Semiconductor Phostocatalysis. ZnS-Nanocrystallite-Catalyzed Photooxidation of Organic Compounds

Article abstract of DOI:10.1246/bcsj.68.1811

Freshly prepared ZnS (nano-ZnS) suspensions catalyze photooxidation of organic substrates under band-gap irradiation with water as a good electron acceptor, while H2 evolves concomitantly.The organic substrates with hetero atoms or carbon-carbon double bonds (?-bonds), such as triethylamine (TEA), diethylamine (DEA), methanol, ethanol, cyclopentene, cyclohexene, 2-methylfuran, toluene, and ethylbenzene, undergo effective one-hole oxidation.This leads to efficient carbon-carbon bond forming reactions between cumulatively formed radicals at the α-carbon adjacent to the hetero atom or the ?-bond.The photooxidation in the presence of a larger quantity of water results in successive oxidation of the intermediary α-carbon radicals, giving the two-hole oxidation products, e.g., DEA and acetaldehyde from TEA and formaldehyde from methanol.The formation of the intermediary α-carbon radical has been clarified by ESR analysis using 2-propanol as an organic substrate.Semi-empirical molecular orbital calculations suggest that the nano-ZnS-catalyzed photooxidation should be predictable from energetics in the formation of the α-carbon radicals through one-hole oxidation and deprotonation, and from change in the bond order of αC-H bond of the α-carbon cation radicals.