The effect of substituents on the anodic oxidation of aliphatic carboxylates and the passage towards a pseudo-Kolbe reaction

Abstract

The oxidation of a series of tetrabutylammonium aliphatic carboxylates, and the chloroacetate and methoxyacetate ions has been performed in acetonitrile on glassy carbon electrodes. The electron transfer activation step and the decarboxylation reaction are stepwise and they occur under a mixed kinetic control. In the case of acetate, butyrate, hexanoate and chloroacetate ions, the high rate of cleavage of the electrochemically produced acyloxy radicals allows the generation of free radicals and carbocations, which react with acetonitrile to afford N-acylamides. The electrochemical oxidation of methoxyacetate is pseudo-Kolbe since it involves the oxidation of methoxy-group instead of the carboxylate group. As products of this reaction, an N-acylamide and dimethoxyethane are yielded. Although this reaction is globally a one-electron transfer process, it involves the competition between a Kolbe and a Non-Kolbe pathways. This pseudo-Kolbe reaction represents an example of intramolecular dissociative electron transfer mechanism.