Reactivity of ketyl free radicals. Part 2.—Dimerization and dismutation of fluorenone and xanthone ketyls

Abstract

Dimerization equilibria and dismutation kinetics of fluorenone and xanthone ketyl radicals were studied by electrochemical methods at various pH. The dimerization equilibrium constant in aqueous-ethanolic solution is 7.1×10¹¹ and 1.3×10¹³ M^–1 for neutral fluorenone ketyl, and for neutral xanthone ketyl, respectively. Dimerization constants for the RH (neutral radical)+R^–(radical anion) systems are much lower; those for R^–+R^– are negligible. Dismutation kinetics were resolved into component reactions. Rate constants of dismutation RH+R^– are much higher than those found for RH+RH or R^–+R^– reactions. The kinetics support the electron-transfer mechanism of dismutation of ketyls.