Free-Radical Chain Reactions Involving Hydrogen and Bromine Atom Transfer Induced by TiO2-Mediated Photocatalysis

Bromoform and cyclohexyl bromide are produced at high yields upon room-temperature UV photolysis of TiO 2 powder suspended in deaerated tetrabromomethane dissolved in cyclohexane or cyclohexane−CCl 4 mixtures. No reaction takes place in the absence of TiO 2 . Cyclohexyl chloride is produced in the presence of CCl 4 when no CBr 4 is added. The CBr 4 −toluene−TiO 2 system behaves similarly, producing high yields of bromoform and benzyl bromide. UV photolysis of toluene solutions containing CBr 4 in the absence of TiO 2 also leads to efficient formation of the same products. The chain reaction mechanisms of the photocatalytic processes are discussed.