Einhorn–Brunner reaction

The Einhorn -Brunner reaction is a name reaction in organic chemistry. It was named after the German chemist Alfred Einhorn, who published them in 1905. 1914, the reaction of Karl Brunner ( 1855-1935 ) was extended and therefore known as Einhorn -Brunner reaction. With the help of the reaction can be 1,2,4- triazoles synthesized from hydrazine and Diacylamines.

Survey

Hydrazines react in the presence of an acid to 1,2,4- triazoles with Diacylamines:

In the case where the organic radicals on Diacylamin are different, a mixture of the two products, as shown is formed. The residue at the imide is derived from the stronger acid primarily found in the 3-position of the triazole. When two identical acyl groups on the amine corresponding to makes only one product.

Mechanism

For simplicity, is shown only one of the resulting reaction Triazolisomere the mechanism presented here.

Let us first protonates the electron-rich nitrogen atom of the hydrazine derivative 1, wherein the cation is 2 is formed. 2 transmits a proton to the oxygen atom of the carbonyl group of the Diacylamins. Furthermore, the amino group attacks the electrophilic carbonyl group, which ensures that an ammonium intermediate 3 is formed. By elimination of water arises from the iminium ion 3 4 The following is a 1.5 - proton shift from the nitrogen atom to the carbonyl group to form the resonance stabilized intermediates 5 ( here 's just a mesomeric structure shown). The carbon atom of the carbonyl group in 5 is then protonated intramolecular attack by the nitrogen atom, which results in closure of a five-membered ring with the formation of 6. With elimination of water and a proton is formed via the intermediates 7 and 8 of the aromatic 9, a 1,2,4- triazole.