Controlled oxidation of benzyl ethers on irradiated semiconductor powders

Irradiation of a suspension of powdered TiO₂, a photoactive semiconductor, in oxygen saturated acetonitrile leads to mild selective oxidation of substrates containing a benzylic methylene by conversion of that carbon to a carbonyl group. The method is shown to be synthetically useful for the preparation of esters from ethers and ketones from hydrocarbons. A critical analysis of the products and of the possible intermediates results in a plausible mechanistic pathway for these photooxidations.