The dimerization of radical anions of aromatic carboxylic acids competing with the self-protonation reaction

Abstract

Quantum-chemical calculations (CNDO/2) of the theoretical relationship between the rate constants for the dimerization and self-protonation of radical anions show that dimer formation in the one-electron electroreduction of aromatic carboxylic acids (benzoic (1), 1-naphthoic (2), and 9-anthroic (3) is most probable for1. It is established that during the constant potential electrolysis (CPE) of1 a mixture of “head-to-tail” dimers is formed in the presence of 0.1M Bu₄NClO₄ (DMF). Their ratio depends on the amount of electricity passed through the solution. The CPE of 2 in the presence of 20 % H₂O affords 1,4-dihydro-1-naphthoic acid in up to 70 % yield. The high yield (∼70 %) of 9,10-dihydro-9-anthroic acid during the CPE of 3 can be accounted for by the decomposition of the dimeric product followed by protonation of the anionic species.