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Gomberg, Moses

Gomberg, Moses

(b. Elisavetgrad, Russia [now Kirovograd, U.S.S.R.], 8 February 1866; d. Ann Arbor, Michigan, 12 February 1947)

organic chemistry

Gomberg prepared the first stable free radical, triphenylmethyl, at the University of Michigan in 1900 and pioneered in the development of free-radical chemistry. He was the son of George and Marie Resnikoff Gomberg; his father was the owner of a modest estate in the Ukraine. Young Gomberg entered the Nicolau Gymnasium in Elisavetgrad in 1878. Six years later his father was accused of anticzarist activities. His estate was confiscated and he fled with his family to Chicago, where he and his son, neither of whom had any knowledge of English, worked at menial jobs in the stockyards and elsewhere in the city.

Moses quickly learned English and completed his high school education in Chicago. He then became a student at the University of Michigan, completing his B.S. in 1890. He continued at Michigan as an assistant in chemistry, receiving his M.S. in 1892 and his Ph.D. in 1894. His work was done under Albert B. Prescott, and his dissertation dealt with some reactions of caffeine. Appointed instructor in organic chemistry in 1893, he never severed his connection with the chemistry department at the University of Michigan. Promotion to assistant professor came in 1899, to junior professor in 1902, and to full professor in 1904. From 1927 until his retirement in 1936 he was chairman of the chemistry department.

In order to procure funds for European Study, Gomberg carried out analyses of water, minerals, fatty oils, foods, drugs, and patent medicines and served as an expert witness in toxicology cases while he was still a graduate student. Taking a leave of absence in 1896-1897, he spent two terms in Adolf von Baeyer’s laboratory in Munich and a term with Victor Meyer in Heidelberg. During this period he turned away from the concentration on analysis which characterized the work of Prescott and his students in order to concentrate on synthetic studies. At Munich he prepared some nitrogen derivatives of isobutyric acid; and at Heidelberg he set out to prepare tetraphenylmethane, a compound which a number of German chemists had unsuccessfully sought to synthesize and which Meyer believed probably could not be synthesized. Meyer suggested that Gomberg undertake a problem more likely to be successful. Gomberg persisted in his objective and, by oxidizing triphenylmethane hydrazobenzene, obtained the corresponding azo compound, which decomposed to tetraphenylmethane on heating at 110-120°C. Although Gomberg was successful in his endeavor, the yield of tetraphenylmethane was poor (2-5 percent).

Upon his return to Michigan, Gomberg sought to prepare hexaphenylethane, the next fully phenylated hydrocarbon of the series. He utilized the classical reaction of a metal on an appropriate halide:

2 (C6 H5)3 CX + metal→(C6 H5)6 C2 + metal halide.

The use of either triphenylmethyl bromide or chloride with sodium failed to yield a product, but substitution of silver for sodium led to a reaction in which a white crystalline product began to separate after heating the reaction mixture for several hours at the boiling point of the benzene solvent. The crystalline product was assumed to be hexaphenylethane, but elementary analysis yielded 87.93 percent carbon and 6.04 percent hydrogen (calculated for hexaphenylethane, C = 93.83, H = 6.17). Carefully repeated syntheses yielded products giving similar analytical results, and Gomberg was forced to conclude that he was preparing an oxygenated compound (which proved to be the peroxide [C6 H5]6 C2 O2).

Gomberg repeated the reaction of triphenylmethyl chloride and silver in an atmosphere of carbon dioxide. Now he obtained no solid product at all, but the yellow color of his solution indicated that a reaction had occurred. Removal of the benzene solvent left a colorless solid of unexpectedly high reactivity toward oxygen and halogens. It had been expected that hexaphenylethane would be a colorless solid characterized by chemical inertness. In his first publication on the subject, Gomberg wrote, “The experimental evidence presented above forces me to the conclusion that we have to deal here with a free radical, triphenylmethyl, (C6 H5)3C. On this assumption alone do the results described above become intelligible and receive an adequate explanation” (Journal of the American Chemical Society) 22 [1900], 768).

The announcement of the preparation of a stable free radical was received with skepticism, for most contemporary chemists had become convinced that such chemical species could not exist. Gomberg set out to establish the soundness of his conclusion by carefully studying the properties of his substance and by preparing additional substances showing freeradical properties. He quickly developed an understanding of the experimental conditions necessary for successful synthesis of related compounds. His major research activities during the remainder of his career were aimed toward extending the understanding of free-radical chemistry.

Results of molecular weight determinations by L. H. Cone in Gomberg’s laboratory proved to be variable in different solvents and fell closer to the theoretical value for the dimer hexaphenylethane than to that for the monomer triphenylmethyl. This was a matter of grave concern for Gomberg and caused him ultimately to accept the idea that the solution must contain an equilibrium mixture of both substances:

Other chemists believed the compound to be merely hexaphenylethane, assuming it to be unstable in the presence of oxygen, halogens, and other highly reactive substances. Gomberg argued that the presence of color supported the free-radical hypothesis. When critics sought to explain the color by use of quinoid structures, Gomberg showed that the addition of oxygen to the solution resulted in loss of color. On standing, the yellow color slowly returned, as if a new equilibrium were being established; but the color could be destroyed again by addition of more oxygen. Change of color with change of temperature also supported the concept of an equilibrium in solution. Jean F. Piccard of Munich showed in 1911 that the colored solution failed to obey Beer’s law when diluted; dilution actually brought about intensification of the color, thereby lending support to the equilibrium concept.

Investigators in other laboratories, particularly Wilhelm Schlenk at Jena, brought forth evidence for free radicals in other hexaarylethane systems. By 1911 many organic chemists were willing to concede the existence of stable free radicals in solution, but only when dealing with compounds such as fully substituted ethanes carrying bulky substituents such as phenyl groups, or even better, substituted phenyl groups or naphthyl groups. Free radicals containing nitrogen, sulfur, and oxygen atoms carrying three aryl groups were also prepared in various laboratories, and in 1929 Fritz Paneth bolstered the free-radical concept by establishing evidence for the transient existence of free methyl radicals. Gradually free radicals came to take on great significance in reaction mechanisms.

Gomberg also carried out studies on organometallic compounds, and during World War I he worked on war gases. He was associated with the civilian chemists who originally worked in the Bureau of Mines and were later absorbed by the newly created Chemical Warfare Service. Although the idea of chemical warfare was abhorrent to him, Gomberg accepted the task of developing the commercial synthesis of ethylene chlorohydrin, required as an intermediate for the synthesis of mustard gas. Later, he was commissioned a major in the Ordnance Department and served as an adviser in the production of smokeless powder and high explosives.

During his forty-three years on the Michigan faculty Gomberg was a respected teacher and administrator. As an effective supervisor of graduate students he considered the development of the man as a scientist more important than the production of publications. Two of his students, C. S. Schoepfle and W. E. Bachmann, in their obituary memoir said of him: “Gifted with a remarkable memory, he presented his lectures with the full use of a wealth of historical material and so vividly that they left an indelible imprint on his students. A great teacher and scholar, he inspired his students by his methods and ideals, and his colleagues by the vigor and clarity of his mind. To this greatness, he added an innate kindliness and unassuming modesty that endeared him to all” ibid., 69 [1947], 2924).

Gomberg was a member of numerous professional societies and was honored by election to the National Academy of Sciences. In 1931 he served as president of the American Chemical Society and at various times was honored by awards administered by it: the Nichols Medal in 1914, the Willard Gibbs Medal in 1925, and the Chandler Medal in 1927.

Although he enjoyed the company of women in a somewhat courtly and reserved manner, Gomberg never married and firmly forbade his graduate students to marry before they finished their degrees. His younger sister Sonja served as his hostess and housekeeper at his cottage in Ann Arbor.

BIBLIOGRAPHY

I. Original Works. There is a bibliography of Gomberg’s published papers in C. S. Schoepfle and W. E. Bachmann, “Moses Gomberg, 1866–1947,” in Journal of the American Chemical Society,69 (1947), 2924–2925. His original paper on triphenylmethyl appeared in Berichte der Deutschen chemischen Gesellschaft, 33 (1900) 3150–3163; and Journal of the American Chemical Society, 22 (1900), 757–771. Gomberg published review articles on free-radical chemistry in Chemical Reviews, 1 (1924), 91–141, and 2 (1925) 301–314; Journal of Industrial and Engineering Chemistry, 20 (1928), 159–164; Journal of Chemical Education9 (1932), 439–451; and Science74 (1931), 553–557.

II. Secondary Literature. There is no lengthy biography of Gomberg. The best short sketch is C. S. Schoepfle and W. E. Bachmann, “Moses Gomberg, 1866–1947,” in Journal of the American Chemical Society, 69 (1947), 2921–2925, repr. in E. Farber, ed., Great Chemists (New York, 1961), pp. 1209–1217. There is a short sketch by A. H. White, in Industrial and Engineering Chemistry, 23 (1931), 116–117. For an evaluation of Gomberg’s role in the history of free-radical chemistry, see A. J. Ihde, in Pure and Applied Chemistry, 15 (1967), 1–13, repr. in International Union of Pure and Applied Chemistry, Free Radicals in Solution (London, 1967), pp. 1–13. These two publications carry the papers presented at the Centennial Symposium on Free Radicals in Solution, which was held under I.U.P.A.C. sponsorship at the University of Michigan in 1966. These papers reflect the consequences of Gomberg’s work.

Aaron J. Ihde

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