A study of the mechanism of certain chemical reactions—I : The mechanism of the leuckart-wallach reaction and of the reduction of schiff bases by formic acid

Abstract

The reduction of benzylidene-bis-piperidine by formic acid in organic solvents has been investigated. This is a chain reaction that depends on the nature of the solvent. The rate of the reaction is decreased by the addition of hydroquinone and increased when diphenylamine is added. In the latter case, an intense transient orange-greenish colour appears. These facts indicate that reduction takes place, according to the free-radical mechanism. As this reaction is closely related to the Leuckart—Wallach reaction and to the reduction of imines by formic acid,the hypothesis has been advanced that these reactions occur through the intermediate formation of esters of α-aminoalcohols and formic acid. These esters suffer decarboxylation according to the radical(crypto-radical or free-radical) mechanism. This hypothesis is in contradiction to the common opinion on the ionic mechanism postulated for these reactions.