The Nobel Prize in Chemistry 1950

KURT ALDER

Kurt Alder was recognized for his contribution to synthetic organic chemistry, especially for the reaction which has been called the diene reaction, or the Diels-Alder reaction, after Alder and his mentor-colleague, Otto Diels. This reaction, discovered in 1928, was so useful in the synthesis of every type of organic compound that Diels and Alder were awarded the Nobel Prize in chemistry in 1950 for their development of the method. It was Alder who explored the reaction deeply, and wrote many papers on the nature of the reactants and products, including the stereochemistry, or geometric consequences, of the reaction.

Alder was born on July 10, 1902, in K?nigsh?tte, Germany. His father, Joseph Alder, was a schoolteacher in the nearby town of Kattowitz. Kurt attended the local schools, but at the end of World War I, the region in which the Alders lived became part of Poland, and Joseph Alder moved his family to Kiel in order to retain their German citizenship. Kurt Alder completed his secondary education in Berlin, and enrolled in the University of Berlin in 1922. He began to study chemistry at Berlin, but transferred to the Christian Albrecht University (now University of Kiel) and worked under Otto Diels, professor of organic chemistry and director of the chemical institute. Alder obtained his Ph.D. in 1926, and remained at the university as Diels' assistant. Diels and Alder collaborated in their research at Kiel for a decade. Alder was promoted to reader in organic chemistry in 1930 and extraordinary professor in 1934. The direct interaction between the two chemists ended in 1936 when Alder accepted an appointment as director of scientific research at the Bayer Werke laboratory at Leverkusen, a branch of I. G. Farbenindustrie. This position gave Alder direct experience with industrial chemistry, and his expertise was directed to the development of synthetic rubber, which was a goal of organic chemists in every nation at that time. Alder left Bayer in 1940 and returned to academic life. He was appointed to the chair of experimental chemistry and chemical technology at the University of Cologne, and he was also director of the university's Chemistry Institute.

He served as Dean of the Faculty of Philosophy in 1949 and 1950. He remained at Cologne until his death on June 20, 1958.

The diene synthesis is one of a few methods which has proven to be so useful to organic chemists that their development led to Nobel Prizes for the chemists who discovered them. The diene synthesis requires two components, the diene and the dienophile. When the diene and dienophile react, a ring containing the six atoms is formed, with new single bonds between all the atoms except 2 and 3, which is joined by a double bond. In general, all of the new bonds are formed in one step, in what is termed a concerted reaction. Because six-membered rings are found in many natural products, the diene synthesis has been used successfully in the syntheses of such complex molecules as reserpine, morphine, and many steroids. Commercial products have been synthesized with the reaction, including the insecticides dieldrin and aldrin (named for the chemists) and chlordane. Alder and his students carried out extensive investigations on the geometry of the ring formation, and discovered regularities which allowed the geometry to be predicted with certainty.

In the course of his research at Bayer Werke, Alder found that the reaction between butadiene, a diene, and styrene, a dienophile, gave a normal diene reaction under certain experimental conditions. However, by allowing the reaction to take place in the presence of peroxides, a polymer--a molecule consisting of similar or identical small molecules linked together--was formed, which was the synthetic rubber known as "Buna S." This was developed commercially in Germany in the 1930s, and was ultimately important during World War II, when supplies of natural rubber were curtailed.

Alder discovered another reaction in 1943, which has been named the ene reaction. This is also a concerted reaction, and Alder recognized its essential similarity to the diene synthesis. In the ene reaction, one reactant contains three atoms, with a double bond between atoms 1 and 2, and a hydrogen atom attached to atom 3: 1=2-3-H. The other reactant contains a double bond: 4=5. In the product, the hydrogen atom moves from atom 3 to atom 4, atom 1 joins atom 5, and a double bond forms between atoms 2 and 3: H-4-5-1-2=3. Alder called this type of reaction a substituting addition. The ene reaction also has found widespread use in synthesis. The mechanism of the diene reaction and the ene reaction was a matter of great interest for many years, for Alder and others. The theoretical foundation was not completely established until 1965, when Robert B. Woodward (Nobel Prize, 1965) and Roald Hoffmann (Nobel Prize, 1981) showed that these concerted reactions were governed by rules determined by quantum mechanics. The Diels-Alder reaction is one of many known "cycloaddition reactions" in which rings are formed from open-chain compounds, and the Woodward-Hoffmann rules accurately predict the course of these reactions.

Alder was committed to world peace and joined other Nobel laureates in 1955 in an appeal to governments to end war. He died in Cologne at the age of 55

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