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 TiO2 powder suspended in deaerated tetrabromomethane dissolved in cyclohexane or cyclohexane-CCl4 mixtures. No reaction takes place in the absence of TiO2. Cyclohexyl chloride is produced in the presence of CCl4 when no CBr4 is added. The CBr4-toluene-TiO2 system behaves similarly, producing high yields of bromoform and benzyl bromide. UV photolysis of toluene solutions containing CBr4 in the absence of TiO2 also leads to efficient formation of the same products. The chain reaction mechanisms of the photocatalytic processes are discussed.