Theoretical studies on the reaction mechanism and kinetics of the atmospheric reactions of 1,4-thioxane with OH radical

The volatile organic compounds (VOC) are emitted as pollutants into the atmosphere from many natural and artificial sources. The oxidation of VOC by the atmospheric species plays a key role in the degradation of VOC. In this investigation, the atmospheric degradation of a cyclic organosulfur compound 1,4-thioxane by OH radical is studied. The pathways for the reaction of 1,4-thioxane with OH radical have been modeled through electronic structure calculations using density functional theory at B3LYP and M06-2X level of theories with 6-31G(d,p) basis set. The structures, energies, and vibrational frequencies obtained from DFT calculations were subsequently used to perform canonical variational transition-state theory calculations to determine the rate constants over the temperature range of 278-350 K and to study the lifetime of 1,4-thioxane in the atmosphere. The OH-initiated reaction of 1,4-thioxane was found to proceed by hydrogen atom abstraction reaction and subsequent O-2 addition, leading to the formation of peroxy radical intermediate, which further undergoes secondary reactions with other atmospheric species. The possibility for the formation of various products from the oxidation of 1,4-thioxane in the atmosphere and their environmental implications are discussed. The rate constant calculated for the reaction of 1,4-thioxane with OH radical is in good agreement with the available experimental data. The reaction energy profile for the initial reaction of 1,4-thioxane with OH radical calculated at B3LYP/6-31G(d,p) level of theory.