Leuckart reaction

The Leuckart -Wallach reaction is a reaction name and named after the German chemist Rudolf Leuckart and Otto Wallach. Describes the reductive amination of ketones and aldehydes with formic acid. Specialized formaldehyde used as alkylating reagent for the formation of methylated amines, called this reaction also Eschweiler- Clarke reaction.

Reaction mechanism

In the Leuckart - Wallach reaction can be produced under simple conditions amines (especially tertiary ). This is given to an aldehyde or a ketone with ammonia or a primary or secondary amine and formic acid. Instead of ammonia and formic acid, ammonium formate can be used, which is dissociated during the reaction by heating ammonia and formic acid. First, one molecule of the amine added to the carbonyl group, a proton is transferred from the nitrogen to the oxygen atom. The thereby formed hemiaminal is protonated by formic acid in the course, and it is a molecule of water is eliminated. This results in the formation of resonance stabilized carbenium immonium ion ( such as, for example, in the Mannich reaction).

This then reacts with formic acid of a cyclic transition state where the formic acid transmits a proton on the nitrogen atom and a hydride ion to the carbon atom. At the same time carbon dioxide is formed. Here, the carbon atom of the cation is reduced, oxidized, the carbon atom of the formic acid. Due to the evolution of CO2, the reaction proceeds in the direction of product.