Polarographic reductions of some carbonyl compounds

Abstract

The complete reduction scheme for aryl alkyl ketones can be elucidated only by studying several series of compounds. The effect of protonation by acids other than hydroxonium ion on the antecedent reaction and the effect of alkali metal cations on the protonation of radical anions are discussed. Effects of substituents in α- and β-positions in the side chain and on the phenyl ring are compared. Effects of electron-accepting substituents indicate increased conjugation in the transition state. Reduction of α,β-unsaturated aldehydes and ketones produces in the first two-electron step the saturated aldehydes or ketones. Proton transfers in various pH-ranges were elucidated and the role of chemical transformations in the reduction of α,β-unsaturated aldehydes and ketones is manifested by a formation of a separate wave. In the study of saturated aldehydes the structural effects on the dehydration reaction were compared. The acid-base reaction that causes with some aldehydes a decrease in the reduction current at high pH was attributed to the formation of the dianion of the hydrated form or more probably to the carbanion formation rather than to the monoanion. This was deduced from the study of the u.-v. spectra, in which the band at 280–300 mµ with Iµ of the order 103 was attributed to the carbanion.