Henry M. Leicester
College of Physicians & Surgeons Son Francisco, California
Contributions of Butlerov to the Development of Structural Theory
The basic theory enunciated by Kekul6 and Couper in 1858 made possible all the modern developments of structural organic chemistry, but neither Kekul6 nor Couper at first went beyond a bare theortical statement or attempted to make any practical applications. Nevertheless, almost as soon as the theory was announced, one investigator realized its full significance and began to think in essentially modern terms. Alexander Mikhailovich Butlerov ( I ) , on the basis of the doctrine of the tetravalence of carbon, was able to establish the principles upon which organic chemistry made its greatest advances. He coined the term "chemical structure," recognized the existence of structural isomers and the number of theoretically possible isomers for a given empirical formula, explained tautomerism, and used the theory as a guide in the synthesis of new and important classes of compounds. All of this was accomplished in the early years of the 1860Js,while most other chemists were still trying to free themselves from the confusion of the various type theories. However, the implications of the structural theory soon began to impress many younger organic chemists, and they too began to use structural ideas, often without realizing that such ideas had already been expressed. Butlerov was keenly aware of his priority in this field, and when he was directly challenged, he did not hesitate to state his claims. Toward the end of the decade, a rather bitter controversy over the question of priority took place between Butlerov and Lothar Meyer. The bitterness was perhaps intensified by a certain spirit of nationalism which is apparent behind the immediate statements of the participants. The Russian school of chemists tended to feel that western scientists neglected their work, while the Germans were not inclined to undervalue the work of their compatriots. It is worth noting, however, that KekulB himself took no part in the controversy, and Butlerov only entered i t when be felt directly attacked, and then his statements were calm and well reasoned. A survey of this controversy casts much light on the early development of the structural theory. Butlerov had been appointed professor of chemistry a t the University of Kazan in 1854, but he had not carried out any important original work during his first years in the chair. In 1857 he was sent abroad for a year of study in Germany and France. During this critical period, in which Kekul6 and Couper were developing their theories and preparing them for publication, Butlerov made the personal acquaintance of both Presented as part of the Kekul4Couper Centennial 8-ymposium on the Development of Theoretical Organic Chemistry before the Division of History of Chemistry at the 134th Meeting of the American Chemical Society, Chicago, September, 1958.
328
/ Journal of Chemicol Fducution
men. He made a lengthy visit to Heidelberg during which he developed a lasting friendship for Kekul6, and he studied for five months in the laboratory of Wurtz in Paris, where Couper was also working. There is no doubt that during this year he became well acquainted with the theory of "the chemical nature of carbon." When he returned to Kazan in August, 1858, he had already begun to develop his ideas on strncture. The basic starting point of his thought was that for any given structural formula there existed only one compound, and for any individual compound only one formula could be written. He discarded the idea of Gerhardt who had said that the formula for a compound should vary according to its different methods of synthesis or reaction. Thus Butlerov discarded the type theory altogether. KekulB continued to use type formulas in his textbook for several years. By 1861, Butlerov's formulation was so clear to himself that he felt able to present it to western chemists. He read a paper to a meeting of German naturalists a t Speyer on September 19; 1861 (2) in which he first used the term "chemical structure."' Hi definition was as folloa-s:
this chemirel srrsngement, or the type and manner of the mutual binding of the atoms in 8. compound suhstmce by the name of "chemical structure" (4).
When Butlerov returned to Kazan, he made a report to the University Senate in which he summed up his impressions of chemical theory in western Europe. None of the ideas which I found in western Europe ~cemed especially new to me. Laying aside here misplaced false modesty, I can say that these ideas sud conclusions have been quite familiar in recent years in th6 Kasen laboratory and they have not been considered especially ariginzl; they were part oi the general chemical inheritance and some %,ereintroduced into the lectures (6).
Butlerov now began to contribute a number of papers on aliphatic hydrocarbons and alcohols to western chemical journals. In these he showed that on the basis of structural theory it was possible to predict the number of isomers of various homologous hydrocarbons. His exposition was essentially that used a t present in introducing the concept of isomerism in elementary organic chemistry courses. Other chemists, with increasing frequency, gradually began to use similar structural formulas without realizing that Butlerov had preceded them. At length, in 1 Menshutkin (3) has pointed out that this term was actually first applied by Lomonosov in 1760, but this usage did not become generally known.
1867. he felt that he must assert his claims to priority. He appended a footnote to his discussion of thenumber of isomers of CIHlo theoretically possible (6), in which he said:
.
. .I have given the theoretically possible structures of the hydrocarbons CaHln. One of these, C(CH& is completely analogous to the ease of C(CH&(CnH&; a hydrocarbon which has this latter structure was recently discovered by Friedel and Ladenhurg. It is clear that if once the formula C(CH& is given, so must also the structural case C(CHJ2(C2H&be foreseen. It appears, however, thet Friedel and Ladenhurg hsve neglected the fact that the view whieh they hsve newly expressed is entirely snalogoua to that already given by me muoh earlier. I must expressly mention that in the chemical literature of recent years such idem as those I have already published are presented %a new and original (without citation). He then indicated that many chemists, including Lothar Meyer, had made unjustified claims, and concluded, The estimation of the mutual chemical method of binding elementary atoms in molecules (the principle of chemical structure) will more and more be the chief basis of most chemical speculations in the newer chemistry; of the need for this estima tion I have already spoken, and I am now obliged to assert that to me belongs an important part of the priority for complete and consequential development of this principle. This assertion of mine, as I hope, will be found to be solidly based, if one will make a closer acquaintance with my publications which have appeared since 1861.
The mention of Lothar Meyer resulted from a paper which the latter chemist had published in 1866 (7) in which he discussed the presence of "unsaturated affinities" (double bonds) in ethylene chloride as follows: Without the sssumption of unsaturated affinities, the constitution of both compounds would be identical, nnmely: HHCCHCI; with the other assumption there are three possible cases: .HHCCHCl.
..HCCHHCI
..CICCHHH
where the monovalent atom next to the C atom is held by this atom and the unsaturated affinity is expressed by a dot.
It can be seen that Meyer was actually using a strnctural formula in these cases. and he amarentlv felt that Butlerov was aiming a &sonal attack a t him. He therefore published biker counterattack a t his assumed foe, which he entitled "To the Defense" (8).
a
In setting up this formula I have neither intended nor believed thet I was establishing s claim to priority. Nor does such a right in the least belong to Prof. Butlerov. This and a thousand other formulas are the obvious consequence of the two propositions that carbon is a tetrevdent element and that its atoms and all other eloments in its compounds are arranged in chains. Both propositions are a pert of the rich heritaze developed through the tireless work of numerous investigators of organic chemistry. But the first of these propositions was clearly reraqiaed and expressed first and only by A. KekulB in 1857. The discovery of the second proposition KekulB divided with A. S. Cauper. KekulB, however, combined these propositions long before Prof. Butlerov, who learned of the chain formation from KekulB and suggested calling it structure. The establishment of these formulas, carried out through a long series of combinations, permutations, and calculus of variables, required in concrete cases neither unusual genius nor great gifts of discovery. Whether one chemist should express sehematicelly the series of signs which expressed the order of stoms from left to right, as is usual in Europe, or like the Hebrew, from right to left, or like the Chinese, from above down, is merely B matter of taste. Whoever by writing down formulas of this type intends to establish a property right deceives himself. . .he claims things as his newly discovered property which are the common goods of science through the servicps oi others years before.
It can here be seen that Meyer completely misinterpreted the real significance of Butlerov's contributions, reading them as a mere manipulation of symbols and that he committed the very common error of claiming that because a given point of view was becoming obvious to everyone, the man who first realized the meaning of this point of view deserved no credit. Butlerw was not slow to accept this new challenge. At the time he was making a third trip to western Europe, largely for the purpose of defending his claims, and he was a t this time in Nice. From there he sent his reply, which he entitled simply "An Answer" (9).
structure is a consequence of the recognition of the valence of
believe that the views exore&ed bv C o u. ~ e r(unfortunatelv . . onlv. t r i d y , arc almmt i.lentiwl n.irh rhose gerrerally arrtprrJ and r h t the fwmuln? yiwn I,J. ( b u p c r nrc sctw~llyrational forrnul~s t cmititutionul fornlula~ in rlre present arner of the s u r d , ~ l u ia, or formulas of chemical structure. But what Herr Meyer says about the development and expanded use of these new propositions will, as I believe not be accepted completely by an impartial man. Aside from the recognition of the new propositions, we still find for several years longer much whieh had either herome superfluous or did not agree with these propositions. This includes the use of types, both compound and mixed, the old way of determining formules by reaction only, so that for one and the same substance several rational formulas could be given, etc. Similarly, assumptions whieh did not entirely agree with the new principles were not entirely absent from the writings of Kekul6 even after I expressed my views on chemical ~tructureand made them the basis for the chief principles of my theoretical speculations. . . I place no value on the outward appemance of formulas.
.
After a challenge to Meyer to reread his various papers, Butlerov concluded that he would not "shrink my contribution to developing the new principles to the mere name 'chemical structure' and the use of a certain way of writingformulas." This reply seems to have ended the polemical part of. the battle. It is probable that Butlerov's acknowledgment of the importance of KekulB's work silenced the German critics. At the same time he stated his own contribution so clearly that it could scarcely be denied. Instead, another fate overtook it. It became so much a part of the basic framework of organic chemistry that it was taken for granted, and the work of the originator was forgotten. This is usually the fate of those who make the initial steps in what later becomes a whole new science in itself. Literature Cited
(1) LEICESTER, H. M., J. CHBM.EDUC.,17, 203 (1940). I.., "Alexander Mikhailovich Butlerov, 182% (2) GUMILEVSKI?, 1886," Moscow, 1952, p. 152. (3) B. N., 'Chemistry and the Way of Its De. . MENSHUTKIN, velopment," Moscow and eni in grad, 1937, p. 204. (4) K A Z A N S KB. ~ , A,, PETROV,A. D., A N D BYKOV,G. V., "Srlectel Works of A. M. Butlerov in Orennie Chemistry," Moscow, 1951, p. 557. (5) MENSHUTKIN, N. A,, J . Rum. P h y ~Chem. Soc., 19, Butlerov Memorial No., 2-12 (1887). (6) BUTLEROY, A. M., Ann., 144, 9 (1867). (7) METER,I,., Ann., 139, 286 (1866). I,., Ann., 145, 124 (1868). (8) MIEYER, A. M., Ann., 146, 260 (1868). (9) BUTLEROV, ~~
~~
Volume 36, Number
7,July 1959
/
329
