbonate, the cold solution of barium ethylsulphate is treated with dilute sulphuric acid as long as a precipitate is produced, and filtered again to separate the barium sulphate, (C2H3SO4)2Ba + H2SO4 = 2C2H8HSO4 + BaSO4. The filtrate is now free from sulphuric acid; it is evaporated at ordinary temperature under reduced pressure over sulphuric acid, when alcohol and water pass off and are absorbed by the sulphuric acid, and ethyl hydrogen sulphate remains as a thick sour liquid. Ethyl hydrogen sulphate has an acid reaction, decomposes carbonates, and is, in fact, like potassium hydrogen sulphate, a monobasic acid, since it contains one atom of hydrogen dis- placeable by metals. The potassium salt, C2H5-KSO4, may be prepared by neutralising the acid with potassium carbon- ate, or by treating a solution of the barium salt with potassium carbonate, and, after filtering, evaporating to dry- ness ; it is a colourless, crystalline, neutral compound, readily soluble in water. The barium salt, (C2H5-SO4)2Ba, is also readily soluble in water, so that ethylsulphuric acid does not give a precipitate with barium chloride. Ethyl hydrogen sulphate is a very interesting substance, as it is an intermediate product in the conversion of alcohol ETHEREAL SALTS. 183 into ethylene and ether, and of ethylene into alcohol. When boiled with water it yields alcohol, so that it cannot be obtained from its aqueous solution by evaporating at 100°, C2H5.HSO4+H2O = C2H5OH + H2SO4; when heated with alcohol it gives ether, C2H5-HSO4 + C2H5-OH = (C2H5)2O + H2SO4; and when heated alone, or with concentrated sulphuric acid, it yields ethylene, C2H5-HSO4 = C2H4 + H2SO4. Other alcohols combine with sulphuric acid, yielding acid salts corresponding with ethyl hydrogen sulphate; these compounds, the alkyl hydrogen sulphates, closely resemble ethyl hydrogen sulphate in properties, and undergo similar decompositions. Ethyl sulphate, (C2H5)2SO4, the normal or neutral salt, is of comparatively little importance ; it may be prepared by warming silver sulphate with ethyl iodide, when double decomposition takes place, just as when silver sulphate is treated with potassium iodide, Ag2SO4 + 2C2H5I = (C2H5)2SO4 + 2AgI. It is a colourless liquid, boiling at 208°, with decomposition. MERCAPTANS AND SULPHIDES. Alcohols form two classes of compounds with hydrogen sulphide-namely, the hydrosulphides and the sulphides; the former bear the same relation to the metallic hydrosulphides as the alcohols to the metallic hydroxides, whereas the sulphides are related to the metallic sulphides just as the ethers to the metallic oxides, 'Ethyl hydrosulphide, C2H5'SH Potassium hydrosulphide, K-SH Ethyl sulphide, (C2Hs)2S Potassium sulphide, K2S 'Ethyl hydroxide, C2H5-OHj ,Potassium hydroxide, K OH1 Ethyl oxide, (C2H5)2O Potassium oxide, K2O The organic hydrosulphides or sulphhydrates are usually called mercaptans (mer curium captans) on account of their property of combining readily with mercuric oxide, forming crystalline compounds ; they may be regarded as sulphur- or thio-alcohols, and the organic sulphides, as thio-ethers. 184 ETHEREAL SALTS. Ethyl mercaptan, C2H5-SH, may be obtained by treating alcohol with phosphorus pentasulphide, 5C.2H5-OH + P2S5 = 5C2H5.SH + P2O5; it is prepared by distilling a concentrated solution of ethyl potassium sulphate with potassium hydrosulphide, C2H6-KSO4 + KSH = C2H5SH + K2SO4. It is a colourless, very unpleasant-smelling liquid, boiling at 36°. The hydrogen atom in the HS- group is displaceable by metals more readily than that in the HO- group of the alcohols ; when ethyl mercaptan is treated with sodium or potassium, it yields sodium or potassium mercaptide, C2H5-SNa, or C2H5SK, with evolution of hydrogen; when shaken with mercuric oxide, it yields mercuric mercaptide, 2C2H5-SH + HgO = (C2H5-S)2Hg + H2O, a crystalline compound, which is decomposed by hydrogen sulphide, giving ethyl mercaptan, (C2H5-S)2Hg + SH2 = 2C2H6.SH + HgS. Other mercaptans can be obtained by similar reactions; they are characterised by having a highly unpleasant, garlic-like smell, and in chemical properties they resemble ethyl mercaptan; on oxidation with nitric acid they are converted into sulphonic acids, C2HbSH + 30 = C2H5SO2OH. Ethylsulphonic Acid. Sulphonic acids contain the group -SO2-OH, the alkyl group being attached to the sulphur atom, and not to oxygen, as in the alkyl sulphites, CH.,-S==O \OH Methylsulphonic Acid. /OCH3 s=o \OCH3. Methyl Sulphite. iney are powernu acius, forming salts, such as potassium ethyl- sulphonate, C2H5-SO2OK ; and they differ from the sulphites in not being hydrolysed when boiled with dilute aqueous potash. They stand, therefore, in much the same relationship to the sulphites as the nitro-paraffins to the nitrites (p. 181). Ethyl sulphide, (C2H5)2S, may be obtained by treating ether with phosphorus pentasulphide, 5(C2H5)2O + P2S5 = 5(C2H5)2S + P2O6, ETHEREAL SALTS. 185 and by distilling a concentrated aqueous solution of ethyl potassium sulphate with potassium sulphide, 2C2H5KSO4 + K2S = (C2H5)2S + 2K2SO4. It is a colourless, neutral, unpleasant-smelling liquid, and boils at 91°; like the ethers, it does not contain hydrogen displaceable by metals, and is a comparatively inert substance. Other sulphides can be obtained by similar methods, and have similar properties. Ethereal Salts of Organic Acids. Ethyl acetate, acetic ether, C2H3O2-C2H5, or CH.,-CO-OC.,H5, m O Lt Lt O* ij L O' is formed when acetyl chloride or acetic anhydride is treated with alcohol, ch3-coci + C2H5.OH = ch3.cooc2h5 + HC1 (CH3-CO)2O + C2H5-OH = CH„.COOC2H5 + CH..-COOH; also when a metallic salt of acetic acid is heated with a halogen salt of ethyl alcohol, CH..COOK + CJLBr = CH.,-COOC2H5 + KBr, and when alcohol is heated with glacial acetic acid, CH3-COOH + C2H3-OH = CH3-COOC2H5 + H2O. It is prepared by gradually adding a mixture of equal volumes of alcohol and acetic acid to a mixture of equal volumes of alcohol and concentrated sulphuric acid, heated at about 140° in a retort connected with a condenser; this process, like that by which ether is prepared, is theoretically continuous, the alcohol and sulphuric acid combining to form ethyl hydrogen sulphate, which then inter- acts with acetic acid, forming ethyl acetate and sulphuric acid, C2H5-OH + h.,so4 = C2H5-HSO4 + H,0 C2H5HSO4 + C2H4O2 = C2H3O2-C2H5 + H2SO4. The distillate is shaken with a concentrated solution of sodium chloride, when the alcohol dissolves, the ethyl acetate separating as an oil ; it is dried with calcium chloride, and purified by fractional distillation. Ethyl acetate is a colourless, mobile liquid, having a pleas- ant fruity odour, and boiling at 77°; it is specifically lighter than water, in which it is moderately easily soluble. It is 186 ETHEREAL SALTS. readily hydrolysed (see below) by hot alkalies, more slowly by hot mineral acids, and by water, CH3-COOC2H5 + H2O = CH3-COOH + C2H5-OH. When treated with concentrated ammonia it yields acetamide and alcohol, CHa.COOC2H5 + NH3 = CH..-CO-NH, + C9H..OH. O 4 0 O O 4 4 0 Sodium acts readily on ethyl acetate, with formation of ethyl acetoacetate (p. 189). Since ethyl acetate has a rather characteristic smell, and is formed, when acetic acid or any of its salts is warmed with alcohol and concentrated sulphuric acid, the presence of acetic acid or an acetate may be readily detected by this reaction, the so-called ' acetic-ether ' test. In hydrolysing ethereal salts, and in many other operations, as, for example, in the preparation of ethylene from ethyl bromide, it is often necessary to boil the aqueous, alcoholic, ethereal, or other solution for a long time; in order, there- fore, to avoid loss of solvent, or of the substances present in solution, the flask or other vessel is connected with a reflux condenser (6, fig. 18), so that the vapours, which would otherwise pass away, are condensed, the liquid running back into the flask. The latter may be heated over a piece of wire-gauze or on a sand-bath, but when alcohol, ether, or other substances of low-boiling point are being used, a water-bath is usually epiployed. A very convenient form of water-bath (c) is that shown in the figure. During use, water slowly but continuously runs from the tube (rf), which is connected with the water supply; the water in (be bath Fig. 18. ETHEREAL SALTS. 187 is thus kept at a constant level, the surplus running away through (e). With apparatus similar to that shown, a liquid may be kept constantly boiling for days without requiring any attention. SUMMARY AND EXTENSION. Although the ethereal salts of mineral acids are, on the whole, very similar in chemical properties, they are derived from acids of such diverse characters that slight differences in behaviour is only to be expected. The ethereal salts of organic acids, on the other hand, being derived from acids of similar nature, resemble one another in chemical properties so very closely that they may be described in a general manner. The ethereal salts of .organic acids may all be produced by treat- ing an alcohol with the chloride or anhydride of the acid, C3H7COC1 + CH3OH = C3H7-COOCH3 + HC1, and by heating a metallic salt of the acid with a halogen salt of an alcohol, C2H5-COOAg + CH3I = C2HSCOOCH3 + Agl. They are all formed when an alcohol is treated with an acid, but the change is never complete, because, after the interaction has proceeded for some time, the quantity of ethereal salt decomposed by the water produced is the same as that formed by the combina- tion of the acid with the alcohol; in other words, a condition of equilibrium is established when the two changes represented by the equations CHpOH + c.,h4o., = C2H3O3CH3 + H.,0 c2h3o2ch3 + h2o = ch3 oh + C2H4O2 balance one another; this is usually expressed by writing the equations thus, ch3oh + C2H4O2 7^ c2h3o2-ch3 + h2o, which indicates that the change takes place in either direction. The proportion of ethereal salt produced depends on the nature of the alcohol and acid, and on their relative quantities; it, is inde- pendent of the temperature, but the higher the temperature the sooner the condition of equilibrium is established. If the water pro- duced during the interaction be prevented in some way from decom- posing the ethereal salt, the desired change is far more complete; when, for example, methyl alcohol is heated with excess of anhy- drous oxalic acid, it is almost completely converted into methyl oxalate, because the anhydrous oxalic acid combines with the water as fast as it is formed, and thus the inverse change is prevented, C2O4H2 + 2CH3 OH = C2O4(CH3)2 + 2H2O. In order, then, to prepare an ethereal salt from an acid anti an 188 ETHEREAL SALTS. alcohol, some dehydrating agent, such as hydrogen chloride, sul- phuric acid, zinc chloride, &c., should be present. Based on these considerations, the two methods usually employed in preparing ethe- real salts of organic acids are (a) by passing hydrogen chloride into a mixture of the acid and alcohol, and then warming the saturated solution ; (b) by warming a mixture of the acid and alcohol with concentrated sulphuric acid. In both cases the mineral acids act as dehydrating agents. If the ethereal salt be readily volatile (ethyl acetate), the mixture is now distilled; if not, it is poured into water and the ethereal salt isolated by filtration, if a solid, by extraction with ether, if a liquid, or if it be soluble in water. When only a small quantity of acid is at disposal, and it is desired to prepare one of its ethereal salts, it is converted into the silver salt, and the latter is warmed with a halogen ethereal salt (see above). Normal ethereal salts are usually colourless, neutral, pleasant- smelling liquids, which distil unchanged under atmospheric pres- sure, and are volatile in steam; a few, such as cetyl palmitate, C16H31O2-C16H33, which occurs in spermaceti, are solid at ordinary temperatures, and distil with decomposition. They are all com- paratively inert substances, and resemble the ethers perhaps more closely than any other class of compounds, although, at the same time, they differ from them in several important respects. The acid ethereal salts are usually non-volatile, and act like feeble acids. All ethereal salts are decomposed by water, mineral acids, and alkalies, the change which they undergo being spoken of as hydro- lysis (or saponification, p. 169), CH3COOC3H7 + KOH = CH3COOK + C.tH7OH 2HCOOCH3 + Ba(OH)2 = (HCOO)2Ba + 2CHs0H. The rapidity with which hydrolysis takes place depends on the temperature and concentration of the solution, as well as on the nature of the ethereal salt and of the hydrolysing agent; as a rule, potash, soda, and barium hydroxide are the most powerful hydro- lysing agents. Since ethereal salts are generally insoluble in water, if they be boiled with aqueous alkalies or mineral acids they are not attacked very quickly; it is usual, therefore, to employ alcoholic potash, &c., in which the ethereal salts are soluble. All ethereal salts of organic acids yield amides on treatment with concentrated aqueous or alcoholic ammonia, C3H7-COOCH3 + NH3 = C3H7CONH2 + CH3OH, whereas the halogen ethereal salts give amines with alcoholic ammonia (p. 200), c2h8i + nh3 = c2h6nh2, hi. ETHEREAL SALTS. 189 The ethereal salts of organic acids afford an excellent example of the special form of isomerism known as metamerism ; ethyl formate, HCOO-CH2CH3, for example, is metameric witli methyl acetate, CH3-CO-O-CH3; propyl formate, H COOC3H7, is meta- meric with ethyl acetate, CH3COOC2H5, and with methyl pro- pionate, C2H5-COOCH3. Many ethereal salts occur in the fruit, flower, and other parts of plants, and it is to their presence in many cases that the scent of the part is due; many are prepared artificially for flavouring sweets, pastry, perfumes, &c. : amyl acetate, CH3-COOC5HU, for example, prepared from commercial amyl alcohol, has a strong smell of pears, and is known as ' pear-oil; ' methyl butyrate, C3H7-COOCH3, is sold as 'pine-apple oil,' isoamyl isovalerate as ' apple-oil,' and so on. CHAPTER XI. SYNTHESIS OF KETONES AND FATTY ACIDS WITH THE AID OF ETHYL ACETOACETATE AND ETHYL MALONATE. In the whole domain of organic chemistry probably no compounds have been more extensively used for synthetical purposes than ethyl acetoacetate and ethyl malonate, and certainly one of the most important uses to which these sub- stances have been put is the synthesis of a great variety of ketones and fatty acids, many of which could have been pre- pared only with great difficulty by other methods. Ethyl acetoacetate, CH3-CO-CH2-COOC2H5, the ethyl salt of acetoacetic acid, is formed when ethyl acetate is treated with sodium, and the product decomposed with dilute acids. The final result is that 2 molecules of ethyl acetate combine with loss of 1 molecule of alcohol, the following equation representing the reaction in its simplest form, CIL-C():()C2H^ = CH3-CO-CH2-COOC2H5 + C2H5-OH. In reality, however, the interaction is a complex one; the sodium derivative of ethyl acetoacetate is first formed, 2CHq-COOC9H5 + 2Na - CH„-CO-CHNa.COOC2H5 O Z U O 25 U + C2H6-O^a + H2, 190 SYNTHESIS OF KETONES AND FATTY ACIDS. and this sodium derivative, when decomposed with dilute acids, yields ethyl acetoacetate, CH3.CO-CHNa-COOC2H6 + HC1 = CH3.COCH2.COOC2H5 + NaCl. Preparation.-Sodium (30 grams), in the form of thin wire or shavings, is added to pure dry ethyl acetate (300 grams) contained in a flask connected with a reflux condenser. As soon as the vigorous action which sets in has subsided, the flask is heated on a water-bath, until bright particles of sodium are no longer visible on shaking. The thick brownish semi-solid product, which consists of the sodium derivative of ethyl acetoacetate, is allowed to cool, and then treated with dilute (1 : 4) hydrochloric acid, until the solution is distinctly acid to test-paper. An equal volume of a saturated solu- tion of salt is now added, and the oily layer separated from the aqueous solution, dried over calcium chloride, and fractionated. At first a quantity of unchanged ethyl acetate passes over; the thermometer then rises rapidly to about 160°, the fraction 170-185° consisting of nearly pure ethyl acetoacetate, and weighing 40-50 grams. Ethyl acetoacetate is a colourless liquid, boiling at 180°, and having an agreeable fruity odour; it is sparingly soluble in water, but readily in alcohol and ether. The alcoholic solu- tion assumes a beautiful violet colour on the addition of ferric chloride. It is remarkable that, although neutral to test-paper, ethyl acetoacetate possesses acid properties. It dissolves in dilute potash or soda, and is reprecipitated on the addition of acids, but it is insoluble in alkali carbonates. The sodium derivative, CH3-CO-CHNa-COOC2H5, which is so largely used for synthetical purposes, may be prepared by adding sodium to a solution of ethyl acetoacetate in ether or benzene, 2CH„.CO-CH2-COOCJI5 + 2Na - 2CHvCO-CHNa.COOC9IL + h2, or by mixing ethyl acetoacetate with an alcoholic solution of sodium ethoxide, SYNTHESIS OF KETONES AND FATTY ACIDS. 191 CH3.CO-CH2.COOC2H5 + NaO-C2H5 = CH„-CO-CHNa-COOC2H5 + CJL-OH. On evaporating the solvent in a current of hydrogen, the sodium derivative is obtained as a white crystalline mass, which is readily soluble in water, alcohol, and ether ; it rapidly deliquesces in contact with moist air, and undergoes decom- position when its aqueous solution is boiled. When shaken with a saturated solution of copper acetate, ethvl acetoacetate forms a green crystalline copper derivative, (csh9o3)2cu. This property of forming metallic derivatives is due to the presence of the group -CO-CH2-CO-; all substances which contain this, or the group -CO-CH-CO-, yield derivatives I with sodium, frequently also with other metals. The sodium derivative of ethyl acetoacetate interacts readily with alkyl halogen compounds with formation of a sodium halogen salt and a mono-substitution derivative of ethyl aceto- acetate, the alkyl group taking the place previously occupied by the metal. Thus methyl iodide interacts with the sodium derivative of ethyl acetoacetate, forming ethyl methyl&ceio- acetate, CH3.CO-CHNa-COOC2H6 + CH3I = CH3.CO-CH(CH3).COOC2H5 + Nai, whereas when propyl bromide is employed, ethyl propyl- acetoacetate, CH3-CO'CH(C3Hr)-COOC.,H5, results, and so on. All the alkyl mono-substitution derivatives of ethyl aceto- acetate contain the group -CO-CH-CO-, and are therefore I capable of forming sodium derivatives such as CH3-CO-CNa(CH3)-COOC2H5, CH3-CO-CNa(C3Hr)-COOC2H5, &c., on treatment with sodium or sodium ethoxide, the metal taking the place of the hydrogen atom in the -CH- group. 1 From these sodium derivatives, by the action of alkyl 192 SYNTHESIS OF KETONES AND FATTY ACIDS. halogen compounds, di-substitution derivatives of ethyl aceto- acetate are produced thus: CH3.CO-CNa(CH3).COOC2H5 + C2H5Br = CH3-CO-C(C2H6)(CH3).COOC2H5 + NaBr. Ethyl EZZij/ZmeM^Zacetoacetate. CH3 CO-CNa(C3H7).COOC2H5 + C3H7I = CH3-CO-C(C3H7)2.COOC2H5 + Nai. Ethyl DipropyZacetoacetate. In order, then, to obtain a di-substituted ethyl acetoacetate, the mono-substitution derivative is first prepared and then treated with sodium ethoxide and the alkyl halogen com- pound ; the introduction of both alkyl groups cannot be carried out in one operation, because ethyl acetoacetate is not sufficiently acid in properties to form a disodium derivative of the constitution CH3-CO-CNa2-COOC2H5. The synthesis of the alkyl substitution products of ethyl aceto- acetate is usually carried out as follows: The theoretical quantity of sodium (1 atom) is dissolved in 10-12 times its weight of absolute alcohol, and the solution of sodium ethoxide is thoroughly cooled. The ethyl acetoacetate, or the mono-substituted ethyl acetoacetate, (1 mol.), and a slight excess of the alkyl halogen compound (1 mol.) are now gradually added, the whole being well cooled during the operation; the flask is then connected with a reflux condenser (p. 186), and the mixture heated to boiling until neutral to test- paper. In order to isolate the product, the alcohol is distilled from a water-bath, the residue mixed with water to dissolve the pre- cipitated sodium salt, and the whole extracted with ether; the ethereal solution is dried with calcium chloride, the ether distilled off, and the residual oil purified by fractional distillation. The following are some of the more important mono- and di-sub- stitution products of ethyl acetoacetate, with their boiling-points : B.p. Ethyl ?ne^yZacetoacetate, CH3-C0-CH(CH3)-C00C2H,.. 187° Ethyl tf/nic^yZacetoacetate, CH3-CO-C(CH3)2-COOC2H5. ...184° Ethyl e^AyZacetoacetate, CH3'CO-CH(C.,H5)'COOC2Hg. 198° Ethyl otoAyZacetoacetate, CH3'CO-C(C2Hg)2-COOC2Hg...218° Ethyl prqpyZacetoacetate, CH3-CO«CH(C3H7)-COOC2H5.209° Ethyl isojoro/n/^acetoacetate, CH3-CO-CH(C3H7)-COOCSH8..201° The mono-substituted ethyl acetoacetates differ from ethyl aceto- SYNTHESIS OF KETONES AND FATTY ACIDS. 193 acetate in that they are insoluble in alkalies, and do not give copper derivatives, although they readily form sodium derivatives. The dz-substituted ethyl acetoacetates do not contain a hydrogen atom displaceable by metals: both classes of compounds give a charac- teristic bluish-violet colouration with ferric chloride. One of the most important reactions of ethyl acetoacetate and its derivatives is the decomposition which these substances undergo when treated with alkalies or mineral acids. Alkalies at ordinary temperatures simply hydrolyse the ethereal salts with formation of the alkali salts of the corresponding acids, CH3-CO-CH2-COOC2H5 + KOH = CH3-CO-CH2-COOK + C2H5-OH. Potassium Acetoacetate. On acidifying the solution and extracting with ether, the free acids are obtained; these ketonic acids are, however, very un- stable, decomposing in many cases at ordinary temperatures, and always very readily on warming, yielding carbon dioxide and a ketone, ch3-co.ch2.cooh = CH3.CO-CH3 + CO2 CH3.CO-C(C2H5)2-COOH = CH3.CO-CH(C2H5)2 + co2. When heated with alkalies, ethyl acetoacetate and its deriva- tives are decomposed in two ways, the course of the decom- position depending to a great extent on the strength of the alkali used. Boiling dilute alcoholic potash converts these substances into ketones, with separation of potassium carbonate (ketonic hydrolysis), CH3-CO-CH2:COOC2H5 + 2K0H = CH3-CO-CH3 + K2CO3 : + C2H5-OH CH3.CO-C(C2H5)2; COOC2H5 + 2K0H = CH3.CO.CH(C2H5)2 : + K2CO3 + C2H5-OH. Ketonic hydrolysis is also brought about by boiling with dilute mineral acids. If, however, strong alcoholic potash be employed, the decomposition takes place in quite a different 194 SYNTHESIS OF KETONES AND FATTY ACIDS. manner, the potassium salt of a fatty acid being the principal product (acid hydrolysis), CH3.CO£H2.COOC2H5 + 2K0H = 2CH3.COOK + C2H5-OH CH3-COiC(C9H6)2-COOC2H5 + 2K0H = CH3-COOK : + (C2H5)2CH-COOK + C2H5-OH. X 4 O r & £ O Potassium Diethylacetate. Ethyl acetoacetate is therefore a very important com- pound, as with its aid any fatty acid, or any ketone (containing the group CH3-CO-) can be synthetically prepared, provided the requisite alkyl halogen compound can be obtained. Example.-If an acid of the constitution (C2H5)(C3H7)CH-COOH -namely, ethylpropylacetic acid-be required, ethyl cthylaeeto- acetate, CH3-CO-CH(C2H5)-COOC2H5, might be first prepared ; on treating the sodium derivative of this substance with propyl iodide, ethyl eMyZprqpyiacetoacetate, CH3-CO-C(C2H5)(C3H7)-COOC2H5, would be formed, and the latter, when heated with strong alcoholic potash, would yield the potassium salt of the acid required, CH3-CO.C(C2H5)(C3H7)-COOCoH5 + 2K0H = CH3COOK + CH(C2H5)(C3H7).COOK + C2H5.OH. Example.-If a ketone of the constitution CH3-CO-CH2-C4H9- namely, butyl acetone-be required, ethyl butylacetoacetate, CH3-CO-CH(C4Hh)-COOC2H5, would be prepared, by treating the sodium compound of ethyl acetoacetate with butyl iodide, and then decomposed by boiling with dilute alcoholic potash or dilute sulphuric acid, CH3.COCH(C4H9).COOC2H5 + 2K0H = CH3COCH2C4H9 + K2CO3 + C2H5-OH. The acid and the ketonic hydrolysis of ethyl acetoacetate and its derivatives always take place to some extent side by side, whether weak or strong alkali be used. It is not possible, for instance, to decompose an ethyl acetoacetate derivative with strong alkali, without a small amount of ketone being formed, and when dilute alkali is used, a certain quantity of the salt of a fatty acid is invariably produced ; nevertheless the relative quantities of the products depend very largely on the strength of the alkali employed. SYNTHESIS OF KETONES AND FATTY ACIDS. 195 Constitution of Ethyl Acetoacetate.-On hydrolysis, ethyl acetoace- tate is converted into acetoacetic acid, which when gently wanned is decomposed into acetone and carbon dioxide ; this acid is there- fore evidently the carboxylic acid of acetone, CH3-CO-CH2-COOH, and its ethereal salt, ethyl acetoacetate, must be represented by tiie formula CH3-CO-CH2-COOC2H5. That ethyl acetoacetate contains a ketonic group -CO- is shown by the fact that it combines with sodium bisulphite, hydroxylamine, phenylhydrazine, and hydrogen cyanide, and that on reduction it is converted into ^-hydroxybutyric acid, CH3-CH(OH)-CH2-COOH, or its ethyl salt. In some of its reactions, however, ethyl acetoacetate behaves as if it contained a hydroxyl-group, and had the constitution represented by the formula CH3-C(OH):CH COOC2H3, and there are reasons for believ- ing that other substances which contain the group -CO-CH2- or -CO-CH- are also capable of existing in two forms; at all events, their behaviour is such that in some cases the assumption must be made that these groups, by intramolecular change (p. 290), are converted into -C(OH):CH- and -C(OH):C- respectively. The constitution of the sodium derivative of ethyl acetoacetate may be expressed by the formula CH3-CO-CHNa-COOC2H5; the sodium atom is represented as directly combined with carbon, because when the sodium derivative is treated with alkyl halogen compounds, substitution products of ethyl acetoacetate are formed in which the alkyl group is certainly directly united with carbon, as is shown by their behaviour on hydrolysis. Other Ketonic Acids. Pyruvic acid, or acetylformic acid, CH3-CO-COOK, is formed by the dry distillation of tartaric acid (p. 241), CH(OH)-COOH_ CO-COOH + CO2 + H2O. CH(OH)-COOH 3 2 2 It is an oily, sour-smelling liquid, distils at 165-170°, and is soluble in water in all proportions. It combines with hydroxyl- amine, and gives with phenyl hydrazine in aqueous solution a very sparingly soluble phenylhydrazone, CH3-C(N2HC6Hp)-COOH, the formation of which serves as a ready means of detecting the acid, even when present in small quantity. When treated with sodium amalgam, pyruvic acid is reduced to lactic acid (p. 225), CH3-CO-COOH + 2H = CH3-CH(OH)-COOH. 196 SYNTHESIS OF KETONES AND FATTY ACIDS. Levidinic acid (/3-acetylpropionic acid), CH3-CO-CH2-CH2-COOH, is produced when starch, cane-sugar, dextrose, levulose, and other carbohydrates containing 6, or a multiple of 6, carbon atoms are boiled with dilute hydrochloric acid. Preparation.-Starch (3 kilos) is gradually added to hot hydro- chloric acid of sp. gr. 1-1 (3 litres), and the thin syrup is then heated in a reflux apparatus for twenty hours on a water- bath. The solution is separated from the humus matter by pres- sure between cloths, and after concentration to a syrup, extracted with ether ; the ethereal solution is evaporated, and the residual crude levulinic acid purified by distillation under reduced pressure. Levulinic acid melts at 33-5° and distils at 250°; it is very soluble in water, combines readily with hydroxylamine and phenylhydrazine, and when reduced with sodium amalgam it yields y-hydroxyvaleric acid, CH3-CH(OH)-CH2-CH2-COOH. Levu- linic acid is isomeric with methylacetoacetic acid or a-acetyl- propionic acid, CH3COCH(CH3).COOH. Ethyl malonate, CH2(COOC2H6)2, does not belong to the same class of substances as ethyl acetoacetate, although, like the latter, it contains the group -CO-CH2-CO-; it is, however, conveniently considered in this chapter on account of its employment in the synthesis of fatty acids. When potassium chloracetate is digested with potassium cyanide in aqueous solution, potassium cyanacetate is produced, CH2C1-COOK + KCN = CH2(CN)-C00K + KC1. This salt, on hydrolysis with hydrochloric acid, yields malonic acid (p. 234), CH2(CN)-C00K + 2HC1 + 2H2O = CH2(COOH)2 + KC1 + NH4C1, but if the dry potassium cyanacetate be mixed with alcohol and the mixture saturated with hydrogen chloride, ethyl malonate is produced, CH2(CN)-COOK + 2HC1 + 2C2H5-OH = CH2(COOC2H5)2 + KC1 + NH4CL Preparation.-Chloracetic acid (100 grams) is dissolved in water (200c.c.) and neutralised with potassium carbonate (76 grams); SYNTHESIS OF KETONES AND FATTY ACIDS. 197 potassium cyanide (75-80 grams) is then added, and the whole heated in a large porcelain basin until a vigorous reaction commences. As soon as this has subsided, the solution is evaporated on a sand-bath, the thick semi-solid residue being constantly stirred with a thermometer until the temperature reaches 135° ; the solid cake of potassium chloride and cyanacetate is powdered, transferred to a flask, an equal weight of alsolute alcohol added, and the boiling mixture saturated with dry hydrogen chloride (compare p. 187-8). When cold, the solution is poured into twice or thrice its volume of ice-water ; the product is then extracted with ether, the ethereal solution washed with water, dried with calcium chloride, and the ether distilled off. The crude oil is purified by fractional distillation; the portion boiling at 195-200°, after two or three distillations, consists of practically pure ethyl malonate. CO-OC H Ethyl malonate, CH^qq OQH? like ethyl acetoacetate, contains the group -CO-CH2-CO-, and is capable of forming a sodium derivative when treated with the metal or with sodium ethoxide, 2CH2(COOC9H5)2 + 2Na = 2CHNa(COOC2H5)2 + H, CH2(COOC2H5)2 + NaO-C2H5=CHNa(COOC2H5)2 + C2H5-OH. Unlike ethyl acetoacetate, it does not dissolve in aqueous alkalies, because its alkali derivatives are decomposed by water, and it does not give a colouration with ferric chloride. The sodium derivative of ethyl malonate interacts readily with alkyl halogen compounds, yielding homologues of ethyl malonate, CHNa(COOC2H5)2 + C2H5I = CH(C2H5)(COOC2H5)2 + Nai; Ethyl Ethylmalonate. these mono-substitution derivatives, like those of ethyl aceto- acetate, are again capable of forming sodium derivatives, which, by further treatment with alkyl halogen compounds, yield di-substitution derivatives of ethyl malonate, CH(C2H5)(COOC2H5)2 + NaO-C2H5 = CNa(C9H5) (C00C9H5)9 + C2H5-OH CNa(C2H5)(COOC2H5)9 + C3H7I = C(C3Hr)(C2H5)(COOC2H5)2 + Nai. Ethyl Propylethylma,lona,te. 198 SYNTHESIS OP KETONES AND PATTY ACIDS. In this way a great variety of derivatives may be obtained, the syntheses being carried out exactly as described in the case of the substitution products of ethyl acetoacetate. Ethyl malonate and its derivatives are readily hydrolysed by boiling alcoholic potash with formation of the potassium salts of the corresponding acids, C2H5-CH(COOC2H5)2 + 2K0H = C2H5.CH(COOK)2 + 2C2H5.OH Potassium Ethylmalonate. ^'>C(COOC2H5)2 + 2K0H = ^J>C(COOK)2 + 2C2H6-OH. Potassium Propylethylmalonate. Malonic acid and the dicarboxylic acids derived from it are rapidly and quantitatively decomposed at about 200° with evolution of carbon dioxide and formation of fatty acids. This behaviour is shown by all acids which contain two carboxy 1-groups directly combined with the same carbon atom (p. 234), CH2(COOH)2 = CH„-COOH + CO2 ^7>C(COOH)2 = Propylethylmalonic Acid. ^r^CH-COOH + CO2. Propylethylacetic Acid. Ethyl malonate is, therefore, of the utmost service in the synthesis of fatty acids, and is indeed more used for this purpose than ethyl acetoacetate, because in the case of the latter, ketones are always formed on hydrolysis as bye- products. The value of both synthetical methods is also much enhanced by the fact that the constitution of the acid (or ketone) obtained is always known, which is very often not the case when other methods are employed. Example.-Normal valeric acid, CH3-CH2-CH2-CH2-COOH, is to be prepared synthetically. In the first place the sodium derivative of ethyl malonate would be heated with propyl iodide, and the resulting ethyl propylmalonate, CH3'CHa-CH2'CH(COOCEH6)2, hydrolysed with boiling alcoholic potash. The propylmalonic acid obtained ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 199 from the potassium salt is heated at about 200' or distilled, when it decomposes into normal valeric acid and carbon dioxide, CH3-CH2-CH2-CH(COOH)2 = ch3.ch2.ch2-ch2-cooh + CO2. CHAPTER XII. ALKYL COMPOUNDS OP NITROGEN, PHOSPHORUS, ARSENIC, SILICON, ZINC, MERCURY, AND OTHER ELEMENTS. Amines. Many of the compounds described in the preceding pages may be conveniently considered as having been derived from the hydrogen compounds of certain non-metals; the alcohols and ethers, for example, may be regarded as derivatives of water, the mercaptans and sulphides as derivatives of sul- phuretted hydrogen, HO-H H-S-H c2h5-oh c2h5-sh C2H5.Q.C2H5 c2h5-s-c2h5. In a similar manner the hydrides of many other elements may be directly or indirectly converted into organic compounds by the substitution of one or more alkyl groups for an equivalent quantity of hydrogen; from ammonia, for example, a very important class of strongly basic substances, termed amines, may be obtained, these compounds being classed as primary, secondary, or tertiary amines, according as 1, 2, or 3 atoms of hydrogen in ammonia have been displaced by alkyl groups. Primary. Methylamine, NH2-CH3 Ethylamine, NH2-C2H5 Propylamine, NH2-C3H7 Secondary. Dimethylamine, NH(CH3)2 Diethylamine, NH(C2H5)2 Dipropylamine, NH(C3H7)2 Tertiary. Trimethylamine, N(CH3)3 Triethylamine, N(C.,H5)3 Tripropylamine, N(C3H7)3. The methods of formation and general character of the amines 200 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. will, perhaps, be best understood from a description of the ethyl compounds. Ethylamine, NH.,C2H5, was first obtained by Wurtz, by distilling ethyl isocyanate (p. 287), with potash, the change being analogous to that which occurs in the case of hydrogen isocyanate (p. 286), CO:N-C2H5 + 2K0H = NH2.C2H5 + K2CO3 CO:NH~+ 2K0H = NH3 + K2CO3. It is formed when methyl cyanide (acetonitrile) is treated with nascent hydrogen, generated from zinc and sulphuric acid (Mendius' reaction), or from alcohol and sodium, CH3CN + 4H = CH3-CH2NH2. It is also produced when ethyl chloride, bromide, or iodide is heated at about 100° in closed vessels with alcohol which has been saturated with ammonia (Hofmann); the halogen acid produced during the interaction combines with the amine, forming a salt, C2H5I + NH3 = NH2-C2H5, HL Ethylamine is prepared by mixing propionamide (1 mol.) with bromine (1 mol.), and then adding a 10 per cent, solution of potash until the colour of the bromine disappears : the solution of the bromamide which is thus produced, C2H5-CONH2 + Br2 + KOH - C2H5 CO NHBr + KBr + H2O, is now gently warmed with excess of potash, when the brom- amide is converted into ethylamine, C2H5.CO-NHBr + 3KOH = C2H5-NH2 + KBr + K2CO3 + H2O. In the conversion of propionamide into ethylamine one atom of carbon and one atom of oxygen are taken away, and a derivative of propionic acid is converted into what may be regarded as a deriva- tive of acetic acid, since ethylamine is readily converted into ethyl alcohol and the latter into acetic acid ; it is possible, therefore, to transform propionic into acetic acid, CH3CH2COOH Propionic Acid. ch3.ch2-conh2 Propionamide. CHSCH2NH2 Ethylamine. CHSCH2OH Ethyl Alcohol. CH;iCOOH. Acetic Acid, ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 201 As, moreover, the amides of other fatty acids behave in this respect like propionamide, it is clear that a given fatty acid may be con- verted into the next lower homologue, and so on down the series. Conversely, a given fatty acid may be transformed into the next higher homologue in the following manner: The calcium salt of the acid is distilled with calcium formate and the resulting aldehyde converted into the corresponding alcohol by reduction ; the alcohol is then transformed into the chloride, the latter treated with potas- sium cyanide, and the resulting cyanide hydrolysed with alkalies or mineral acids, ch3-cooh Acetic Acid. CH3-CHO Acetaldehyde. CH3-CH2OH Ethyl Alcohol. CH3-CH2C1 Ethyl Chloride. ch3-ch2-cn Ethyl Cyanide. CH3-CH2-COOH. Propionic Acid. The cyanide may be converted into the acid in another way ; it is first reduced with sodium and alcohol, yielding an amine, from which the fatty acid is obtained in the manner already stated. Primary amines may also be obtained by reducing the nitro- paraffins, CH3-NO2 + 6H = CH3-NH2 + 2H2O, and by heating the alkyl nitrates with alcoholic ammonia, C3H--O-NO2 + NH3 = C3H7 NH2, hno3. Ethylamine is a colourless, mobile, inflammable liquid of sp. gr. 0-689 at 15°, and boils at 18-7°; it is soluble in water in all proportions, and the solution, like the liquid itself, has a pungent, slightly fish-like odour, distinguishable from that of ammonia only with difficulty. An aqueous solution of ethyl- amine might, in fact, be easily mistaken for a solution of ammonia, so closely do they resemble one another in properties; the former, like the latter, has a strongly alkaline reaction, and gives, especially on warming, a pungent-smelling gas, which fumes when brought into proximity with concentrated hydro- chloric acid. It precipitates metallic hydroxides from solutions of their salts, and neutralises even the most powerful acids, forming salts, which are readily soluble in water. Ethyl- amine, therefore, is an organic base, and its basic properties are even more pronounced than those of ammonia, since it liberates ammonia from ammonium salts; the salts of ethyl- 202 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. amine are, however, decomposed by the hydroxides and car- bonates of sodium and potassium. In spite of the fact that ethylamine is so readily soluble in water, it separates from the solutions as an oil on the addition of a large quantity of solid potash or potassium carbonate; it is very hygroscopic, and readily absorbs carbon dioxide from the air, forming with it a salt. * Although, speaking generally, ethylamine is very stable, it is rapidly converted into ethyl alcohol on treatment with nitrous acid in aqueous solution, nitrogen being liberated, C2H5-NH2 + HO-NO = C2H5-OH + H2O + N2; this reaction is exactly analogous to that which occurs when ammonia and nitrous acid (ammonium nitrite) are heated together, NH4NO2 or NH3 + HO-NO = 2H-0H + Ethylamine is also quickly changed when it is warmed with chloroform and alcoholic potash. The intensely disagreeable smell of the product (ethylcarbylamine, compare p. 285) is at once recognisable, and affords a sure indication of the presence of a primary amine (Hofmann's carbylamine reaction), CJL-NH, + CHCL + 3K0H = CJL-NC + 3KC1 + 3H.2O. z u z o zu z The two reactions just mentioned are characteristic of all primary amines, and are of considerable practical importance; the first is employed for the conversion of the primary amines into hydroxy-compounds, the second for their detection. Ethylamine is a monacid base, and, like ammonia, forms salts by direct combination, in virtue of the possible pentavalency of the nitrogen atom ; these salts are all soluble in water, and some of them, like those of ammonia, readily sublime, even at ordinary temperatures; they usually differ from ammonium salts in being soluble in alcohol, a property which is fre- quently made use of in isolating the amine. ^NH*C IT- * Probably not a carbonate, but a carbamate (p. 291), CO\qj] ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 203 Ethylamine hydrochloride, C2H6-NH3C1, or C2H5*NH2, HC1, as usually written, crystallises in large plates, melts at about 80°, and is deliquescent. The sulphate, 2C2H5-NH2, H2SO4, has similar properties. The halogen salts, like those of ammonia, form double salts with many other metallic halogen salts; of these compounds the platinochlorides and the auro- chlorides are the most important; they correspond with the ammonium double salts of similar composition, Ethylamine platinochloride, (C2H5-NH2)2, H2PtCl6 Ammonium platinochloride, (NH3)2, H2PtCl6 Ethylamine aurochloride, C2H5-NH.„ HAuC14 Ammonium aurochloride, NH3, HAuC14. These organic platinum and gold salts are usually yellow, orange, or red, and are generally much more sparingly soluble in water than the simple salts; for the latter reason they are very serviceable in detecting and isolating the amines; on ignition they give a residue of pure metal. Diethylamine, NH(C2H5)2, is formed when ethyl iodide is heated with alcoholic ammonia, just as described in the case of ethylamine; one molecule of the hydrogen iodide produced combines with the base to form a salt, the other uniting with the excess of ammonia, 2C2H5I + NH3 = NH(C2H5)2, HI + HI. Diethylamine is a colourless, inflammable liquid, boiling at 56°; it is a stronger base than ethylamine, which it resembles very closely in smell, solubility, &c., and also in forming simple and double salts. It is readily distinguished from ethylamine inasmuch as it does not give the carbylamine reaction; its behaviour with nitrous acid is also totally different from that of ethylamine, since, instead of being con- verted into an alcohol, it yields ethylnitrosamine, (C2H5)2NH + HO-NO = (C2H5)2N-NO + H2O. All secondary amines behave in this way; that is to say, on treatment with nitrous acid, they are converted into nitros- amines by the substitution of the monovalent nitroso-group 204 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. -NO for the atom of hydrogen which is directly united with nitrogen. When a nitrosamine is mixed with phenol (part ii.) and concen- trated sulphuric acid, it gives a dark-green solution which, after diluting with water, becomes red, and on adding excess of alkali, assumes a beautiful and intense blue or green colour; this reaction (Liebermann's, or the nitroso-reaction) affords a means, not only of detecting a nitrosamine, but also a secondary amine, as the latter is convertible into the former. Diethylamine hydrochloride, (C2HS)2NH, HC1, is colourless, and readily soluble in water ; its platinochloride, [(C2H5)2NH]2, H2PtCl6, and aurochloride, (C2H5)2NH, HAuC14, are orange, and less readily soluble. Triethylamine, N(C2H5)3, like the primary and secondary amines, is produced when ethyl iodide is heated with alcoholic ammonia, 3C2H5I + NH3 = N(C2H5)3, HI + 2HI. It is a pleasant-smelling liquid, boiling at 89°, and except that it is more sparingly soluble in water, and is a stronger base even than diethylamine, it resembles the primary and secondary compounds in most ordinary properties. It does not give the carbylamine reaction, and is not acted on by nitrous acid at ordinary temperatures, so that it is readily distinguished from the primary and secondary amines; other tertiary amines resemble triethylamine in these respects. The salts of triethylamine correspond with those of the other bases. Triethylamine, and other tertiary amines, combine directly with one molecule of the alkyl halogen compounds, yielding salts corresponding with those of ammonia, N(C2H5)3 + C2H6I = N(C2H6)4I; NH3 + HI = NH4I. These salts are more stable than those of the amines, and are either not acted on, or only very slowly attacked by potash or soda, even on boiling; when, however, their aqueous solutions are shaken with freshly precipitated silver oxide (which acts like a hydroxide), double decomposition ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 205 results, and hydroxy-compounds, corresponding with ammon- ium hydroxide, are formed, N(C2H5)4I + Ag-OH = N(C2H5)4-OH + Agl NH4I + Ag-OH = NH4-OH + Agl. The hydroxides obtained in this way are termed quaternary ammonium bases, or tetralkylammonium hydroxides ; although, in constitution, they are similar to ammonium hydroxide, they differ from the latter in several important respects, and resemble rather the hydroxides of sodium and potassium. Tetrethylammonium hydroxide, N(C2H5)4-OH, for ex- ample, is a crystalline, deliquescent substance, and has only a faint smell, like that of potash ; it has a powerful alkaline reaction, absorbs carbon dioxide from the air, and is a stronger base even than potash or soda; when strongly heated, it is resolved into triethylamine and ethyl alcohol, or its decompo- sition products, N(C2H5)4.OH = N(C2H5)3 + c2h4 + h2o. The salts of tetrethylammonium hydroxide, such as the iodide (see above), may also be obtained by treating the hydroxide with acids; they are mostly crystalline. The tetralkylammonium halogen salts undergo decom- position or dissociation on dry distillation, yielding a tertiary amine and an alkyl halogen salt, just as ammonium chloride is resolved into ammonia and hydrogen chloride, N(C2H5)4C1 = N(C2H5)3 + C2H5C1 NH4C1 = NH3 + HC1. Under ordinary circumstances the halogen ethereal salt, being much more volatile than the tertiary amine, can be separated from the latter before re-combination takes place. In a similar manner the halogen salts of some tertiary amines may be converted into secondary, and those of secondary into primary, amines, N(CH3)3, HC1 = N(CH3)2H + CH3C1 N(CH3)2H, HC1 = N(CH3)H2 + CH3C1. Separation of Amines.-'Three of the general methods for the 206 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETO. preparation of amines-namely, the decomposition of alkyl iso- cyanates, the reduction of nitriles, and the decomposition of amides of the fatty acids with bromine and potash, give the primary com- pounds only; when, however, an alkyl halogen compound is heated with alcoholic ammonia, not only are primary, secondary, and tertiary amines all produced at the same time, but the tertiary amine combines with the alkyl halogen compound to form a quaternary ammonium derivative ; the product consists, therefore, of a mixture of four organic salts, and contains also ammonium salts. In order to separate and isolate the several compounds, the mixture is first evaporated to expel ammonia, alcohol, and any unchanged alkyl salt, and then distilled with excess of potash ; the primary, secondary, and tertiary amines, which, together with ammonia, are thus liberated from their salts, collect in the receiver, and may be absorbed with hydrochloric acid, whilst the residue contains the stable salt of the tetralkylammonium base ; the latter may usually be isolated by neutralising the solution with hydro- chloric acid, evaporating to dryness, and extracting the powdered residue with alcohol. The acid solution of the three amine salts is evaporated almost to dryness and treated with solid potash, when a mixture of the bases rises to the surface as an oil and is separated with the aid of a funnel ; the oil is dried by distilling it with lumps of potash and then treated with ethyl oxalate, when, in the case of the ethyl bases, for example, the following changes occur : The primary amine is converted into ethyloxamide, a derivative of oxamide (p. 233), 2NH2-C2H5 + + 2CA'0H; the secondary amine gives ethyl diethyloxamate, a derivative of oxamic acid (p. 234), NHT H 1 + ?00CA = CO-N(C2H8)2 (C2Hs)2 + ^00C2Hs COOC2H5 + C-Hi5'0H ' the tertiary amine is not acted on, and is easily separated from the two less volatile products by heating the mixture as long as oil passes over. The residue is allowed to cool, and the crystalline ethyloxamide separated from the liquid ethyl diethyloxamate by filtration or by treatment with water, in which the former alone is soluble; the two compounds are then separately distilled with potash, the bases being collected and isolated as described in the case of the mixture, ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 207 CO NHC TT \ « 2 5 2K0H = 2NH c H + caO4Ko CONHC2H5 2 2 6 2K0H = nh«W2 + C2O4K2 + C2H5.OH. C CJ Cz Co pig The three ethylamines and the tetrethylammonium com- pounds may be taken as typical examples of the several classes of alkyl derivatives of ammonia; the corresponding methyl bases, and those of the higher alkyl radicles, are pre- pared by methods so similar to those described in the case of the ethylamine compounds, and have properties so closely resembling those of the latter, that a detailed description would be of little value. Methylamine, NH2-CH3, dimethylamine, NH(CH3)2, and tri- methylamine, N(CH3)3, are usually produced in small quantities during the decomposition of nitrogenous organic substances, and occur in herring brine, the last named especially in large relative proportions. Dimethylamine and trimethylamine are prepared on the large scale by distilling the waste-products obtained in refining beet-sugar, and are used in considerable quantities for various technical purposes; trimethylamine is employed in the manufac- ture of potassium carbonate, and its hydrochloride is used in the preparation of methyl chloride (p. 172). The physical properties of the amines undergo a gradual change with increasing molecular weight, just as is the case in other series ; the boiling-points of the four simplest primary amines may be taken as an illustration : Methylamine, CH3-NH2 B.p. - 6° Propylamine, C3H7-NH2 B.p. 49° Ethylamine, C2H3-NH2 B.p. 19° Butylamine, C4H9-NHO B.p. 76°. The higher amines, like the higher ethers, ethereal salts, &c., exist in various metameric forms : there are, for example, three compounds of the molecular formula C3H9N (see below). The amines, like the ethers, may be classed into simple amines, such as propylamine, C3H7-NH2, diethylamine, (C2H5)2NH, &c., and mixed amines, such as methylethylamine, NH(CH3)-C2H5, dimethylethylamine, N(CH3)2-C2H5, according as they contain alkyl groups of the same or of different kinds. 208 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. Identification of Amines.-The most important methods by which a given amine may be recognised as a primary, secondary, or tertiary compound consist, as already stated, firstly, in applying the carbylamine reaction, and secondly, in treating the compound with nitrous acid. If a primary amine, it is converted by nitrous acid into a primary alcohol with evolution of nitrogen; if a secondary base, it yields a nitroso-compound, the presence of which is readily detected by Liebermann's reaction ; if a tertiary amine, it is usually unchanged. The experiment is made as follows : To a concentrated neutral solution of the hydrochloride of the base a small quantity of a solution of sodium nitrite is added ; evolution of nitrogen, the separation of an oily nitrosamine (which is insoluble in water), or no visible change occurs, according to the nature of the base; further tests, which readily suggest themselves, are then made to confirm the results of the experiment. As methylamine is a gas, and all the lower amines are volatile liquids, which are very difficult to characterise by ordinary tests, the nature of a given amine is usually ascertained by preparing and analysing its platinochloride or aurochloride ; the percentage of metal in the salt, together with the behaviour of the base with nitrous acid, afford evidence sufficient, in most cases, to determine the identity of the compound. Example.-A base produced by the destructive distillation of the molasses obtained in the preparation of beet-sugar gave a platino- chloride, which, on analysis, was found to contain 37*2 per cent, of platinum ; the probable molecular weight of the base is there- fore 59 (see p. 40), so that it maybe propylamine or isopropylamine, C3H7-NH.2, methylethylamine, CH3(C2H5)NH, or trimethylamine, (CH3)3N. On treatment with nitrous acid, it is found to be a tertiary amine ; it is, therefore, trimethylamine. Phosphines. Since phosphorus and. nitrogen belong to the same natural group of elements, it might be expected that phosphoretted hydrogen, PH3, like ammonia, would be capable of yielding substitution products analogous to the amines. As a matter of fact, the phosphines, or alkyl substitution products of phos- phorus trihydride, are readily obtained by heating the alkyl ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 209 iodides with phosphonium iodide in presence of zinc oxide. In the case of ethyl iodide, for example, salts of ethylphos- phine and diethylphosphine, corresponding with those of the primary and secondary amines respectively, are formed, 2PH4I + 2C2H5I + ZnO = 2[PII2-C2H5, HI] + Znl2 + H.,0 PH4I + 2C2H5I + ZnO = PH(C2H5)2, HI + Znl2 + H2O. Tertiary phosphines, such as triethylphosphine, are not pro- duced under the above conditions, but may be prepared by heating the alkyl iodides with phosphonium iodide alone; as in the case of the corresponding amines, the tertiary phos- phines combine with alkyl iodides, forming salts of quaternary bases, such as tetrethylphosphonium iodide, so that the pro- duct is a mixture of two organic compounds, PH4I + 3C2H5I = P(C2H5)3, HI + 3HI P(C2H5)3 + C2H5I = P(C2H5)4L With the exception of methylphosphine, PH2-CH3, which is a gas, the primary, secondary, and tertiary phosphines are colourless, volatile, highly refractive, very unpleasant-smelling liquids; they differ from the amines in smell, in being, as a rule, insoluble, or only sparingly soluble, in water (PH3, un- like NH3, is only sparingly soluble), and in readily undergoing oxidation on exposure to the air ; in many cases, so much heat is developed during this process, that the compound takes fire-that is to say, many of the phosphines are spontaneously inflammable. When tertiary phosphines undergo slow oxida- tion in presence of air, they are converted into stable oxides, such as triethylphosphine oxide, P(C2H-)3O. Although phosphoretted hydrogen is only a feeble base compared with ammonia, and forms salts, such as phosphonium iodide, PH4I, which are decomposed even by water, each suc- cessive substitution of an alkyl group for an atom of hydrogen is accompanied by an increase in basic properties, just as in the case of the amines. Salts of the primary phosphines, such as ethylphosphine hydriodide, PH2-C2H5, HI, are almost, if not quite, as unstable as those of hydrogen phosphide, and 210 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. are decomposed into acid and base on treatment with water; they may thus be separated from the more stable salts of the secondary and tertiary phosphines, such as diethylphosphine hydr iodide, PH(C2H5)2, HI, and triethylphosphine hydriodide, P(C2II5)3, HI, which are not acted on by water as a rule, but are readily decomposed by potash and soda. Salts of the tetralkylphosphonium compounds, such as tetrethylphos- phonium iodide, P(C2H5)4I, are not acted on by water or by alkalies, but, on treatment with moist silver oxide, they are converted into quaternary phosphonium hydroxides, P(C2H5)4I + Ag-OH = P(C2H5)4.OH + AgL These compounds have a strong alkaline reaction, readily absorb carbon dioxide, and dissolve freely in water; they are, in fact, similar in properties to the hydroxides of the fixed alkalies, and their salts are much more stable than the phos- phine salts, just as those of the corresponding tetralkyl- ammonium bases are more stable than those of ammonia. Arsines. Arsenic, antimony, and bismuth, although belonging to the same natural group as nitrogen and phosphorus, differ from these two elements in many important particulars; although the two former give hydrides, the hydrogen atoms in which may be (indirectly) displaced by alkyl groups, substitu- tion products corresponding with the primary and secondary amines and phosphines have not yet been prepared ; in other words, the only known alkyl compounds theoretically derived from the trihydrides of arsenic, antimony, and bismuth corre- spond with the tertiary amines and phosphines, and have the composition AsR3, SbR3, and BiR3 respectively. The tertiary arsines are obtained by treating arsenious chloride with the zinc alkyl compounds (p. 215), or by heat- ing the alkyl iodides with sodium arsenide, 2AsCL + 3Zn(C2H5)2 = 2As(C9HX + 3ZnCL AsNa3 + 3CH3I = As(CH3)3 +' 3NaI. ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 211 Triethylarsine, As(C2H5)3, may be described as a typical arsine. It is a colourless, very unpleasant-smelling, highly poisonous liquid, and is only sparingly soluble in water; it fumes in the air, and takes fire when heated, but does not ignite spontaneously. It differs from the amines and phos- phines in being a neutral compound, and, like arseniuretted hydrogen, it does not form salts with acids; it resembles the tertiary amines and phosphines in combining readily with alkyl iodides, forming salts of quaternary arsonium hydroxides, As(C2H6)3 + C2H5I - As(C2H5)4L Tetrethylarsonium iodide, As(C2II5)4I, for example, is a crystalline substance, and, like other quaternary organic salts, it is not decomposed by potash, although it interacts with silver hydroxide, giving tetrethylarsonium hydroxide, As(C2H5)4I + Ag-OH = As(C2H5)4.OH + Agl. This substance has a strong alkaline reaction, and neutral- ises even the most powerful acids ; here, again, as in the case of nitrogen and phosphorus, the basic character increases with the number of alkyl groups in the molecule. The tertiary arsines resemble the tertiary phosphines in readily undergoing oxidation on exposure to the air, forming oxides such as triethylarsine oxide, As(C2H5)3O. The tertiary stibines, the organic derivatives of antimony, are on the whole similar to those of arsenic, but have not been so carefully investigated; the tertiary bismuth compounds, such as Bi(CH3)3, cannot be converted into quaternary hydroxides, corresponding with those of arsenic and antimony, and owing to the more pronounced metallic character of bismuth, its compounds resemble rather those of the metals zinc, mercury, &c. (p. 214). Derivatives of the Arsines.-Tertiary arsines combine directly with two atoms of a halogen, forming compounds, such as triethylarsine dichloride, As(C2H5)3Cl2, in which the arsenic atom is pentavalent; these substances are decomposed on 212 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. heating, yielding an alkyl halogen compound and a halogen derivative of a secondary arsine, As(C2H5)3C12 = As(C2H5)2C1 + C2H5C1. Although, then, the secondary arsines are unknown, their halogen derivatives can be prepared; so, also, can those of primary arsines, since, when the derivatives of the secondary compounds are treated with halogens, direct union takes place, As(C2H5)2C1 + Cl2 = As(C2H5)2C13, and the products, on heating, are decomposed into dihalogen derivatives of primary arsines, As(C2H5)2C13 = As(C2H5)C12 + C2H5C1. The derivatives of dimethylarsine are of considerable interest, and have been very carefully investigated by Bunsen. Dimethylarsine oxide, or cacodyl oxide, AS(U±i3}2 is formed when a mixture of equal parts of arsenic trioxide and potassium acetate is submitted to dry distillation; during the operation highly poisonous gases are evolved, and an oily liquid collects in the receiver, As2O3 + 4CH3-COOK = As2(CH3)4O + 2K2CO3 + 2CO2. This liquid has an intensely obnoxious smell,* and is excessively poisonous, for which reasons its preparation, except in minute quantities, should not be attempted; its formation may, however, be used as a test for acetates if due care be taken, as the substance is readily recognisable by its smell. Cacodyl oxide boils at 150°, and is insoluble in water; the substance prepared in the above-mentioned manner is spontaneously inflammable owing to the presence of cacodyl, but the pure compound is not. In chemical properties cacodyl oxide resembles the feebly basic metallic oxides ; it has a neutral reaction, but interacts readily with acids, * The name cacodyl is derived from the Greek ko.kw8vs, 'stinking.' ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 213 forming salts, such as cacodyl chloride and cacodyl cyanide, As(CH3)2-CN, + 2HC1 = 3A»(CHS)2CI + H2O. When cacodyl chloride is heated with zinc in an atmo- sphere of carbon dioxide, it yields cacodyl or diarsenic tetra- methyl, a change which is analogous to the formation of ethane from methyl iodide, 2As(CH3)2C1 + Zn = As(CH3)2 - As(CH3)2 + ZnCl2 2CH3I + 2Na = CH3 - CH3 + 2NaL Cacodyl, like the oxide, is a colourless, excessively poison- ous liquid, and has an intensely disagreeable smell ; it takes fire on exposure to the air. Cacodylic acid, (CH3)2AsO-OH, is formed when cacodyl oxide is oxidised with mercuric oxide, AsfCH^0 4 2Hg0 4 H2° = 2(CH3)2AsO-OH + 2Hg; it is a crystalline, odourless substance, and seems to be non- poisonous. Organic Silicon Compounds. The organic compounds of silicon are of exceptional interest, because their study exhibits in a very strong light the close relationship between silicon and carbon. Just as the paraffins may be considered as derived from the hydride, methane, CH4, by the substitution of alkyl groups for hydrogen, so may the simplest silicon compounds be regarded as derivatives of silicon hydride, SiH4. Up to the present, however, only those compounds containing four alkyl radicles have been prepared, as, for example, silicon tetra- methyl, Si(CH3)4, corresponding with carbon tetramethyl or tetramethylmethane, C(CH3)4; substances such as SiH(CH3)3, SiH2(CH3)2, &c., which would be analogous to the hydro- carbons CH(CH3)3, CH2(CH3)2, &c., are not known. Silicon tetramethyl, Si(CH3)4, is produced when silicon tetrachloride is heated with zinc methyl, SiCl4 + 2Zn(CH3)2 = Si(CH3)4 + 2ZnCl2. 214 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. It is a colourless, mobile, volatile liquid, boiling at 30°, and has properties very similar to those of tetramethylmethane. Silicon tetrethyl, Si(C2H5)4, may be obtained from silicon tetrachloride and zinc ethyl in a similar manner, and closely resembles the normal paraffin, nonane, C9Ho0, in properties. It may, in fact, be regarded as derived from the as yet unknown isomeride of nonane, tetrethylmethane, C(C2H5)4, by the sub- stitution of one atom of silicon for one atom of carbon; for this reason it is sometimes named silicononane. The great similarity between silicononane and nonane is strik- ingly shown by the following facts : Silicononane, like nonane, is a colourless liquid, insoluble in, and specifically lighter than water ; like nonane, it is a very stable substance, and is not acted on by nitric acid or caustic alkalies. On treatment with chlorine it behaves like a paraffin, and yields the substitution product silico- nonyl chloride, Si(C2H5)3-C2H4Cl, a colourless liquid, boiling at 185°; this chloride closely resembles the alkyl chlorides in properties, and, like the latter, interacts with silver acetate, giving silicononyl acetate, Si(C2H5)3.C2H4Cl + C2H3O2Ag = Si(C2H8)3.C2H4.C2H3O2 + AgCl. This ethereal salt is readily hydrolysed by alkalies, yielding silicononyl alcohol, just as ethyl acetate gives ethyl alcohol, Si(C2H6)3-C2H4-C2H3O2 + KOH = Si(C2H5)3-C2H4.OH + C2H3O2K; this alcohol, again, is a colourless, neutral liquid, boiling at 190°, analogous in most respects to the higher alcohols of the general formula CnH2n + rOH. Organic silicon compounds, such as Si2(C2H8)6, corresponding wit h Si2Cl6, are known, but are of less importance. Organo-Metallic Compounds. Many of the metals, such as mercury, zinc, tin, and lead, form compounds with alkyl groups, although their hydrides are unknown. These alkyl compounds are named ' organo- metallic ' compounds, but there is no sharp division between them and the alkyl compounds of other elements, just as there is none between the metals and non-metals. If, in fact, the alkyl compounds of elements belonging to the same natural group be considered, it will be evident that they show ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 215 a gradual change in properties, just as do the elements them- selves, and pass into organo-metallic compounds without any abrupt transition. The compounds of the elements of the fourth group, for example, such as C(CH3)4 Si(CH3)4 Sn(CH3)4 Pb(CH3)4, may be divided into two fairly distinct classes; but in the case of those of the elements of the fifth group, N(CH3)3 P(CH3)3 As(CH3)3 Sb(CH3)3 Bi(CH3)3, it is practically impossible to say which of them, if any, should be classed as organo-metallic compounds. The zinc alkyl compounds are perhaps of the greatest importance, on account of their frequent employment in the synthesis of other organic substances, of which many examples have already been given; their properties, moreover, are in many respects typical of those of other organo-metallic compounds. Zinc ethyl, Zn(C2H5)2, is formed when ethyl bromide or iodide is digested with an alloy of sodium and zinc, ZnNa2 + 2C2H-I = Zn(C2H,)2 + 2NaI. Zi 4 0 \ 4 Of 4 It is usually prepared by heating zinc with ethyl iodide in an atmosphere of carbon dioxide; the first product is a colourless, solid substance (zinc ethiodide), containing iodine, Zn + C2H5I = Zn<j 2H5, but on heating more strongly, a second change occurs, and zinc ethyl is formed, 2Zn<j A = Zn(C2H5)2 + Znl2. Zinc filings (100 grams) and an equal weight of ethyl iodide are placed in a flask connected with a reflux condenser, and the air is completely expelled from the apparatus by passing a stream of dry carbon dioxide through a narrow tube which runs through the con- denser to the bottom of the flask. The condenser is then quickly fitted with a cork through which passes a tube, dipping under mer- 216 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. cury, in order to prevent access of air; the materials and the apparatus must be perfectly dry. The flask is now heated on a water-bath, when a rapid evolution of gas (butane) takes place, and the white intermediate product is gradually formed ; after two to three hours' time the interaction is at an end. When cold, the flask is quickly fitted with a cork and glass tubes (just as in an ordinary wash-bottle), and the smaller tube is connected with a condenser ; the flask is then heated in an oil-bath, and the zinc ethyl distilled, a stream of dry carbon dioxide being passed through the longer tube into the apparatus during the whole operation ; the distillate is collected in a vessel which can be easily sealed. Zinc ethyl is a colourless liquid, and boils at 118° without decomposition; it must be distilled in an atmosphere free from oxygen, since it inflames spontaneously on exposure to the air, burning with a luminous, greenish flame, and emitting clouds of zinc oxide. It decomposes water with great energy, yielding ethane and zinc hydroxide, Zn(C2H6)2 + 2H2O = 2C2H, + Zn(OH)2, and owing to its dehydrating action, it causes painful sores when brought into contact with the skin ; it is also decom- posed by alcohol, but not so quickly as by water, Zn(C2H5)2 + 2C2H5.OH = 2C2H„ + Zn<g°A, Zinc ethyl interacts readily with all substances containing the hydroxyl-group, and also with almost all halogen com- pounds, whether organic or inorganic, as, for example, with acid chlorides (pp. 107 and 136), alkyl halogen compounds (p. 69), and metallic chlorides ; for these reasons it is exten- sively used in the synthesis of paraffins, ketones, tertiary alcohols, &c., as well as in the preparation of other organo- metallic compounds. Zinc methyl, Zn(CH3)2, resembles zinc ethyl in most respects, and is prepared by heating methyl iodide with zinc, or, better, with the zinc-copper couple. It is a colourless liquid, boiling at 46°, and is decomposed by water, yielding methane and zinc hydroxide. ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 217 Mercuric ethyl, Hg(C2H5)2, is formed when zinc ethyl is treated with mercuric chloride, Zn(C2H5)2 + HgCl2 = Hg(C2H5)2 + ZnCl2, but it is usually prepared by shaking ethyl iodide with sodium amalgam, HgNa2 + 2C2H5I = Hg(C2H5)2 + 2NaI. Mercuric ethyl is a colourless, very heavy liquid, of sp. gr. 2-44; it boils at 159° without decomposition, and is not spontaneously inflammable at ordinary temperatures, although it ignites readily when strongly heated. It is much less active than zinc ethyl, does not oxidise on exposure to the air, and is not decomposed by water, in which it is only sparingly soluble; both the liquid and its vapour are highly poisonous. On treatment with halogen acids, mercuric ethyl is converted into salts, analogous in some respects to the halogen salts of the alkali metals, Hg(C2H5)2 + HC1 = Hg<^H= + C2He. Mercuric Ethochloride. These salts are also formed by the direct union of mercury and alkyl halogen compounds at ordinary temperatures, especially in sunlight, Hg + C2Hs1 = Hg<°A' Mercuric Ethiodide. and by treating di-alkyl mercury compounds with halogens, Hg(C2Hs)2 + I2 = Hg<CA + C2H6I. They interact with moist silver oxide, being converted into hydroxides, just as sodium iodide, for example, gives sodium hydroxide, Hg<CA + AgOH = Hg<gA + Agl. The hydroxides thus formed are thick, caustic liquids, readily soluble in water; they have an alkaline reaction, neutralise acids, liberate ammonia from its salts, and precipitate metallic 218 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. hydroxides from their salts. Here, as in the case of nitrogen, phosphorus, arsenic, &c., the influence of alkyl groups in increasing the basic character of an element is very pro- nounced ; mercuric oxide is a comparatively feeble base. Of the other organo metallic compounds those of tin, lead, and aluminium may be mentioned. Tin and lead form compounds, such as Sn(C2H5)4 and Sn2(C2H5)6, Pb(C2H5)4 and Pb2(C2H5)6, in which the metal is tetravalent; stannous ethyl, Sn(C2H6)2, corre- sponding with stannous chloride, is also said to exist. Aluminium appears only to give alkyl compounds, such as A1(CH3)3 and A1(C2H6)s, in which the metal is trivalent. The organo-metallic compounds are of great service in determining the valency of metals, because, unlike the great majority of metallic compounds, most of them vaporise without decomposition; by ascertaining experimentally the density of the vapour, the molecular weight of the substance and the valency of the metal may be established. CHAPTER XIII. THE GLYCOLS AND THEIR OXIDATION PRODUCT'S. It may be assumed as a general rule that the changes which any particular group of atoms is capable of under- going are independent of the nature of the groups with which it is combined; just as ethane, CH3-CH3, for ex- ample, may be successively transformed into ethyl chloride, CH3-CH2C1, ethyl alcohol, CH8-CH2-OH, and acetic acid, CII3-CO-OH, by changes in which only one of the methyl groups takes part, so also may it be converted into ethylene dichloride (dichlorethane), CHOCLCH2C1, dihydroxyethane, OH.CH2.CH2-OH, and oxalic acid, HO-CO-CO-OH, by causing the other methyl group also to undergo the same modifica- tions. It follows, therefore, that, in many cases, a series of mono- substitution products of the paraffins may be directly or indirectly converted into a corresponding series of di-substi- THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 219 tution products, between which there is, on the whole, a close relationship. The glycols, or dihydroxy-derivatives of the paraffins, discovered by Wurtz in 1856, afford an example of this point; they form a homologous series of the general formula CnH2w(OH)2, and are closely related to the monohydric alcohols. Ethylene glycol, ethene glycol, or ethylene alcohol, C2II4(OH)9, is the simplest glycol, and corresponds with ethyl alcohol, the compound, methylene glycol, CH2(OH)2, which wTould correspond with methyl alcohol, being unknown. Ethylene glycol is formed in small quantities when ethylene is oxidised with a dilute alkaline solution of potassium permanganate, C2H4 + H2o + 0 = C2H4(OH)2. It is prepared by heating ethylene dibromide, or ethylene dichloride, with dilute aqueous alkalies, or alkali carbonates, the change which occurs being similar to that which takes place in the formation of ethyl alcohol from ethyl chloride, C9H4Br9 + 2K0H = C9H4(0H)9 + 2KBr. For this purpose potassium carbonate (138 grams) is dissolved in water (1 litre), ethylene dibromide (188 grams) added, and the mix- ture boiled in a flask connected with a reflux condenser. As the insol- uble oily dibromide is converted into ethylene glycol, it passes into solution, so that the change is known to be complete when globules of oil are no longer visible. The solution is then slowly evaporated on a water-bath* to expel most of the water, the semi-solid residue mixed with alcohol and ether (which precipitate potassium bromide, but dissolve the glycol), and the glycol isolated from the filtered solution by fractional distillation. Ethylene glycol is a thick, colourless liquid, and has a rather sweet taste; it boils at 197-5°, and is miscible with water and alcohol in all proportions, but is only sparingly soluble in ether. Although it is a neutral substance, it dis- solves sodium at ordinary temperatures with evolution of hydro- gen, yielding sodium glycol, C2H5O2Na, one atom of the metal * If the solution be kept in rapid ebullition, a considerable quantity of the glycol escapes with the steam. 220 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. displacing one atom of hydrogen; if this substance be now heated with sodium, hydrogen is again evolved, and disodium glycol, C2H4O2Na2, is formed by a repetition of the substitu- tion process. These sodium derivatives, like those of the monohydric alcohols, are colourless, crystalline, and hygro- scopic, and are readily decomposed by water, being recon- verted into glycol, C2H4O2Na2 + 2H2O = C2H6O2 + 2NaOH. From its behaviour with sodium it might be assumed that glycol contained hydroxyl-groups, and that the reason of its giving di-substitution products (whereas the monohydric alcohols yield only mono-substitution products) was due to the presence of two hydroxyl-groups. If this were so, it would be expected that glycol, like alcohol, would be readily attacked by the chlorides and bromides of phosphorus; this is indeed the case. When glycol is treated with phosphorus pentabromide, it is converted into ethylene dibromide, whereas with phosphorus pentachloride it yields the dichloride, C2H4(OH)2 + 2PBr5 = C2H4Br2 + 2POBr3 + 2HBr. Again, it has been shown that ethyl alcohol and other hydroxy-compounds interact with acetic anhydride and with acetyl chloride, so that if glycol contain two hydroxyl-groups, it should be converted into a diacetyl-derivative; this, also, is the fact, since glycol diacetate is readily obtained on heating glycol with acetic anhydride, C2H4(OH)2 + 2(CH3.CO)2O = C2H4(O-CO-CH3)2 + 2C2H4O2. Glycol diacetate is also formed when ethylene dibromide is digested with silver acetate, C2H4Br2 + 2C2H3O2Ag = C2H4(C2H3O2)2 + 2AgBr; this ethereal salt is decomposed by boiling alkalies, yielding ethylene glycol, which was first obtained by Wiirtz in this way. Constitution of Glycol.-The facts already stated show THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 221 clearly that glycol contains two hydroxyl-groups; the only matter requiring further attention is, therefore, whether these two groups are combined with the same, or with different carbon atoms-that is to say, whether glycol has the constitu- tion CH3-CH<^ or OH CH2.CH2 OH. This question is easily answered on considering the formation of glycol from ethylene dibromide; since the latter has the constitution CH2Br-CH2Br, and its conversion into glycol is a simple process of substitution, glycol must be represented by the CH2-OH formula OH-CH2-CH2-OH or This conclusion is confirmed by a study of the behaviour of glycol under other conditions, and of its relation to other compounds. Homologues of Ethylene Glycol.-The higher glycols, or dihydroxy-derivatives of the paraffins, as, for example, afi-propylene glycol, CH3-CH(OH)-CH2-OH, and ay-butylene glycol, CH3-CH(OH)-CH2-CH2-OH, are named after the unsaturated hydrocarbons of the olefine series, from which they may be regarded as derived. As they exist in isomeric forms, these are distinguished by employing a, [3, y, &c. to denote the positions of the hydroxyl-groups, commencing at the terminal carbon atom. The glycols are neutral, thick liquids, similar to ethylene glycol in properties; they are usually prepared by treating the olefines with bromine, and decomposing the dibromo- additive products obtained in this way by boiling with alkali carbonates. The great advantage of employing constitutional formulae is well illustrated by the case of ethylene glycol. From a consideration of its method of formation and of one or two simple reactions, it is concluded that glycol has the constitution OH-CH2-CH2-OH. Assuming this to be true, its behaviour under given conditions can be foretold with tolerable certainty from the facts established in the case of ethyl alcohol, because the constitutional formula of a com- pound is a summary of its most important reactions. Ethylene glycol contains two -CH2OH groups, each of which is similar to 222 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. that in ethyl alcohol ; it may be supposed, then, that any property of ethyl alcohol which is dependent on the presence of this group will also be exhibited by glycol. Since, for example, alcohol acts like a metallic hydroxide, and forms salts with one molecule of a monobasic acid, ethylene glycol, which contains two hydroxyl- groups, should behave as a diacid hydroxide, and form salts with two molecules of a monobasic acid. When hydrogen chloride is passed into glycol heated at about 100°, glycol chlorohydrin is formed, OH-CH2.CH2OH + HC1 = CH2C1CH2OH + H2O, and when this product is heated with hydrogen chloride at a higher temperature, glycol dichloride, or ethylene dichloride, is produced, CH2C1CH2OH + HC1 = CH2C1CH2C1 + HjO, changes which are strictly analogous to the conversion of alcohol into ethyl chloride. Again, when ethyl alcohol is carefully oxidised, it is first con- verted into aldehyde (the group -CH2-OH being transformed into -CHO), and then into acetic acid (by the oxidation of the -CHO group to -COOH). Since, therefore, glycol contains two -CH2-OH groups, each of which may undergo these changes, it might be fore- told that, on oxidation, glycol would probably yield several compounds, according as one or both the -CH2-0H groups were attacked. This also is the fact; on oxidation with nitric acid glycol yields the following compounds : CH2OH COOH Glycollic Acid. CHO I CHO Glyoxal. CHO I COOH Glyoxylic Acid. COOH ioOH Oxalic Acid. These examples show clearly that the constitution of any sub- stance having been ascertained from a study of some of its reactions, its behaviour under given conditions may be foretold with tolerable certainty ; in other words, the general reactions and the constitutional formulae of organic compounds are the most important points to bear in mind. When an olefine is treated with hypochlorous acid, direct com- bination ensues, and a chlorohydrin is formed, CH2:CH2 + H0C1 Ethylene. = OHCH2.CHoC1 Ethylene Chlorohydrin. CH3CH:CH2 + H0C1 Propylene. = CH3CHC1CH2OH. Propylene Chlorohydrin. These chlorohydrins are usually readily acted on by alkalies, THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 223 being converted into oxides by loss of one molecule of hydrogen chloride, a change which recalls the conversion of ethyl bromide into ethylene, CH..-0H | " + KOH CH.,Cl CH2\ = I >0 + KC1 + H.,0. ch/ Ethylene Oxide. ch2.oh CHC1 + KOH (in £1 q CH> । /° = CH/ + KC1 + H20. ch3 Propylene Oxide. Ethylene oxide is isomeric with aldehyde, C2H4O ; it is a liquid, boils at 13-5°, and is slowly decomposed by water, being converted into glycol. OXIDATION PRODUCTS OF THE GLYCOLS. Glyoxal, CHO-CHO, is produced by the oxidation of glycol, but it is usually prepared by slowly oxidising alcohol or aldehyde with nitric acid, CH3-CHO + 20 = CHO-CHO + H20. It is an amorphous substance, readily soluble in alcohol and ether; it shows all the properties of an aldehyde, reduces ammoniacal silver nitrate, and combines with sodium bisulphite to form a crystalline compound of the composition C2H2O2, 2NaHSO3 + H2O. It also combines with hydroxyl- amine and with phenylhydrazine, giving the compounds H0N:CH CH:N0H and C6H5N2H:CH-CH:N2HC6H5. Hydroxy carboxylic Acids. GlycoIlic acid, 0H-CH2-C00H, may be obtained by the oxidation of glycol, OH-CH2-CH2-OH, with nitric acid, just as acetic acid is produced by the oxidation of alcohol, CH3-CH2-OH, ch9-oh ch2-oh CH2-0H + 20 = COOH + H2°' As, however, several other substances are formed, the isolation of the acid from the oxidation product is very troublesome. 224 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. It is also formed when amido-acetic acid (glycine, p. 292) is treated with nitrous acid, a reaction exactly analogous to the conversion of ethylamine into alcohol, ch9-nh9 ch9.oii i " + HO-NO = i + H9O + N9. COOH COOH 2 2 GlycoIlic acid is prepared by boiling the potassium salt of chloracetic acid with water, when the hydroxyl-group is sub- stituted for one atom of chlorine, just as in the formation of alcohol from ethyl chloride, ch9ci ch9-oh COOK + H°H = COOH + KCL The solution is evaporated to dryness, and the residue extracted with acetone, which dissolves the glycollic acid, hut not the potas- sium chloride. Glycollic acid is a crystalline, hygroscopic substance, and melts at 80°; it is readily soluble in water, alcohol, and ether. Assuming that its constitution is correctly represented by the formula given above, and of this there can be little doubt when its methods of formation are carefully considered, it is almost unnecessary to describe at length the chemical behaviour of glycollic acid, because this is expressed by its con- stitutional formula. Glycollic acid contains one carboxyl-group; therefore, like the fatty acids, it is a monobasic acid, neutralises carbonates, and forms salts with metallic hydroxides and with alcohols. Glycollic acid also contains one -CH2-OH group; therefore it behaves like a primary alcohol, as well as like an acid. On oxidation, for example, it yields glyoxylic acid and oxalic acid, just as alcohol gives aldehyde and acetic acid, CH9-0H . CHO COOH + ° = COOH + H2° CH9-OH COOH COOH + 20 COOH + H2°' Even when the hydrogen atom of the carboxyl-group has THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 225 been displaced, glycollic acid still contains one atom of hydrogen, which, like that in alcohols, may be displaced by the alkali metals and by the acetyl-group; ethyl glycollate, for example, is readily converted into an acetyl-derivative on treatment with acetyl chloride, CH2-OH CHo-O-CO-CH.. cooc.hC CH"'C0C1 = iooc2H5 + hcl Homologues of Glycollic Acid.-Glycollic acid may be re- garded as hydroxyacetic acid, or acetic acid in which a hydroxyl-group lias been substituted for one atom of hydro- gen ; as, moreover, other fatty acids yield similar hydroxyl- derivatives, a homologous series of hydroxycarboxylic acids may be obtained. The more important members of the series are : Glycollic acid, or hydroxyacetic acid, OH-CH2-COOH. Lactic acid, or hydroxy propionic acid, OH-C2H4-COOH. These compounds may also be regarded as oxidation pro- ducts of the glycols; just as glycollic acid is formed on oxidising ethylene glycol, so the higher members of the series may be obtained from the corresponding glycols by oxidising a -CH2-OH group to -COOH. The lowest member of this series, carbonic acid or hydroxy- formic acid, OH-COOH, is not known in the free state, since, when liberated from its salts, it immediately loses water, and is converted into the anhydride, carbon dioxide. The third member of the series exists in two isomeric forms-namely, as a- and /Lhydroxypropionic acid ; these isomerides are related to propionic acid, in the manner shown by the following formulse : ch3-ch2-cooh Propionic Acid. CH3-CH(OH)-COOH a-Hydroxypropionie or Lactic Acid. CH2(OH)-CH2-COOH. ^-Hydroxypropionic or Hydracrylic Acid. Lactic acid, or a-hydroxypropionic acid, C3H6O3, or CH3-CH(OH)-COOH, 226 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. is formed during the lactic fermentation of sugar, starch, and other substances in presence of nitrogenous animal matter, and occurs in sour milk. It can be obtained by methods analogous to those given in the case of glycoIlic acid-namely, by oxidising a/3-propylene glycol with nitric acid, CH3.CH(OH).CH2.OH + 20 = CH3.CH(0H).C00H + H20, by heating a-chloro- or a-bromo-propionic acid with water, alkalies, or silver hydroxide, CH3CHBr.C00H + H20 = CH3-CH(0H)-C00H + HBr, and by treating a-amido-propionic acid with nitrous acid, CH3.CH(NH2).COOH + H0-N0 = CH3.CH(0H).C00H + N2 + H2O. It is prepared by the lactic fermentation of sugar (see butyric acid, p. 156), or simply by heating sugar with alkalies. Lactic acid is a thick, sour, hygroscopic liquid, miscible with water, alcohol, and ether in all proportions; it cannot be distilled as it undergoes decomposition into aldehyde, water, carbon monoxide, and other products. When heated with dilute sulphuric acid, it is decomposed into aldehyde and formic acid, a fact which shows that, compared with the fatty acids, lactic acid is very unstable, CH3.CH(0H).C00H = CH3.CH0 + H-COOH. Lactic acid is a monocarboxylic acid, and forms metallic and ethereal salts. Calcium lactate, [CH3-CH(OH)-COO]2Ca + 5H2O, anti zinc lactate, (C3H5O3)2Zn + 3H2O, are crystalline, and readily soluble in hot water. Ethyl lactate, CH3-CH(OH)-COOC2H5, is a neutral liquid, but, since it contains aX>CH(OH) group, it yields metallic derivatives with potassium and sodium, and, like other hydroxyl- compounds, it interacts with acetyl chloride, giving ethyl acetyl- lactate, CH3-CH(O-C2H3O)-COOC2H5, an ethereal salt of acetyl- lactic acid, CHg-CH^^j^ns Lactic acid also contains the group ^>CH0H, and shows, THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 227 therefore, most of the reactions of a secondary alcohol. When, for example, it is heated with concentrated hydrobromic acid, it is converted into a-bromo-propionic acid, just as isopropyl alcohol gives isopropyl bromide, CH3-CH(OH).COOH + HBr = CH3-CHBr-COOH + H2O; with concentrated hydriodic acid, however, it yields propionic acid, because the a-iodo-propionic acid which is first produced is reduced by the excess of hydriodic acid, ch3-chi-cooh + HI = CH3.CH2.COOH + I2. On oxidation with potassium permanganate, lactic acid again behaves like a secondary alcohol, and is converted into pyruvic acid, just as isopropyl alcohol gives acetone, CH3-CH(OH).COOH + 0 = ch3.co-cooh + h2o. Sarcolactic acid, or paralactic acid, C3H6O3, is the name given to an acid which occurs in animals, more especially in the muscle juices, and which is best prepared from extract of meat. It has the same constitution as lactic acid, because it undergoes the same chemical changes, and differs from it only in being optically active (part ii.). Hydracrylic acid, or ^-hydroxypropionic acid, C3H6O3, or CH2(OH).CH2.COOH, is not formed during lactic fermentation, but may be obtained by reactions exactly similar to those which give the corresponding a-acid-namely, by oxidising ay-propylene glycol, and by boiling /2-chloro-, bromo-, or iodo-propionic acid, CH2X-CH2-COOH, with water or weak alkalies. It is a thick, sour syrup, and, when heated alone or with moderately dilute sulphuric acid, it is converted into acrylic acid (p. 257), with loss of the elements of water, a change analogous to the conversion of ethyl alcohol into ethylene, CH2(OH).CH2.COOH = CH2:CH-COOH + h2o. In most respects hydracrylic behaves like lactic acid; it is a monocarboxylic acid, but also contains a -CH2-OH group, so that it shows most of the reactions of a primary alcohol as 228 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. well as those of a monobasic acid; on oxidation with chromic acid, for example, it yields malonic acid, CH2(OH).CH2.COOH + 20 = cooh-ch2.cooh + h2o. Constitutions of the Hydroxypropionic Acids.-Since lactic acid and hydracrylic acid are both hydroxymonocarboxylic acids of the molecular composition C3H6O3, and only two formulae-namely, CH3-CH(0H) C00H and CH2(OH)-CH2.COOH I. IL -can be constructed, making the usual assumptions regarding valency, all that is necessary is to determine which represents the one and which the other acid. This point is, of course, already settled if the constitutions of the chloro-propionic or amido-propionic acids be taken as known; supposing, how- ever, this were not the case, the following syntheses of the hydroxy-acids establish their constitutions. When aldehyde is treated with hydrocyanic acid, direct combination occurs, and the product is converted into lactic acid on boiling it with hydrochloric acid, CH3.CH(0H).CN + 21^0 = CH3.CH(0H).C00H + nh3. Lactic acid, therefore, is represented by formula I., a con- clusion which is fully borne out by all other facts. When ethylene is treated with an aqueous solution of hypochlorous acid, glycol chlorohydrin is formed (p. 222); this compound interacts with potassium cyanide in dilute alcoholic solution, giving glycol cyanohydrin, CH2(OH).CH2C1 + KCN = CH2(OH).CH2.CN + KC1, which, when boiled with mineral acids, is converted into hydracrylic acid, CH2(OH).CH2.CN + 2H2O = CH2(OH).CH2.COOH + nh3. Hydracrylic acid, therefore, is represented by formula II. Since, moreover, aldehyde and ethylene may be prepared THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 229 from their elements, this is also true as regards the two hydroxypropionic acids. Lactic acid is sometimes called eth/ylidenelactic acid, hydracrylic acid being named ethylenclactic acid; these names serve to recall the facts that lactic acid contains the ethylidene group CH3-CH<7, hydracrylic acid the ethylene group -CH2-CH2-. Dicarboxylic Acids. GlycoIlic acid, CH2(OH)-COOH, being derived from ethylene glycol, CH2(OH)-CH2-OH, by the oxidation of one of the -CH2-OH groups, it might be concluded that the other -CH2OH group would be capable of undergoing a similar change; this is found to be so, since on further oxidation glycoIlic acid is converted into oxalic acid, COOH-COOH. As, moreover, other glycols, such as ay-propylene glycol, CH2(OH)-CH2-CH2-OH, which contain two -CH2-OH groups, behave in the same way as ethylene glycol, it is possible to prepare a homologous series of dicarboxylic acids of the general formula C?iH2n(COOH)2. These compounds may also be considered as derived from the fatty acids by the substitu- tion of the carboxyl-group for one atom of hydrogen, and, since they contain two such groups, they are dibasic acids. The most important members of this series are : , COOH Oxalic, or carboxyformic acid C2H2O4 or COOH Malonic, or carboxyacetic acid C3H4O4 or CH2<^cqq£| o • - „ , . . ., CH.,.COOH Succinic, or /3-carboxypropionic acid ...C.ELO, or | 461 ch2-cooh Isosuccinic, or a-carboxypropionic acid C4H6O4 or CH3-CH\2qq^ Glutaric acid ..C5H8O4 Adipic acid C(iH1()O4 . . COOH Oxalic acid, C2H2O4, or occurs rhubarb (rheum), the dock (rumex), sorrel (oxalis acefosella), and other plants, usually in the form of its potassium hydrogen salt, or as 230 THE GLYCOLS AND THE1R OXIDATION PRODUCTS. calcium oxalate; it is formed when alcohol, glycol, sugar, fats, and a great many other organic substances are oxidised with nitric acid, and may be obtained by numerous reactions, of which the following are the most instructive : It is formed when sodium is heated at about 350° in a stream of carbon dioxide, 2CO2 + 2Na = C2O4Na2, Sodium Oxalate. and when sodium or potassium formate is quickly heated to about 440°, 2HCOONa = C2O4Na2 + H2; it is also produced, together with many other compounds, when an aqueous solution of cyanogen (p. 277) is kept for some time, a change which is analogous to the conversion of methyl cyanide into acetic acid, (CN)2 + 4H2O = C2O4(NH4)2. Ammonium Oxalate. Each of these three reactions affords a means of synthesing oxalic acid from its elements, since carbon dioxide, formic acid, and cyanogen may be obtained from their elements. Oxalic acid may be prepared by gently warming cane- sugar with about six times its weight of concentrated nitric acid. The operation is performed in a good draught cupboard, and as soon as brown fumes appear the heating is discontinued, in spite of which oxidation proceeds very vigorously; after some time, as the solution cools, crystals of oxalic acid are deposited. The solu- tion is decanted or filtered through glass wool, and the oxalic acid purified by crystallisation from boiling water; further quantities may be obtained from the acid mother-liquors. Oxalic acid is prepared on the large scale from sawdust, which contains organic compounds (cellulose, lignin, &c.) somewhat similar in composition to cane-sugar, and which, when heated with alkalies, undergo profound decomposition. The sawdust is made into a paste with a concentrated solution of a mixture of equal parts of potash and soda, and then heated in iron pans at about 210°; afterwards the mass is treated with water, THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 231 the solution of potassium and sodium oxalates boiled with lime, the precipitated calcium oxalate washed with water and decomposed with dilute sulphuric acid, C2O4Ca + H2SO4 = C,O4H2 4- CaSO4; the solution of oxalic acid is then filtered from the calcium sulphate and evaporated to crystallisation. The acid obtained in this way contains small quantities of potassium and sodium hydrogen oxalates, from which it is separated only with great difficulty, so that on ignition it gives a residue of alkali carbonates; the pure acid is most conveniently prepared from cane-sugar. The formation of oxalic acid from sawdust and from sugar cannot be expressed by a simple equation ; in both cases a complex molecule containing -CH-OH groups undergoes simultaneous decomposition and -CH-OH oxidation. Oxalic acid crystallises in colourless prisms, which contain two molecules of water ; it is readily soluble in alcohol and moderately so in water, but only sparingly in ether. When quickly heated, it melts at about 100° and loses its water; the anhydrous acid sublimes at about 150°, but, if heated too strongly, it decomposes into carbon dioxide and formic acid, or its decomposition products, C2O4H2 = HCOOH + CO2 = H2O + CO + CO2; the anhydrous acid is very hygroscopic, and a powerful dehydrating agent. Oxalic acid is decomposed by concentrated sulphuric acid, but only on heating moderately strongly (distinction from formic acid), C2O4H2 = CO2 + CO + H2O; it is a feeble reducing agent, precipitates gold from its solu- tions, and is readily oxidised by warm potassium perman- ganate (or chlorine water), being converted into carbon dioxide and water, a reaction which is employed for the volumetric estimation of oxalic acid and also in standardising permangan- ate solutions, C2O4H2 + 0 = 2CO2 + H2O. 232 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. Oxalic acid is dibasic, and forms salts with two equivalents of a metallic hydroxide, and with two molecules of a mono- hydric alcohol ; it has an acid reaction, decomposes carbonates, and dissolves certain metallic oxides. The salts of the alkalies are readily soluble in hot water, but most of the other salts are sparingly soluble or insoluble. Ammonium oxalate, C2O4(NH4)2, is decomposed into oxamide when carefully heated, just as ammonium acetate yields acetamide, COONH4 CO-NIL i 4 = i 2 + 2H9O. coonh4 conh2 Potassium oxalate, C2O4K2 + H2O, is readily soluble in water, but potassium hydrogen oxalate, C2O4KH, a salt which occurs in many plants, is more sparingly soluble; the latter forms with oxalic acid a crystalline compound of the composition C2O4KH 4- C2O4H.> + 2H2O, known as ' salts of sorrel,' or potassium quadroxalate; this salt is used in removing iron- mould and ink-stains, as it converts the iron into soluble iron potassium oxalate. Silver oxalate, C2O4Ag2, is obtained in crystals on adding silver nitrate to a neutral solution of an oxalate; it is only sparingly soluble in water, and explodes when quickly heated in the dry state, leaving a residue of silver. Calcium oxalate, C2O4Ca + H2O, occurs in crystals in the cells of various plants, and is obtained as a white precipitate on adding a solution of a calcium salt to a neutral or ammoni- acal solution of an oxalate ; it is insoluble in water, and also in acetic acid, whereas magnesium oxalate is soluble in the latter, a fact which is made use of in the separation of the two metals. Oxalic acid and its salts are used to a consider- able extent in the manufacture of organic dyes, in calico- printing, in photography (as developers), and in analytical chemistry. The metallic salts of oxalic acid are all decom- posed by dilute mineral acids, yielding oxalic acid, whereas, when heated with concentrated sulphuric acid, they give THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 233 carbon dioxide, carbon monoxide, water, and a sulphate. Oxalic acid and its soluble salts are poisonous. The detection of oxalic acid or of an oxalate is chiefly based on (a) the behaviour of the neutral solution with calcium chloride, and the insolubility of the precipitate in acetic acid ; (ft) the behaviour of the dry substance with sulphuric acid. Methyl oxalate, C2O4(CH3)2, is a colourless, crystalline com- pound, melting at 54°, and is easily prepared by boiling anhydrous oxalic acid with methyl alcohol; it is readily hydrolysed by alkalies and boiling water, and is sometimes employed in the preparation of pure methyl alcohol. Ethyl oxalate, C2O4(C2HS)2, can be obtained in a similar manner ; it is a pleasant-smelling liquid, boiling at 181°, and sparingly soluble in water. It is a curious fact that the methyl salts of organic acids are frequently crystalline, even when the ethyl, propyl, butyl, &c., salts are liquid at ordinary temperatures. The constitution of oxalic acid is determined by its forma- tion from glycol, glycoIlic acid, and formates; it may be regarded as composed of two carboxyl-groups, and is for this reason sometimes called dicarboxyl. Probably owing to the fact that oxalic acid is very rich in oxygen, it is a comparatively unstable compound ; its an- hydride is unknown, and, when treated with phosphorus COCI pentachloride, instead of yielding the chloride, i , as might COCI have been expected, oxalic acid is decomposed into the oxides of carbon and water. co-nh2 Oxamide, I , is formed as an intermediate product in CO-NH2 the conversion of cyanogen into ammonium oxalate (p. 278), also when ammonium oxalate is heated. It is prepared by shaking methyl or ethyl oxalate with concentrated ammonia, a method very generally employed in the preparation of amides from ethereal salts. C2O.(C2H5).? + 2NH3 = C2O2(NH2)2 + 2C2H5.OH. 234 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. It is a colourless, crystalline powder, insoluble in water; when heated with water, alkalies, or mineral acids, it is converted into oxalic acid or an oxalate, a change exactly analogous to that undergone by acetamide (p. 162), C2O2(NH2)2 + 2H2O = C2O4H2 + 2NH3. If methyl oxalate be treated with an aqueous solution of a primary or secondary amine instead of with ammonia, alkyl substitution products of oxamide or of oxanric acid, NH2-CO-COOH, respec- tively are formed (compare amines, p. 206). Malonic acid, CH2(COOH)2, the next homologue of oxalic acid, has already been mentioned, and the preparation of its ethyl salt from chloracetic acid has been described (p. 196). If instead of the ethyl salt the free acid be required, the product of the action of potassium cyanide on potassium chloracetate is mixed with twice its volume of concentrated hydrochloric acid, and the solution saturated with hydrogen chloride ; the clear liquid is then decanted from the precipitated potassium chloride, evaporated to dryness on a water-bath, and the malonic acid extracted from the residue by digesting with ether. Malonic acid is a colourless, crystalline substance, readily soluble in water; it melts at 132°, and at higher temperatures undergoes decomposition into acetic acid and carbon dioxide, CH2(COOH)2 = ch3-cooh + co2. Other dicarboxylic acids, in which both the carboxyl-groups are united to one and the same carbon atom, are decomposed in a similar manner under the influence of heat. CHyCOOH Succinic acid, C.HrO., or i " , occurs in amber, 4 6 4 ch2.cooh and also in smaller quantities in lignite (fossil-wood), in many plants, and in certain animal secretions. It is formed during the alcoholic fermentation of sugar, and in several other fermentation processes; also when fats are oxidised with nitric acid. It can be obtained from its elements in the following manner: acetylene, which can be prepared from carbon and THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 235 hydrogen, is reduced to ethylene, the latter passed into bromine, and the ethylene dibromide thus produced boiled with potassium cyanide in aqueous alcoholic solution, when ethylene dicyanide is formed, C2H4Br2 + 2KCN = C2H4(CN)2 + 2KBr; this compound is decomposed by boiling it with alkalies or mineral acids, succinic acid and ammonia being obtained, CH0.CN CH,-COOH i 2 + 4H.?O = i 2 + 2NH„. CH2-CN 2 CH2-COOH 3 It may also be prepared synthetically from ethyl acetoacetate (or ethyl malonate) and ethyl chloracetate, CH3COCHNa + CH2CLCOOC2H6 = CH3COCH.CH2-COOC2H5 COOC2H5 COOC2H5 + NaCl CH.-CO-CHCHo-COOCiHg I ' + 3K0H = COOC3H5 ch2-ch,-cook + CH3-COOK + 2C.,H5-OH. COOK Succinic acid is usually prepared by distilling amber from iron retorts; the dark-brown oily distillate is evaporated, and the dirty-brown crystalline residue of succinic acid purified by recrystallisation from hot dilute nitric acid. Succinic acid crystallises in colourless prisms, melts at 180°, and sublimes readily; it has an acid, unpleasant taste, and is only sparingly soluble in cold water, alcohol, and ether. It is a dibasic acid, and its salts, the succinates, with the exception of those of the alkalies, are sparingly soluble or insoluble in water. Ammonium succinate, C4H4O4(NH4)2, is sometimes employed in the separation of iron from manganese, as, on adding a solution of a ferric salt to ammonium succinate, the whole of the iron is converted into an insoluble basic salt, which is obtained as a buff precipitate. 236 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. The constitution of succinic acid is determined by its forma- tion from ethylene dibromide, and by the fact that the only alternative formula for a dicarboxylic acid of the molecular composition C4H6O4 must be assigned to isosuccinic acid (see below). CH.yCO\ , , Succinic anhydride, i " ^0, is formed when succinic CH^CO^ acid is distilled, C4H6O4 = C4H4O3 + H20, but a large pro- portion of the acid passes over unchanged. It is prepared by heating the acid with phosphorus oxychloride for some time and then distilling, the oxychloride combining with the water which is produced, and thus preventing the reconver- sion of the anhydride into the acid; phosphorus pentoxide, acetyl chloride, or some other dehydrating agent may be used in the place of the oxychloride. Succinic anhydride is a colourless, crystalline substance, and melts at 120°; it resembles the anhydrides of the fatty acids in chemical properties, and when boiled with water or alkalies, it is reconverted into succinic acid or a succinate. Succinic anhydride differs from the anhydrides of fatty acids in this, that it is formed from one molecule of the acid with elimination of one molecule of water, whereas the anhy- dride of a fatty acid is produced from two molecules of the acid in a similar manner, CHo-COOH CH9-CCK i 2 = i 2 >O + HoO CH2C00H CH^CCT 2 CH3.C00H _ CH3-C0\n w n CH3.C00H " the constitution of succinic anhydride is therefore expressed by the above formula, which recalls the fact that both the carboxyl-groups take part in the change, as is shown by the neutral character of the anhydride. Many other dicarboxylic acids are converted into their anhydrides in a similar manner. THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 237 CH2-COC1 Succinyl chloride* | , is formed when succinic acid is CH..-COC1 treated with two molecules of phosphorus pentachloride, the inter- action recalling that which occurs in the formation of acetyl chloride, CH2COOH CH2COC1 + 2PC15 = | + 2POC13 + 2HC1. ch2-cooh ch2-coci It is a colourless liquid, boils at 190°, and resembles acetyl chloride in chemical properties; like the latter, it is decomposed by water, alkalies, and hydroxy-compounds, yielding succinic acid or a suc- cinate. ch2.conh2 Succinamide, | , is prepared by shaking ethyl CH2CONH2 succinate with concentrated ammonia; it is a crystalline substance, melts at 242-243°, and is only very sparingly soluble in cold water. When heated with water, it is slowly converted into ammonium succinate, just as oxamide is converted into ammonium oxalate, CH.,CONH2 CH2COONH, | + 2H.,0 = | ch2-co-nh2 ch2-coonh4. Succinamide cannot be obtained by distilling ammonium succinate, although oxamide and acetamide are produced by the distillation of the corresponding ammonium salts ; this fact shows that it is not always safe to judge by analogy, since compounds very closely related in constitution may, in certain respects, behave very differ- ently. When, in fact, ammonium succinate or succinamide is heated, it is converted into succinimide. CH2CO\ Succinimide, I /NH, is also formed when succinic anhv- CH2.COZ dride is heated in a stream of dry ammonia ; it is readily soluble in water, from which it crystallises with one molecule of water, the anhydrous substance melting at 126°. When boiled with water, alkalies, or mineral acids, it is converted into succinic acid, CHo-COx CHo-COOH J)NH + 2H9O = | + NH3. CH2-C(r ' ch2-cooh * The constitution of succinyl chloride is not definitely established, CH2-CC12\ certain facts pointing to the formula | /O. ch2-co/ 238 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. The constitution of succinimide, as expressed by the above formula, is based principally on its methods of formation ; it may be regarded as a di-substitution product of ammonia-that is to say, as ammonia in which two atoms of hydrogen have been displaced by the CH2-CO- divalent succinyl-grm^ | , just as an amide is a mono- CH2CO- substitution product of ammonia. Many other dicarboxylic acids yield imides similar in constitution to succinimide. Although succinimide is not an acid in the ordinary sense of the word, has a neutral reaction, and does not decompose carbonates, it contains one atom of hydrogen displaceable by metals. When, for example, a solution of potash in alcohol is added to an alcoholic solution of succinimide, a crystalline derivative, potassium succin- ch2-cox imide, I /NK, is produced; this compound interacts with CH2C(y silver nitrate, giving silver succinimide, and the latter, on treatment with ethyl iodide, yields ethyl succinimide, CH2-COX CH2COk I " >NAg + C2HSI = | >N-C2H5 + Agl. ch2.co/ CH2COz It has already been pointed out, that hydrogen in combination with carbon becomes displaceable by metals when the carbon atom is directly united with two ^>CO groups, as in ethyl acetoacetate and ethyl malonate. From the behaviour of succinimide, and of other imides, it is found that the hydrogen atom of an imido- group /NH is also displaceable by metals when the imido-group is directly united with two S>CO groups. Jsosuccinic acid, CH3-CH(COOH)2, is isomeric with succinic acid ; it may be prepared by treating an alcoholic solution of the sodium derivative of ethyl malonate with methyl iodide, and hydrolysing the product, a reaction which shows that isosuccinic acid is methyl- malonic acid, CHNa(COOC2H3)2 + CH3I = CH3-CH(COOC2H3)2 + Nai. It is a crystalline substance, sublimes readily, and melts at 130°; it does not form an anhydride, and when heated alone, or with water, it is decomposed into propionic acid and carbon dioxide, just as malonic acid gives acetic acid and carbon dioxide, CH3-CH(COOH)2 = CH3-CH2.COOH + CO2. The higher members of this series of dicarboxylic acids exist in several isomeric forms; four acids of the composition C3H8O4, for THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 239 example, are theoretically possible, and four are actually known- namely, /CHo COOH "^•-cjpcooh Normal Glutaric Acid. ch3-chcooh 6h2cooh Pyrotartaric Acid or Methylsuccinic Acid. rwr z.rr-^00011 Ethylinalonic Acid. CH3^p^COOH CH^^^COOH. Dimethylmalonic Acid. Adipic acid, C6H10O4, is of some importance, as it is often obtained on oxidising fats with nitric acid ; it may be produced synthetically by heating jS-iodo-propionic acid with finely divided silver, the reaction being analogous to the production of ethane by the action of sodium or zinc on methyl iodide, aCHJ CH. COOH + 2Ag = COOH-fCH^-COOH + 2AgI; it is a crystalline substance, melting at 148°. Hydroxy dicarboxy lie Acids. With the exception of oxalic acid, the dicarboxylic acids just considered are capable of yielding substitution products inexactly the same way as the fatty acids; malonic acid, for example, may be converted into chloromalonic acid, CHC1(COOII)2, hydroxymalonic acid, HO-CH(COOH)2, &cg succinic acid into bromosuccinic acid, COOH-CHBr-CH2-COOH, di- bromosuccinic acid, COOH-CHBr-CHBr-COOH, hydroxy- succinic acid, COOH-CH(OH)-CHo-COOH, dihydroxysuccinic acid, COOH.CH(OH).CH(OH).COOH, and so on. Some of these compounds-namely, the hydroxy-derivatives-occur in nature, and for this and other reasons are of considerable importance. CH(OH)-COOH Malic acid, i or C4H6O5, a monohydroxy- CHL-COOH derivative of succinic acid, occurs, not only in the free state, but also in the form of salts, in many plants, more specially in (unripe) apples, from which it derives its name (acidum malicum), in grapes, and in the berries of the mountain ash. It may be obtained by boiling bromosuccinic acid with water 240 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. and silver hydroxide, a reaction analogous to the formation of lactic acid from a-bromo-propionic acid, CHBr-COOH CH(0H)-C001I i + Ag-OH = i + AgBr. CII2-COOH CH,COOH As, therefore, bromosuccinic acid is easily prepared by heating succinic acid with bromine and water, and succinic acid may be synthesised in the manner already described (pp. 234-5), it is possible to obtain malic acid from its elements. Malic acid is produced on treating amidosuccinic acid, or aspartic acid (a compound which may be obtained indirectly from asparagus*), with nitrous acid, just as lactic acid may be prepared from a-amido-propionic acid, CH(NH2).COOH CH(OH)-COOH I 2/ + HO-NO = i ' + N„ + H2O. CHyCOOH CH2COOH It is usually prepared from the juice of unripe berries of the mountain ash. The expressed juice is boiled with milk of lime and the crystal- line, sparingly soluble calcium salt, C4H4OsCa + H2O, which is precipitated, dissolved in hot dilute nitric acid; the calcium hydrogen malate, (C4H5O5)2Ca + 6H2O, which separates in crystals, is then decomposed with the theoretical quantity of oxalic acid, and the filtered solution evaporated. Malic acid is a crystalline, deliquescent substance, melts at 100°, and is readily soluble in water and alcohol, but only sparingly in ether; its metallic and ethereal salts are of little importance. Many of the reactions of malic acid may be foretold from a consideration of its constitution, which is established by its methods of formation. Since, for example, it is a hydroxy- derivative of succinic acid, it is to be expected that, on reduction with hydriodic acid at a high temperature, it will be * Asparagine, COOHCH(NH2)CH2-CONH2, the amide of aspartic acid occurs, in asparagus ; when boiled with acids or alkalies, it is converted into aspartic acid, COOH-CH(NH)2-CH2COOH. THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 241 converted into succinic acid, just as lactic acid is converted into propionic acid; also that, when heated with hydrobromic acid, it will yield bromosuccinic acid, a change which would be analogous to the conversion of lactic into bromopropionic acid. Both these changes actually take place, COOH.CH(OH).CH2.COOH + 2HI = COOH-CH2.CH2.COOH + H2O + I2 COOH.CH(OH).CH2-COOH + HBr = COOHCHBrCH2COOH + H2O. Although the malic acid obtained from plants undergoes exactly the same chemical changes as that prepared from bromosuccinic acid, and that obtained from aspartic acid, the three acids are not identical in all respects; they differ principally in their action on polarised light, a point which is referred to later (part ii.). When malic acid is heated for a long time at 130°, it does not form malic anhydride, as might have been expected from the behaviour of succinic acid, but is slowly converted into fumaric acid and water, CH(OH)COOH CH-COOH I = || ; ch2cooh chcooh if now the fumaric acid be distilled, part passes over unchanged, the rest being converted into maleic anhydride and water, CHCOOH CH-CO\ II = || >O + H.,O. CHCOOH CHCOZ Maleic anhydride is decomposed by boiling water, giving maleic acid, which has the same constitution as fumaric acid-that is to say, both compounds are unsaturated dicarboxylic acids of the constitution COOH-CH:CH-COOH ; the existence of these two isomerides, and other cases of isomerism of a similar kind, are accounted for by the theory of stereochemical isomerism proposed by Van't Hoff and Wislicenus, for an account of which other works must be consulted. Tartaric acid, or dihydroxysuccinic acid, C4H6O6 or CH(0H).C00H . p , i is one of the most commonly occurring CH(0H)-C00H vegetable acids, and is contained in grapes, in the berries of 242 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. the mountain ash, and in other fruits; during the (secondary) fermentation of grape-juice, which takes place in the casks, a considerable quantity of ' argol,' or impure potassium hydro- gen tartrate, is deposited, and it is from this salt that the tartaric acid of commerce is obtained. Tartaric acid can be obtained from succinic acid, and, therefore, from its elements, by reactions similar to those employed in the synthesis of malic acid ; dibroinosuccinic acid is first prepared by heating succinic acid with bromine (2 mols.) and water, and two hydroxyl-groups are then substituted for the two atoms of bromine in the usual way-namely, by heat- ing the dibromo-derivative with water and silver hydroxide,* CHBr-COOH CH(OH)-COOH l + 2A"-0H = I + 2A"Br CHBr-COOH 8 CH(OH)-COOH ° ' Tartaric acid may also be obtained synthetically from glyoxal (p. 223), which, like other aldehydes, combines directly with hydrocyanic acid, CHO CH(OH)-CN i + 2HCN = I : CHO CH(OH)-CN the dicyanohydrin thus produced is decomposed by mineral acids, giving tartaric acid,t just as cyanoacetic acid yields malonic acid, CH(OH)-CN CH(OH)-COOH CH(OH)-CN + 4H2° = CH(OH)-COOH + 2NHr Tartaric acid is prepared on the large scale from argol. This crude, dark-red deposit is partially purified by recrystallisation from hot water, and its aqueous solution is then boiled with chalk, when insoluble calcium tartrate is precipitated, neutral potassium tartrate remaining in solution, 2C4H6O6K + CaCO3 = C4H4O6Ca + C4H4O6K2 + CO2 + H2O ; the calcium salt is separated, and the solution treated with * The tartaric acid obtained in this way is optically inactive (part ii.), and is a mixture of racemic acid and mesotartaric acid. + This product is also optically inactive, and consists of racemic acid only. THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 243 calcium chloride, when a second precipitate of calcium tartrate is obtained, C4H4O6K2 + CaCl2 = C4H4O6Ca + 2KC1. The calcium tartrate from these two operations is washed with water, and decomposed with the theoretical quantity of dilute sulphuric acid; finally, the filtered solution of the tartaric acid is evaporated to crystallisation. Tartaric acid forms large transparent crystals, and is readily soluble in water and alcohol, but insoluble in ether; it melts at about 167°, but not sharply, owing to decomposition taking place. When heated fora long time at about 150°, it is con- verted into tartaric anhydride, C4H4O5, and several other compounds, and on dry distillation it yields a variety of pro- ducts, among others, pyruvic acid and pyrotartaric acid. Tartaric acid, like other dicarboxylic acids, forms both neutral and acid salts, some of which are of considerable importance. Normal potassium tartrate, C4H4O6K2 + -^H2O, is readily prepared by neutralising the acid, or the acid potassium salt, with potash; it is readily soluble in cold water, in which respect it differs from potassium hydrogen tartrate, C4H5O6K, which is only sparingly soluble. The latter is precipitated* on adding excess of tartaric acid to a concentrated neutral solution of a potassium salt (test for potassium), and also on treating an aqueous solution of normal potassium tartrate with one equivalent of a mineral acid, C4H4O6K2 + HC1 = C4H5O6K + KC1; it is known in commerce as 'argol' or 'cream of tartar.' Potassium sodium tartrate, or ' Rochelle salt,' C4H4O6KNa + 4H.,O, is obtained when potassium hydrogen tartrate is neutralised with sodium carbonate and then concentrated; it forms large transparent crystals, and is employed in the pre- paration of Fehling's solution (p. 263). * The precipitation is much hastened by shaking or stirring with a glass rod. 244 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. Calcium tartrate, C4H4O6Ca 4-4H2O, being insoluble in water, is precipitated on adding a soluble calcium salt to a neutral solution of a tartrate; it is readily soluble in potash, but is reprecipitated on boiling the solution, a behaviour which is made use of in testing for tartaric acid. Tartar emetic, or potassium antimonyl tartrate, C4H4O6K(SbO) + |H2O, is prepared by boiling potassium hydrogen tartrate with anti- monious oxide and water; it is readily soluble in water, and is used in medicine as an emetic, and in calico-printing as a mordant. The detection of tartaric acid or of a tartrate is based (a) on the behaviour of the neutral solution with calcium chloride (in the cold), and on the solubility of the precipitate in potash; (b) on the behaviour of the neutral solution with an ammoniacal solution of silver nitrate, from which a mirror of silver is deposited on warming ; (c) on the fact that the solid compound rapidly chars when heated alone, giving an odour of burnt sugar; it also chars when heated with con- centrated sulphuric acid, sulphur dioxide and the two oxides of carbon being evolved. That the constitution of tartaric acid is expressed by the formula given above is shown by the methods of formation of the acid; it is a dihydroxy-derivative of succinic acid, just as malic acid is a monohydroxy-derivative of the same compound. On reduction with hydriodic acid, tartaric acid is converted first into malic, then into succinic acid, CH(OH)-COOH CH(OH)-COOH CH(OH) -COOH + 2HI = CH2.COOH + H2° + Is' CH(OH)-COOH CH2-COOH i + 4HI = i 2 + 2HQO + 2I„, CH(OH).COOH CH2-COOH 2 2 whereas, when heated with concentrated hydrobromic acid, it yields dibromosuccinic acid, as was to be expected, THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 245 CH(OH)-COOH CHBr-COOH I + 2HBr = ! + 2H„O. CH(OH)-COOH CHBr-COOH It is a remarkable fact that four distinct modifications of tartaric acid are known-namely, dextrotartaric acid (the compound just described), levotartaric acid, racemic acid, and mesotartaric acid. These four compounds have the same con- stitution-that is to say, they are all dihydroxy-derivatives of succinic acid, as represented by the formula COOH-CH(OH).CH(OH)-COOH; they differ, however, in certain physical properties, as, for example, in crystalline form, solubility, &c., but more especially in their behaviour towards polarised light; the salts of the four acids exhibit similar differences. This point is referred to later (part ii.). Dextrotartaric acid rotates the plane of polarisation to the right, levotartaric acid to an equal extent to the left. Racemic acid is optically inactive ; it is produced when equal quantities of the dextro- and levo-acids are dissolved in water, and the solution of the mixture allowed to crystallise. It may he obtained synthetically by heating an aqueous solution of dibromo- succinic acid with silver hydroxide, as described above; also from glyoxal. Racemic acid may be resolved into dextro- and levo- tartaric acids. Mesotartaric acid, like racemic acid, is optically inactive, but it cannot be resolved into the two optically active modifications; it is formed, together with racemic acid, when dextrotartaric acid is heated for a long time with a small quantity of water at about 165°, and when dibromosuccinic acid is heated with silver hydroxide. Hydroxytricarboxylic A c ids. Citric acid, C6H8O7, like tartaric acid, occurs in the free state in the juice of many fruits; it is found in com- paratively large quantities in lemons, in smaller quantities in currants, gooseberries, raspberries, and other sour fruit. It is prepared on the large scale from lemon-juice, which is first boiled, in order to coagulate and precipitate albuminoid matter, and then neutralised with calcium 246 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. carbonate; the calcium salt, which is precipitated from the hot solution, is washed with water, decomposed with the theoretical quantity of dilute sulphuric acid, and the filtrate from the calcium sulphate evaporated to crystallisation. Citric acid forms large transparent crystals which contain one molecule of water and melt at 100°, but do not lose their water until about 130°; it is readily soluble in water and fairly so in alcohol, but insoluble in ether. Like tartaric acid, and several other organic acids, it has the property of preventing the precipitation of certain metallic hydroxides from solutions of their salts. Solutions of ferric chloride and of zinc sulphate, for example, give no precipitate with potash or ammonia, if citric acid be present; on account of this property, citric acid and tartaric acid are employed in analytical chemistry and in calico-printing. Citric acid is a tricarboxylic acid, and like phosphoric acid forms three classes of salts, as, for example, the three potassium salts, C6H5O7Ky, C6H6O7K2, and C6H7O7K, all of which are readily soluble in water. Calcium + 4H2O, is not precipitated on adding a solution of a calcium salt to a neutral solution of a citrate, because it is readily soluble in cold water; on heating, however, a crystalline precipitate is produced, as the salt is less soluble in hot than in cold water. This behaviour, and the fact that the precipitate is insoluble in potash, distinguishes citric from tartaric acid. When heated alone, citric acid chars and gives irritating vapours, but no smell of burnt sugar is noticed ; it also differs from tartaric acid, inasmuch as it does not char when gently heated with concentrated sulphuric acid until after some time. Citric acid may be obtained synthetically by a series of reactions which show it to be a hydroxy tricarboxylic acid of the constitution CH2COOH C(OH)COOH. (^H2COOH Symmetrical dichloracetone, CHaCl-CO-CR2Cl, which may be THE GLYCOLS AMD THEIR OXIDATION PRODUCTS. 247 obtained by oxidising aa-dichlorohydrin (p. 252) with chromic acid, like other ketones, combines with hydrogen cyanide, forming /'OH the cyanohydrin, (CH2C1)2C\q^ ; this product, like other com- pounds containing the -CN group, is converted into a carboxylic ^OH acid,(CH2Cl)2C\QQQjp by boiling mineral acids. The two atoms of chlorine in this acid may now be displaced by -CN groups by treating the potassium salt of the acid with potassium cyanide, ch2ci ch2cn C(OH).COOK + 2KCN = C(OH)-COOK + 2KC1, ch2ci ch2-cn and this dicyano-derivative may then be converted into citric acid by boiling it with hydrochloric acid, CH,CN CHoCOOH I I C(OH)-COOH + 4H2O = C(OH)-COOH + 2NH3. CH2-CN ch2-cooh This view' of the constitution of citric acid is borne out by all the reactions of the compound; it is shown to contain one hydroxyl- group by the fact that ethyl citrate, C3H4(OH)(COOC2H3)3, yields a monacetyl-derivative with acetyl chloride. When heated alone at 175°, citric acid is converted into aconitic add, just as malic is converted into fumaric acid, CH2.COOH CHCOOH i(OH)-COOH = i.COOH + H2O; ino-cooH in2-cooH when carefully warmed with sulphuric acid, it yields acetone- dicarboxylic acid, with evolution of carbon monoxide, ch2-cooh ch2-cooh C(OH)-COOH = CO + CO + HqO, I I ch2-cooh ch2-cooh and on reduction with hydriodic acid, it is converted into CH2COOH I tricarballylic acid, CHCOOH. CH2COOH TRIHYDRIC AND POLYHYDRIO ALCOHOLS. 248 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. CHAPTER XIV. In the preceding chapter it has been shown that it is possible to convert a paraffin first into a monohydric alcohol, and then into a dihydric alcohol, or glycol, by the substitution of hydroxyl-groups for atoms of hydrogen; ethane, for example, may be converted into ethyl alcohol and ethylene glycol, propane into propyl alcohol and propylene glycol. In a similar manner those paraffins containing three or more carbon atoms may be converted into trihydric alcohols, com- pounds which stand in the same relation to the glycols as the latter to the monohydric alcohols, Propvl Alcohol. ch3-ch2-ch,-oh Propylene Alcohol. CH3.CH(OH).CH2-OH Propenyl Alcohol. CH2(OH)-CH(OH).CH2.OH. As, however, the preparation of such trihydric alcohols from the paraffins is a matter of very considerable difficulty, their study has necessarily been very limited except in the case of glycerol, which, from its occurrence in such large quantities in natural fats and oils, has offered exceptional opportunities for investigation. Glycerol, glycerin, propenyl alcohol, or trihydroxypropane, C3H5(OH)3, or CH2(OH)-CH(OH).CH2.OH, has been pre- viously referred to as one of the unimportant products of the alcoholic fermentation of sugar, and its preparation from fats and oils, which consist essentially of tripalmitin, tristearin, and triolein (ethereal salts of which glycerol is the base) has been described. The concentrated glycerol obtained on evaporating its aqueous solution (p. 167) may he further purified and freed from water by distillation under reduced pressure, the first TRIHYDRIC AND POLY HYDRIC ALCOHOLS. 249 fractions, which contain the water, being collected separ- ately. Glycerol may be obtained from propane, and therefore from its elements, by treating the hydrocarbon with bromine, and then heating the tribromopropane which is thus formed with water at 170°, CH2Br-CHBr-CH2Br + 3H.,0 = CH2(OH).CH(OH)-CH2.OH + 3HBr. Pure glycerol is a colourless, crystalline substance, melting at 17°; as ordinarily prepared, however, it is a thick syrup of sp. gr. 1-265 at 15°, and does not solidify readily owing to the presence of water and traces of other impurities. It boils at 290° under ordinary atmospheric pressure, without decom- position ; if however, it contain even traces of salts, it under- goes slight decomposition, so that in such cases it must first be distilled in a current of steam. Glycerol is very hygro- scopic, and rapidly absorbs water from the air, mixing with it and also with alcohol in all proportions; it is insoluble in ether, a property which is common to most substances which contain many hydroxyl-groups. It has a distinctly sweet taste; this property also seems to be connected with the presence of hydroxyl-groups, as is shown by the fact that other trihydric alcohols, and to an even greater extent the tetra-, penta-, and hexa-hydric alcohols, are sweet, sugar-like compounds. Glycerol readily undergoes decomposition into acrolein (p. 256) and water, C3H5(OH)8 - C3H4O + 2H2O; this change takes place to a slight extent when impure glycerol is distilled, but much more readily and completely when glycerol is heated with potassium hydrogen sulphate, sulphuric acid, phosphorus pentoxide, or other dehydrating agents. Glycerol, like glycol, yields a variety of oxidation products according to the conditions under which it is treated; when 250 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. carefully oxidised with dilute nitric acid, it is converted into glyceric acid, a change analogous to the formation of glycoIlic acid from glycol, CH2(OH).CH(OH)CH2.OH + 20 = CH2(0H).CH(0H).C00H + H20; under other conditions, however, it is usually oxidised to a mixture of oxalic, glycoIlic, and carbonic acids, CH2(OH)-CH(OH)-CH2-OH + 40 = CH2(0H)-C00H + C02 + 2H2O CH2(OH)-CH(OH)-CH2.OH + 60 = C00H-C00H + C02 + 3H2O. Glycerol is extensively used in the preparation of nitro- glycerin (p. 252) and toilet-soaps, also for filling gas-meters; it is used in smaller quantities in medicine and as an anti- putrescent in preserving food materials. Derivatives of Glycerol.-Assuming that glycerol is a trihydric alcohol of the constitution given above, its behaviour under various conditions may be foretold with a good prospect of success, if that of ethyl alcohol and of glycol be borne in mind. The fact, for example, that glycerol contains hydrogen displaceable by sodium, was only to be expected, and, just as in the case of glycol, only one atom of hydrogen is displaced at ordinary temperatures; the product, C3H5(OH).,-ONa, is hygroscopic, and is immediately decomposed by water. Again, the behaviour of glycerol with acids is analogous to that of alcohol and of glycol; when treated with acetic acid, for example, it yields the ethereal salt, triacetin, or glyceryl acetate, and water, C3H5(OH)3 + 3CH3-COOH = C3H5(O-CO.CH3)3 + 3H2O. It is obvious, however, that triacetin is not the only ethereal salt which may be produced by the interaction of glycerol and acetic acid, because, being a triacid base, glycerol may yield compounds, such as monacetin and diacetin, by the displace- ment of only one or of two atoms of hydrogen, TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 251 C3H5(OH)3 + CH3.COOH = C3H5(OH)2.O-CO.CH3 + h2o C3H5(OH)3 + 2CH3-COOH = C3H5(O-CO-CH3)2-OH + 2H2O. These three compounds may all be prepared by heating glycerol with acetic acid, the higher the temperature and the larger the relative quantity of acetic acid employed, the larger the proportion of triacetin produced. Acetic anhydride acts more readily than acetic acid, but gives the same three products. Chlorohydrins.-The action of concentrated hydrochloric acid on glycerol is similar to that of acetic acid; at moderately high temperatures, and employing only the theoretical quantity of the acid, one atom of chlorine is substituted for one hydroxyl-group, and glycerol chlorohydrin is formed, just as ethylene glycol is converted into glycol chlorohydrin, C3H5(OH)3 + HC1 = C3H5C1(OH)2 + H2O; with excess of hydrochloric acid, however, glycerol dichloro- hydrin is produced, C3H5(OH)3 + 2HC1 = C3H5C12-OH + 2H2O. Glyceryl trichloride, or propenyl trichloride, CH2C1-CHC1.CH2C1, cannot easily be obtained by heating glycerol with hydrochloric acid, but may be prepared by treating the dichlorohydrin with phosphorus pentachloride, C3H5C12-OH + PC15 = C3H5C13 + POC13 + HC1; it is a colourless liquid, boiling at 158°, and smells like chloroform. The name ' glyceryl,' or propenyl, is sometimes given to the group of atoms -CH2-CH-CH2-, which may be regarded as a trivalent radicle. Glycerol chlorohydrin and the dichlorohydrin exist in two isomeric forms, CH2(OH)-CH(OH)-CH2C1 a-Chlorohydrin. CH2(OH)-CHC1CH2OH /3-Chlorohydrin. CH2C1CH(OH)CH2C1 aa-Dichlorohydrin. CH2C1CHC1CH2OH. a/3-Dichlorohydrin. 252 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. Glycerol a-chlorohydrin is formed, together with small quantities of the /3-compound, when glycerol is heated at 100° with hydrochloric acid ; it is an oily liquid, soluble in water. Glycerol ^-chlorohydrin can be obtained by treating allyl alcohol (p. 254) with hypochlorous acid. Glycerol aa-dichlorohydrin is produced when glycerol is heated with a solution of hydrogen chloride in glacial acetic acid; it is a mobile liquid, only sparingly soluble in water, and on oxida- tion with chromic acid it yields symmetrical dichloracetone, CH2CICOCH2C1. Glycerol aft-dichlorohydrin is obtained on treating allyl alcohol (p. 254) with chlorine; on oxidation with nitric acid it gives a^-dichloropropionic acid, CH2C1-CHC1-COOH. When treated with potash, both aa- and a/3-chlorohydrin yield epichlorhydrin, CH2C1-CH-CH2 (compare ethylene oxide, p. 223). O When glycerol is treated with acetyl chloride, it does not yield triacetin, as might have been expected, but diacetylchlorohydrin, C8H5(OH)3 + 2CH(COC1 = C,H5C1(OCOCH3)2 + H2O + HC1. This behaviour, although apparently abnormal, is not really so ; in the first place, the glycerol is converted into a rfface^-derivative in the usual manner, C3H3(OH)3 + 2CH;t-COCl = C3H5(OCO-CH3)2OH + 2HC1, and the hydrogen chloride produced during the reaction then acts on the diacetyl-derivative just as it does on other monohydric alcohols, C3H5(OCOCH3)2OH + HC1 = C3H5(OCOCH3)2C1 + H2O. Ethylene glycol and other di- and poly-hydric alcohols show a similar behaviour. Nitro-glycerin, glyceryl trinitrate, or propenyl trinitrate, C3H5(O-NO2)3, is an ethereal salt of glycerol and nitric acid. It is prepared by slowly adding pure glycerol drop by drop, or in a fine stream, to a well-cooled mixture of concentrated sulphuric acid (4 parts) and nitric acid of sp. gr. 1'52 (1 part); the solution is run into cold water, and the nitro-glycerin, which is precipitated as a heavy oil, washed well with water and dried. It is a colourless oil of sp. gr. 1'6, has a sweetish taste, and is poisonous; although readily soluble in ether, it is only TRIHYDRIC AND POLYHYDRTC ALCOHOLS. 253 sparingly soluble in alcohol, and insoluble in water, so that, as regards solubility, its behaviour is almost the exact opposite of that of glycerol, a fact which shows the influence of hydroxyl- groups in a very distinct manner. It explodes violently when suddenly heated, or when subjected to percussion, but when ignited with a flame it burns without explosion, and is even rather difficult to ignite. Nitro-glycerin is readily hydrolysed by boiling alkalies, being converted into glycerol and a nitrate,* C3H5(O-NO2)3 + 3K0H = C3H5(OH)3 + 3KNO3; on reduction with ammonium sulphide (p. 94) it yields glycerol and ammonia, C3H5(O.NO,)3 + 12H2S = C3H5(OH)3 + 3NH„ + 6H2O + 12S. In these two reactions the behaviour of nitro-glycerin is exactly analogous to that of ethyl nitrate, CH3-CH2-O-NO2, but quite different from that of nitro-ethane, CH3-CH2-NO2, which, as previ- ously stated, is not decomposed by alkalies, ami on reduction yields amido-ethane or ethylamine; since, moreover, groups of atoms in a similar state of combination show a similar behaviour, it is clear that nitro-glycerol, like ethyl nitrate, is an ethereal salt, and not a nitro-derivative; in other words, the nitro groups (-NO2) in nitro glycerin are directly combined with oxygen, and not with carbon. The name nitro-glycerin is, therefore, misleading, but, being so well known, it is usually employed instead of the more correct names, glyceryl trinitrate, or propenyl trinitrate. Nitro-glycerin is extensively employed as an explosive, sometimes alone, sometimes in the form of dynamite, which is simply a mixture of nitro-glycerin and kieselguhr, a porous, earthy powder, consisting of the siliceous remains of small marine animals; the object of absorbing the nitro- glycerin with kieselguhr is to render it less liable to explode, and, consequently, safer to handle and to transport. The presence of acids in nitro-glycerin make it liable to undergo spontaneous decomposition and explosion ; great care must, therefore, be taken in washing it thoroughly. Nitro-glycerin * An alkali nitrite is also formed owing to reduction, the glycerol undergoing partial oxidation. 254 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. is also employed, mixed with gun-cotton (p. 274), as blasting- gelatine, and in the preparation of smokeless gunpowder; it is used in medicine in cases of heart disease. Unsaturated Compounds related to Glycerol. Allyl alcohol, CH^CH-CHj-OH, is formed when anhydrous glycerol is slowly heated with crystallised oxalic acid until the temperature rises to about 260°, and the mixture then distilled; in the first place, the glycerol is converted into monoformin, with evolution of carbon dioxide, water, and a little formic acid (p. 144), C3H5(OH)3 + C2HQO4 - C3H5(OH)9.O.CHO + co2 + H90 C3H5(OH)2-O-Ch6 + H2O = C3H5(OH)3 + HCOOH, but, on further heating, the rest of the monoformin undergoes decomposition, and allyl alcohol collects in the receiver, CH2(OH)CH(OH)CH9OCHO = CH2(OH)-CH:CH2 + CO2 + H2O. Allyl alcohol is also produced when acrolein (acraldehyde, p. 256) is treated with nascent hydrogen, a change which is exactly analogous to the formation of alcohol from aldehyde, CH2:CHCHO + 2H = CH2:CHCH2-OH. It is a colourless, neutral liquid, boils at 96-97°, and has a very irritating smell; it is miscible with water, alcohol, and ether in all proportions. Allyl alcohol is an unsaturated compound, and has, there- fore, not only the properties of a primary alcohol, but also those of unsaturated compounds in general. Its alcoholic character is shown by the following facts : it dissolves sodium with evolution of hydrogen, 2CH2:CH-CH2-OH + 2Na = 2CH2:CH-CH2.ONa + H2, forms ethereal salts with acids, CH2:CH-CH2-OH + HC1 = CH2:CH-CH2C1 + H2O, and on oxidation is converted, first into acrolein, then into acrylic acid, TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 255 CH.,:CH-CH.,-OH + 0 = CH2:CH-CHO + H2O CH2:CH-CH2-OH + 20 = CH2:CH-C00H + H20. In all these reactions its behaviour is so closely analogous to that of ethyl alcohol and other primary alcohols, that it must be concluded that allyl alcohol contains the group -CH9-0H. That it is an unsaturated compound is shown by its behaviour with chlorine and bromine, with which it combines directly, forming a dichloro- or dibromo- hydrin, isomeric with the corresponding compounds obtained by treating glycerol with halogen acids, CH2:CH-CH2-OH + Br2 = CH2Br-CHBr.CH2-OH. Allyl iodide, CH2:CH-CH2I, is an unsaturated ethereal salt, related to allyl alcohol in the same way as ethyl iodide to ethyl alcohol. It may be obtained by treating allyl alcohol with iodine and phosphorus, but is more conveniently pre- pared directly from glycerol. For this purpose iodine (10 parts) is dissolved in glycerol (15 parts), and small pieces of dry phosphorus (6 parts) added from time to time, the mixture being very gently warmed at first to start the reaction; the operation is conducted in a large retort connected with a condenser, a stream of carbon dioxide being passed through the apparatus during the experiment. It is probable that the glycerol is first converted into the tri-iodide, CH.J-CHLCHJ, which then undergoes decomposition into iodine and allyl iodide ; if excess of phosphorus and iodine be employed, isopropyl iodide is formed, CH2:CHCH2I + HI = CH2:CHCH3 + I2. CH2:CHCH3 + HI = ch3-chlch3. Allyl iodide is a colourless liquid, boiling at 101°, and has an odour of garlic; it resembles ethyl iodide in many respects, but has also the properties of an unsaturated com- pound. When heated with potassium sulphide in alcoholic solution, it is converted into allyl sulphide (see below), just as ethyl iodide gives ethyl sulphide, 2CH2:CH-CH2I + K2S = (CH2:CH-CH2)2S + 2KI. Allyl bromide, CH2:CH-CH2Br, may be obtained by treating 256 TRIHYDRTC AND POLYHYDRIC ALCOHOLS. allyl alcohol with phosphorus tribromide; it is a heavy liquid, and boils at 70-71°. Allyl sulphide occurs in nature in many Cruciferae, but is especially abundant in garlic {Allium sativum'), from which it is obtained by distilling the macerated plant with water ; it is therefore known as oil of garlic. It is a colourless, very unpleasant-smelling liquid, boiling at 140°. Another allyl derivative-namely, allyl isothiocyanate, occurs in nature in considerable quantities in black mustard seeds, and is known as oil of mustard (p. 289). Acrolein, or acraldehyde, CH2:CH-CHO, is formed during the partial combustion of fats, and when impure glycerol is distilled under ordinary pressure; also when allyl alcohol undergoes oxidation. It is prepared by distilling glycerol with some dehydrating agent, potassium hydrogen sulphate being usually employed, C3H5(OH)3 = C3H4O + 2H2O. Acrolein is an aldehyde, and is related to allyl alcohol in the same way as aldehyde to ethyl alcohol; it is a colourless liquid, boils at 52°, and has an exceedingly irritating and dis- agreeable odour, like that of partially burnt fat; it produces sores when brought on to the skin, and its vapours cause a copious How of tears. Like other aldehydes, it reduces ammoniacal solutions of silver oxide with formation of a mirror, and readily undergoes polymerisation into an amor- phous, brittle substance named disacryl; it also gives the aldehyde reaction with rosaniline, but, on the other hand, it does not combine with sodium hydrogen sulphite. On reduction it yields allyl alcohol; on exposure to the air, or on treatment with silver oxide, it readily undergoes oxidation, yielding acrylic acid. That it is an unsaturated compound is shown by the fact that it combines directly with bromine, forming an additive-product of the composition CH2BrCHBr-CHO. Crotonaldehyde, CH8-CH:CH-CHO is a homologue of acralde- TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 257 hyde; it is obtained on heating acetaldehyde with dilute hydro- chloric acid, or with a solution of zinc chloride, aldol being formed as an intermediate product (p. 124), 2CH3-CHO = CH3CH(OH)CH„.CHO CH3-CH(OH)CH2CHO = CH3.CH:CH-CHO + H2O. It boils at 104-105°, and closely resembles acraldehyde in properties ; on reduction it yields, first, crotonalcohol, CH3-CH:CH-CH2-OH, and then butyl alcohol, CH3-CH2-CH2-CH2-OH; on oxidation it gives crotonic acid, CH3-CH:CHCOOH. Acrylic acid, CH2:CHCOOH, the oxidation product of allyl alcohol and of acrolein, may also be obtained from hydra- crylic acid (p. 227), which on distillation loses the elements of water, CH2(OH)CH2.COOH = CH2:CHC00H + h2o, a change analogous to the formation of ethylene from alcohol; acrylic acid is also produced when /?-bromopropionic acid is treated with alcoholic potash, just as ethylene is formed from ethyl bromide, CH2Br-CH2-COOH = CH2:CHCOOH + HBr. Acrylic acid is a liquid at ordinary temperatures, and boils at 139-140°; it smells like acetic acid, is miscible with water in all proportions, and its solutions have an acid reaction. It is a monocarboxylic acid, and forms metallic and ethereal salts just as do the fatty acids; it differs from the latter, however, in being an unsaturated compound, as is shown by its forming additive-products. It combines directly with bromine, giving dibromopropionic acid, CH2:CH-COOH + Br2 = CH2Br-CHBr-COOH; with halogen acids, yielding /^-halogen derivatives* of propionic acid, CH2:CHCOOH + HC1 = CH2CLCH2-COOH, and with nascent hydrogen, giving propionic acid, CH2:CH-COOH + 2H = CH3.CH2-COOH. * This behaviour is abnormal, as usually the halogen combines with that carbon atom which is combined with the least number of hydrogen atoms (p. 80). 258 TRI HYDRIC AND POLYHYDRIC ALCOHOLS. Crotonic acid, CH3-CH:CH-COOH, the next homologue of acrylic acid, may be obtained by methods similar to those mentioned in the case of acrylic acid-namely, by the oxidation of crotonalcohol or of crotonaldehyde, by the distillation of /3-hydroxybutyric acid, CH3-CH(OH)-CH2-COOH, and by treating a-bromobutyric acid with alcoholic potash. It melts at 72®, and resembles acrylic acid in general behaviour. Oleic acid, C1SII34O2, one of the higher members of the acrylic series, has been previously mentioned (p. 168). Polyhydric Alcohols. The existence of tetra-, penta-, and hexa-hydric alcohols, which theoretically should be obtained from the higher paraffins by the substitution of four, five, or six hydroxyl- groups for an equivalent quantity of hydrogen, just as glycerol is derived from propane, was of course to be expected; never- theless, owing to the difficulties which would be met with in the actual synthesis of such complex compounds from the paraffins, or by other methods, it is highly probable that they might still have been unknown, were it not that many of them occur in nature, and may also be prepared from products of the vegetable kingdom by simple processes. Erythritol, CH2(OH)-CH(OH).CH(OH)CH2-OH, for ex- ample, is a tetrahydric alcohol which occurs in many lichens, and in certain seaweeds. Arabitol and xylitol are penta- hydric alcohols of the constitution CH2(OH)-CH(OH)-CH(OH)-CH(OH)-CH2-OH; they may be respectively prepared by reducing arabinose and xylose, two sugar-like compounds which occur in various vegetable products, with sodium amalgam. Hexahydric alcohols, such as mannitol and dulcitol, also occur in nature. Mannitol, CH2(OH)CH(OH)CH(OH)CH(OH).CH(OH)CH2.OH, is found in manna, the dried sap of a species of ash, from which it may be extracted with boiling alcohol; it may also be obtained by reducing levulose, mannose, or dextrose (p. 264) with sodium amalgam. It is a colourless, crystalline sub- TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 259 stance, has a very sweet taste, and is readily soluble in water and hot alcohol, but insoluble in ether. When carefully oxidised with nitric acid it yields the aldehyde, mannose, and the ketone, levulose (p. 265); on reduction with hydriodic acid it is converted into (secondary) hexyl iodide, a derivative of normal hexane, CH2(OH)-CH(OH)CH(OH)-CH(OH).CH(OH).CH2.OH + 11HI = CH3CH2CH2CH2.CHLCH3 + 6H2O + 5I2. This conversion of mannitol into a derivative of normal hexane is a fact of great importance, as it throws much light on the constitu- tion, not only of mannitol, but also of mannose, levulose, and dextrose ; since these compounds yield mannitol on reduction, it is proved that they also are derivatives of normal hexane, and not of some secondary or tertiary paraffin, isomeric with hexane. The constitution of mannitol is further established by the usual methods; that it contains six hydroxyl-groups is shown by the fact that it yields a hexacetyl-derivative, C6H8(O-CO-CH3)6, and a hexa-: nitrate, CGH8(O-NO2)6. As, moreover, it is known from experience that in all stable hydroxy-compounds one carbon atom does not unite with more than one hydroxyl-group, each of the six hydroxyl- groups in mannitol must be combined with a different carbon atom. Mannitol, like tartaric acid, exists in several modifications, which differ principally in their optical properties. CHAPTER XV. THE CARBOHYDRATES. The compounds usually known as the carbohydrates do not form a well-defined group, inasmuch as the term is applied to substances widely different both in properties and in con- stitution ; they may, however, be roughly described as naturally occurring substances, composed of carbon, hydrogen, and oxygen, in which the ratio of hydrogen to oxygen is the 260 THE CARBOHYDRATES. same as in water. The word carbohydrate was originally given to such compounds because they might be represented as com- posed of carbon and water in different proportions: grape- sugar, C6II12O6, for example, might be represented as GC + 6H2O; cane-sugar, C12H22OU, as 12C + 11H2O; and starch, C6H10O5, as 6C + 5H2O. The carbohydrate group is one of the most important in organic chemistry, as it includes all the principal constituents of plants, except water. To this group belong (a) the sugars, substances which are of great value as food-stuffs and as sources of alcohol, and to which the sweetness of fruits is due; (b) the starches, the most abundant of all foods; and (c) the celluloses, substances of which the cell membranes anil tissues of plants are principally composed. The Sugars. Cane-sugar, or saccharose, C12H22O11, is very widely dis- tributed in nature ; it occurs in large quantities in the sugar- cane (15-20 per cent.) and in beetroot (some kinds of which contain as much as 16 per cent.), in smaller quantities in strawberries, pine-apples, and other fruits. The sugar-cane and beetroot are the raw materials from which practically the whole of the sugar of commerce is manufactured, the processes of extraction being much the same in both cases, and requiring expensive apparatus in order to obtain the largest possible yield of crystallised sugar. The material is crushed in hydraulic presses, and the expressed juice boiled with about 1 per cent, of milk of lime, in order to neutralise acids present, and to coagulate the vegetable albumin which is always contained in the extract. The solution is treated with carbon dioxide, in order to precipitate any excess of lime, decolourised as far as possible by boiling with animal charcoal, and filtered ; it is then evaporated under reduced pressure in an appara- tus heated with steam, until the syrup is of such a consistency that it deposits crystals on cooling. These crystals are separated from the brown mother-liquor (molasses, or treacle) in a centrifugal machine, and purified by recrystallisation from water. THE CARBOHYDRATES. 261 The molasses still contains about 50 per cent, of sugar which does not crystallise from the syrup even on further evaporation, owing to the presence of impurities; nearly the whole of this sugar, however, can be profitably extracted, by adding strontium hydroxide, and separating the insoluble strontium saccharosate (see below) from the dark mother-liquor by filtration. This pre- cipitate is suspended in water, decomposed by passing carbon dioxide, and the filtrate from the strontium carbonate evaporated to a syrup ; the impurities having now been removed, the cane- sugar separates in the crystalline form. The annual production of cane-sugar is about 5-6 million tons. Cane-sugar crystallises from water in hard four-sided prisms, and is soluble in one-third of its weight of water at ordinary temperatures, but only sparingly soluble in alcohol. It melts at about 160-161°, and on cooling does not immediately crystallise, but solidifies to a pale-yellow, glassy mass, called barley-sugar, which, however, on long standing, gradually becomes opaque and crystalline. At about 200-210° cane- sugar loses water, and is gradually converted into a brown mass called caramel, which is largely used for colouring liqueurs, soups, gravies, &c. Warm concentrated sulphuric acid chars cane-sugar; if a strong aqueous solution of sugar be mixed with an equal volume of concentrated sulphuric acid, the sugar blackens and the carbonaceous product swells up enormously, owing to the evolution of steam, carbon dioxide, sulphur dioxide, and ■other gases. Cane-sugar is dextrorotatory-that is, its solutions have the property of rotating the plane of polarisation of light to the right,* and the strength of a solution of sugar may be esti- mated by determining the amount of rotation which it causes. The apparatus used for this purpose is called a saccharimeter, and the operation itself, saccharimetry. If a trace of a mineral acid be added to a solution of cane- sugar, and the liquid warmed or simply allowed to stand, the * [a]D= + 66-5°. For a description of the action of sugar solutions on polarised light, works on physics must be consulted. 262 THE CARBOHYDRATES. cane-sugar is hydrolysed, with formation of equal quantities of dextrose (see below) and levulose (p. 265), C12H22OU + II2O = ^6^12^6 Dextrose. + C6H12O6. Levulose. This process is usually called inversion, and the mixture of dextrose and levulose is called invert sugar. Invert sugar comes into the market as a somewhat brownish-coloured mass, and is extensively used in the manufacture of preserves, con- fectionery, &c., as well as for the preparation of alcohol. Prolonged boiling with hydrochloric acid (sp. gr. 1-1) con- verts cane-sugar into levulinic acid (p. 196). Cane-sugar does not reduce Fehling's solution (p. 263), and it does not directly undergo alcoholic fermentation with yeast; when, however, it is left for some time in contact with yeast, a ferment, invertase, which is present in the yeast converts it into dextrose and levulose, and then alcoholic fermentation sets in. When boiled with acetic anhydride and sodium acetate, cane-sugar is converted into octacetylsaccharose, (-'12^14^3(^2^3^2)3' and therefore contains eight hydroxyl- groups ; its constitution, however, has not yet been clearly established. Cane-sugar combines readily with certain hydroxides, such as those of calcium, barium, and strontium, with formation of metallic compounds called saccharosates, in which one or more of the hydroxyl-groups in the sugar is displaced by the metal or hydroxide. These saccharosates are produced by simply mixing the sugar solution with the metallic hydroxide. They are readily decomposed by much water and by carbon dioxide into sugar and the hydroxide or carbonate of the metal. Strontium saccharosate, C12H2o(SrOH)2Ou, is agranular substance of great commercial importance, owing to its use in separating sugar from molasses (p. 261). Dextrose, C6H12O6, or CH2(OH).[CH-OH]*.CHO, also known as glucose, or grape-sugar, is found in large quantities in grapes-hence its name, grape-sugar ; when the grapes are dried in the sun, in the preparation of raisins, the dextrose * Compare foot-note, p. 134. THE CARBOHYDRATES. 263 in the juice is deposited in hard, brownish-coloured nodules. Dextrose is more frequently met with associated with levu- lose as invert sugar, mixtures of these sugars occurring in the juice of a great many sweet fruits, and also in the roots and leaves of plants, and in honey. Pure dextrose may be prepared from cane-sugar by inversion with acids, and recrystallisation of the product (invert sugar) from alcohol, when the more readily soluble levulose remains in solution. Alcohol (1 litre, 90 per cent.) is mixed with concentrated hydro- chloric acid (40 c.c.), heated at about 50°, and powdered cane-sugar (350 grams) added in small portions, the whole being well stirred during the operation. The mixture is now kept for two hours at this temperature, then allowed to cool, and crystallisation promoted by stirring, or, better, by the addition of a crystal of dextrose. After some days the crystals are collected and purified by recrystallisa- tion from 80 per cent, alcohol. Dextrose crystallises with 1 mol., HoO, in warty masses which melt at 86°, the anhydrous substance melting at 146°; it is almost insoluble in absolute alcohol, but soluble in about its own weight of water at ordinary temperatures, the solution being less sweet than that of cane-sugar. It is not carbonised when gently warmed with sulphuric acid (distinction from cane-sugar); its solutions are dextrorotatory,* hence the name dextrose. Dextrose is a strong reducing agent, and quickly pre- cipitates gold, silver, and platinum from solutions of their salts on warming. If a solution of dextrose be mixed with potash, and then copper sulphate added, a deep blue solution is obtained, and on gently warming, a bright red precipitate of cuprous oxide, Cu2O, is deposited, the solution becoming colourless if sufficient dextrose be added; as, moreover, a given quantity (1 molecule) of dextrose always reduces exactly the same quantity (approximately 5 molecules) of cupric to cuprous oxide, this behaviour affords a method of estimating sugar by simple titration. The solution used for this purpose is known as Fehling's solution, and as it decomposes on keeping, it is best prepared as required by * [a]D = + 52-5°. 264 THE CARBOHYDRATES. mixing equal quantities of the following solutions : (1) 34-6 grams of crystallised copper sulphate, made up to 500 c.c. with water; (2) 173 grams of Rochelle salt, and 60 grams of sodium hydrate, made up to 500 c.c. with water. 10 c.c. of the deep blue solution thus obtained are completely reduced-that is, the colour discharged -by 0-05 gram of dextrose, or by 0-0475 gram of cane-sugar (after inversion). Dextrose ferments readily with yeast in dilute aqueous solution at a temperature of about 20-30°, yielding principally alcohol and carbon dioxide, C6H12O6 = 2C2H6O + 2CO2, but at the same time fusel-oil and small quantities of glycerol, succinic acid, and other substances are formed. Like cane-sugar, dextrose readily combines with certain metallic hydroxides, forming glucosates, such as calcium glucosate, C6H11(CaOH)O6, and barium glucosate, C6Hu(BaOH)O6 ; these compounds are readily soluble in water, and are decomposed by carbonic acid, with regeneration of the sugar. Dextrose has the properties of an aldehyde, and at the same time those of a polyhydric alcohol; its constitution may be expressed by the formula CH2(0H).CH(0H).CH(0H)CH(0H).CH(0H)-CH0, which is based on a number of facts, only a few of which can be given here. On reduction with sodium amalgam in aqueous solution, it is converted into the primary alcohol, mannitol, CH2(OH).[CHOH]4.CHO + 2H = CH2(OH) [CH OH]4-CH2 O1I; whereas, when oxidised with bromine water, it yields gluconic acid, CH2(OH)-[CH.OH]4-COOH. These changes are clearly analogous to those undergone by acetaldehyde, and the fact that gluconic acid contains the same number of carbon atoms as dextrose, shows that the latter is an aldehyde and not a ketone (p. 139). Powerful oxidising agents, such as nitric acid, convert dextrose into saccharic acid, THE CARBOHYDRATES. 265 COOH.[CH.OH]4-COOH, the -CHyOH group, as well as the -CHO group, undergoing oxidation; ultimately it is resolved into oxalic acid. Dextrose, like other aldehydes, interacts readily with hydroxylamine and with phenylhydrazine, with formation of the oxime, CH2(OH)-[CH-OH]4-CH:NOH, and the hydrazone (p. 133), CH2(OH). [CH • OH]4-CH :N2H • C6H5. Dextrose gives a pentacetyl derivative, C5H6(C2H3O2)5-CHO, when warmed with acetic anhydride and a little zinc chloride, showing that it contains five hydroxyl-groups. Levulose, C6H12O6, or CH2(OH)<CH-OH]3.CO-CH2-OH, also called fructose, or fruit-sugar, occurs, together with dextrose, in most sweet fruits and in honey; it may be prepared from invert sugar by taking advantage of the fact that its lime compound is sparingly soluble in water, whereas that of dextrose is readily soluble. Invert sugar (10 grams) is dissolved in water (50 c.c.), the solution well cooled with ice, and slaked lime (6 grams) added in small quantities at a time, with constant stirring. The sparingly soluble lime compound of levulose is collected on a filter, washed with a little water, well pressed, and then decomposed by suspending it in water, and passing carbon dioxide ; the filtrate yields, on evapora- tion, nearly pure fructose as a transparent, uncrystallisable syrup. Pure crystallised levulose is prepared from inulin, (C6H10O5),M a starch which occurs in many plants, and especially in dahlia tubers; for this purpose the inulin is simply boiled with dilute sulphuric acid, (C6H10O5)n + wH20 = ??C6H12O6. An aqueous solution of inulin is heated on a water-bath for one hour, with a few drops of sulphuric acid ; the sulphuric acid is then removed by precipitation with barium hydroxide, and the solution evaporated at 80°. On the addition of a crystal of levulose the syrup slowly solidifies, and the crystals may then be purified by recrystallisation from alcohol. Levulose separates from alcohol in small hard crystals, and melts at 95°; it is more soluble in 'water and alcohol than dextrose, and its taste is just about as sweet as that of the 266 THE CARBOHYDRATES. latter. Levulose is levorotatory*-hence its name ; it rotates the plane of polarisation to the left to a somewhat greater extent than dextrose to the right-hence invert sugar, which consists of equal parts of dextrose and levulose, is slightly levorotatory. When, therefore, a solution of cane-sugar, which is dextrorotatory, is boiled with acids, the resulting solution of invert sugar is levorotatory-that is to say, the direction of the rotation has been reversed or 'inverted.' Levulose ferments with yeast, but less rapidly than dextrose, consequently, in fermenting a solution of invert sugar, the dextrose is decomposed first, and the operation can be stopped at a point when the solution contains only levulose ; by the further action of yeast, however, the levulose also undergoes fermentation, yielding the same products as dextrose (p. 264). Levulose has even stronger reducing powers than dextrose, and reduces Fehling's solution more rapidly, although to exactly the same extent as dextrose ; this behaviour is due to the presence of the group -CO-CI I2-OH, as all substances (ketonic alcohols) which contain this group are strong reducing agents. Levulose has the properties of a ketone, as well as those of a polyhydric alcohol, and its constitution may be expressed by the formula CH2(OH)-CH(OH).CH(OH).CH(OH).CO-CH2-OH. It is reduced by sodium amalgam in aqueous solution more readily than dextrose, mannitol being formed, CH2(OH).[CH.OH]3-CO.CH2.OH + 2H = CH2(OH).[CH-OH]3-CH(OH).CH2-OH, just as acetone, under similar treatment, yields isopropyl alcohol. When oxidised with nitric acid or bromine water, it yields tartaric acid and glycoIlic acid, CH2(OH)-CH(OH)-CH(OH)-CH(OH)- co-ch2oh + 40 = C00H-CH(0H)-CH(0H)-C00H + C00H.CH20H + H20; * [a]D = -93°. THE CARBOHYDRATES. 267 whereas, when boiled with mercuric oxide in aqueous solution, it is oxidised to trihydroxybutyric acid and glycoIlic acid, CII2(OH).CH(OH).CH(OH).CH(OH).^ + 20 = CH2(0H).CH(0H)-CH(0H).C00H + cooh.ch2oh. This behaviour shows that levrdose is a ketone, and not an aldehyde; it does not, like dextrose, yield, on oxidation, an acid containing the same number of carbon atoms, but is decomposed in a variety of ways which throw considerable light on its constitution. Levulose, like other ketones, interacts with hydroxylamine (yielding the oxime, CH2(OH)-[CH.OH]3.C(NOH).CH2-OH), and with phenylhydrazine ; it also combines directly with hydrocyanic acid. When digested with acetic anhydride and zinc chloride, levulose yields a pentacetyl derivative, CcH7O(C2H3O2)5, a fact which shows that it contains five hydroxyl-groups. Dextrose and levulose have recently been prepared syn- thetically from formaldehyde and also from glycerol. When an aqueous solution of formaldehyde is treated with milk of lime at ordinary temperatures, a sugar-like substance called formose (or methylenitan) is produced. Formose consists of a mixture of various sugars of the composition C6H12O6, pro- duced by the polymerisation of formaldehyde, 6CH2O = C6H12O6. From this mixture E. Fischer isolated a sugar which he called a-acrose, and from which, by a series of operations, too numerous to discuss here, he succeeded in preparing both dextrose and levulose. Action of Phenylhydrazine on Dextrose (Glucose) and Levulose (Fructose). When the sugars glucose and fructose are treated with phenyl- hydrazine (1 mol.), they yield hydrazones, just as do other aldehydes and ketones, 268 THE CARBOHYDRATES. *MCH(OH)CHO + CA-NHNHo = Glucose. MCH(OH).CH:N2HCtiH5 + h2o. Glucosephenylhydrazone. mcoch2oh + c8h3nhnh. Fructose. = MC(N2HC8H5).CH.,.OH + h2o. Fructosephenylhydrazone. These hydrazones, when heated with excess of phenylhydrazine, undergo oxidation, the -CH-OH group of the one and the -CH2-OH group of the other being transformed into -CO and -CHO respectively by loss of hydrogen, some of the phenyl- hydrazine being reduced to aniline (part ii.) and ammonia, C«H5NHNH2 + 2H = C6H5NH2 + NH3. These oxidation products of the hydrazones then combine with a second molecule of phenylhydrazine, with formation of osazones, M.CH(OH)-CH:N2HC6H5 MC(N2HC8H5)CH2OH Hydrazones. MCOCH:NoHC6H5 MC(N2HC8H3).CHO Intermediate Oxidation Products. MC(N2HC6H5).CH:N2HC6H5. Osazone. Although the hydrazones of glucose and fructose are quite distinct substances, they yield one and the same osazone; this fact proves that the two sugars differ in constitution only as regards the two terminal groups. Many other sugars show a similar behaviour, and yield hydra- zones and osazones according as 1 mol. or excess of phenylhydrazine is employed. The hydrazones are usually readily soluble in water, but the osazones are only sparingly soluble ; the latter are there- fore of the greatest service, not only in the detection and identifica- tion of a sugar, but also as offering a means of isolating it from a mixture. When treated with strong hydrochloric acid, the osazones are decomposed with separation of phenylhydrazine hydrochloride, and formation of osones, substances which contain the group -CO-CHO, and which are therefore both ketones and aldehydes, MC(N2HC6H5)CH:N2HC8H5 + 2HC1 + 2H2O = Glucosazone. MCOCHO + 2C8H5NHNH2, HC1. Glucosone. As, moreover, osones may be reduced to sugars with the aid of zinc dust and acetic acid, the sugars may be prepared indirectly * The group CH2(OH)-CH(OH)CH(OH)-CH(OH)-, which takes no part in the reaction, is represented by M, for the sake of clearness. THE CARBOHYDRATES. 269 from the osazones. A given osazone does not, however, necessarily yield the sugar from which it was derived; glucosazone, for example, yields first glucosone and then fructose (the group -CO-CHO in the osone being converted into -CO-CH2-OH), MCOCHO + 2H = MCOCH2OH. Glucosone. Fructose. This series of reactions affords, therefore, a means of converting glucose into fructose. Maltose, C12H22On, is produced, together with dextrin (p. 272), by the action of malt on starch ; this change may be roughly represented by the equation 3(C6H10O5)w + nH2O = wC12H22Ou + ftC6H10O5, and, as already stated in describing the manufacture of alcohol and spirituous liquors, it is brought about by an unorganised ferment, diastase, which is contained in the malt. Preparation of Maltose.-Potato starch (1 kilo) is heated with water (4 litres) on a water-bath until it forms a paste, and after- cooling to 60°, malt (60 grams) is added, the mixture being kept at this temperature for an hour. The solution is then heated to boil- ing, filtered, and evaporated to a syrup, which crystallises on the addition of a crystal of maltose ; the crude substance is purified by washing with alcohol, and then recrystallising from this solvent. Maltose crystallises with one molecule of water in needles, and is very soluble in water, the solution being strongly dextrorotatory ;* it reduces Fehling's solution, but only about two-thirds as much as the same weight of dextrose, and ferments readily with yeast. When boiled with dilute sulphuric acid, it is completely converted into glucose, C12H22On + H2O = 2C6H12O6, a change which indicates that maltose is an anhydride of the latter. Maltose combines with phenylhydrazine, yielding phenylmalt- osazone, C12H2l,O9(N2HC6H5)2, and gives with acetic anhydride oct- acetylmaltose, CI2H14(C2H3O2)8O;). Milk-sugar, or lactose, C12H22On, has so far only been * [«]D = + 140-6°. 270 THE CARBOHYDRATES. found in the animal kingdom. It occurs in the milk of all mammals to the extent of about 4 per cent., and is obtained as a bye-product in the manufacture of cheese. When milk is treated with rennet, the casein separates, and milk-sugar remains in solution; on evaporation, the crude sugar is deposited in crystals, which are readily purified by recrystallisation from water. Milk-sugar forms large, hard, colourless crystals, which •contain one molecule of water of crystallisation. It dissolves in six parts of water at ordinary temperatures, and is very much less sweet than cane-sugar'; it is dextrorotatory.* It reduces Fehling's solution on boiling, but much more slowly than dextrose. Like cane-sugar, it does not ferment with pure yeast, but ordinary yeast decomposes it into alcohol and lactic acid. When oxidised with nitric acid, it yields a mixture of saccharic and mucic acids, both of which have the constitution COOH-[CH-OH]4-COOH, and which differ from one another, like the tartaric acids, in their action on polarised light (part ii.). Milk-sugar is decomposed, by boiling with dilute sul- phuric acid, into dextrose and galactose, C12H220jj + H2O = ^6^12^6 Dextrose. + C6H12O6. Galactose. Galactose, C6H12Ofi, or CH2(OH)[CHOH]4-CHO, is formed by the hydrolysis of milk-sugar (see above), together with dextrose, from which it may be separated by crystallisation from water. It is also formed by boiling gum-arabic and other gums with dilute sulphuric acid. It is less soluble than dextrose, and crystallises from water in prisms, which melt at 168°. Its solutions are strongly dextro- rotatory, + and ferment readily with yeast. When oxidised with nitric acid, it yields mucic acid, COOH[CH-OH]4-COOII. It com- bines with phenylhydrazine, yielding galactosazone, CH2(OH)-[CH OH]3.C(N2HC6H5) CH: N2HC6H3; and on reduction with sodium amalgam it is converted into the corresponding alcohol, dulcitol, CH2(OH)[CHOH]4-CH2OH, which is isomeric with mannitol, as explained later (part ii.). * [a]D = + 52-53°. + [«]D = + 80-3°. THE CARBOHYDRATES. 271 Starch, or amyluni, (C6H10O5)?l, is widely disseminated throughout the vegetable world, and is found in almost all the organs of plants in the form of nodules. It occurs in large quantities in all kinds of grain, as, for example, rice, barley, and wheat, and also in tubers, such as potatoes and arrowroot. In Europe, starch is manufactured principally from potatoes, but sometimes also from wheat, maize, and rice. The potatoes are well washed, crushed, and macerated with water in fine sieves, when the starch passes through with the water, leaving a pulp, consisting of gluten, cellulose, and other substances. The milky liquid, on standing, deposits the starch as a paste, which is repeatedly washed by decantation, and then slowly dried. The grain is first softened by soaking in warm water, then ground in a mill, and the product run into a large vat, where it is allowed to undergo lactic fermentation. During this process the sugar in the grain is converted into lactic, butyric, and acetic acids, and the gluten (see below) is brought into a less tenacious condition, which favours the subsequent washing of the starch, an opera- tion which is carried out in the manner described above, the crude starch being washed by decantation, and dried. Starch is a white powder, which, when examined under the microscope, is seen to be made up of peculiarly striated granules, having a definite shape and structure. These granules vary very much in appearance and in size, those •composing potato starch being comparatively large, those of wheaten starch considerably smaller. Starch is insoluble in cold water, but when heated with water, the granules swell up and then burst. The contents of the cells, or the granulose, dissolve, but the cell-wall, or starch ■cellulose, is insoluble, and remains in suspension. The homogeneous, gelatinous mass obtained in this way is called starch paste, and is largely used for stiffening linen and calico goods, and also as a substitute for gum. It is best prepared by rubbing starch into a thin paste with cold water, and then adding a considerable quantity of boiling water. Characteristic of starch is the brilliant blue colour which is 272 THE CARBOHYDRATES. produced when a solution of iodine is added to starch paste, or to its solution in water; this colour disappears on heating, but reappears on cooling. When boiled with dilute acids, starch is first converted into dextrin (C6H10O5)'1, and then into dextrose, (C6H10O5)„ + nH2O = »C6HI2O6. Malt extract, containing the ferment, diastase, decomposes starch at 60-70°, with formation of dextrin and maltose, 3C6H10O5 + H2O = C6H10O5 + C12H22On, a process which, as already mentioned (p. 98), is of the utmost importance in the manufacture of alcohol and spirituous liquors from grain. The empirical formula of starch is C6H10O5 ; the actual molecular formula has not as yet been determined, but it is undoubtedly many times that represented by the empirical formula, and, therefore, the composition of starch is usually expressed as (C6H10O5)h. Gluten.-Wheaten flour contains about 70 per cent, of starch and 10 per cent, of a sticky, nitrogenous substance called gluten. An approximate separation of these two constituents may be brought about by kneading flour in a thin calico bag under water, when the starch passes through with the water, forming a milky liquid, from which it is deposited on standing. The gluten remains in the bag as a tenacious, sticky, gray mass, which soon decomposes and smells disagreeably. Both starch and gluten are very valuable food-stuff's. Dextrin, (C6H10O5)n, is the name given to the substance, or mixture of substances, obtained as an intermediate product in the conversion of starch into dextrose (see above). It is produced on heating starch to about 210°, or on treating it with dilute acids or infusion of malt. Dextrin is a colourless, amorphous substance, soluble in water, and is largely used as a cheap substitute for gum ; when boiled with dilute acids, it is converted into dextrose. It is probably a mixture of various isomeric substances of the empirical formula C6H10O5. THE CARBOHYDRATES. 273 Cellulose, (C6H10O5)jl, like starch, occurs very widely, distrib- uted throughout the vegetable kingdom. It is the principal constituent of cell membrane and of wood, and constitutes indeed the framework of all vegetable tissues. Linen, cotton-wool, hemp, and flax, which have been freed from inorganic matter by repeated extraction with acids, consist of almost pure cellulose; an even purer form may be obtained by extracting Swedish filter-paper with hydrofluoric acid, in order to remove traces of silica, washing well with water, and drying at 100°. Cellulose is insoluble in all the ordinary solvents, but it dissolves in an ammoniacal solution of cupric oxide (Schweitzer's reagent). It is reprecipitated from this solution on the addition of acids, in the form of a jelly, which, when washed with water and dried, is obtained in the form of a grayish powder. Concentrated sulphuric acid gradually dissolves cellulose, and if the solution be diluted with water and boiled, dextrin and ultimately dextrose are produced. It is thus possible to convert wood into sugar, and indirectly into alcohol. If unsized paper be subjected to the action of sulphuric acid for a few seconds, then washed with water and dilute ammonia, and again with water, it is converted into a tough substance called parchment paper on account of its resem- blance to parchment. Such paper serves as a convenient substitute for animal membrane, and is used for a variety of purposes. Cellulose gives on analysis results agreeing with the formula C6H10O5, but its molecular weight is certainly very much greater than that expressed by this formula, and probably very much higher than that of starch. Its formula is, therefore, generally written (C6H10O5)n, or, more frequently, (C12H20O10)h. It contains ten hydroxyl-groups, because when heated with acetic anhydride and a trace of zinc chloride, it yields cellulose decacetate, C12H10(C2H3O2)10, a white flocculent mass, which is reconverted into cellulose by alkalies. 274 THE CARBOHYDRATES. Gun-cotton and Collodion.-When cotton-wool is treated with nitric acid, or, better, with a mixture of nitric and sul- phuric acids, nitrates of cellulose of variable composition are produced, according to the amount and concentration of the acids employed, and the length of time during which they are allowed to act. If cotton-wool be soaked in ten parts of a mixture of one part of nitric acid (sp. gr. 1 '5) and three parts of concentrated sulphuric acid for twenty-four hours, the resulting mass, after thoroughly washing and drying, constitutes gun-cotton. This substance has, approximately, the composition C12H14(NO3)6O4, and is, therefore, cellulose hexa-nitrate. It is insoluble in a mixture of alcohol and ether. When treated with nitric and sulphuric acids for a short time only, cellulose is converted principally into tetra-nitrate, C12H16(NO3)4O6, and penta-nitrate, C12H15(NO3)5O5, both of which dissolve in a mixture of alcohol and ether; a solution of 14 grams of the mixed nitrates in 450 c.c. of alcohol and 550 c.c. of ether constitutes collodion, which is largely used for photographic and other purposes. The nitrates of cellulose are decomposed by alkalies, yielding nitrates of the alkalies and cellulose; they are, therefore, true ethereal salts. SUMMARY AND EXTENSION. The carbohydrates are usually subdivided into the following groups : The saccharoses or nionoses. The disaccharoses or bioses. The polysaccharoses or polyoses. The saccharoses, as, for example, dextrose, levulose, and galactose, have the composition C6H12O6. They all resemble dextrose more or less closely in ordinary physical properties, reduce Fehling's solution, and usually undergo alcoholic fermentation with yeast; they are not resolved into simpler substances on treatment with dilute acids. The disaccharoses, such as cane-sugar, milk-sugar, and maltose, have the composition CjoH^On. From their behaviour under various THE CARBOHYDRATES. 275 conditions, more especially with dilute mineral acids, they must be regarded as composed of 2 mols. of identical or of different sac- charoses, less 1 mol. of water-that is to say, they are anhydride or ether-like derivatives of the saccharoses. Cane-sugar, for example, is an anhydride or ether-like substance formed from 1 mol. of dextrose and 1 mol. of levulose, whereas milk-sugar is derived from dextrose and galactose in a similar manner. With the exception of maltose, the disaccharoses are not, as a rule, directly fermentable with yeast (compare cane-sugar), nor do they immedi- ately reduce Fehling's solution, as in both cases they must first be converted into saccharoses by hydrolysis. The polysaccharoses, such as starch and cellulose, have the com- position (C6H10O5)w, and are much more complex than the disacchar- oses, as is shown by their behaviour on hydrolysis ; starch, for example, yields, under certain conditions, not only maltose, C12H22O1], but also dextrin, a compound which has itself a very high molecular weight, so that the molecule of starch must be highly complex. The high molecular weight of the polysaccharoses, com- pared with the saccharoses and disaccharoses, is also indicated by their general physical properties, as, for example, their insolubility and their non-crystalline character. The polysaccharoses do not ferment with yeast, and do not reduce Fehling's solution. The constitutions of the members of the carbohydrate group have been ascertained only in the case of some of the saccharoses, and even here the facts are sometimes not quite conclusive. That the saccharoses are either aldehydes (aldoses) or ketones (ketoses), is shown by their behaviour on oxidation and reduction, and also by the fact that they interact with phenylhydrazine, hydroxylamine, &c. ; that they contain hydroxyl-groups is proved by their conversion into acetyl-derivatives (and in the case of the poly saccharose, cellulose, by its conversion into various nitrates). The constitutions of the saccharoses are further determined by a method which was worked out by Kiliani, and which is based on the following reactions : The saccharoses, like the simpler aldehydes and ketones, combine directly with hydrocyanic acid, forming cyanohydrins (p. 139), MCHO + HCN = MCH(OH)-CN MCOCH2OH + HCN = M-C(OH)(CN)-CH2-OH, and these products are converted into polyhydric acids on hydro- lysis with a mineral acid, MCH(OH)CN + 2HoO = M-CH(OH)COOH + NH3 M-C(OH)(CN).CH2-OH + 2H2O = M-C(OH)(COOH)-CH2.OH + NH3. 276 THE CARBOHYDRATES. When these polyhydric acids are heated at a high temperature with a large excess of hydriodic acid and a little amorphous phosphorus, all the hydroxyl-groups in the molecule are displaced by hydrogen atoms-that is to say, complete reduction of all the and -CH2-OH groups is effected, and a fatty acid is obtained. In the case of the polyhydric acid prepared from glucose cyanohydrin, this change is represented by the equation CHo(OH)-[CHOH]rCH(OH)COOH + 12HI = CH3[CH2]4CH2.COOH + 6H2O + 6L, and normal heptylic acid is obtained; whereas on reducing the corresponding polyhydric acid prepared from levulose cyanohydrin, methylbutylacetic acid, an isomeride of normal heptylic acid, is formed, CHo(OH)[CHOH]3.C(OH)(COOH).CH2.OH + 12HI = CH3[CH2]3CH(COOH)CH3 + 6H2O + 6I2. These facts show that dextrose is an aldehyde and a derivative of normal hexane. Had it been a ketone, the polyhydric acid pro- duced from it could not have contained the group -CH(OH)-COOH, but must have contained the group c^Q^/CfOHj-COOH; this, on reduction, would have been transformed into -ch2>chcooh' and consequently the fatty acid finally produced would not have been normal heptylic acid, but one of its isomerides. In a similar manner, the conversion of levulose into methylbutylacetic acid, taken in conjunction with other facts, shows that this sugar is a ketone and not an aldehyde, and that its constitution is expressed by the formula already given (p. 265). In addition to this evidence, the fact that dextrose and levulose may be converted into man- nitol, shows them to be derivatives of normal hexane. CHAPTER XVI. The cyanogen compounds, like the carbohydrates, do not form a natural group or series, such as that of the paraffins, alcohols, fatty acids, &c.; nevertheless (with the exception of CYANOGEN COMPOUNDS. CYANOGEN COMPOUNDS. 277 urea and uric acid) they may all be considered as derived from cyanogen, (CN)2, just as the chlorides, hypochlorites, &c., may be regarded as derivatives of chlorine, Cl2. In many cases the cyanogen compounds are closely related to the compounds of chlorine in properties, although they differ from the latter in composition, and contain the monovalent group of atoms -CN in the place of a single atom of chlorine, -Cl, as shown by the following examples : Cl2, HC1, KC1, AgCl, HgCl2, H0C1, C2H6C1 (CN)2, HCN, KCN, AgCN, Hg(CN)2, HOCN, C2H5-CN. This fact brings out very clearly the meaning of the term 'radicle,' the monovalent group -CN* playing much the same part as the atom of chlorine, just as the radicle ammonium may play the part of a single atom of an alkali metal. Cyanogen, dicyanogen, C2N2, or Cy2, or N=C-C=N, is produced in small quantities when the electric arc passes between carbon poles in an atmosphere of nitrogen, 2C + N2 = C2N2; also when ammonium oxalate is strongly heated, NH4OOC-COONH4 = N=C-C=N + 4H2O, a reaction of considerable interest, as it shows that cyanogen is the nitrile (p. 280) of oxalic acid. Cyanogen is prepared by heating silver cyanide or mercuric cyanide (p. 282) in a hard glass tube, the gas being collected over mercury, Hg(CN)2 = Hg + C2N2. During the operation a considerable quantity of a brown amorphous substance called paracyanogen, (CN)H, is produced; this compound is a polymeride of cyanogen, and when heated at a high temperature it is completely resolved into cyanogen gas, just as paraformaldehyde is converted into formaldehyde under like conditions. Cyanogen is a colourless gas, which condenses to a liquid * The cyanogen radicle -CN is often written Cy. 278 CYANOGEN COMPOUNDS. at ordinary temperatures under a pressure of four atmo- spheres ; it has a peculiar smell, is excessively poisonous, and burns with a characteristic purple or peach-coloured flame, yielding carbon dioxide and nitrogen. It is moderately soluble in water, readily in alcohol, but its aqueous solution soon decomposes, a brown amorphous pre- cipitate ('azulmic acid') being deposited; the solution then contains ammonium oxalate and other substances. When an aqueous solution of cyanogen is treated with acids or with alkalies, oxalic acid or an oxalate is produced, N=C-C~N + 4H2O = NH4OOCCOONH4, this change being the reverse of that which occurs when ammonium oxalate is heated alone. All substances which contain the cyanogen group -C=N behave in a similar manner, and are converted on hydrolysis into carb- oxylic acids or their salts, amides being formed as intermediate products. Cyanogen is readily absorbed by potash, potassium cyanide and cyanate being produced, C2N2 + 2K0H = KCN + KOCN + H2O, just as potassium chloride and hypochlorite are formed when chlorine is led into potash, Cl2 + 2K0H = KC1 + K0C1 + H2O. Derivatives of Cyanogen.-Cyanogen chloride, CNC1, is formed by the action of chlorine on a solution of hydrocyanic acid, HCN + Cl2 = CNC1 + HC1. It is a colourless, very poisonous liquid, boils at 15-5°, and readily undergoes spontaneous polymerisation, yielding cyanuric chloride, C3N3C13, a solid substance which melts at 146°, and is decomposed by alkalies, yielding cyanuric acid, C3N3C13 + 3H2O = C3N3(OH)3 + 3HC1. The corresponding bromo- and iodo- derivatives of cyanogen, CNBr and CNI, are also known. Hydrocyanic acid (prussic acid), H-C=N, is found in the free state in plants, sometimes in considerable quantities; CYANOGEN COMPOUNDS. 279 more frequently it occurs in combination with glucose and benzaldehyde in the form of the glucoside amygdalin (part ii.). Bitter almonds and cherry kernels contain this glucoside; when macerated and kept in contact with water, fermentation soon sets in, due to the presence of a ferment, emulsin, and the amygdalin is decomposed into hydrocyanic acid, benzal- dehyde (part ii.), and glucose, C20H2TNOu Amygdalin. + 2H2O = C7H6O + Benzaldehyde. HCN + 2C6H12O6. Glucose. Hydrocyanic acid is formed when the silent electric discharge passes through a mixture of hydrogen and cyanogen, H2 + C2N2 = 2HCN; and also when ammonium formate is heated, a change which is analogous to the formation of cyanogen from ammonium oxalate, H.COONH4 = HCN + 2H2O. Hydrocyanic acid is prepared by distilling potassium cyanide, or, more usually, potassium ferrocyanide, with dilute sulphuric acid, KCN + H2SO4 = KHSO4 + HCN 2K4Fe(CN)6 Potassium FerrocvanidB. + 3H2SO4 = 6HCN + FeK2Fe(CN)6 Fer ri o Pntn «si nfprrnn vo n i rl p + 3K2SO4; in the latter reaction, only half of the potassium ferrocyanide yields hydrocyanic acid. Powdered potassium ferrocyanide (10 parts) is mixed with con- centrated sulphuric acid (7 parts) previously diluted with water (10-40 parts, according to the desired strength of the hydrocyanic acid), and the mixture distilled from a retort connected with a condenser. The anhydrous acid may be prepared from the aqueous solution thus obtained by fractional distillation and dehydration over calcium chloride. Anhydrous hydrocyanic acid is a colourless liquid; it boils at 26°, and solidifies in a freezing mixture to colourless crystals, which melt at -14°; it has an odour similar to that of oil of bitter almonds, and burns with a pale blue flame, with formation of carbon dioxide, water, and nitrogen. It is 280 CYANOGEN COMPOUNDS. a terrible poison, very small quantities being sufficient to cause death. Hydrocyanic acid dissolves readily in water, but the solution rapidly decomposes, with separation of a brown substance, and the liquid then contains ammonium formate and other compounds, HCN + 2H2O = HCOONH4. This hydrolysis takes place only slowly if a trace of some mineral acid be present, more quickly if the solution be heated with mineral acids or alkalies. The facts that hydrocyanic acid is formed on heating ammonium formate, and is reconverted into this substance on hydrolysis, show that it is the nitrile of formic acid. On reduction with nascent hydrogen, hydrocyanic acid is converted into methylamine, HCN + 4H = CH3.NH2. The constitution of hydrocyanic acid is expressed by the formula HC:N for the following reasons: The acid is pro- duced from ammonium formate, by a change similar to that by which acetonitrile is formed from ammonium acetate, H.COONH4 = HCN + 2H2O CH3.COONH4 = CH3CN + 2H2O; when heated with mineral acids, it is converted into formic acid, just as methyl cyanide is converted into acetic acid, HCN + 2H2O = HCOOH + NH3 CH3-CN + 2H2O = CH3.COOH + NH3. As, moreover, many facts show that the methyl group in methyl cyanide and in acetic acid is directly united with carbon, it is very probable that the hydrogen atom in hydro- cyanic acid is in a similar state of combination (p. 286). Hydrocyanic acid is the nitrile of formic acid, or rather of ammonium formate, the name nitrile being given to those com- pounds which are derived from ammonium salts by the elimination of 2 mols. of water. The fact that the hydrogen atom in hydro- cyanic acid, like that in hydrochloric acid, is displaceable by metals, although it is directly united with carbon (and not with oxygen, as CYANOGEN COMPOUNDS. 281 in the case of the carboxylic acids), is accounted for by the close similarity between -CN and -Cl, both of which have acid-forming or electro-negative properties. Hydrocyanic acid is a feeble acid, and scarcely reddens blue litmus. It forms salts with the hydroxides (but not with the carbonates) of potassium, sodium, and many other metals; the alkali salts are decomposed by carbon dioxide with liberation of the acid, and this is the reason why potassium cyanide, for example, in contact with moist air, always smells of hydro- cyanic acid. Potassium cyanide, KCN, may be obtained synthetically by passing nitrogen into a mixture of carbon and fused potash, and by burning potassium in cyanogen. It is prepared on a large scale by strongly heating potassium ferrocyanide, K4Fe(CN)6 = 4KCN + FeC2 + N2; the fused product is filtered through hot, porous crucibles, to free it from finely-divided iron carbide, and then cast into sticks. The pure salt may be prepared by neutralising hydro- cyanic acid with pure potash, and evaporating the solution out of contact with air. Potassium cyanide crystallises in colourless plates, and is very readily soluble in water, but nearly insoluble in absolute alcohol; it is excessively poisonous. Fused potassium cyanide is a powerful reducing agent; it liberates the metals from many metallic oxides, being itself converted into potassium cyanate, KCN + PbO = KCNO + Pb, hence its use in analytical chemistry and in some metallurgical operations. The aqueous solution of potassium cyanide gives, with silver nitrate, a curdy white precipitate of silver cyanide, AgCN, which is insoluble in dilute acids, but soluble in ammonia and potas- sium cyanide; in the latter case, with formation of the soluble double salt, KAg(CN)2, which is used in electroplating. Silver cyanide is thus very similar in its properties to silver chloride, 282 CYANOGEN COMPOUNDS. from which, however, it differs in this, that when heated, it is decomposed completely into silver and cyanogen, 2AgCN = 2Ag + C2N2. Mercuric cyanide, Hg(CN)2, is prepared by dissolving mercuric oxide in hydrocyanic acid, HgO + 2HCN = Hg(CN)2 + H2O. The solution, on evaporation, deposits the salt in colourless crystals, which are moderately soluble in water; when strongly heated, the salt is decomposed into mercury and cyanogen. The detection of hydrocyanic acid or of a cyanide is usually based on the following tests : (a) The aqueous solution is made strongly alkaline with potash, a few drops of ferrous sulphate added, and the liquid warmed; potassium ferro- cyanide is thus formed, and on acidifying and adding ferric chloride, a blue colouration or precipitate of Prussian blue is produced. (6) The solution is mixed with a few drops of ammonium sulphide, and evaporated to dryness on a water- bath ; the residue contains ammonium thiocyanate, and on the addition of ferric chloride, an intense blood-red colouration is produced. The cyanides of many of the metals, like many of the metallic chlorides, are capable of forming ' double salts ' with the compounds of other metals. Silver cyanide, for instance, is soluble in potassium cyanide, with which it forms a double salt of the composition AgK(CN)2; the compound KAu(CN)4 may be obtained in a similar manner by dissolving auric cyanide, Au(CN)3, in potassium cyanide. These 'double salts ' crystallise unchanged from water, but are decomposed by mineral acids in the cold, with evolution of hydrocyanic acid. Like the soluble simple cyanides, they are excessively poisonous. In addition to these double salts, complex metallic cyanides of a different class are known, the most important of which are potassium ferrocyanide, K4Fe(CN%, and potassium ferri- cyanide, K3Fe(CN)6. These salts are not poisonous, and are CYANOGEN COMPOUNDS. 283 more stable than the double salts just referred to. On treat- ment with mineral acids, in the cold, they do not yield hydrocyanic acid, but hydrogen is substituted for one of the metals only, and an acid, such as hydroferrocyanic acid, is liberated, K4Fe(CN)6 + 4HC1 = H4Fe(CN)6 + 4KC1. Potassium ferrocyanide, or yellow prussiate of potash, K4Fe(CN)6, is formed when ferrous hydrate is dissolved in potassium cyanide, 6KCN + Fe(OH)2 = K4Fe(CN)6 + 2K0H. It is manufactured by fusing together in an iron pot nitrog- enous animal refuse (horn-shavings, hair, blood, &c.), crude potashes (containing potassium carbonate), and scrap-iron. The product is extracted with hot water, the solution filtered, and evaporated to crystallisation. Potassium ferrocyanide cannot be present in the melted mass, because it is decomposed at a high temperature ; it must, therefore, be formed when the product is extracted with water. Probably the melt contains iron, potassium cyanide, and ferrous sulphide (the latter having been produced by the action of the sulphur in the animal refuse on the scrap-iron); these substances would interact in the presence of water, yielding potassium ferrocyanide, 6KCN + FeS = K4Fe(CN)6 + K2S 2KCN + Fe + 2H.0 = Fe(CN)2 + 2K0H + H2 Fe(CN)2 + 4KCN = K4Fe(CN)6. Potassium ferrocyanide crystallises in lemon-yellow prisms, which contain 3 mols. of water of crystallisation ; it is soluble in about 4 parts of water. When ignited it decomposes, yielding potassium cyanide, nitrogen, and a compound of iron and carbon (iron carbide), K4Fe(CN)6 = 4KCN + N2 + FeC2, . a reaction which is made use of in the preparation of potassium cyanide. When warmed with strong (90 per cent.) sulphuric acid, it gives carbon monoxide, 284 CYANOGEN COMPOUNDS. K4Fe(CN)6 + 6H.,O* + 6H2SO4 = 6CO + 2K2SO4 + FeSO4 + 3(NH4)2SO4, but when boiled with dilute sulphuric acid, hydrocyanic acid is produced. Solutions of ferric salts in excess give with potassium ferro- cyanide a precipitate of 'Prussian blue,' or ferric ferrocyanide, Fe4[Fe(CN)6]3. Potassium ferricyanide, or red prussiate of potash, K3Fe(CN)6, is prepared by passing chlorine into a solution of potassium ferrocyanide until the liquid ceases to give a blue precipitate with ferric salts; on evaporation, potassium ferricyanide separates out in dark-red crystals. The transformation of potassium ferrocyanide into ferricyanide is simply a process of oxidation, as other oxidising agents, such as nitric acid, produce the same result; this change is easily under- stood if it be assumed that potassium ferrocyanide is a compound of potassium cyanide and ferrous cyanide, (4KCN + Fe(CN)2). On oxidation, the ferrous is converted into ferric cyanide, and potassium ferricyanide, which may be regarded as a compound of potassium cyanide and ferric cyanide, (3KCN + Fe(CN)3), is formed. Potassium ferricyanide gives, with ferrous salts, a pre- cipitate of Turnbull's blue, or ferrous ferricyanide, Fe3[Fe(CN)6]2; it is employed as a mild oxidising agent, as in alkaline solution, in presence of an oxidisable sub- stance, it is converted into potassium ferrocyanide, 2K3Fe(CN)6 + 2K0H = 2K4Fe(CN)6 + H2O + 0. The nitriles, or alkyl cyanides, as the ethereal salts of hydrocyanic acid are termed, may be prepared by heating the alkyl halogen compounds with potassium cyanide, KCN + C2H5I = C2H5-CN + KI, or by distilling the ammonium salts, or the amides, of the fatty acids either alone or with some dehydrating agent, such as phosphorus pentoxide, * The water necessary for this decomposition is partly derived from the crystals of the salt, partly from the acid, which is not anhydrous. CYANOGEN COMPOUNDS. 285 CH.^COONH, = CH..CN + 2H.,0 6 4 o J C2H5.CO.NH2 = c2h5-cn + h2o. The lower members of the series, such as methyl cyanide (b.p. 81°) and ethyl cyanide (b.p. 97°), are colourless liquids, possessing a strong, but not disagreeable smell, and are readily soluble in water; the higher members, as, for example, octyl cyanide, C8H17-CN, are almost insoluble in water. When boiled with acids or alkalies, they are decomposed, with formation of fatty acids, the -CN group being converted into the -COOH group, CH3.CX + KOH + H2O = CH3-COOK + NH3 CoHyCN + HC1 + 2H2O = C2H5-COOH + NH4C1. For this reason, and also because they may be obtained from the ammonium salts of the fatty acids, the nitriles are named after the acids which they yield on hydrolysis : methyl cyanide, CH3-CN, for example, is called acetonitrile; ethyl cyanide, C2H5CN, propionitrile, and so on. On reduction with zinc and sulphuric acid, or, better, with sodium and alcohol, the alkyl cyanides are converted into primary amines, a fact which shows that the alkyl group is directly united with carbon, CH3CN + 4H = CH3-CH2NH2. The isonitriles, carbylamines or isocyanides, are isomeric with the nitriles : they may be prepared by heating the alkyl halogen compounds with silver cyanide, C2H5I + Ag-N=C = C2H5N=C + Agl, and by treating primary amines with chloroform and potash, CH3NH2 + 3K0H + CHC13 = CH3-N=C + 3KC1 + 3H2O. The isonitriles or carbylamines are colourless liquids, sparingly soluble in water; they have an almost unbearable odour and poisonous properties. They boil at lower temperatures than the isomeric cyanides ; methyl isonitrile, CH3-NC, for example, boils at 58°; ethyl isonitrile, C2H5-NC, at 82°. They differ from the nitriles, inasmuch as they are not decomposed by boiling alkalies ; they are, however, 286 CYANOGEN COMPOUNDS. readily decomposed by dilute mineral acids, yielding formic acid and an amine, C2H5NC + 2H2O = H-COOH + C2H5-NH2. This behaviour is also totally different from that of the nitriles, and shows that the alkyl group in the isonitriles is united with nitrogen and not with carbon-that is to say, the nitriles are ethereal salts of hydrocyanic acid, H-C:N, whereas the isonitriles may be regarded as derivatives of an isomeric modification of hydrocyanic acid, H-N^C. In order to explain the difference in the constitution of the pro- ducts produced by the action of alkyl halogen compounds on potassium and silver cyanide respectively, it is necessary to assume either that in the formation of silver cyanide from potassium cyanide by precipitation, intramolecular change (p. 290) has taken place, K-CzEN yielding Ag-N=C, or that silver cyanide, Ag-C=N, first yields, with the alkyl halogen compound, an additive pro- duct, which is then decomposed, yielding the isonitrile, Ag-C=N + C2H8I = Ag.C;N<52Hi5 = C=NC2H5 + Agl. Cyanic acid, HO-CN, is produced when cyanuric acid (see below) is heated, and the vapours condensed in a receiver cooled in a freezing mixture, C3N3(OH)3 = 3H0-CN. It is a strongly acid, unstable liquid, and at temperatures above 0° rapidly undergoes polymerisation into an opaque, porcelain-like mass called cyamelide. Its aqueous solution decomposes very rapidly into carbon dioxide and ammonia, HO-CN + H2O = CO2 + NH3, and therefore the acid cannot be prepared by the decomposi- tion of its salts with mineral acids. Potassium cyanate, KO-CN, is produced when potassium cyanide slowly oxidises in the air; it is usually prepared by heating potassium cyanide (or ferrocyanide) with some readily reducible metallic oxide, such as litharge or red-lead, and then extracting the product with dilute alcohol, KCN + PbO = KO-CN + Pb. It is a colourless, crystalline powder, readily soluble in water CYANOGEN COMPOUNDS. 287 and dilute alcohol, but insoluble in absolute alcohol; its aqueous solution rapidly decomposes with formation of ammonia and potassium bicarbonate, KOCN + 2H2O = NH3 + KHCO3. When a solution of this salt is mixed with ammonium sulphate and evaporated, urea is formed, ammonium cyanate, NH4O-CN, being the intermediate product (p. 289). Ethereal Salts of Cyanic Acid.-Cyanic acid, like hydrocyanic acid, yields two series of ethereal salts-namely, the normal cyanates, such as C2H5O-CN, derived from HO-CN; and the isocyanates, such as C2H5N:CO, derived from H-N:CO. The alkyl (normal) cyanates are produced by the action of cyanogen chloride on the sodium compounds of the alcohols, NaO-C2H5 + Cl-CN = C2H3OCN + NaCl; they are colourless, ethereal-smelling liquids, and are decomposed by alkalies into alkali carbonates, ammonia, and alcohols ; this fact shows that the alkyl group is united with oxygen and not with nitrogen. The alkyl isocyanates are obtained by the action of the alkyl halogen compounds on silver isocyanate (obtained as a white pre- cipitate on adding silver nitrate to an aqueous solution of potassium cyanate), AgN:CO + CH3I = CH3N:CO + Agl. They are very unpleasant-smelling, volatile liquids ; when heated with alkalies, they are decomposed into alkali carbonates and primary amines (Wurtz), a reaction which shows that the alkyl group is united with nitrogen, CH3N:CO + 2K0H = CH3.NH2 + K2CO3. Cyanuric acid, N3C3O3H3, is produced by the action of water on cyanuric chloride (p. 278), N3C3C13 + 3H2O = N3C3(OH)3 + 3HC1. It is a crystalline, tribasic acid, forming well-defined salts, of which the crystalline trisodium salt, N3C3(ONa)3, is the most characteristic. On distillation, the acid is converted into cyanic acid. Thiocyanic acid, or sulphocyanic acid, HS-CN, is obtained 288 CYANOGEN COMPOUNDS. ill the form of its salts when the alkali cyanides are heated with sulphur, KCN + S = KSCN, the change being analogous to the formation of cyanates by the oxidation of cyanides. Thiocyanic acid may be obtained by distilling potassium thiocyanate with dilute sulphuric acid; it is a liquid, solidifies at 12-5°, and has a very penetrating odour. It is decomposed by moderately concentrated sulphuric acid, with evolution of carbon oxysulphide, HSCN + H2O = COS + NH3. Potassium thiocyanate, KS-CN, is prepared by fusing potassium cyanide (or ferrocyanide) with sulphur, and extracting the mass with alcohol. On concentrating the alcoholic solution, the salt is. deposited in colourless, very deliquescent needles. The ammonium salt, NH4S-CN, is most conveniently prepared by agitating strong ammonia with carbon bisulphide, 4NH3 + CS2 = NH4SCN + (NH4)2S. The thiocyanates are used in inorganic analysis, as reagents for ferric salts, with which they give an intense blood-red colouration, caused by the formation of a double salt. Thiocyanates are also employed in dyeing and calico-printing as mordants, and are known commercially as ' rhodanates.' Thiocyanic acid, like cyanic acid, forms two series of ethereal salts-namely, the normal thiocyanates, such as C2H5S-CN, derived from HS-C-N, and the isothiocyanates, such as C2H5N:CS, derived from HN:C:S. TheoZZq/Z (normal) thiocyanates are produced by the action of the alkyl iodides on potassium thiocyanate, or from the mercaptides (especially lead mercaptide), by the action of cyanogen chloride, (C2H5S)2Pb + 2C1CN = 2C2H5SCN + PbCI2, a reaction which is exactly similar to the formation of ethyl cyanate by the action of cyanogen chloride on sodium ethoxide (see above). The normal thiocyanates are volatile liquids possessing a slight though not penetrating smell of garlic ; when oxidised with nitric CYANOGEN COMPOUNDS. 289 acid they are converted into alkyl sulphonic acids, C2H5S-CN, for example, yielding C2H5-SO3H, a reaction which shows that the alkyl group is united with sulphur. The alkyl isothiocyanates, or mustard-oils, are produced by heating the normal thiocyanates at 180°, or by simply repeatedly distilling them, intramolecular change (p. 290) taking place; the alkyl group in these compounds is combined with nitrogen, because when heated with hydrochloric acid they are decomposed into primary amines, carbon dioxide, and sulphuretted hydrogen, C2H3N:CS + 2H2O = C2H5NH2 + CO2 + SH2. Allyl isothiocyanate, or ' mustard-oil,' CH2:CHCH2-N :CS, is prepared by distilling macerated black mustard seeds with steam. Mustard seeds contain a glucoside, ' potassium myronate,' C10H18NS2O10K, which is soluble in water; its solution gradually undergoes fermentation, owing to the presence of a ferment, 'myrosin,' mustard-oil, glucose, and potassium hydrogen sulphate being produced, C10H18NS2O10K = C3H5-N:CS + C6H12O6 + KHS04. Allyl isothiocyanate is a colourless, pungent-smelling liquid, which boils at 151°; when dropped on the skin, it produces blisters. Urea,* or carbamide, CH4N2O or CO(NH2)2, is a compound of great physiological importance. It occurs in the urine of mammals and of carnivorous birds and reptiles, and is one of the principal nitrogenous constituents of human urine, of which it forms about 3 per cent. It was discovered in urine in 1773, and was first artificially produced in 1828 by Wohler, who found that on warming an aqueous solution of ammonium cyanate the salt was converted into urea, NH4-0-CN = CO(NH2)2, a discovery which, being the first synthetical production of an animal product, was of fundamental importance (compare p. 10). * .Although urea, uric acid, and glycine are not derivatives of cyanogen, they are in many ways related to the cyanogen compounds, and for this reason may be conveniently considered in this chapter. 290 CYANOGEN COMPOUNDS. When one substance is converted into another which has the same molecular formula, the change is spoken of as ' intramolecular. ' Ammonium cyanate, NH4OCN, has the same molecular formula as urea, CO(NH2)2; but the atoms in the molecules of the two com- pounds are arranged differently-that is to say, their constitutions are different. Many cases of intramolecular change are met with in organic chemistry. Urea may be prepared from urine by evaporating to a small bulk and adding strong nitric acid. The precipitate of crude urea nitrate (see below) is recrystallised from nitric acid, dissolved in boiling water, and decomposed with barium carbonate ; the solution is then evaporated to dryness, and the urea extracted with alcohol, in which barium nitrate is insoluble. It is more commonly prepared by mixing a solution of potassium cyanate (2 mols.) with an equivalent quantity of ammonium sulphate (1 mol.), evaporating to dryness, and extracting with alcohol. In both cases the crude urea is purified by recrystallisation from water or alcohol. Urea may be also synthetically obtained by treating ethyl carbonate, or phosgene gas* (carbonyl chloride), with ammonia, CO(OC2H5)2 + 2NH, = CO(NH.,)2 + 2C2H5-OH COC12 + 4NH3 = CO(NH2)2 + 2NH4C1. It crystallises in colourless needles, melts at 132°, and is readily soluble in water and alcohol, but almost insoluble in ether; when heated with water at 120°, or boiled with dilute acids, it is decomposed into carbon dioxide and ammonia (or one of its salts), CO(NH2)2 + H2O + 2HC1 = CO2 2N + H4C1, but when heated alone it yields ammonia, cyanuric acid, and complex cyanogen compounds, 3CO(NHA, = lUC.NoOo + 3NHr Urea is decomposed by nitrous acid into nitrogen and carbon dioxide, * Ethyl carbonate is formed when silver carbonate is treated with ethyl iodide: it is an agreeably-smelling, neutral liquid, which boils at 126°. Carbonyl chloride is obtained by the direct combination of carbon monoxide and chlorine in sunlight; it is a gas which decomposes rapidly in contact with water, into carbon dioxide and hydrochloric acid. CYANOGEN COMPOUNDS. 291 CO(NH2)2 + 2HNO2 = C02 + N2 + 2H2O, a similar change taking place when it is mixed with solutions of hypochlorites or hypobromites, CO(NH2)2 + 3NaOCl = CO2 + N2 + 2H2O + 3NaCl; by measuring the volume of nitrogen given off, on treating a solution of urea with nitrous acid, the quantity in solution can be readily estimated. Urea possesses basic properties, and combines with one, equivalent of acids to form salts, most of which are soluble in water. The most characteristic salt is urea nitrate, CO(NH2)2,HNO3, which crystallises in glistening plates, and is sparingly soluble in nitric acid. Constitution.-The formation of urea from the ethyl salt and from the chloride of carbonic acid is exactly analogous to the formation of acetamide from ethyl acetate and from acetyl chloride; urea is therefore the diamide of carbonic acid-hence the name carbamide-and its constitution is represented by the formula 0 = The monamide of carbonic acid, O = C<^yjj (carbamic acid), is not known in a free state. Ammonium carbamate is formed by the action of carbon dioxide on ammonia, CO2 + 2NH3 = CO(NH2)-ONH4, and is one of the constituents of commercial ammonium carbonate, which is frequently prepared by this method. Uric acid, C5H4N4O3, occurs in small quantities in human urine, from which it separates on exposure to the air in the form of a light yellow powder; it also occurs in the excrements of birds and reptiles, and is present in large quantities in guano. The excrements of serpents consist almost entirely of ammonium urate ; from this source uric acid is conveniently prepared by boiling the excrement with caustic soda until all the ammonia has been expelled, and pouring the hot filtered liquid into hydrochloric acid ; on cooling, uric acid separates as a fine crystalline powder. 292 CYANOGEN COMPOUNDS. Uric acid is insoluble in alcohol and ether, and very sparingly soluble in water (1 part dissolves in 1800 parts of water at 100°). If uric acid be moistened with nitric acid in a porcelain basin, and the mixture then evaporated to dryness on a water-bath, a yellow stain is left, which, on the addition of ammonia, becomes intensely violet (murexide reaction). Uric acid is a weak dibasic acid; when dissolved in sodium carbonate, it yields an acid sodium salt, C5H3N4O3Na + |H2O ; the neutral sodium salt, C5H2N4O3Na2 + H2O, is formed when uric acid is dissolved in caustic soda. The salts, like the acid itself, are all sparingly soluble in water. Uric acid has been prepared synthetically by heating glycine with urea at 200-230°. Glycine, glycocoll, or amido-acetic acid, CH2(NH2)-COOH, like urea and uric acid, is found in animal secretions, but usually in combination. As hippuric acid, or benzoylglycine, CcH5-CO-NHCH2-COOH (part ii.), it occurs in considerable quantities in the urine of horses, and it is best prepared from this substance by treatment with hydrochloric or sul- phuric acid, CfiHr-CO-NHCH2.COOH + H2O + HC1 - C6H5COOH + Benzoic Acid. NHo CH^COOH, HC1. Glycine Hydrochloride. It may also be conveniently prepared by treating monochlor- acetic acid with ammonia, CH2C1COOH + 3NH3 = CH2(NH2)-COONH4 + nh4cl Glycine crystallises from water in colourless prisms, and melts at 235°. It is readily soluble in water; the aqueous solution gives with ferric chloride a red colouration, and with phenol and sodium hypochlorite an intense blue colouration. Glycine contains an amido-group and a carboxyl-group, and is therefore capable of forming salts both with acids and bases. The most characteristic metallic salt is the copper salt,. CYANOGEN COMPOUNDS. 293 {C2H4NO2)2Cu, which is readily formed by dissolving cupric hydrate in a hot, strong, aqueous solution of glycine; on cooling, the salt crystallises in deep blue needles. Glycine hydrochloride, C2H5NO2, HC1, is produced by dis- solving glycine in hydrochloric acid, or by decomposing hippuric acid with hydrochloric acid; it crystallises in colour- less needles, is readily soluble in water, and is decomposed by alkalies or alkali carbonates, with liberation of glycine. When treated with nitrous acid, glycine is converted into glycollic acid (p. 223), ■ \ CH2(NH2)-COOH + NOJI = CH2(OH).COOH + N2 + H2O. Other amido-acids such as alanine or a-amidopropionic acid, CH3-CH(NH2).COOH, may be prepared from the corresponding halogen acids by the action of ammonia; in their properties they are very similar to glycine. INDEX. [Where more than one reference is given, and one of them is in heavy type, the latter refers to the systematic description of the substance.] PAGE Acetal 125 Acetaldehyde 83, 96, 120, 134 Acetaldehyde hydrazone 133 Acetaldoxime 122 Acetals 140 Acetamide 162 Acetic acid 96, 147, 164 Acetic acid, electrolysis of 60 Acetic acid, salts of 150 Acetic anhydride t6i Acetic ether 185 Acetoacetic acid 189 Acetone 87, 128, 134 Acetonedicarboxylic acid 247 Acetone dichloride 139 Acetone hydrazone 134 Acetone pinacone 138 Acetone sodium bisulphite 129 Acetonitrile 162, 285 Acetoxime 132 Acetyl chloride 158 Acetylcellulose 273 Acetylene 73, 81 Acetylene series 81 Acetylformic acid 195 Acetylglucose 265 Acetyllevulose 267 5-Acetylpropionic acid 196 Acid amides 161, 166 Acid anhydrides 160, 166 Acid bromides 160 Acid chlorides 158, x66 Aconitic acid 247 Acraldehyde 256 Acrolein 249, 254, 256 Acrolein bromide 256 Acrylic acid 257 Active amyl alcohol 105, 106 Adipic acid 229, 239 PAGE Alcohol 92 Alcohol, determination of tor Alcohol, manufacture of 99 Alcoholic liquors 102 Alcoholometry too Alcohols, monohydric 88 Alcohols, nomenclature of 102 Alcohols, oxidation of 109 Alcohols, polyhydric 248, 258 Alcohols, trihydric 248 Aldehyde ammonia 122 Aldehyde resin 122 Aldehydes 116 Aldehydes, condensation of 141 Aldehydes, oxidation of 139 Aldol 124 Aldoximes 132 Alkyl chlorides 116 Alkyl cyanates 287 Alkyl cyanides 284 Alkyl hydrides 115 Alkyl hydrogen sulphates 80, 183 Alkyl isocyanates 287 Alkyl radicles 115 Alkylene radicles 116 Allene. 86 Allyl alcohol 254 Allyl bromide 255 Allyl iodide 255 Allyl isothiocyanate 256, 289 Allyl sulphide 255, 256 Allylene 86 Aluminium ethyl 2x8 Amidoacetic acid 224, 292 Amidopropionic acid 226, 293 Amines 199 Amines, separation of primary, second- ary, and tertiary 205 Amygdalin 279 I INDEX. PAGE Capraldehyde *34 Caproic acid 158 Caramel 261 Carbamide 289 Carbinol 88 Carbohydrates 259 Carbon, detection of 21 Carbon, estimation of 25 Carbon tetrachloride 174 Carbonyl chloride 290 Carbonyl group 130 Carboxyacetic acid 229 Carboxyl-group 154 a-Carboxypropionic acid 229 ,3-Carboxypropionic acid 229 Carbylamine reaction 174 Carbylamines 285 Carius' method of analysis 33 Casein 270 Cetyl alcohol 108 Cetyl palmitate 188 Chloracetic acid 163 Chloral 125 Chloral alcoholate 125 Chloral hydrate 127 Chlorethane 176 Chlorethylene 78 Chlorine carrier 163 Chlorine, detection of 22 Chlorine, estimation of 33 Chloroform 126, 172 Chlorohydrin 222 a-Chlorohydrin 251, 252 |3-Chlorohydrin 251, 252 Chlorohydrins 80, 251 Chloromalonic acid 239 Chloromethane 171 a-Chloropropionic acid .164 /3-Chloropropionic acid 164 Citric acid 245 Citric acid, salts of 246 Collodion 274 Combustion apparatus..... 26 Condensation 131 Constitutional formula: 53 Constitution of organic compounds.. 51 Copper acetylene 83 Cream of tartar 243 Crotonaldehyde 124, 256 Crotonic acid 258 Crotonylene 86 Crystallisation 14 PAGE Amyl acetate 189 Amyl alcohol, commercial 106 Amyl alcohols 105 Amyl hydrogen sulphate 105 Amylene 79 Amylum 271 Arabinose 258 Arabitol 258 Argol 242 Arsines 210 Asparagine 240 Aspartic acid 240 Azulmic acid . 278 Barley-sugar 261 Beer, preparation of 97 Benzene 84 Benzine 71 Bioses 274 Bismuth, alkyl compounds of 211 Boiling-point 17 Bromacetic acids 164 Bromethane 176 Bromethylene 78 Bromine, detection of 22 Bromine, estimation of. 33 a-Bromopropionic acid 226, 227 /3-Bromopropionic acid 227 Bromosuccinic acid 239 Butaldehyde 127, 134 Butane, 62, 66, 68 Butter. 17° Butyl alcohol, normal 105, 106 Butyl iodide 177 Butyl iodide, secondary 80 Butyl iodide, tertiary 178 Butylamine 207 a-Butylene 79 /3-Butylene 79 y-Butylene 79 Butylene glycol 81, 221 Butyric acid 164 Butyric acid, normal 156 Butyric acid, salts of. 157 Butyrone .134 Cacodyl 213 Cacodyl chloride 213 Cacodyl cyanide 213 Cacodyl oxide 212 Cacodylic acid 213 Cane-sugar 260 II INDEX. PAGE Cyamelide - 286 Cyanic acid 286 Cyanides 281 Cyanides, double 282 Cyanogen 230, 277 Cyanogen bromide 278 Cyanogen chloride 278 Cyanogen compounds 276 Cyanogen iodide 278 Cyanuric acid 287 Cyanuric chloride 278 Decane 68 Dextrin.. 97, 272 Dextrose 262 Dextrotartaric acid 245 Diacetin 250 Diacetylchlorohydrin 252 Diallyl 87 Diarsenic tetramethyl 213 Diastase 97, 269, 272 Dibasic acids, electrolysis of 73, 77 Dibromopropionic acid 257 Dibromosuccinic acid 239, 242 Dicarboxylic acids 229 Dichloracetic acid 163 Dichloracetone, asymmetrical 131 Dichloracetone, symmetrical- 131, 246, 252 Dichlorethylene 83 aa-Dichlorohydrin 247, 251 a^-Dichlorohydrin 251, 252 /3-Dichloropropane 129, 139 a/3-Dichloropropionic acid 252 Dicyanogen 277 Diethyl 62 Diethyl ketone 134 Diethylamine 199, 203 Diethylamine, salts of 204 Diethylphosphine 209 Diethylphosphine hydriodide 210 Dihexyl ketone 134 Dihydroxysuccinic acid 239, 241 Di-isoamyl ether 113 Di-isobutyl ether 113 Di-isopropyl 66 Di-isopropyl ether 113 Di-isopropyl ketone 134 Dimethyl 59 Dimethyl carbinol 104 Dimethyl ketone 128, 134 Dimethylacetic acid 157 PAGE Dimethylamine 199. 207 Dimethylarsine oxide 212 Dimethylethylamine 207 Dimethylmalonic acid 239 Di-olefines S7 Dipropyl ether Dipropyl ketone 134 Dipropylamine 199 Disacryl 256 Distillation 15 Distillation in steam 15 Distillation of wood 88 Dulcitol 258, 270 Dutch liquid 78 Dynamite 253 Earth-wax 71 Empirical formulae '..... 37 Emulsin 279 Enzymes 98 Epichlorhydrin 252 Erythritol 258 Esters 171 Ethaldehyde 120 Ethane 59, 68, 83 Ethene 72 Ethene glycol 219 Ether Ethereal salts 166, 171 Ethers 109 Ethoxides 95 Ethyl acetate 185 Ethyl acetoacetate 189 Ethyl acetoacetate, hydrolysis of.... 193 Ethyl acetylglycollate 225 Ethyl acetyllactate 226 Ethyl alcohol 92, 106 Ethyl bromide 176 Ethyl butylacetoacetate 194 Ethyl carbinol, normal 104 Ethyl carbonate 290 Ethyl chloride 175 Ethyl copper acetoacetate 191 Ethyl diethylacetoacetate 192 Ethyl diethyloxamate 206 Ethyl dimethylacetoacetate 192 Ethyl dipropylacetoacetate 192 Ethyl ether no Ethyl ethylacetoacetate 192 Ethyl ethylmalonate 197 Ethyl ethylmethylacetoacetate 192 Ethyl ethylpropylacetoacetate 194 III INDEX. PAGE Ethyl formate 189 Ethyl glycollate 225 Ethyl hydride 59 Ethyl hydrogen sulphate 75, 182 Ethyl iodide . 177 Ethyl isocyanate 200 Ethyl isopropylacetoacetate 192 Ethyl lactate 226 Ethyl malonate 196 Ethyl mercaptan 184 Ethyl methylacetoacetate 191, 192 Ethyl nitrate 179 Ethyl nitrite 180 Ethyl oxalate - 233 Ethyl propylacetoacetate 191, 192 Ethyl propylethylmalonate 197 Ethyl propylmalonate 198 Ethyl sodioacetoacetate 190 Ethyl sodiomalonate 197 Ethyl succinimide 238 Ethyl sulphate 183 Ethyl sulphide 184 Ethyl sulphonic acid 184 Ethylamine 199, 200, 207 Ethylamine, salts of 203 Ethylates 95 Ethylcarbylamine 202 Ethylene 72, 83 Ethylene alcohol . 219 Ethylene chlorohydrin 222 Ethylene dibromide 78 Ethylene dichloride 78 Ethylene glycol 81, 219 Ethylene oxide 223 Ethylene series..., 72 Ethylenelactic acid 229 Ethylidene chloride 78, 139 Ethylidene dibromide 78 Ethylidenelactic acid 229 Ethylmalonic acid 239 Ethylnitrosamine 203 Ethyloxamide 206 Ethylphosphine 209 Ethylphosphine hydriodide 209 Fats .166 Fatty acids T42 Fatty acids, electrolysis of 60, 69 Fatty acids, synthesis of, from ethyl acetoacetate 194 Fatty acids, synthesis of, from ethyl malonate 198 PAGE Fatty acids, synthesis of, from next higher homologues 200 Fatty acids, synthesis of, from next lower homologues 201 Fehling's solution 263 Ferment 97 Fermentation 105, 165 Fermentation, acetic .96, 97, 148 Fermentation, alcoholic 97 Fermentation, butyric 157 Fermentation, diastatic 97, 269 Fermentation, lactic 156, 226 Formaldehyde ..91,117, 134 Formaldoxime 118 Formamide 162 Formic acid 91, 142, 164 Formic acid, salts of 145, 146 Formose 120, 267 Formula, calculation of a 36 Fractional crystallisation 14 Fractional distillation .. 18 Fructose 265 Fructosephenylhydrazone 268 Fruit sugar 265 Fumaric acid 241 Fusel oil 98, 99, 106 Galactosazone 270 Galactose 270 Gasoline ". 71 General formulae 68 Glacial acetic acid 150 Gluconic acid 264 Glucosates 264 Glucose 262 Glucosephenylhydrazone 265, 268 Glucosone 268 Glucosoxime .265 Glutaric acid 229, 239 Gluten 272 Glyceric acid .250 Glycerides 167 Glycerin 248 Glycerol 167, 169, 248 Glycerol chlorohydrin 251 Glycerol dichlorohydrin ...251 Glyceryl acetate .250 Glyceryl trichloride 251 Glyceryl tri-iodide 255 Glyceryl trinitrate 252 Glycine 292 Glycine hydrochloride 293 IV INDEX. PAGE Glycocoll 292 Glycol chlorohydrin 222, 228 Glycol cyanohydrin. 228 Glycol diacetate 220 Glycol, sodium compounds of. ..219, 220 Glycollic acid 222, 223 Glycols 218 Glyoxal 222, 223, 242 Glyoxylic acid 222 Granulose 271 Grape-sugar 262 Graphic formulae 53 Gun-cotton 274 Hard soap 169 Heptaldehyde 127, 134 Heptane 68 Heptyl alcohol, normal 127 Heptylic acid 164 Heptylic acid, normal 127, 158 Hexachloracetone 131 Hexane 66, 68 Hexylic acids 158 Hippuric acid 292 Homologous series 67 Hydracrylic acid 225, 227 Hydrazones 132, 133, 267 Hydrocyanic acid 278 Hydrogen, detection of 22 Hydrogen, estimation of. 25 Hydrolysis 169, 188 Hydroxides, quaternary arsonium.. .211 Hydroxides, quaternary phospho- nium 210 Hydroximes 132 Hydroxyacetic acid 223 /3-Hydroxybutyric acid T95 Hydroxycarboxylic acids 139, 223 Hj'droxycyanides 139 Hydroxydicarboxylic acids 239 Hydroxyethyl cyanide 139 Hydroxyisopropyl cyanide 139 Hydroxylamine 180, 181 Hydroxymalonic acid 239 a-Hydroxypropionic acid 225 (9-Hydroxypropionic acid 225, 227 Hydroxysuccinic acid 239 Hydroxysulphonic acids 137 Hydroxytricarboxylic acids 245 y-Hydroxyvaleric acid 196 Inulin 265 PAGE Inverse substitution 59 Inversion 262 Invertase 262 Invert sugar 262 lodacetic acids 164 lodethane 177 Iodine, detection of 22 Iodine, estimation of. 33 Iodoform 175 Iodoform reaction 96 Iso-alcohols 103 Isoamyl alcohol 105, 106 Isoamyl isovalerate 189 3-Isoamylene 79 Isobutaldehyde 134 Isobutane 63, 66 Isobutyl alcohol 105, 106 Isobutyl carbinol 105 Isobutylene 79 Isobutyric acid 157, 164 Isobutyrone 134 Isocyanides 285 Iso-hydrocarbons 66 Isomerism 65 Isonitriles 285 Isopentane 65 Isopropyl alcohol 104, 106, 128 Isopropyl bromide 80 Isopropyl carbinol 105 Isopropyl iodide 178 Isopropylacetic acid 157 Isosuccinic acid 229, 238 Isothiocyanates, alkyl 289 Isovaleraldehyde 134 Isovaleric acid 155, 157, 164 Kerosene 71 Ketones 127 Ketones, condensation of 141 Ketones, oxidation of. 140 Ketoximes 132 Lactic acid 195, 225 Lactic acid, salts of 226 Lactose 156, 269 Lard 166 Lauric acid 164 Laurone 134 Lead ethyl 218 Levotartaric acid. 245 Levulinic acid 196 Levulose 265 V INDEX. PAGE Levulosehydrazone 267 Levuloseoxime 267 Liebermann's reaction 204 Light petroleum 71 Ligroin 71 Maleic acid 241 Maleic anhydride 241 Malic acid 239, 244 Malonic acid 229, 234 Maltose 97, 269 Mannitol 258 Margaric acid 158 Margarine 170 Marsh-gas 55 Melissyl alcohol 108 Melting-point 20 Mendius' reaction 200 Mercaptans 183 Mercaptides 184 Mercuric ethiodide 217 Mercuric ethochloride 217 Mercuric ethohydroxide 217 Mercuric ethyl 217 Mesityl oxide 131 Mesitylene 131 Mesotartaric acid 245 Metachloral 126 Metaldehyde 125 Metamerism 114 Methaldehyde 117 Methane 55, 68 Methane series 55, 68 Methene dichloride 172 Methoxides 90 Methyl acetate 189 Methyl alcohol 88, 106 Methyl bromide 174 Methyl butyrate 189 Methyl carbinol 92 Methyl chloride 90, 171, 207 Methyl ether 109 Methyl ethyl ether 113 Methyl hydrogen sulphate 90 Methyl iodide 174 Methyl isopropyl ether 114 Methyl nitrate 180 Methyl nitrite 181 Methyl oxalate 89, 233 Methyl propionate 189 Methyl propyl ether 114 Methyl sulphate 90 PAGE Methyl sulphite 184 Methylacetylene 86 Methylal 120 Methylamine 199, 207 Methylated spirit 100 Methylates 9a Methylene dichloride 172 Methylenitan 267 Methylethyl 61 Methylethyl carbinol 105, 106 Methylethyl ketone 135. Methylethylacetic acid 155, 157 Methylethylamine 207 Methylethylene 78 Methylisopropyl ketone 135 Methylnonyl ketone 132- Methylphosphine . 209. Methylpropyl 62 Methylpropyl ketone 135 Methylsuccinic acid 239. Methylsulphonic acid 184 Milk-sugar 269 Mineral naphtha 70 Mixed amines 207 Mixed anhydrides 161 Mixed ethers 114 Mixed ketones 134 Molecular formula 38 Molecular weight, determination of. 38 Molecular weight, determination of, by chemical methods 38 Molecular weight, determination of, by Raoult's method 48 Monacetin 250 Monocarboxylic acids 154 Monochloracetone 131 Monoformin 144, 254 Monoses .274 Mucic acid 270 Mustard-oil 289 Myristic acid 164 Myrosin 289 Natural gas 70 Nitrates, ethereal 179 Nitrates of cellulose -274 Nitriles 133, 284 Nitrites, ethereal 180 Nitroethane . .181 Nitrogen, detection of 23 Nitrogen, estimation of 29 VI INDEX. PAGE Nitroglycerin 252 Nitrometer, Schiff's 31 Nitroparaffins 181 Nitrosamines 203 Nonane 68 Normal alcohols 103 Normal butylene 79 Normal hydrocarbons 66 Octacetylmaltose 269 Octacetylsaccharose 262 Octane 68 <Enanthol 127, 134 (Enanthone 134 Oil of garlic 256 Oil of mustard 256 Oil of rue. 132 Oil of wintergreen 88 Oils 166 Olefiant gas 72 Olefines 72 Oleic acid 168, 258 Oleomargarine 170 Organic acids, ethereal salts of 185 Organo-metallic compounds 214 Osazones . 268 Osones 268 Oxalic acid 229 Oxalic acid, salts of 232 Oxamide ...... .233 Oxidising agents 91 Ozokerite 71 Palmitic acid 158, 164 Palmitone 134 Paracetaldehyde 141 Paracyanogen 277 Paraffins 55, 67 Paraffin-wax 71 Paraformaldehyde 119, 141 Paralactic acid 227 Paraldehyde 124 Paraldehydes 141 Parchment paper 273 Pentane 65, 68 Pentylene 79 Perchloracetone 131 Petroleum 70 Petroleum ether 71 Phenylcarbylamine 173 Phenylhydrazones 133, 268 Phenylisocyanide 173 PAGE Phenylmaltosazone 269 Phorone 131 Phosphines 208 Phosphorus, detection of 24 Phosphorus, estimation of. 35 Photogene 71 Pinacoline 138 Pinacones 138 Polymerisation 119 Polyoses 274 Potassium ferricyanide 284 Potassium ferrocyanide 283 Potassium myronate 289 Primary alcohols 103 Primary hydrocarbons 66 Proof-spirit tor Propaldehyde 104, 127, 134 Propane 61, 68 Propenyl alcohol 248 Propenyl iodide 255 Propenyl trichloride 251 Propenyl trinitrate 252 Propionamide .'... .200 Propione 134 Propionic acid 104, 155, 164 Propionic acid, salts of. 156 Propionitrile 285 Propionyl chloride 160 Propyl alcohol 104, 106 Propyl bromide 177 Propyl carbinol 105 Propyl formate 189 Propyl hydride 6r Propyl iodide 178 Propylamine 199, 207 Propylene ... 78 Propylene alcohol 221, 248 Propylene chlorohydrin 222 Propylene dibromide 79 a/8-Propylene glycol 221, 226 ay-Propylene glycol 227 Propylene oxide 223 Propylethylacetic acid 198 Propylethylmalonic acid 198 Propylmalonic acid 198 Prussian blue 284 Prussic acid 278 Purification of compounds 12 Pyroligneous acid 147 Pyrotartaric acid 239 Pyruvic acid .... 195, 227 Pyruvic acid hydrazone 195 VII INDEX. PAGE Qualitative elementary analysis 21 Quantitative elementary analysis.... 25 Racemic acid 242, 245 Radicles 114 Rational formulae 53 Reducing agents 93 Refined petroleum 71 Refined spirit 100 Rhodonates 288 Rochelle salt 243 Saccharic acid 264, 270 Saccharimeter 261 Saccharosates 262 Saccharose .. 260 Saponification 169, 188 Sarcolactic acid 227 Saturated compounds 59 Schiff's, or the rosaniline reaction... 122 Schweinfurth's green 151 Schweitzer's reagent 273 Sealed tubes 34 Secondary alcohols . 103 Secondary butyl carbinol 105 Secondary hydrocarbons 66 Separation of compounds 12 Silicon, organic compounds of 213 Silicon tetramethyl 213 Silicon tetrethyl 214 Silicononane 214 Silicononyl acetate 214 Silicononyl alcohol 214 Silicononyl chloride 214 Silver acetylene 83 Soaps 168 Sodium glycerol 250 Sodium hydroxyethylsulphonate... .,138 Sodium hydroxyisopropylsulphonate. 138 Soft soap 169 Solar oil 71 Spirits, manufacture of. 99 Spirits of wine 92 Stannic ethyl 218 Stannous ethyl 218 Starch 271 Starch cellulose 271 Stearic acid 158, 164 Stearin 169, 170 Stearone 134, 136 Stibines Strontium saccharosate 262 PAGE Substitution 58, 59. Succinamide 237 Succinic acid 234. Succinic acid, electrolysis of 73, n Succinic acid, salts of 235 Succinic anhydride 236 Succinimide 237 Succinimide, metallic derivatives of..238 Succinyl chloride 237 Sugars 260 Sugars, hydrazones of 267 Sulphates, ethereal 181 Sulphides 183 Sulphocyanic acid 287 Sulphonic acids 184 Sulphovinic acid 182 Sulphur, detection of... ► 24 Sulphur, estimation of 35 Sulphuric ether no Tallow 166 Tartar emetic 244 Tartaric acid .............. 241 Tartaric acid, salts of 243 Tension of aqueous vapour 32 Tertiary alcohols .... 104 Tertiary butyl alcohol 105, 106 Tertiary hydrocarbons ,. 66 Tetrachlorethane 83 Tetrachloromethane 174 Tetralkylammonium bases 205 Tetramethylmethane 65, 67 Tetrethylammonium hydroxide 205 Tetrethylammonium iodide 204 Tetrethylarsonium hydroxide 211 Tetrethylarsonium iodide 211 Tetrethylphosphonium iodide. ..209, 210 Thiocyanates, alkyl 288 Thiocyanic acid 287 Thiocyanic acid, salts of 288 Triacetin 167, 250- Tribromopropane 249 Tributyrin 170 Tricarballylic acid 247 Trichloracetal 126 Trichloracetic acid 163 Trichloraldehyde 125 Trichloromethane 172 Triethylamine 199, 204 Triethylarsine 211 Triethylarsine dichloride 211 Triethylarsine oxide 2ir VIII INDEX. PAGE Triethylphosphine 209 Triethylphosphine hydriodide 210 Triethylphosphine oxide 209 Trihydroxypropane 248 Tri-iodomethane 175 Trimethylacetic acid 155 Trimethylamine 199, 207 Trimethylamine hydrochloride 172 Trimethyl carbinol 105 Trimethylethylene 79 Trimethylethylmethane 67 Trimethylmethane 63 Triolein 168 Tripalmitin 167 Tripropylamine 199 Tristearin 167 Turnbull's blue 284 Unsaturated acids, electrolysis of- 82, 85, 87 Unsaturated compounds 77 Unsaturated hydrocarbons 72 Urea 10, 179, 289 Urea nitrate 291 Uric acid .291 Uric acid, salts of 292 PAGE Valency of carbon 53 Valeraldehyde 134 Valeric acid 164 Valeric acid, active 157 Valeric acid, normal 155, 164 Vapour density, determination of.... 42 Vaseline 71 Verdigris 151 Vinegar 148 Vinyl bromide 78 Vinyl chloride 78, 83 Vulcan oil 71 Wood spirit 88 Xylitol 258 Xylose 258 Yeast 98 Zinc alkyl compounds- 69, 107, 136, 210, 215 Zinc ethiodide 215 Zinc ethyl 59, 215 Zinc methyl 56, 216 Zinc-copper couple 57 IX THE END. Edinburgh: Printed by W. & R. Chambers, Limited.