Induced decomposition of benzoyl peroxide by the benzophenone ketyl radical

Abstract

Benzophenone ketyl radicals [(C 6H 5COH] induce the decomposition of benzoyl peroxide in benzene at 25°. In the presence of benzhydrol, the resulting benzoyloxy radicals (C 6H 5COO·) abstract hydrogen from the alcohol, resulting in the formation of benzoic acid and more benzophenone ketyl radicals. Chain lengths are short. Termination is principally between phenylcyclohexadienyl radicals (or possibly between phenylcyclohexadienyl and benzoyloxy radicals), indicating that the rate determining step is the hydrogen abstraction from alcohol. This result is contrasted with the results of thermolysis of benzoyl peroxide in alcohols at higher temperatures. By comparing the reactivity of the benzophenone ketyl radical with its O-Me analog, it is concluded that the transition state for the induced decomposition probably involves a partial hydrogen transfer from the ketyl radical to one of the peroxide O atoms.