Effect of the solvent on reduction of azomethine dyes with ketyl radicals and recombination of ketyl radicals

The rate constants of transfer of a hydrogen atom from ketyl radicals to azomethine dyes (k_H) and the rate constants of recombination of ketyl radicals (2k_r) in different solvents were measured by the method of pulsed photolysis. The dependences of k_H and 2k_r on the polarity of the solvent are V-shaped: k_H and 2k_r are maximum in weakly solvating solvents and in water and are minimum in nucleophilic solvents of medium polarity. This is due to the fact that nucleophilic solvation decreases and electrophilic solvation increases the reactivity of the ketyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1745–1749, August, 1989.