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.