Reactions of benzophenone in its triplet state with aliphatic substrates: hydrogen isotope exchange, formation of organochromium(III) species, and related reactions

Abstract

U.V. irradiation (for up to 20 min) of benzophenone in 54%(v/v) dioxane–water in the presence of chromium(II) trifluoromethanesulphonate results in the formation of the penta-aquadioxanylchromium(III) complex. The complex is thought to arise from the trapping by CrII of dioxanyl radicals which are the result of H-atom abstraction by 3Ph2CO* from dioxane. On prolonged irradiation (1 h) in the presence of tracer quantities of tritiated water, the products are Cr(H2O)63+ and tritium-labelled dioxane, formed by reaction of the penta-aquadioxanylchromium(III) complex with hydronium ions present in the solution. When the irradiation of benzophenone and chromium(II) trifluoromethane-sulphonate is carried out in 54%(v/v) tetrahydrofuran–water and in 54%(v/v) 1,2-dimethoxyethane–water, the more acid-stable penta-aquachromium(III) complexes derived from tetrahydrofuran and 1,2-dimethoxyethane are formed.