Claisen, Ludwig

(b. Cologne, Germany, 14 January 1851; d. Godesberg-am-Rhein, Germany, 5 January 1930),

chemistry.

The son of Heinrich Wilhelm Claisen, a notary, and of the former Emilia Theresa Berghaus, Claisen had two brothers and a sister. After graduating in 1869 from the Gymnasium of the Apostles Church in Cologne, he enrolled in the University of Bonn, where he studied chemistry under Kekulé and physics under Clausius. His studies were interrupted by the Franco Prussian War and Claisen enlisted as a medical corpsman. At Göttingen he attended Tollen’s lectures on organic chemistry and worked in Wöhler’s laboratory. He returned to Bonn in 1872 and received the doctorate there in 1874.

Claisen taught at Bonn from 1875 to 1882 and at Owens College in Manchester, England, from 1882 to 1885. During the next four years he worked in Baeyer’s laboratory at Munich, leaving to teach at the Aachen Technische Hochschule from 1890 to 1897. He was associate professor at the University of Kiel from 1897 to 1904 and worked in Emil Fischer’s laboratory in Brelin from 1904 to 1907. In 1907 Claisen established his own laboratory at Godesberg, continuing work in organic synthesis until 1926.

Claisen’s early interest in condensation reactions led him to develop the so-called Claisen condensation for synthesizing keto esters and 1,3-diketones. He used sodium hydroxide, hydrogen chloride, sodium ethoxide, and sodamide as condensing agents and found that nitriles, as well as carbonyls, may be condensed. Claisen contributed greatly to the understanding of tautomerism when, in 1893, he reported the isolation of dibenzoyl acetone in two solid modifications, identifying the acidic form as enol and the neutral as keto and extending these terms to apply to all tautomers. In 1912 Claisen began work on the rearrangement of allyl aryl ethers into phenols. The mechanism of this rearrangement was the subject of the last (1926) of his 125 published papers.

Eulogizing Claisen, Richard Anschütz said that he was endowed with first-rate talent and that his discoveries placed him among the most renowned researchers in organic chemistry.

BIBLIOGRAPHY

For a complete list of Claisen’s publications, see the Anschütz article (below), pp. 165–169.

For a carefully written biography, a discussion of Claisen’s contributions to chemistry, and a list of his publications and patents, see Richard Anschütz, “Ludwig Claisen, ein Gedenkblatt,” in Berichte der Deutschen chemischen Gesellschaft, 69 (1936), 97–170. See also Ernest E. Gorsline, A Study of the Claisen Condensation (Easton Pa., 1908); and Ernest H. Huntress, “Centennials and Sesquicentennials During 1951 With Interest for Chemists and Physicists,” in Proceedings of the American Academy of Arts and Sciences, 79 (1951), 10–11.

A. Albert Baker, Jr.