Electroreduction of substituents on a pyridine ring in aqueous sulfuric acid

Abstract

Hydroxymethyl, aminomethyl, carboxyl, methoxycarbonyl, carbamoyl, hydrazinocarbonyl, formyl, vinyl and phenyl groups attached to various positions of a pyridine ring were reduced at a mercury cathode in an aqueous sulfuric acid solution. These groups, except for the phenyl group, at the 2- and 4-positions could be reduced, while the reduction of the groups at the 3-position seemed to be difficult. The reduction potential of the groups at the 4-position was generally less negative than that of the same group at the 2-position. Current efficiencies for the reduction of hydroxymethyl, aminomethyl and vinyl groups were higher in the case of 4-substituted-pyridines than 2-substituted-pyridines, while this tendency reversed in the case of the other groups. An obvious steric hindrance effect on the current efficiency was also observed in the reduction of substituted-hydroxymethyl groups attached to the 2-position. On the basis of these results, reduction mechanism is discussed and also the synthetic scope is described.