The kinetics of the thermal decomposition of acetophenone

Abstract

The mechanisms involved in the thermal decomposition of aldehydes and ketones are varied, and the relations between them somewhat complex. In particular, an interesting contrast in behaviour has recently been found between benzaldehyde and acetaldehyde. An investigation of acetophenone has therefore been made for comparison with acetone. The thermal decomposition of acetophenone takes place predominantly by the step C 6 H 5 COCH 3 = C 6 H 5 CH 3 + CO, the toluene undergoing a subsequent decomposition to give chiefly benzene, methane and carbon. It differs from that of acetone in yielding hardly any ketene. It is homogeneous and nearly of the first order, with no sharp falling off in rate at 20 mm . There is no retardation by nitric oxide or by greatly increased surface, nor can an increased rate of decomposition be induced by the presence of radicals from decomposing diethyl ether. This is taken as evidence for the absence of reaction chains. In this respect the behaviour resembles that of acetone, but other differences in kinetics exist. These are briefly discussed.