The reactions of substituted acyclic 1,3-butadienes on photoexcited TiO2 in acetonitrile

The reactivities of 2,3-dimethyl-1,3-butadiene, 1,4-diphenyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, and isomeric 2,4-hexadienes in irradiated TiO(2)/acetonitrile suspensions were studied. The sterically hindered and conformational restricted dienes appear to be adsorbed at the surface to a lesser extent and/or in a less reactive conformation. The formation of the reaction products is rationalized in terms of hole catalyzed reaction pathways leading to the formation of resonance stabilized radical cations which react with surface adsorbed superoxide anion to yield peroxy radical adducts. Based on the major products it does not appear hydroxyl radicals, even with the addition of water to solvent, can compete with the radical cation reaction pathways under these experimental conditions. (C) 1999 Elsevier Science S.A. All rights reserved.