FREUDENBERG, KARL JOHANN

(b Weibheim Germany, 29 January 1886; d Weinheim, 3 April 1983)

Organic Chemistry.

The third of ten children of Hermann Ernst Freudenberg, co-owner of one of the biggest German tanneries and leather plants, and Helene Siegert, daughter of a professor at the Düsseldorf Academy of Arts, Freuedenberg was educated in Weinheim and Frankfurt am Main. In 1904 he enrolled at Bonn to study science and botany. He soon concentrated on chemistry, which he pursued at the University of Berlin beginning in 1907. In 1910, Freudenberg completed his doctoral dissertation on Chinese gallotannin under Emil Fischer, then the unquestioned leader of Germany’s organic chemists. In July of the same year he married Doris Nieden; they had three daughters and two sons.

Freudenberg’s early work on tannins and the stereochemistry of organic acids followed very much in the footsteps of Fischer, whose assistant he was from 1910 to 1914. Eventually he felt the need to escape from his teacher’s overwhelming influence and moved to the University of Kiel in April 1914, becoming privatdozent there in July. The war soon interrupted his career; and for some time Freudenberg, like many other chemists, served as an adviser on gas warfare. After returning to Kiel, he received the title professor in 1919. In the autumn of 1920 he went to Munich to work with Richard Willstätter at the State Chemical Laboratory. In October 1921 he was appointed extraordinary professor of organic chemistry at the University of Freiburg im Breisgau, and one year later became full professor and director of the Chemical Institute at the Technische Hochschule in Karlsruhe. In April 1926, Freudenberg succeeded Theodor Curtius in the chemistry chair at the University of Heidelberg. He retained this position until his retirement in 1956, except for a sabbatical spent at the University of Wisconsin, Madison, and the Johns Hopkins University, in 1931. Until 1969 he continued working in Heidelberg as head of the Research Institute for the Chemistry of Wood and Polysaccharides, which had been created for him in 1938.

Most of Freudenberg’s early work sprang from the foundation laid by Emil Fischer, but he soon extended the classical approach to include the more complicated and less easily obtainable carbohydrates. The combination of chemical and spectroscopic methods enabled him to assign absolute configurations to carbohydrates, terpenes, and steroids. Much effort was spent on the preparation of acetone sugars and their use in syntheses. Freudenberg’s studies on tannins and their relations to catechins, dating back to his dissertation and taken up again after World war II were first summarized in Die Chemie der natürlichen Gerbstoffe, which he wrote while a Privatdozent at Kiel. The comprehensive handbook Stereochemie, which he contributed to and edited in 1933, was a lasting success.

In 1916 the wartime need for a substitute for vegetable tannins made Freudenberg familiar with the main components of wood tissue—cellulose and lignin—on which he later did the work that brought him fame as a chemist. As early as 1921 he concluded from quantitative acetolysis that cellulose is a linear polymer composed of glucose residues linked throughout by covalent glycosidic bonds. In 1928 he published the first correct formula. In the same year the controversy between Hermann Staudinger and Mark and Meyer about the macromolecular concept emerged. Freudenberg, however bred in the preparative tradition and not overly concerned with priority claims, was little inclined to enter this dispute. Instead he proceeded to extend the idea of a highly ordered cellulose structure to other natural polymers, and in 1930 he was able to confirm that starch is a chain-type macromolecule. For the next.

ten years Freudenberg studied Schardinger dextrines produced from starch, and in 1933 he inferred that they are cyclic saccharides with a helical structure, which explained the starch-iodine test result as an inclusion compound. In the 1930’s this research was complemented by extensive studies on the spectroscopic behavior of carbohydrates that were carried out in close out in close cooperation with the physical chemist Werner Kuhn.

Freudenberg’s method of pursuing different analytical and synthetical pathways simultaneously revealed its value when he brought together this accumulated expertise in order to determine the structure of lignin, an extremely complicated natural polymer responsible for the stability of vascular plants and therefore one of the most abundant natural products. However, its separation and chemical treatment presented major problems. New analytical methods, degradation procedures, and model syntheses had to be developed. They supported Freudenberg’s assumption that coniferyl alcohol was a major precursor of lignin, an assumption he was able to confirm by simulating the enzymatic lignification in the laboratory, interrupting the polymerization, and identifying the oligomeric intermediates. For almost three decades, however, progress on the lignin problem was disappointingly slow. In 1952 Freudenberg achieved the first real breakthrough when he succeeded in isolating the oligomers, determining their structure, and explaining the mechanism of their formation through intermediate radicals. Lignin then became the main field of his research, which from 1962 to 1965 culminated in the design of a formula scheme for the constitution of spruce lignin, involving eighteen C₆—C₃ units.

Over a period of sixty years Freudenberg published more than 450 papers as well as several books and received international recognition, including foreign membership in the Royal Society in 1963. His talent also was applied in academic and civic affairs. He served as rector of Heidelberg University in 1949 and 1950 and as a member of the City Council from 1951 to 1956, primarily engaging in city planning and adult education. He also devoted a considerable amount of time and energy to local and family history, as well as to the history of chemistry.

BIBLIOGRAPHY

I. Original Works. The most comprehensive bibliography (on microfiche) is in the memoir by Stevens (see below). Freudenberg’s books include Die Chemie der natuürlichen Gerbstoffe (Berlin, 1920), revised as Tannin, Cellulose, Lignin (Berlin, 1933); Stereochemie, eine Zusummenfassung der Ergebnisse, Grundlagen und Probleme (Leipzig and Vienna, 1933): and Constitution and Biosynthesis of Lignin (New York, 1968), written with Arthur C. Neish, which contains Freudenberg’s most detailed account of his research. For an earlier presentation, see Freudenberg’s “Lignin im Rahmen der polymeren Naturstoffe,” in Angewandte Chemie, 68 (1956), 84–92.

Freudenberg’s personal papers, including an unpublished autobiography, are held by his family.

II. Secondary Literature. The most comprehensive biography is T.S. Stevens, ’Karl Johann Freudenberg,” in Biographical Memoirs of Fellows of the Royal Society, 30 (1984), 167–189, with bibliography on microfiche. Angewandte Chemie, 68 (1956), 81–120, is dedicated to Freudenberg and contains articles by B. Helferich, W. Kuhn, O.T. Schmidt, and F. Cramer, on various aspects of his work. Another account is A. Wacek, “Karl Freudenberg zum 70.Geburtstag, ’in Öterreichische Chemiker-Zeitung, 57 (1956), 33–38. His life and personality are portrayed in Friedrich Cramer, “Leben und Werk von Karl Freudenberg,” in Heidelberger Jahrbücher, 28 (1984), 57–72.

Christoph Meinel