(b. Königsberg, Prussia [now Kaliningrad, R.S.F.S.R.], 27 March 1847; d. Göttingen, Germany, 26 February 1931), Chemistry.
Wallach came from a family of lawyers, but his father was a Prussian state official, who was transferred from Königsberg to Stettin and, in 1855, to Potsdam. The boy was educated at the Potsdam Gymnasium, where he acquired his two major interests: chemistry and the history of art. Although he became a professional chemist, he remained an art collector throughout his life and spent many vacations visiting the art galleries of Europe.
In the spring of 1867 Wallach entered the University of Göttingen, where he attended Wöhler’s lectures. A short stay in Berlin with A. W. von Hoffmann convinced him that Göttingen was a better place for him to work and he returned there to study fro his doctorate with Hans Hübner. He received the degree in 1869 with a dissertation on position isomerism in the toluene series. Wallach worked for a short time in Berlin; but in the spring of 1870 he was called to Bonn as assistant to Kekulé who was then gradually withdrawing from active laboratory work. He remained at Bonn for nineteen years, with a short interlude of industrial experience at the Aktien Gesellschaft für Anilin-Fabrikation (Agfa) plant in Berlin. His health was never good, and the noxious fumes at the plant soon drove him back to Bonn. In 1889 Wallach succeeded Victor Meyer at Göttingen, where he served as director of the Chemical Institute until his retirement in 1915. He continued experimental work until he was eighty.
Wallach’s early work included a number of studies in general organic chemistry. In 1879 he was assigned to teach pharmacy, with which he had had little experience. In teaching this course his attention was drawn to the chemistry of natural compounds. He found in a cupboard at Bonn a number of bottles of plant essential oils that Kekulé had collected but never studied. Wallach decided to investigate these substances, and the rest of his life was devoted to the study of such compounds, on which he published 126 papers.
At the time Wallach began this work, the field was in a state of extreme confusion. No one had obtained truly pure compounds from the natural mixtures; and various names had been proposed for many of the substances thought to be pure. A skilled and patient experimentalist. Wallach set himself the task of characterizing individual compounds beyond doubt and then of determining their relationships. For this purpose he separated the pure substances by careful distillations and studied their reactions with a series of relatively simple reagents.
After three years Wallach had distingished eight pure terpenes, as he called this class of compounds. He suggested that they were composed of five carbon atom fragments known as isoprene units and showed that in many cases it was possible to rearrange one terpene into another by the action of strong acids and high temperatures. He was particularly interested in the relations among the various compounds and was less concerned with preparing new substances, the chief occupation of most organic chemists of the time. Wallach often left the task of synthesizing and determining structures of his compounds to others, for he realized that the field of terpene chemistry was so large that one man could not cover it completely. His methods were so successful and had progressed so far by 1895 that when, in that year, he and others determined the structure of α-terpineol, the structures of an entire series of terpenes were at once established. This accomplishment was an outstanding example of the value of Wallach’s experimental methods. After he had made the fundamental discoveries, a number of chemists continued his work, and terpene chemistry became an important branch of organic chemistry. It was soon extended to the biologically important carotenoids and steroids.
Wallach received wide recognition for his work, becoming an honorary member of many universities and scientific societies. These honors culminated in the award of the Nobel Prize in chemistry in 1910.
1. Original Works. Among Wallach’s important papers were his suggestion of isoprene units in terpenes, “Zur Kenntniss der Terpene und ätherischen Oele. IV,” in Justus Liebigs Annalen der Chemie, 238 (1887), 78–89; and his work on terpineol, “Zur Constitutionsbestimmung des Terpineols,” in Berichte der Deutschen chemischen Gesellschaft, 28 (1895), 1773-1777. He summarized his work in Die Terpene und Campher (Leipzig, 1909; 2nd ed., 1914).
II. Secondary Literature. The longest account of Wallach is the Pedlar lecture by L. Ruzicka, “The Life and Work of Otto Wallach,” in Journal of the Chemical Society (1932), 1582-1597, repr, in Eduard Farber, ed., Great Chemists (New York, 1961), 833–851. A shorter account is William S. Partridge and Ernest R. Schierz “Otto Wallach: The First Organizer of the Terpenes,” in Journal of Chemical Education, 24 (1947), 106–108.
An account of the industrial significance of Wallach’s work is Albert Eller, “Otto Wallach and seine Bedeutung für die Industrie der ätherischen Öle.” in Zeitschrift für angewandte Chemie…, 44 (1931), 929–932.
Henry M. Leicester