Kolbe, Adolf Wilhelm Hermann

(b. Eliehausen near Göttingen, Germany, 27 September 1818; d. Leipzig, Germany, 25 November 1884)

chemistry.

Hermann Kolbe was the oldest of fifteen children of a Lutheran pastor and was raised in the towns of Eliehausen and Stockheim, in the vicinity of Göttingen, where his father held pastorates. His mother, Auguste, was the daughter of A. F. Hempel, professor of anatomy at the University of Göttingen. Kolbe showed an early interest in science. When he entered the Göttingen Gymnasium, at the age of fourteen, he was introduced to chemistry by a fellow student who had studied this subject with Robert Bunsen, then a privatdocent at the university. Kolbe later said that this encounter led him to choose chemistry as his career. In 1838 he entered the University of Göttingen, where Wöhler had recently begun to teach chemistry. While he was a student he met Berzelius, who was visiting Wöhler, and was deeply impressed by him; Berzelius later took a great interest in Kolbe’s first major research. It is not surprising that the young chemist accepted Berzelius’ theories wholeheartedly and founded his later theoretical ideas upon them.

In 1842 Kolbe published his first short paper, on fusel oil, and began work on his doctoral dissertation. While this dissertation was in progress he was offered an assistantship with Bunsen, who had been called to Marburg. He accepted and completed his dissertation at Marburg. While there he perfected his knowledge of Bunsen’s methods of gas analysis

In 1845 Lyon Playfair, at the School of Mines in London, was studying firedamp in coal mines and needed a chemist qualified to perform gas analyses. He asked Bunsen to recommend someone. Bunsen proposed Kolbe, who went to London in the autumn of that year and remained until 1847. He met most of the English chemists, and became a close friend of Edward Frankland, who was beginning the studies that led him to the theory of valence . Together Kolbe and Frankland began a study of the conversion of nitriles to fatty acids. Kolbe himself investigated the action of the galvanic current on organic compounds; the results of these studies led him directly to the development of his chemical system. He returned to Marburg in the spring of 1847, accompanied by Frankland, and they continued their joint studies for a time.

In the autumn of the same year, Kolbe undertook a new activity. The publishing firm of Vieweg and Son had been bringing out a Handwörterbuch der Chemie, edited by Liebig, Wöhler, and Poggendorff. Kolbe was asked to continue this work and moved to Brunswick for the purpose. Temporarily abandoning most of his experimental work, he began the literary activity which he continued for the rest of his life. During this period he developed a number of theoretical ideas which he became anxious to test in the laboratory; when offered a professorship at Marburg, he gladly accepted.

Kolbe returned to the university in 1851. Since he had never served as a privatdocent and was only thirty-two years old, he was received with some jealousy by a few of the older professors, but his ability was soon recognized. With the aid of a number of talented students he established a solid reputation. In 1853 he married the youngest daughter of Major General von Bardeleben. During the next fourteen years he developed his theoretical ideas and wrote oa comprehensive textbook of chemistry.

In 1865 he was called to Leipzig. Here he constructed the largest and best equipped chemical laboratory of its day, completed in 1868. It attracted so many students that in spite of its size, which had been criticized by Liebig, it was soon filled. Kolbe carried out most of his instruction in the laboratory rather than in lectures. In 1870 he took over the editorship of the Journal für praktische Chemie which he used to express his very personal opinions of the state of chemistry. In his violent criticism of many of his contemporaries, Kolbe used terms that were outspoken even for his time, when polemical arguments were frequent and vigorous. The death of his wife in 1876 was a severe blow to him, and his health began to fail soon afterwards. He continued his writings until 1884, when he died at the age of sixty-six.

Kolbe was a brilliant experimenter, and his laboratory work in organic chemistry resulted in the discovery of many important compounds and reactions. He was also interested in the nature of chemical composition and developed his own system for representing the structure of the compounds and reactions. He was also interested in the nature of chemical composition and developed his own system for representing the structure of the compounds with which he worked. Although this system involved a number of incorrect ideas, he stubbornly refused to abandon them until the evidence against them became overwhelming. Nevertheless, his chemical intuition was so keen that in spite of his conservatism he was able to make important predictions about the chemical behavior of many compounds. His own method of representing structure eventually gave way to the much simpler structural theory based on the work of Kekulé, but his unorthodox formulas actually embodied many of the ideas which Kekulé developed.

One of the major difficulties in Kolbe’s formulas was that he refused to abandon equivalent weights for atomic weights until 1869, long after other chemists had adopted them. He still followed Berzelius in using the values C =6 and O = 8, so that he had to double the number of atoms of these elements in his formulas —thus, his notation for the methyl group was C₂ H₃, and hydrated carbonic acid became 2HO. C₂ O₄.

Kolbe’s early work was strongly influenced by the copula theory of Berzelius. The latter had been forced to abandon his original radical theory, expressed in terms of the dualistic electrochemical theory, when studies of substitution showed that positive hydrogen could be replaced by negative chlorine in organic compounds. Berzelius then assumed that in acetic acid the methyl radical was copulated with oxalic acid and water, so that his formula was written.

C₂ H₃+C₂ O₃+HO.

The methyl group was a passive partner in which substitution by chlorine could produce the radical C₂ CI₃ without altering the properties of the compound greatly, since these depended chiefly on the active C₂ O₃ radical. This was the theory that Kolbe adopted in his dissertation, and from which most of his later speculations were derived. His profound admiration for Berzelius made it impossible for him to abandon the concept of radicals, although he eventually modified his view. Precisely because he thought ion terms of radicals and of their relative positions in the molecule, he was able to avoid the difficulties encountered by the adherents of the type theory, who were unable to conceive of a general reaction affecting specific parts within the molecule.

In his doctoral investigation Kolbe studied the action of moist chlorine on carbon disulfide. Among other products he obtained trichloromethylsulfonic acid (CCl₃ SO₂ OH), which he formulated as HO + C₂ Cl₃ S₂ O₅. He at once saw the similartity to trichloroacetic acid, which he called trichlorocarbon oxalic acid, HO + C₂ Cl₃.C₂ O₃. Each of these compounds contained a group C₂ Cl₃, which could be reduced to methyl, C₂ H₃. Kolbe’s attention was thus focused on organic acids and these became the basis for his later studies. In the course of this work he described the synthesis of acetic acid from its elements, the second time an organic compound had been so synthesized. (The first instance had been Wöhler’s synthesis of urea.)

Kolbe was now convinced that methyl groups actually existed in his compounds and could be isolated. By the electrolysis of potassium acetate he obtained a gas which met the analytical criteria for methyl (although it was really ethane). Frankland had obtained “free ethyl” (butane) through the action of zinc on ethyl iodide; and Kolbe and Frankland were now sure that they had proved the existence of radicals in organic compounds. Their study of the conversion of nitriles to fatty acids seemed to prove that these acids must consist of the acidic group joined to the proper radical, since methyl cyanide gave methyl oxalic acid, ethyl cyanide gave ethyl oxalic acid, and so on, thus confirming the copulaformulas. Kolbe had actually recognized what is known today as carboxyl, a single group joined to a hydrocarbon radical in all the fatty acids, and his copula formulas thus contained an essential truth that made many of his further speculations fruitful. The adherents of the type theory, with their formal attempts to squeeze all compounds into a few rigid types, missed this point completely, for which Kolbe criticized them, pointing out that any number of different types could be assumed to fit any number of special cases.

By 1857 Kolbe had worked out all the essentials of his system. Since the controlling group in his acids was “oxalic acid,” all acids could be derived from hydrated carbonic acid, 2HO.C₂ O₄, by replacing an OH (and an O to keep the equivalent balance) with another radical such as methyl. Thus he wrote acetic acid HO (C₂ H₃) C₂ O₃. Other organic compounds, however, notably aldehydes and alcohols, contain less oxygen, and the other oxygens in his formula could therefore also be replaced by methyl radicals. This consideration led him to accept as the fundamental radical “acetyl,” which he wrote as the oxygen-free group (C₂ H₃) C₂. In this new radical the point of attack by other elements was the double carbon atom attached to the methyl group. When an oxygen of acetic acid (that is, an HOO group) was replaced by hydrogen, the product was , which must therefore represent the first substance produced in the reduction of an acid, an aldehyde. Here a new phenomenon could be observed. A replaceable hydrogen appeared, and if a methyl group replaced it, the product was acetone. The relationship of aldehydes and ketones was thus explained, and a new group, carbonyl, was identified.

To go on a step, reduction of the aldehyde to an alcohol could lead only to the formula and another important fact thus emerged. Either one or both of the hydrogens could be replaced, leading to a “singly or doubly methylated alcohol,” and Kolbe could predict their behavior on oxidation. The discovery of secondary alcohols by Friedel in 1862 and of tertiary alcohols by Butlerov in 1864 fully confirmed Kolbe’s predictions.

Although Kolbe’s system involved many of the same ideas that were expressed by Kekulé in his famous paper of 1858, Kolbe was never able to see the similarity. He bitterly opposed the whole idea of structural formulas and kept some of his most scathing and sarcastic invective for the theories of Kekulé and their development by others. He ridiculed the theory of stereochemical isomerisom of van t’Hosff and Le Bel. The pages of the Journal für praktische Chemie were filled with his diatribes.

In spite of his literary ferocity, however, he was a delightful companion, and his students thought highly of him and remembered the personal interest he took in them. He claimed that in attacking what he felt to be false theory he was defending the science he loved against “inexact scientific principles,” rather than making personal attacks on any chemists. His criticisms, however, do not sound as if this had been the case.

In his later years Kolbe worked with the nitroparaffins and developed a method for large-scale synthesis of salicylic acid. He was impressed by the antiseptic and food-preserving power of this acid and founded an industry on its manufacture.

During the first part of his life, Kolbe’s outstanding experimental work won him the respect and admiration of his colleagues. He was always highly regarded as a chemist, although his later refusal to accept new chemical theories and his bitter attacks on other chemists somewhat isolated him from the rest of his profession. Nevertheless, his criticisms of the type theory helped to weaken it and prepare the way for Kekulé. With the passage of time, however, it has become possible to see that kolbe’s system was basically sound; and the greater simplicity of Kekulé’s structural system should not blind us to kolbe’s acute chemical insight.

BIBLIOGRAPHY

I. Original Works. The complete exposition of Kolbe’s system was given by hime in “Ueber den natürlichen Zusammenhang der organischen mit den unorganischen Verbindungen; die wissenschaftliche Grundlage zu einer natürgemässen Classification der organischen chemischen Körper,” in Annalen der Chemie, 113 (1860), 293-332.

Kolbe’s account of how he developed his theories, with an extensive bibliography and a full-scale attack on the structural theory of Kekulé and his successors, is given in a series of articles entitled “Meine Betheiligung an der Entwicklung der theoretischen Chemie,” in Journal für praktische Chemie, n.s. 23 (1881), 305-323, 353-379, 497-517, and 24 (1881), 375-425. These were collected and published as Zur Entwicklungsgeschichte der theoretischen Chemie (Leipzig, 1881).

II. Secondary Literature. There is a rather sympathetic obituary of Kolbe in Journal of the Chemical Society,47 (1885), 323-327, and a very cool and restrained obituary in Berichte der deutsched chemischen Gesellschaft, 17 (1884), 2809-2810, which probably reflects the resentment that Kolbe aroused. The most complete account of his life and work is given by his son-in-law, E. von Meyer, in “Zur Erinnerung an Hermann Kolbe,” in Journal für prakticsche Chemie n.s. 30 (1884), 417-466. There is also a useful biography by G. Lockeman, in G. Bugge. Das Buch der grossen Chemiker,2 (Berlin, 1930), 124-135.

Henry M. Leicester