Electron spin resonance and kinetic studies on the liquid-phase autoxidation of cumene with lead dioxide

The autoxidation of cumene with lead dioxide has been studied over the range 291-323 K. By use of e.s.r. the concentration of cumylperoxyl radical (a chain-propagating agent) was monitored during autoxidation. The kinetics of this reaction were determined by measuring the concentration of cumylperoxyl radical and the rate of oxygen consumption under the same conditions. Both the radical concentration and the rate of oxygen consumption were constant with time and were independent of the catalyst weight: liquid volume ratio. The variation in radical concentration was first order in cumene concentration, while the rate of oxygen consumption was second order. Chain initiation involves the formation of cumylperoxyl radical from decomposition of the hydroperoxide over the catalyst surface and desorption into the homogeneous phase where chain propagation and termination proceed. Rate equations derived from the proposed reaction mechanism explain quantitatively the experimental observations. Values of the rate constants have been determined.