Oxygenation of α-Methylstyrene with Molecular Oxygen, Catalyzed by 10-Methylacridinium Ion via Photoinduced Electron Transfer

Abstract

Photooxygenation of α-methylstyrene with oxygen occurs efficiently in the presence of 10-methylacridinium perchlorate (AcrH+ClO4-) under visible light irradiation in oxygen-saturated acetonitrile (MeCN) to yield acetophenone as the main oxygenated product. No photoinduced oxygenation of α-methylstyrene occurs in the absence of AcrH+ under otherwise the same experimental conditions. Little photodegradation of AcrH+ occurs in the present photocatalytic system, which provides a clean method of photoinduced oxygenation reaction with molecular oxygen, alternate to the ene reaction of singlet oxygen. The photocatalytic oxygenation of α-methylstyrene with oxygen is shown to proceed via photoinduced electron transfer from α-methylstyrene to the singlet excited state of AcrH+ (1AcrH+*) on the basis of the fluorescence quenching of 1AcrH+* by α-methylstyrene, the quantum yield determination, and the detection of radical intermediates by laser flash photolysis and ESR measurements.