Dye sensitized photooxidation of 1,3-Diphenyl-2-pyrazoline

Abstract

Dye sensitized photooxidation of 1,3-diphenyl-2-pyrazoline in methylene chloride yields 1,3-diphenyl- pyrazole and in methanol yields 1,3-diphenylpyrazole and β,β-dimethoxypropiophenone. The formation of 1,3-diphenylpyrazole is quenched by the singlet oxygen quencher β-carotene, whereas the formation of β-dimethoxypropiophenone does not appear to be affected. The photooxidation in methanol shows a large deuterium isotope effect, the rate being approximately ten times faster in methanol[D4] than in methanol. Under anaerobic conditions, 1,3-diphenyl-2-pyrazoline quenches the phosphorescence of eosin Y and rose bengal B with quenching rate constants 1.0 x 108 and 3.0 x 108 1, mol-1 s-1, respectively. Photobleaching of the dyes is shown to occur by reduction to the semi-reduced dye radicals.