Primary photochemical processes in aromatic molecules. Part 15.—The photochemistry of aromatic carbonyl compounds in aqueous solution

Abstract

Phosphorescence has been observed from oxygen-free aqueous solutions of benzophenone and acetophenone. In the case of benzophenone the phosphorescence is strongly self-quenched. Rate constants for quenching of triplet benzophenone by various species have been measured.

The photoreactivity of benzophenone in water has been reinvestigated. Photolysis does occur, the quantum yield being low and somewhat irreproducible. Benzopinacol is a product of the photolysis in oxygen-free solution, while in aerated solution hydroxybenzophenones are formed with a very low quantum yield.

Flash photolysis experiments have characterized the triplet-triplet absorption of benzophenone in aqueous solution and show that the ketyl radical and another radical are intermediates in the reaction. It is suggested that hydrogen abstraction from water occurs to give free OH radicals which then attack benzophenone to give a cyclohexadienyl radical. The energetics of this process are considered.