Bucherer-Bergs synthesis

The Bucherer-Bergs synthesis or Bucherer-Bergs reaction is a reaction in organic chemistry . With the help of this reaction, carbonyl groups are converted into hydantoins . Ethanol and water act as solvents . It is named after the German chemists Hans Theodor Bucherer (1869–1949) and Hermann Bergs.

Overview reaction of the Bucherer-Bergs reaction; R ¹ and R ² denote either a hydrogen atom or an organic radical

mechanism

In this reaction, an aldehyde or ketone reacts with ammonium carbonate and cyanide to form a hydantoin .

Mechanism of the Bucherer-Bergs reaction; R ¹ and R ² denote either a hydrogen atom or an organic radical.

First, the carbonyl compound 1 is reacted with ammonium carbonate . An iminium ion 2 forms . This is mixed with cyanide from hydrogen cyanide or potassium cyanide . The aminonitrile 3 simultaneously contains an amino group and a nitrile group . The amino group now attacks the carbon dioxide which was released by the reaction of the carbonyl compound 1 with the ammonium carbonate. A carbamate ion 4 is formed , which reacts to carbamate 5 through proton transfer . An intramolecular attack of an oxygen particle on the carbon atom of the nitrile group then takes place. As a result, a heterocyclic five-membered ring 6 is formed, which is again subject to proton transfer. This is how 7 . Rotation about the CC single bond of 8 leads to 9 . This allows the NH ₂ group to attack the carbon atom of the isocyanate intramolecularly, thereby forming the five-membered ring compound 10 . A final proton transfer leads to hydantoin 11 .

Applications

There are numerous practical applications for the hydantoins formed in the Bucherer-Bergs synthesis in the laboratory and in technology:

• Synthesis of heterocyclic drugs, e.g. B. the drug 5,5-diphenylhydantoin ( phenytoin )
• Educts for the industrial production of amino acids , e.g. B. Methionine of which several 100,000 tons are produced annually; Evonik Industries is the world market leader for this
• Manufacture of sugar derivatives

Individual evidence

1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 1: A-Cl. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1979, ISBN 3-440-04511-0 , p. 531.
2. ↑ Patent DE566094 : Process for the preparation of hydantoins. Registered on May 26, 1929 , inventor: Hermann Bergs (Bergs was a chemist at IGFarben). ‌
3. ↑ BP Mundy, MG Ellerd, FG Favaloro: Name Reactions and Reagents in organic synthesis . 2nd edition, Wiley-Interscience, Hoboken, NJ 2005, ISBN 978-0-471-22854-7 , p. 122.