Organic electrode processes: generalized reduction mechanisms

Abstract

Prototype formulations are considered for the reaction pathways commonly encountered for the electrolytic reduction of organic compounds in aqueous and nonaqueous media on the basis that the essential feature is severance of a chemical bond which requires transfer into the reaction site of one or two electrons; multiple electron processes result from instability at the applied potential of initially produced species or their chemically altered products. To obtain electrical neutrality, uptake of electrons may have to be accompanied by that of a cation, generally a proton. Pertinent factors in the path followed in the overall electrode process may include a sequence of free radical or radical anion going to dimeric or carbanion species (depending on the relative rates of chemical and charge-transfer steps), possible interaction of intermediate products with their progenitors, proton donor activities, medium properties (e.g in respect to rates of chemical reactions accompanying charge-transfer and control of the chemical states of reactants and intermediates), stereochemical factors inherent in reactant and intermediate species, and chemical interaction with the electrode material. Application of the general mechanistic considerations are illustrated by various types of electrolytic reductions: aromatic hydrocarbon, nitrogen heterocycle, carbon–halogen bond, ketone carbonyl group, and beta halogenated and/or unsaturated acids.