Photooxidation of Methylbenzenes and Methylnaphthalenes Sensitized by Cyanoanthracenes

Abstract

9-Cyanoanthraccne, 9,10-dicyanoanthracene and 3,7,9,10-tctracyanoanthraccne photosensitize the oxidation in acetonitrile of toluene, durene. hexamethylbenzene, 1-methyl- and 2-methvl- naphthalene to the corresponding aldehydes, with low yield of the alcohols and. in the case of hexamethylbenzene, of tetramethylphthalidc. In benzene, only hexamethylbenzene reacts through a different pathway involving singlet oxygen. Comparison with fluorescence quenching data and experiments in the presence of good donors, halides or radical traps, as w-ell as the effect of solvents and of oxygen concentration show that the reaction involves electron transfer from the methylaromatic to the singlet excited state of the sensitizer, followed by proton transfer to CA˙̄ or O2˙̄ yielding benzyl radicals, which react with oxygen or can be trapped.