Baeyer Adolf Johann Friedrich Wilhelm von

(b. Berlin, Germany, 31 October 1835; d. Starnberg, Oberbayern, Germany, 20 August 1917)

chemistry

Adolf von Baeyer was the eldest of the five children of Johann Jacob Baeyer and Eugenie Hitzig. His father a lieutenant general in the Prussian army, took part in the government project to measure degrees of latitude and longitude directed by the astronomer W.F. Bessel. He subsequently participated in a general European measurement program and published these results, as well as other investigations on the shape of the earth. Baeyer’s mother was daughter of Julius Eduard Hitzig, a criminal judge. Her uncle the art historian Franz Kugler, and her grandfather made Bayer’s first home on Friedrichstrasse a center for Berlin literary life by attracting E. T. A. Hoffman and others for weekly evenings of conversation. Bayer’s mother was Jewish but had been converted to the Evangelical faith and had been confirmed by Schleiermacher. Baeyer was of the same faith as his parents.

Baeyer’s early education at the Friedrich-Wilhelms Gymnasium and at the University of Berlin under P.G. Dirichlet and G. Magnus emphasized mathematics and physics In 1856 after a years military service he decided to study experimental chemistry with R Bunsen in Heidelberg where the emphasis was on applied physical chemistry. Dissatisfied with this approach baeyer in 1858 entered Kakulès private laboratory in heidelberg Since he was pleased with kekulès tuition in organic chemistry Baeyer followed him to Ghent and remained there until 1860, taking time out only in 1858 to receive his doctoral degree from Berlin for work on arsenic methyl chloride. After leaving Ghent, Baeyer returned to Berlin and held various teaching positions at the technical institute and the military academy. He married Lida, daughter of Emil Bendemann, in 1868; the couple had three children: Eugenie, Hans, and Otto. In 1872 Baeyer was appointed ordinary professor of chemistry at the new imperial university at Strasbourg. There years later he moved to Munich as successor to Justus von Liebig.

Bayer’s contributions to science were widely recognized during his lifetime. He received the Liebig Medal of the Berlin Chemists Congress the Royal Society’s Davy Medal, and in 1905 the Nobel Prize for his work on dyes and hydroaromatic compounds. Among the many scientific societies to which he belonged were the Berlin Academy of Sciences and the German Chemical Association.

Most of Baeyer’s scientific interests grew out of work he began at the technical institute in Berlin. His early work, in which he followed the lead of Liebig and Wöhler, centered on the derivatives of uric acid. He prepared various derivatives, including barbiturates. From his uric acid studies Baeyer turned to another physiological problem, that of assimilation in green plants. He thought that the ease with which a water molecule could be eliminated from a carbon atom with two hydroxyl groups would explain the formation of sugars in plants. Baeyer also saw that a study of condensation reactions where water was eliminated might be used to probe the structure of complicated organic molecules. He and his students conducted a series of investigations on condensation reactions of aldehydes and phenols which led to the discovery of phenolphthalein and other members of the phthalein group. Bayer developed the dyestuffs gallin and coerulein from his class of compounds.

Connected with his work on phthaleins was his work with phthalic acid, which led Baeyer to investigate the structure of benzene. He started with mellitic acid, which he showed was a benzene derivative rather than an alkyne, as he had first believed. He then investigated the carboxylic acids of benzene and found one new tricarboxylic and two new tetracarboxylic acids. From the reduced forms of these acids, prepared by heating them with zinc dust—a method he had previously introduced—he tried to elucidate the structure of benzene. Failure to find cis-trans isomers led him to reject Kekulè’s double-bond model and Ladenberg’s prism model and to adopt his own model of benzene, in which one valence bond from each carbon was directed invar But in 1892 he produced cis-trans derivatives of benzene. which made him reject any one theory of benzene structure.

Baeyer’s best-known research, on indigo, was begun in 1865 and followed up earlier work on phthalein dyes. In 1841 Laurent had investigated indigo and had obtained isatin by oxidation. Baeyer reversed Laurent’s process, and in 1870 he and Emmerling produced indigo by treatment of isatin with phosphorous trichloride, followed by reduction. In 1878, by synthesizing isatin from phenylacetic acid, Baeyer demonstrated the possibility of a complete synthesis of indigo. However, neither the exact process nor the structure of indigo was yet known. Baeyer had worked on isatin in 1865-1866 and had produced a series related compounds, dioxindole and oxindole, with successively less oxygen. It occurred to him that this series bore a similarity to the alloxan series he had developed with uric acid. Consequently, he predicted and found a final member of the series, which he named indole, containing no oxygen. He found the structure of indole, the kernel of the indigo molecule, through work with pyrrole. To determine the structural formula of indigo, Baeyer examined the linkage of the two indole kernels. He prepared indigo from several other reagents, and finally in 1883 he showed, through a synthesis from o-dinitrodiphenyldiacetylene, the exact location of the link, and thus the exact structural formula.

Naturally the German dye industry was interested in the synthesis of indigo, and spent large sums on research to discover a practical process. Baeyer declined to take an active part in eliminating commercial difficulties, and the resulting ill feeling on the part of the dye industry caused him to discontinue further work on dyestuffs and to turn his attention elsewhere. He began an investigation of the polyacetylenes and prepared a number of highly explosive compounds. The properties of these compounds focused his attention on the resistance of double and triple carbon bonds.From these considerations he developed his strain theory, in which the stability of a ring structure is related to the amount of bending necessary to form a closed ring.

A final area of extensive research for Baeyer was that of oxonium compounds. In the course of his work on terpenes Baeyer had used peroxide compounds and had suggested that hydrogen peroxide had the formula HO.HO. Certain phthalein salts derivatives of pyrone, also had unusual oxygen linkages. At first Baeyer opposed the idea of J. N. Collie and T. Tickle that the oxygen in these compounds becomes quadrivalent and basic, but work with the peroxides and perchloric acid convinced him of the weak basic preperties of oxygen, and he called such compounds of oxygen “oxonium compounds”

Baeyer’s chemical research was in many ways an extension of kekulè’s work on the tetravalency of carbon. He used this framework to elucidate the structure of compound after compound. His work on indigo indicated that he was not interested merely in synthesis but also believed the understanding a compound required knowing its exact structure. Bayer’s work on the stability of ring structure showed his concern with the direction of valence bonds and the extent to which the direction can be changed. with the idea that valence bonds can strained and with his criticism of existing benzene formulas, Baeyer went beyond Kekulè’s earlier picture. His final unwillingness to assign a definite structure to benzene his work on stable and unstable isomers of isatin and indoxyl, which he called lactim and lactam forms, as well as that on phloroglucinol, pointed up difficulties in determining exact structure, which were later resolved with the concept of tautomerism.

Baeyer’s approach to chemistry, however, was different from that of Kekulè. Baeyer had little interest in theoretical statements and attacked most problems empirically. His work on benzene, he explained, was only an experimental investigation and not an attempt to prove a particular hypothesis. He was a master at test-tube analysts, and eschewed complicated apparatus.

Most of Baeyer’s investigations of compounds grew out of his early work on uric acid derivatives which Liebig had also investigated. He was instrumental in setting up a chemical laboratory at Munich in 1877 and thus was a successor of Liebig in several senses, As a teacher Baeyer’s strength lay in the laboratory rather than in the lecture hall. He gathered about him a large group of students and assistants, among whom were C. Lieberman C. Graebe V. and R. Meyer and E. and O. Fischer. The enormous number of articles by Baeyer himself those written with his students, and those written by his students indicates both the scope of the activities in his laboratory and the cooperative nature of the research. Baeyer filled out and extended existing theory by the vast amount of his empirical research, stimulated the chemical dye industry through his work on indigo and laid the foundation for subsquent work in biochemistry through his investigation of complex ring structures.

BIBLIOGRAPHY

I Original Works. Baeyer’s works are collected in Gesammelte Werke (Brunswick 1905). Also of interest are unpublished letters to H. Caro, which are in the library of the Deutschces Museum, Munich

II Secondary Literature. Works on Baeyer include Günther Bugge, “Adolf v. Baeyer,” in Prometheus, 29 (1917), 1-5; W. Dieckmann O. Dimroth, F. Friedläder, C. Harries, P. Karrer, R. Meyer, W. Schlenk, H. Wieland, and R. Willstätter, Die Naturwissenschaften, Sonderheft zum 80 Geburtstag von Adolf v. Baeyer 44 (29 Oct. 1915); J. Gillis, “Lettres d’Adolf Baeyer áson ami Jean Servais Stas,” in Mèmores del’ Acadèmie royale de beligique Classe des sciences32 (1960), 1-45; J. Prtington “Adolf von Baeyer,” in Nature136 (1935),669; H. Rupe, Adolf von Beyer als Lehrer and Forscher (Stuttgari, 1932); Karl Schmorl, “Adolf von Baeyer,” (Stuttgari, 1952); Richard Will-stätter “Adolf von Baeyer” in Das Buch der grossen Chemiker ed Günther Bugge (Weinheim, 1955).

Ruth Anne Gienapp