Addition of toluene and ethylbenzene to mixtures of H2 and O2 at 772 K: Part 2: formation of products and determination of kinetic data for H+ additive and for other elementary reactions involved

A detailed product analysis was carried out at 773 K when toluene (TOL) and ethylbenzene (EB) were added separately in small amounts to H2 + O2 + N2 mixtures at 500 Torr total pressure. Benzaldehyde is the major initial product from TOL, formed in (26), (26) and (26) and in the overall (31) and (31). C6H5CH2+HO2→OH+C6H5CH2O (+O2→C6H5CHO) C6H5CH2+O2→C6H5CHO+OH The electron-delocalised benzyl radical reacts very slowly with O2, and the importance of radical-radical reactions is confirmed by the observation that bibenzyl is formed in relatively high yields. Values of k26 = (5.1 ± 1.5) × 109 dm3 mol−1 s−1 and k29 = 2.8 × 103 s−1 (for the 1,3 Hatom transfer involved in ((31) and (31))) are obtained.C6H5CH2OO→C6H5CHOOH Styrene is the major initial product from EB. The electron-localised radical C6H5CH2CH2 reacts almost completely in a fast reaction (k = 2 × 108 dm3 mol−1 s−1) with O2 to give styrene, but the more stable electron-delocalised C6H5CHCH3 radicals also undergo radical-radical reactions to give benzaldehyde with k38 = (7.3 ± 3.0) × 109 dm3 mol−1 s−1. \C6H5CHCH3+HO2→C6H5CH(OOH)CH3 Measurements of the yields of benzene from TOL and EB gave rate constants for the reaction H + TOL/EB → C6H6 + CH3/C2H5, and combination with independent data gives K = 950T2exp(−475) dm3 mol−1 s−1 for the TOL reaction. Rate expressions are given in non-Arrhenius form for all H abstractions by H atoms from TOL and EB. Further evidence is provided that H abstraction from the α-carbon atom in alkyl benzenes is considerably slower than expected on thermochemical grounds. It is, however, concluded that abstraction from the benzene ring by H atoms is significantly more important than hitherto suggested.Keywords: aromatic oxidation, kinetics, mechanism