Benkeser Reduction

Abstract

Benkeser reduction is the reduction of aromatic and olefinic compounds with lithium or calcium to unsaturated olefins and fully reduced hydrocarbons in the presence of low molecular weight amines. It has been found that low molecular weight monoamines, particularly methylamine and ethylamine, are excellent media for reduction with lithium. The study finds that the neat monoamines, aromatic compounds are reduced to mono olefins, whereas in monoamine‐alcohol solution, di‐olefins are obtained. The Benkeser reduction in ethylenediamine frequently results in overreduction of the substrate, giving a mixture of products. This drawback has been overcome by using 1 mole of ethylenediamine or N, N ′‐dimethylethylenediamine per gram‐atom of lithium with or without the proton donor (alcohol). So far, the lithium‐reducing systems have been applied to this type of reaction. The amination to hydrocarbon has also been reported under certain conditions. The calcium‐reducing systems have also been applied extensively besides electrochemical‐reducing systems.