Kinetics of catalyst-free thermal and photo-oxidation of cumene

Abstract

Kinetics of thermal and photo-oxidation of cumene in the absence of catalyst was studied using high-pressure differential scanning calorimetry and low-pressure photocalorimetry. Kinetics of oxidation was followed by cumene hydroperoxide (CHP), acetophenone, and phenol formation. The amount of CHP formed was deduced from the total heat of reaction of thermal degradation of CHP at 453 K and using a new gas chromatographic method. CHP solution in cumene oxidized at 453 K and 680 psi of oxygen reproducibly with the heat of reaction linearly dependent on peroxide concentration in cumene. It was confirmed that cumene thermal oxidation was slow at <453 K, but at ≥453 K could occur explosively. Autocatalysis by CHP during thermo-oxidation was confirmed. Apparent activation energy of the photo-oxidation of cumene was found to be E a = 22.3 kJ mol−1. The value corresponds to radical chain process of the cumene autoxidation. Under assumption of pseudo-first order reaction, the rate constant of CHP formation was found to change from k CHP ≈ 0.76 s−1 during the first 4 h of photo-oxidation to k CHP ≈ 0.2 s−1 at the later stages at 2.0 W cm−2 of UV exposure dose. It was established that the initial presence of the CHP in cumene does not change the photo-oxidation kinetics, but shifts the kinetic curve to earlier time. Finite difference method was employed to numerically model kinetics of cumene oxidation. The result indicated higher than expected thermal and photo-stability of both, cumene and CHP.