CONSTITUTION ORGANIC COMPOUNDS; A BRIEF ACCOUNT OF THE DIFFERENT THEORIES ADVANCED ON THIS SUBJECT. BY PROF. HENRY EENI-V/ HeaB before tfie ffiambrttojje Scientific Association, NOV. 1852. BOSTON: OTIS CLAPP, 23, SCHOOL STREET. 1853. boston: PRINTED BY JOHN WILSON AND SON, 22, School Street. CONSTITUTION OF ORGANIC COMPOUNDS. Organic Chemistry embraces an almost endless number of bodies, the formation of which^we must ascribe to the in- fluence of a peculiar modification of the molecular forces; better known under the name of vital force. The constituents of organic compounds are comparatively very limited, and consist principally of carbon, hydrogen, oxygen, nitrogen, and occasionally of phosphorus and sul- phur. In the first period of this now so extensive department of science, organic bodies were considered to be products of a peculiar organic force, since their formation could not be explained according to purely chemical laws: consequently, no distinction was made between proximate and ultimate constituents, and the atoms of the different elements were considered as simply joined to one another, their arrange- ment not being influenced by chemical attraction. The vital force formed here the cloak which concealed ignorance, and retarded the development of Organic Chemistry, like that of some other branches of natural science; since, by giving an apparently satisfactory explanation, it prevented, for a long time, further investigations. But, when philosophers recog- nized this force in its manifestations to be only a complication 4 of modified molecular forces, the difference between organic and inorganic bodies was at once greatly diminished. Berzelius, whose sound and accurate researches enriched every branch of science, was the first who spoke thus : " I lie application of that which is known, and will be, of the mode of combination of the elements in inorganic nature, must be the guide by means of which we may hope to get a true and harmonious conception of the composition of those bodies which are formed under the influence of the vital process. Such a proposition — to compare inorganic nature with, and to apply its laws to, organic bodies—at once created the idea that the latter likewise consist of proximate and ultimate parts. The discovery of organic compounds of equal per- centage-composition and atomic weight, but endowed with different physical and chemical properties, rendered this argument still more conclusive. We must, then, necessarily seek in their different internal composition an explanation of this fact. To these so called isomeric compounds belong, for instance, many of the essential oils of the formula C^llig; further, tartaric and racemic acid, both of the formula, = c4ii8ov By looking for the proximate constituents of organic bodies or radicals in general, we meet with many difficulties. Organic compounds can rarely be prepared directly by artifi- cial means: their composition, consequently, cannot be inves- tigated synthetically, but simply by way of analysis. The analysis of organic bodies comprises, 1, the ultimate analysis, by means of which we find the exact relative quantity of the elements combined in an organic substance, and from that the relative number of atoms of its constituents; 2, the deter- mination of the atomic weight, which gives us the absolute number of atoms. The execution of these two operations makes us acquainted with the empirical formula of a body. The empirical formula for alcohol is, for instance, = C4H0O , which gives us no further indication how these twelve single atoms are arranged among each other. In order to obtain the rational formula, which presents to us more closely the 5 inner constitution of a compound, we have to decompose it by various means and ways, and to study the relations of these products to the original substance. Alcohol, e.g., may be converted into ether by simply depriving it of water. The formula of ether is known to be C4HsO; and we may, therefore, consider C4H60 -f- HO the formula for alcohol. C4H50 is found, on further investigation, to bear a close analogy to an inorganic oxide, in which C4H6, or ethyl, rep- resents the radical or electro-positive atom. According to these considerations, we imagine the rational formula of alco- hol to be C4H5-j-0-f-HO; i.e., the hydrate of the oxide of ethyl. The establishment of rational formula from the products of decomposition of organized bodies has, however, also given rise to many extravagant and unsustainable views. Persoz, e.g. adopted for acetic acid (C4H404) the formula C2H3+CO-(-C02+HO; and dissected most organic acids in this manner, by presuming in them the existence of ready- formed water, carbonic acid, and carbonic oxide. All organic bodies are, with few exceptions, easily decom- posed: the slightest disturbance of the equilibrium of the chemical forces is often sufficient to recall the original affini- ties between the elements. The products of decomposition must vary with the different destructive agencies we employ. It is also obvious, that, from these products, different views respecting the constitution of an organic substance may be adopted, all more or less capable of accounting for the pheno- mena of decomposition. Of all the theories advanced concerning the constitution of organic bodies, the so called " Radical Theory " — the development of which we will follow here somewhat in de- tail — alone is founded on the established laws of inorganic chemistry, and appears to be, more than any other, in accord- ance with experience. This theory is still, up to this day, the predominating one among chemists, particularly in Germany. Berzelius first advanced this theory, after the publication 6 of the investigations on alcohol and ether by Gay Lussac and Dumas. He then assumed that organic bodies containing oxygen were oxides of organic radicals. By applying this view to ether, it becomes the oxide of an organic radical, capable of combining with acids like an inorganic oxide ; and this analogy with inorganic compounds justifies the conclu- sion that compounds of Se. Te. S. CI. Br, with this radical, could be prepared. Liebig, whose attention was called to this subject, persuaded himself of the correctness oi this theory, applied it at once to the compound ethers, and named the radical (C4H5) of ether, ethyl, and considered alcohol as an hydrated oxide of ethyl ((\l\_,) O+HO. He predicted, at the time, the future isolation of the radical C41 ly On this occasion ensued a critical discussion with Dumas, who con- sidered ether to be the hydrate of etherine, C4H4-}-aq; but, in consequence of a mutual exchange of opinions, Dumas altered his view, and became a zealous advocate of the radi- cal theory. Soon after, he declared, in a note to the Academy of Sciences in Paris in his and Liebig's name, the difficult question respecting the constitution of organic bodies solved; exhibited the radical theory as the only possible one; and stated further, that, for the future, his object would be to discover and study those radicals. Berzelius, in pointing out the direction which had to be pursued for that purpose, declared that the laws after which organic compositions take place could best be studied from the products of the metamorphosis of organic bodies, when those latter were exposed to different temperatures. Hereby, without the influence of what has been called vital force, new compounds are formed, many of which are the same produced by vitality. The theory of organic radicals considers organic substances as consisting of compound bodies called radicals, able to play the part of elements, and which unite with other simple bodies, or form among themselves double compounds. With the discovery of cyanogen, the theory of organic radicals received the first fact of the existence of compound bodies 7 exhibiting the functions of an element. A radical combines with elements according to the common laws of inorganic chemistry, and may be replaced by another element. But all radicals do not fulfil these conditions. The best criterion for considering a compound to be a radical is, that, when combinations with oxygen, sulphur, chlorine, &c. exist, this radical, under proper circumstances, can be transferred from one compound to the other. Iodide of ethyl -|- chlorine. Chloride of iodide -f- iodine. (C4H5)I + CI = (C4H,)C1 +1 (free). Metals, such as iron, manganese, zinc, chromium, tin, anti- mony, arsenic, which enter into the composition of radicals, cannot be recognized by common reactions. An organic radical, like an element in inorganic chemistry, gives a foundation for a series of compounds. The following table affords a view of a series of com- pounds of the radical Kakodyl, which can be prepared, partly direct, partly by substitution. Kakodyl (C4H6+As) = Kd. Oxide of kakodyl = Kd+O. Kakodylic acid = Kd+03+HO. Cyanide of kakodyl = Kd+Cy. Chloride of kakodyl = Kd+CL Salts of oxide kakodyl = KdO+S (S oxygen acid). Salts of kakodylic acid =z Kd03+MO (M = metal). Inorganic chemistry may be defined as that branch of chemistry which treats of single radicals and compounds, in contradistinction to organic chemistry, which treats of com- pound radicals. Kakodyl and cyanogen were for a long time the only positive support of the radical theory; since the principal objection brought formerly against it was that the existence of a great many compounds had to be assumed, and were not known in an isolated state. But we may ask, 8 Could any one reasonably deny the existence of fluorine, although chemists succeeded only recently in isolating it from its compounds ? But this objection has been removed by the late important researches of Frankland and Kolbe, which proved beyond doubt the existence of the so-called alcohol-radicals, as ethyl, methyl, valyl, and amyl; and confirmed the theoiy — at least with regard to. the composition of alcohol and ether — advanced more than seventeen years ago by Berzelius and Liebig. Lowig, Schweizer, and Landolt discovered still later a series of highly interesting radicals, which have a composition similar to the kakodyl of Bunsen, and enter into composition with elements in the manner of simple substances. The authors call them " stybethyl, ethyl-stibyl, stybmethyl." We will now, in succession, briefly describe the prepara- tion and properties of these radicals. Ethyl = C4H6 = E. Prepared by the; action of zinc on iodide of ethyl, in sealed tubes, at a temperature of 150° C. C(II,I-j-Zn = CjHj+ZnL* Constitutes a colorless gas, without smell; at —18° C. not yet liquified; by cold and pressure, condensed to a colorless fluid. Methyl = C2H,. Prepared, 1, by the electrolyses of acetate of potassa (Kolbe); 2, by decomposition of iodide of methyl by means of zinc. The properties are the same, prepared either way. It is a colorless gas, not condensable at —18°. Amyl = Cj0H„. Results from the action of amalgamated zinc on iodide of amyl, above 100° C. Forms a transparent colorless liquid, of an ethereal odor and burning taste, not decomposed by potassium at 155° C. Valyl = C8H9. Prepared by the action of a galvanic current on valerianic acid (Kolbe). Forms a colorless liquid of an ethereal odor. The formation of this radical from vale- rianic acid is explained thus : C10H10O4 = 0,1 Ia+2CO„+H. time, two secondary products (methyl and elayl) are formed. 9 Frankland states the chemical character of the radicals ethyl, methyl, &c. to be as follows: — 1. They show the general deportment of hydrogen, but are less electropositive. 2. They are able to replace the hydrogen in any com- pound in which this element plays the part of a simple radical, and, when it does not occur in a group, where it dis- plays the functions of a compound radical. 3. The haloid compounds of the named radicals may be considered as hydrogen acids, in which the hydrogen is re- placed by one of these radicals. ' 4. They replace hydrogen in ammonia, as is shown in the alkaloids discovered by Wurtz and Hofmann, whereby the assumption of the hyothetical radical, amid, is useless. 5. They exhibit, besides the property of uniting with electro-negative elements, likewise that of combining with hydrogen. Up to the present time, Frankland did not succeed in preparing the oxides of these radicals, as ether, &c.; these radicals namely show in general very indifferent chemical properties. This chemical indifference, when in an isolated state, is not surprising; they exhibit, in this respect, the same deportment as many elements (hydrogen, platinum), which combine with other bodies only when in statu nascente. When the iodides of ethyl, methyl, &c. are decomposed by the action of zinc, arsenic, and phosphorus, ethyl, methyl, &c. will partly combine with those elements, whereby a num- ber of new radicals are formed corresponding to kakodyl. The existence of compounds of hydrogen with Ars, Sb, Te, as also the fact, that, in the new alkaloids of Wurtz, methyl and ethyl may be substituted for hydrogen, led Frankland to the conclusion, that, ere long, all the following compounds may be prepared. Those marked with * have already been isolated. 2 10 Hydrogen Scries HZn ns.As *Hx.Sb *H3,P Methyl Series. *(C„H3)Zn *(C2H3)2.As (C2H3)x,Sb n('2H3)8,P Ethyl Series. (C4H,)Zn (C4H,)vAs (C/iyx,Sb (QH5)3,P Butyryl Series. (C0H!)Zn (C6Hr)2,As (C6H7)x,Sb (CUH7)3,P Valyl Series. (C,lI„')Zn (CJI^.As (C8n9)xsb (C8H9)S,P Amyl Series. *(rl0H„)Zii (C10IIuy,Aa (C10Hn)x,Sb (C10nn)3,p Phenyl Scries. (C'„Hfl)Zn (CuH,)«;As ((J.jr.^Sb (C12HJ8,P Stybethyl = (C4H5)3, Sb (Lowig and Schweizer). It is prepared by the mutual decomposition of iodide of ethyl and antimoniuret of potassium: forms a colorless liquid, of an onion-like odor. Its disposition to combine with other bodies is, with exception of potassium, kakodyl, and the haloides, unequalled. It unites, at a common temperature, with O, S, Se, CI, &c, with evolution of heat. "From its compounds it can, by means of potassium, again be separated, with all its original properties. One atom of stybethyl com- bines with two atoms of an element. Under certain circumstances, two atoms of ethyl are dropped from stibethyl,^ and a new radical formed of the composition C4H5Sb, which has been called ethyl-stibyl, one atom of which unites with five atoms of an element. Lowig and Schweizer have succeeded in preparing compounds of bismuth and phosphorus similar to ethyl-stybyl. Stibmethyl == (C2H3)3,Sb. Landolt, called upon by Lowig, isolated and examined stybmethyl. It is prepared by distil- ling iodide of methyl together with antimoniuret of potas- sium. It is a liquid in every respect analogous to stybethyl. United with two atoms of oxygen, it constitutes a base satu- 11 rating two atoms of an acid, and forms also compounds with S2, Cl2, Br2, &c. Oxide of stibmethylium = (4C2H3,Sb)0. — By pouring iodide of methyl into stibmethyl, Landolt received a crystal- lized compound of the formula (SbMe4)I. Me = C4H3, which he calls iodide of stibmethylium. Its radical (SbMe4), not yet isolated, he gives the name of stibmethylium (analo- gous to ammonium). The oxide of this radical (SbMe4)0, which he isolated, is the more important, since its constitution confirms the ammo- nium theory of Berzelius. It occurs in white crystals. In its alkaline properties, it resembles most closely hydrate of potassa; is very corrosive; soluble in water and alcohol; attracts C02 from the air, which is separated again by caustic lime. The aqueous solution of this body tests and smells like ley, feels soapy between the fingers, and evolves ammo- nia in the cold from the salts of ammonia. Lime, oxides of lead, mercury, copper, zinc, are at once precipitated; the last is redissolved in an excess: chloride of platinum yields a yellow precipitate. In a word, this compound body might, by simply qualitative reaction, be confounded with potassa: it forms with acids neutral and acid salts, resembling the corresponding potassa salts. The investigations just mentioned are at a time when such contradictory views concerning the constitution of organic bodies are advanced, of the highest importance; and even the opposers of the radical theory will allow that of late it has gained considerable ground. Although now perhaps most chemists agree with regard to the constitution of organic compounds, there is, however, still considerable arbitrariness respecting the composition of radicals. Some, like Liebig and Wohler, assume, besides binary radicals, consisting of C and H, ternary ones of CH and 0; which latter Berzelius and Lowig reject. Berzelius, on the ground of his electro-chemical theory, denies, likewise, the existence of radicals containing CI, Br, I; which scarcely 12 admits, now-a-days, of contradiction, as we will see hereafter. There are, also, probably radicals which contain S and Ph. The following diagram will, with regard to the internal composition of oil of bitter almonds, exemplify how even advocates of the radical theory may be led to different con- clusions. View of Ternary Radicals. Radical = CMIIs02 = Benzoyl. Oil of bitter almonds = C14H502-}-H. Chloride of benzoyl = C14Ha02+CL Sulphuret of benzoyl = C14H502-|-S. View of Binary Radicals. Cj4H6 = Picramyl. oxide of picramyl. oxide of picramyl, in which' one atom of chlo- rine replaces one atom of hydrogen. ©xide of picramyl, in which one atom of sul- phur replaces one atom of hydrogen. Lowig believes in the existence of single radicals, for the following reason: oxalic acid, combined with oxide of lead, dried at 100° C. has the formula C203. Those chemists who consider this acid to be a higher oxide of carbon than car- bonic oxide, = 2CO-J-0, render obvious the reason why it is so easily decomposed into CO and C02. But its strongly acid properties are not explained; besides, oxalic = rhodi- zonic = krokonic acid, belonging to one series, must then, although of organic origin, be ranked among inorganic acids j then oxides of carbonic oxide cannot be considered as organic bodies. To remedy this, Lowig assumes the existence of singular radicals, which consist of one or several atoms of one and the same element united as a whole by polar attrac- tion. Oxalic acid contains, then, a radical (C2), = oxatyl, Radical = (CMH6)Oa = C"H« l 4- O — 13 combined with three atoms of oxygen, and stands now in the same relation to carbonic acid as sulphurous to sulphuric acid; thus : — C02 (C2)03 S02 s 03 The radical theory was not enlarged by Liebig, but kept in its original limits. Berzelius extended it further, until, by the discovery of coupled compounds, he arrived at a new conclusion, namely, that the number of radicals was not very large, and deduced the apparently unHmited variety of combinations relative to organic bodies from the manifold proportion in which copulations may occur. What is meant by coupled compounds we will illustrate by an example. Sulphovinate of baryta has the empyrical formula, (C4H5)0,S03+BaO,S03. Sulphovinate of baryta is soluble in water. In this and similar salts— (C4H5)0,S03 — is the copula, which adheres still to the liberated sulphu- ric acid by the separation of the base. By the addition of S03 to the solution of sulphovinate of baryta, a precipitate of sulphate of baryta is formed, and again (C4H-)0,S03-f- S03,HO. This reaction proves, that, in the sulphovinate of baryta, there exists no ready-formed sulphate of baryta, but that it contains a coupled acid. The rational formula of sul- phovinic acid is then HO-(-(EO,S03),S03, when E = C4H5; and for its salts (M = metal), MO+(EO,S03)S03. Berzelius applied his theory of copulas likewise to organic bases (alkaloides), supposing their properties to be derived from ammonia (NH3), able to unite with organic compounds to copulas or coupled compounds. Dumas, who first defended zealously the radical theory, more lately advanced a new theory, called " Theory of Sub- stitution." Experiments of the effect of haloides on various organic compounds gave the result, that, from the latter, a part or all their hydrogen can be withdrawn, and CI, Br, I, in the same atomical proportion be substituted, without the physical and chemical properties of the new compounds differing essentially from those of the original substance. 14 Organic acids retained their acid, — alkaloids their basic qualities ; thus : — Acids. Acetic acid = C4H:,().1+HO. Chloracetic acid = C4C1303+H0. Alkaloids. Aniline = C12HrN. Chloraniline =■ Vl.}le') ~C1$ Bichloraniline = Cr,H5) ci2yv (Even compounds of X04, IIN3, have of late been substituted for H.) Dumas, in speculating on these results, adopted the fol- lowing view: — Organic compounds are made up of a series of original groups of elements, in which every element may successively be replaced by another element (or compound), without the total group undergoing essential change in its original pro- perties. These groups he calls "types" (primary forms). The chemical nature of the substitutes does not come into consideration when only the substitute replaces the elements in equivalents, and takes the same position in the group. For the sake of an illustration, let us apply what has just been said to ether. C4HaO (type) = 10 atoms. C4H4) >o ci S = 10 „ >o C12)U = 10 , C4H/) ci8r = 10 „ c