Butleroy, Kekulé, and Kolbe
The accession of Czar Alexander II to the Russian throne in 1855 soon led to a quickening interest in modern science, and his government embarked on an urgent program to encourage foreign education of eligible candidates, especially at German and Swiss universities.[53] One of the earliest of these scholars was Aleksandr Mikhailovich Butlerov,[54] who was already full professor at Kazan (although he had not yet done any significant chemical research) when he arrived in western Europe in 1857 on a government-sponsored komandirovka (educational tour). Butlerov was influenced by two visits with Kekulé in Heidelberg, but he spent his longest period (five months) in Wurtz' laboratory in Paris. This was just when Couper was there as well, formulating his ideas on what members of Wurtz' research group were already beginning to call the "structure" of chemical compounds. Butlerov participated in this program as well, presenting a lecture to the new Société Chimique (on 17 February 1858) that outlined a carbon type theory similar to that of Odling, Kekulé, Frankland, and Kolbe.[55] Unfortunately, this lecture was never published. By the end of May, Butlerov was back in Kazan, but the year that he had spent in Germany and France determined the course of his research for the rest of his life.
Three years later Butlerov was back in the West. In September 1861 he presented to the Speyer meeting of the Gesellschaft Deutscher Naturforscher und Ärzte a paper "On the Chemical Structure of Com-
pounds" that Soviet historians have always considered the locus classicus of structure theory.[56] The real purpose of the paper was to try to move the chemical community from a halfway position, mixing older type and radical theories with the new theory of atomicity of elements, to the position of full structuralism. This was just the sort of transition to which Erlenmeyer later referred, and the timing matches, as well. It is therefore likely that Erlenmeyer's and Butlerov's conversions were connected, but it is not easy to determine who played the leading role for the other. Erlenmeyer wrote Butlerov eight months after the Speyer meeting to lodge a mild priority protest. "I think I can assume with certainty," he stated, "that the ideas [in Butlerov's Speyer paper] were, in large part at least, influenced by our conversations." These ideas included the constancy of tetratomicity of carbon, double bonds in unsaturated hydrocarbons, and the variable strength of the four valences of carbon, all of which, he asserted, he had been earlier to emphasize than Butlerov.[57]
It is in any case clear that Erlenmeyer and Butlerov agreed closely with each other from 1861 on. Erlenmeyer printed Butlerov's Speyer speech in full; it was otherwise unpublished, perhaps otherwise unpublishable due to its purely theoretical content. In part because Heidelberg was proving to be increasingly popular with Russian chemistry students, Erlenmeyer began to teach ever larger numbers of Russians; at times this national contingent comprised more than a third of his students. Similarly, his Zeitschrift was the most common publication outlet for Russian chemists in the early 1860s.[58]
In articles published in the Zeitschrift over the next few years, Butlerov instantiated his theoretical manifesto by means of innumerable examples from the science of organic chemistry, most of them having to do with the structural elucidation of isomers and many incorporating novel syntheses emanating from his laboratory.[59] In so doing, he established himself in the forefront of the fast-moving field of structural organic chemistry.
Butlerov was also concerned to integrate what seemed to be a fractured and fractious field, by attempting a substantive and semantic analysis of the language and theories of some of the leading chemists of the day. The leading personalities among the theoretically active chemists were Kekulé and Kolbe. Despite their strong apparent differences, Butlerov wrote, their "basic principles are nearly, or perhaps entirely identical," the conflicts arising only because of their incomplete or inconsistent application of those principles. Kolbe was inconsistent, Butlerov felt, because he sometimes assumed divalent or even trivalent carbon and because he used equivalents rather than atomic weights. Kekulé was inconsistent because of his assumption of "molecular com-
pounds" for certain structures, which violate atomicity rules, and because he sometimes failed to propose a single unique structure for every compound.[60]
Semantically, Butlerov also tried to shed light rather than heat. If one really examines what each author means by his denotations, whether he uses the term "reaction formulas," "constitutions," "relative constitutions," or "topographic position" is of little consequence. Kekulé, Kolbe, Erlenmeyer, Wurtz, Heintz, and other advocates of the new theory, he claimed, were talking about essentially the same things and interpreting their formulas largely the same way. This was why Butlerov thought a relatively new and unused expression should be introduced, namely, chemical structure . Butlerov wrote
In Kolbe, as in Kekulé, one sees the same tendency to judge the chemical connections of the individual atoms forming a complex molecule, or the points of attack of chemical affinity, which is saying the same thing. Kolbe defines constitution as the manner of this connection; I call this chemical structure . . . Be that as it may, most of Kekulé's as well as Kolbe's formulas are clearly based on the principle of chemical structure. I might add that ever since the importance and role of atomicity was recognized this principle has formed the real point of departure for almost all theoretical considerations.[61]
During the 1860s, Kolbe agreed with Butlerov's identification of "constitution" with "structure," for he commented in a letter to Frankland that the two terms had identical denotations.[62] After 1870, however, Kolbe began to draw increasingly sharp distinctions between them.
Butlerov had high respect for both Kolbe and Kekulé as leaders of the structuralist school. The influx of Russian chemists, mostly from Kazan, into Kolbe's lab during the years 1862-1867 can only have been due to Butlerov's recommendations to his students. Butlerov also knew of the importance of Kekulé's work for the rise of structure theory; he only resented Kekulé's attitude, especially his imperialistic manner of promoting his own work.
Kekulé had been reading all of this literature as it came out and was induced to add some clarifying comments. It makes little difference, he said, if one chooses to speak of "chemical structure," "constitutions," or "topographic positions"; the ideas were those on atomicity of elements that he had been the first to publish in 1857-1858.[63] He took strong exception to Erlenmeyer's and Butlerov's opinion that he had remained tainted by residues of type-theoretical thinking until 1861. Recent historical assessments suggest that Kekulé's claim to exclusive right to valence and structure theory is at the very least simplistic (as he later implicitly conceded), but that his avowal that he had been a
full structuralist since 1857-1858 is consistent with what is known of his views in the late 1850s.[64]
It was during these years that Kekulé's relationship with Kolbe went from uneven to very bad. Despite his early close association with Kolbe's enemies such as Gerhardt and Williamson, Kekulé's view of Kolbe's work was not unremittingly negative. During the Kolbe-Wurtz polemic over lactic acid, Kekulé expressed to Erlenmeyer the wish to "negotiate" with Kolbe and to accustom his friend Wurtz to "better manners." In a letter to Lothar Meyer, he referred to Wöhler's and Kolbe's "lovely " syntheses (his emphasis), and a few years later publicly praised Kolbe's "sagacity" in successfully predicting the existence of secondary and tertiary alcohols.[65]
But Kolbe never had any use for Kekulé. He considered Kekulé a "foolish chatterer," a self-promoting and ostentatious pretender whose thin reputation would very soon collapse.[66] In 1861 and 1862 their work came uncomfortably close together, when both made tentative attempts to explain certain of the isomeric relationships of aromatic monoacids and unsaturated diacids. In one of his papers, Kekulé refused to comment on Kolbe's views on the first of these subjects, since the whole matter was still uncertain; moreover, he said, Kolbe's views changed so often that he had become a moving target, difficult to hit.[67] Kekulé had a second opportunity to upbraid Kolbe when he publicly identified two errors in one of Kolbe's papers. Kolbe conceded "a slip of the pen" for one of them, but tried to excuse the other by an unsatisfactory semantic ploy that did not satisfy the editor of the Annalen , Kolbe's good friend Hermann Kopp, who added an explanatory footnote.[68]
A third occasion caused Kolbe the most embarrassment. Shortly after arriving in Marburg, Kolbe had one of his students electrolyze succinic acid, expecting from theory to obtain ethylene. Kolbe was surprised to find his student reporting both eudiometric and gravimetric combustion analyses of the product as indicating methyl ether. He was never able to explain this result; moreover, he lost the data given to him by the student and even forgot the student's name. But he never forgot this curious result. In the fall of 1859, in the midst of that wondrous burst of activity that did so much to burnish his reputation, he appended a description of the experiment, including a statement only on the eudiometry and no analytical data, to a series of short notices published in the Annalen .[69]
In 1864 Kekulé repeated Kolbe's experiment and stated that Kolbe had misidentified the product: it was ethylene, after all. He then added insult to injury by expressing surprise that such a "skilled chemist" as Kolbe could confuse two such different compounds and pointing out
that eudiometric combustion analysis is never sufficient to establish organic formulas.[70] Kekulé's reproof was printed in Erlenmeyer's journal, and Kolbe wrote Erlenmeyer soon thereafter:
Kekulé is a cheeky insolent wretch to purport to teach me that eudiometric analysis alone does not suffice to determine the composition of a gas. But I will have a hard time answering him. . . . I can well imagine that Kekulé is very unhappy that his type theory no longer satisfies even him or gives him nourishment, and I can understand that such a petty man would loose his anger on someone who is traveling a better road with his chemical views. But regarding the succinic acid electrolysis he may be right.[71]
He was right—again—and Kolbe was forced to admit it publicly. Herr Kekulé "ought to have proceeded just a bit more modestly," but in the matter at hand he was "completely correct." Indeed, methyl ether as a product of succinic acid electrolysis had always seemed inconsistent with Kolbe's own theories. "By his demonstration of the error and by clearing the matter up Herr Kekulé has freed me from this embarrassment, and I am therefore doubly grateful to him."[72] Kolbe had done the right thing by graciously conceding to a man he despised. What is curious is how he had gotten himself in this position in the first place. He had published a highly anomalous observation that was eight years old, without data, without even remembering the name of the student who had performed the work, and without even attempting to repeat the relatively straightforward experiment. It was a careless and thoughtless act, and Kolbe was justly embarrassed by it. But years later, he would find repeated occasion to repay Kekulé for his insolence in pointing out Kolbe's mistake to all the world.