A Theoretical Study of Oxidation of Phenoxy and Benzyl Radicals by HO2

We present a quantum chemical study of oxidation of phenoxy and benzyl radicals by HO2. All calculations were carried out using the modified Perdew-Wang (MPW1K) density functional method. We found that adsorption of HO2 in the ortho and para positions of the aromatic ring leads to stable phenyl-OOH and benzyl-OOH adducts with dissociation energies from 16 to 27 kcal/mol. Calculations indicate that the barriers for various decomposition pathways for phenoxy-OOH and benzylOOH complexes are at least 10 kcal/mol above the dissociation thresholds, thus precluding the possibility of chemically activated decomposition. The main products from the decomposition of phenoxy-OOH adduct are found to be phenol, 1,4benzoquinone, and 1,2-benzoquinone. Similarly, the decomposition of benzyl-OOH leads to toluene and methylenecyclohexadienone. 1,2-benzoquinone is the least stable specie among these compounds. We found that subsequent thermal decomposition of 1,2-benzoquinone into carbon monoxide and cyclopentadienone proceeds via a 48 kcal/mol barrier.