Kinetics and Mechanisms of Reactions of Organic Cation Radicals in Solution

Abstract

The dimerization of cation radicals of simple benzene derivatives is usually accompanied by the formation of the corresponding biphenyl derivative. This, by virtue of the extended conjugation is more easily oxidized, and frequently only intractable tars are found as final products. If the reaction medium is carefully selected, so that the biphenyl cation radicals are stable, useful synthetic procedures can be developed. Two mechanisms are probable for the dimerization of cation radicals of anisoles and related compounds. They are termed “radical–radical dimerization” (RRD) and “radical–substrate coupling” (RSC). The oxidation of aromatic hydrocarbons and alkylaromatic compounds in media of low nucleophilicity results in the formation of dimers. The cation radicals of triphenylamines form dimers in high yield when generated in acetonitrile. The products are tetraphenylbenzidines.