The autoxidation of diphenylketene

Abstract

The mechanism of reaction of diphenylketene with ground-state molecular oxygen was investigated by use of qualitative trapping studies and quantitative kinetic techniques. Key intermediates implicated in the mechanism are 1,1-diphenylacetolactone, 4,4-diphenyl-1,2-dioxetan- 3-one, benzophenone oxide and diphenyldioxirane. 1,1-Diphenylacetolactone, a 1,3-dipolar ion, was trapped by addition across the carbonyl of pentafluoroacetone and hexafluoroacetone. 4,4-Diphenyl-1,2-dioxetan- 3-one was implicated through luminescent behavior of the solution and the use of bromoform as a "heavy atom" solvent. Benzophenone oxide and 1,1-diphenyldioxirane were postulated as a result of the discovery of phenyl benzoate as a reaction product. Quantitative studies showed that, kinetically, the reaction is neither purely first order nor purely second order in diphenylketene. Solvent effects on the rate of reaction were less than ten-fold with no significant effect on product distribution. Significantly, however, use of bromoform as a solvent suppressed the formation of phenyl benzoate and dramatically increased the yield of benzophenone. Neither the rate of reaction nor the product distribution was affected by changes in oxygen concentration. The cyclic ketene acetal, 2-diphenylmethylene-5,5-diphenyl, 1-3-dioxolan-4-one, conceivably an adduct of diphenylketene and diphenylacetolactone, was isolated from the pot residue after distillation of diphenylketene.