Kinetics of the (photo)oxidation of the thionine leuco base with uranyl nitrate

Spectrophotometry and lamp and laser flash photolysis have been used to investigate the kinetics of the formation and decay of thionine and semithionine, obtained in the photooxidation of the thionine leuco base with uranyl nitrate. It has been shown that after the light flash a certain amount of thionine is formed in the cage oxidation of semithionine with uranoyl UO₂⁺ (concentration ratio of thionine and semithionine leaving the cage 595). A kinetic scheme of the reaction has been proposed, which describes satisfactorily the experimental data. The equilibrium constant K=1.2±0.3)·10^–4 has been obtained for the dark oxidation of the thionine leuco base with uranyl nitrate in aqueous sulfuric acid (pH 1.0) which is close to the calculated value.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 13–18, January, 1990.