Oxidation of the 1-naphthyl radical C₁₀H₇? with oxygen: Thermochemistry, kinetics, and possible reaction pathways

The reaction of the 1-naphthyl radical C10H7 center dot (A2 center dot) with molecular (O-3(2)) and atomic oxygen, as part of the oxidation reactions of naphthalene, is examined using ab-initio and DFT quantum chemistry calculations. The study focuses on pathways that produce the intermediate final products CO, phenyl and C2H2, which may constitute a repetitive reaction sequence for the successive diminution of six-membered rings also in larger polycyclic aromatic hydrocarbons. The primary attack of O-3(2) on the 1-naphthyl radical leads to a peroxy radical C10H7OO center dot (A2OO center dot), which undergoes further propagation and/or chain branching reactions. The thermochemistry of intermediates and transition state structures is investigated as well as the identification of all plausible reaction pathways for the A2 center dot + O-2 / A2 center dot + O systems. Structures and enthalpies of formation for the involved species are reported along with transition state barriers and reaction pathways. Standard enthalpies of formation are calculated using ab initio (CBS-QB3) and DFT calculations (B3LYP, M06, APFD). The reaction of A2 center dot with O-3(2) opens six main consecutive reaction channels with new ones not currently considered in oxidation mechanisms. The reaction paths comprise important exothermic chain branching reactions and the formation of unsaturated oxygenated hydrocarbon intermediates. The primary attack of O-3(2) at the A2 center dot radical has a well depth of some 50 kcal mol(-1) while the six consecutive channels exhibit energy barriers below the energy of the A2 center dot radical. The kinetic parameters of each path are determined using chemical activation analysis based on the canonical transition state theory calculations. The investigated reactions could serve as part of a comprehensive mechanism for the oxidation of naphthalene. The principal result from this study is that the consecutive reactions of the A2 center dot radical, viz. the channels conducting to a phenyl radical C6H5 center dot, CO2, CO (which oxidized to CO2) and C2H2 are by orders of magnitude faster than the activation of naphthalene by oxygen (A2 + O-2 -> A2 center dot + HO2).