STRUCTURAL EFFECTS IN THE TIO2-PHOTOCATALYZED OXIDATION OF ALKYLAROMATIC COMPOUNDS IN ACETONITRILE IN THE PRESENCE OF AG2SO4

The TiO2-sensitized photochemical reactions of some alkylbenzenes (ArCH(2)R; R = H, Me), 1-aryl-2-propanols, and corresponding methyl ethers (ArCH2C(OR'')R'CH3; R', R'' = H, Me) have been investigated in MeCN, in the presence of Ag2SO4, which traps the photogenerated electrons. With ArCH(2)R, the corresponding radical cations are generated by the photoexcited TiO2 and are then deprotonated to form benzyl radicals; from the latter 1,2-diarylethanes, 3-arylpropanonitriles, and benzylacetamides are obtained as major products. With ArCH2C(OR'')R'CH3, the formed radical cations undergo C-C bond cleavage as the only observed route, when Ar = Ph. However, when Ar = 4-MeOPh and R' = H, the radical cation undergoes C-H bond cleavage as the major or exclusive reaction path. These results are compared with those obtained in the corresponding homogeneous photochemical reactions, and their implications with respect to the role of the structure on the side-chain reactivity of aromatic radical cations are discussed.