Gas-Phase Hydroxyl Radical Reactions. Products and Pathways for the Reaction of OH with Aromatic Hydrocarbons

Article abstract of DOI:10.1021/j150619a011

The reactions of OH with benzene, toluene, 1,4-dimethylbenzene, and 1,3,5-trimethylbenzene have been investigated in a discharge flow system at total pressures of 6-12 torr.In the presence of NO, NO2, and O2 the intermediate radicals are converted quantitatively to stable products from which two major reaction pathways are identified.Abstractionof a hydrogen atom from the methyl group by OH leads primarily to the corresponding aldehyde, and addition to the aromatic ring by OH gives primarily the corresponding phenols.Nitro substitution of the aromatics via the OH adduct competes with phenol formation; however, the amount depends on the ratio of NO2/O2.In the case for toluene, the ratio of rate constants, k_NO2/k_O2, for the two processes is (4+/- 2) X 10³.The isomer distributions for OH addition to toluene were determined to be 0.806 +/- 0.022 ortho, 0.051 +/- 0.009 meta, 0.143 +/- 0.019 para, and <0.008 ipso.The contributions of methyl attack (k₁) relative to total reaction (k₁ + k₂) are 0.15 +/- 0.02 for toluene, 0.15 +/- 0.02 for 1,4-dimethylbenzene, and 0.021 +/- 0.006 for 1,3,5-trimethylbenzene.