THE DIMERIZATION OF RADICAL-ANIONS OF AROMATIC CARBOXYLIC-ACIDS COMPETING WITH THE SELF-PROTONATION REACTION

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 for 1. It is established that during the constant potential electrolysis (CPE) of 1 a mixture of ''head-to-tail'' dimers is formed in the presence of 0.1 M 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 (approximately 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.