Assistant to Playfair
In 1845 an opportunity arose for a temporary foreign position for Kolbe. The British government had just established a Museum of Economic Geology near St. James' Park in London and had hired Lyon Playfair, a former student of Liebig, as the museum's organic chemist. One important assignment given Playfair was the analysis of mixtures of naturally occurring hydrocarbons, required in connection with a Parliamentary Commission on Explosions in Coal Mines. The acknowledged master of such analytical methods was Bunsen, to whom Play-fair turned for advice. Bunsen thought to send Kolbe as assistant to
Playfair and persuaded Kolbe to accept the position. This was to be Kolbe's only extended trip of his life outside the European continent.
Kolbe entered into his duties in London in October 1845, the same month that another assistant, Edward Frankland, arrived at the museum and the same month that August Wilhelm Hofmann arrived from Bonn as Professor of Chemistry at the new Royal College of Chemistry. Hofmann later related that he met Kolbe soon after their arrival at a meeting of the Chemical Society. He had been given a large official residence rent-free, and he invited Kolbe to live with him there. They became intimate friends.[12]
Frankland was seven years younger than Kolbe and not very knowledgeable in chemistry, especially regarding the latest experimental methods then current in Germany, having come directly from an unhappy pharmaceutical apprenticeship. When Hofmann married in August 1846, Kolbe established lodgings on Belvedere Road, near Frankland's residence on Doris Street. Frankland later recollected
At this time Kolbe could speak only a few words of English, but we arranged to give each other lessons in German & English and we met, for this purpose on two evenings in the week at his lodgings. . . . He made rapid progress and was soon able to speak with facility. It was not long after this intercourse became established between us, before he began to explain to me his great interest in organic chemistry.[13]
Frankland reported that Kolbe had a "supreme contempt" for inorganic analysis, of the type that Frankland had been hired to perform, as it was of "little or no theoretical interest."[14] He was soon infected by his friend's enthusiasm for experimental and theoretical organic chemistry. Kolbe instructed him both in Bunsen's "then but little known but beautiful & delicate processes of gas-analysis" and in Berzelian theory.[15] In addition to Hofmann and Frankland, Kolbe became acquainted with most of the London chemical community, and it is said he made a particularly strong impression on Thomas Graham and Michael Faraday.[16]
Frankland described the "profound impression upon all of us" made from the first by Kolbe's exemplary care and skill in laboratory operations. "He never grudged any amount of trouble in fitting up apparatus or performing an operation, if a greater amount of accuracy could thereby be secured." After Kolbe sent a sample apparatus for explosion eudiometry, Wöhler replied with thanks, in awe of Kolbe's glass-blowing skill. If all else failed, his former teacher opined, Kolbe could easily make a living as a skilled artisan.[17]
Kolbe's official duties were to analyze mixtures of gases gathered
from coal mines in the hope of providing for better means of preventing explosions. He reported on this work both to Bunsen and officially to Playfair for the British government.[18] Frankland related that there was insufficient room at the museum's laboratory for these analyses, so they were all performed in Kolbe's lodgings. Playfair, as it happened, was not often present in London due to other governmental duties such as service on a commission on the potato blight and a lectureship at the military college at Addiscombe.[19] Perhaps due to this circumstance, Kolbe had considerable free time on his hands, and by December 1845 we find him using Playfair's lab for his own research purposes.[20] Toward the end of his stay in England, in the spring of 1847, he published two important papers, the second of which was a joint project with Frankland.
Kolbe knew that he of all European chemists was in a unique position to exploit a certain new field of research. He had mastered improved and as yet unpublished gas-analytical methods, as well as the mode of construction of a novel and very powerful carbon-zinc battery, both of which he had learned from Bunsen, and unlike his master, he was entranced by the theoretical goal of investigating the constitutions of organic molecules. With these tools, Kolbe set out to accomplish what decades earlier had repeatedly frustrated Berzelius himself: the electrolysis of organic acids. One of his laboratory notebooks preserved in the Deutsches Museum in Munich records experiments in this direction from 1 October 1846 to February 1847.[21] With solutions of potassium acetate, butyrate, and valerate, Kolbe made the electrolysis work, but he obtained a daunting number of solid, liquid, and gaseous products. After electrolyzing potassium valerate, for instance, he isolated, in addition to potash, hydrogen, and carbonic acid, a new saturated hydrocarbon possessing the formula C8 H9 , a new olefin C8 H8 , and an ethereal oil apparently of the formula C8 H9 O+C8 H9 C2 O3 . In his first paper on this subject Kolbe conceded that these were still preliminary results, but he stressed that they supported the copula formula for valeric acid, which would be C8 H9 ·C2 O3 ·HO.[22] Although he was not able to bring this work to a fully satisfactory conclusion while in England, this was the origin of the still useful "Kolbe electrolysis" reaction.
Frankland joined Kolbe in an attack from a different direction on the question of the constitution of organic acids. It was known that upon hydrolysis, cyanogen and benzonitrile yield oxalic acid and benzoic acid, respectively. The latter reaction, developed in 1844 by Fehling, suggested the correctness of the copula formulas for benzonitrile and benzoic acid:
Kolbe and Frankland determined to generalize this reaction for the simple aliphatic acids and succeeded admirably:
In the view of the authors, this work supported the existence of copulas and, in Frankland's later assessment, established "for the first time the internal molecular structure of these acids . . . ."[23]
But in the published paper, Kolbe and Frankland expressed their views with diffidence. Well cognizant of their youth (Frankland was only twenty-one) and lack of established positions, they wisely chose to soft-pedal their novelties. Investigations of the molecular constitutions of compounds, they wrote,
. . . are always attended with more or less danger, and those who, leaving the safer road of experiment, plunge into the depths of hypothesis, and build up theories apparently ingenious, though often untenable, frequently stumble and fall amongst a host of contradictions. It is a common error, as experience teaches, into which young chemists are very apt to fall, that, persuaded of the infallibility of their own views, and blind to well-founded objections, they endeavor to convince by quick and ready argument rather than by solid reasoning, and consequently they either offend others or feel themselves offended when contradicted.
Hence, they felt a "certain degree of timidity" in presenting these views, against those "generally received." They professed no intention of giving a "decided preference" to the ideas here defended or of forcing their opinion on others. They did, however, aver that the views were worthy of consideration.[24] One can imagine Kolbe writing these lines, worrying about being put in the. same category as the French chemists and bearing Berzelius' published cautionary remarks of the previous year in mind.
In fact, Kolbe and Frankland were aware that one could explain these reactions without recourse to copulas, or even to any constitutional hypothesis, by simply using empirical formulas, as Liebig had
begun to do since 1840. However, they argued that their explanation, using what we would now refer to as more resolved structural formulas, had manifold advantages. It was simpler and more consistent than empirical formulas, and it revealed direct analogies to other reactions of nitriles and cyanides otherwise hidden. Furthermore, one could then propose a single homologous series of hydrocarbon radicals as the constitutional basis not just for nitriles and acids but also for alochols and hydrides, not to mention Kolbe's own alkyl hyposulfuric acids. They even speculated on the reaction mechanism of the oxidation of ethyl alcohol to acetic acid. This was, therefore, a bold publication for two professionally unestablished academic chemists. No one else at that time was publishing this sort of experimentally grounded theoretical work in organic chemistry.
It would be hard to overemphasize the significance of the Kolbe and the Kolbe-Frankland papers. Read to the Chemical Society on the same day (19 April 1847), they represent inverse synthetic methods: a carbon atom-increasing carboxylation reaction (through the corresponding nitrile) and, apparently at least, a carbon atom-decreasing decarboxylation reaction. These reactions were the first general synthetic routes between hydrocarbons and organic acids and represent the two first great general synthetic methods ever published. Together with Kolbe's acetic acid synthesis, they were the earliest planned reactions where the carbon content of an organic molecule was deliberately altered. They were also the first synthetic reactions whose purpose was to elucidate "constitutions," or what we now refer to as chemical structures. The few pre-1847 reactions that might be considered "synthetic" were fortuitous transformations whose constitutional import was only dimly or not at all appreciated.