Mechanistic and kinetic study of the oxidation of trifluoroacetonitrile by hydroxyl and oxygen

Trifluoroacetonitrile (CF3CN) is one of the perfluoronitriles to be used as replacements for electrical insulation, working fluids, and biomedical applications. Potential energy surfaces for the reactions of CF3CN with OH radicals in the presence of molecular O-2 have been calculated in details using the second-order Moller-Plesset perturbation theory (MP2) and coupled-cluster theory with single and double substitutions (CCSD) for geometrical optimization, and the restricted open-shell complete basis set quadratic ROCBS-QB3, multireference second-order Rayleigh-Schrodinger perturbation theory extrapolated to complete basis set limit (RS2/CBS), and the explicitly-correlated RS2 theory (RS2-F12) for energetics. The CF3CN + OH reaction undergoes predominantly via the C-O addition/elimination mechanism, leading to CF3C(OH)N radical adduct followed by the formation of CF3 and HOCN. The OH radicals could be recycled through the interception of CF3C(OH)N by O-2 to form the orientation-dependent CF3C(OH)NO2 radicals, leading to CF3C(O)NO + OH via the successive H-migration and O-O bond fission. Under the typical atmospheric conditions, the OH-recycling mechanism is dominant for the oxidation of CF3CN. The production of CF3 and HOCN can be significant at high temperatures and low pressures. Theoretical rate coefficients are in excellent agreement with the experimental data. The effect of substitution on the reactivity of the perfluoronitriles toward OH was revealed. The present work provides a fundamental understanding on the degradation of CF3CN and serves as a theoretical basis for its secondary chemistry.