Structural stabilities of N-permethylated tetracations of meso-tetrakis(4-pyridyl)porphyrin, meso-tetrakis[4-(dimethylamino)phenyl]porphyrin, and their manganese(III) complexes toward hydrogen peroxide, tert-butylhydroperoxide, and sodium hypochlorite

Abstract

The degradation rate constants of the tetracations 5,10,15,20-tetrakis( N -methylpyridinium-4-yl)porphyrin and 5,10,15,20-tetrakis( N , N , N -trimethylanilinium-4-yl)porphyrin as well as their manganese(III) complexes toward the oxidants H 2 O 2, t- BuOOH , and NaOCl were measured at various pH values, I = 0.2 M and 30°C. The free-base and manganese porphyrins showed high structural stabilities toward H 2 O 2 and t- BuOOH in strong acidic solutions and their degradation constants were on the order of 10-6 min-1 or no porphyrin degradation was observed at all. As the pH increased, their stability towards these peroxides decreased and in basic solutions, they showed almost no stability toward H 2 O 2 and a moderate stability toward t- BuOOH . When NaOCl was employed as the oxidant, they showed only moderate stabilities in strong basic solutions and almost no stability in slightly basic, neutral or acidic solutions. The degradation rate constants in the presence of NaOCl in strong basic solutions varied from 10-2 min-1 to 10-4 min-1.