High-accuracy theoretical studies on the gas-phase reaction mechanisms of sulfur mustard with reactive oxygen species (OH/O2/HO2/O)

Abstract

The gas-phase reaction mechanisms of sulfur mustard (HD) under oxygenated conditions constitute the theoretical foundation for understanding its environmental evolution processes and evaluating its incineration efficiency. In this work, the gas-phase reaction mechanisms and kinetics between HD and reactive oxygen species (OH, O₂, HO₂, O) were investigated at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(d,p) theoretical level. The study reveals that all four oxygen species can participate in hydrogen abstraction reactions with HD, with the OH-mediated and O-mediated pathways being the most favorable. Furthermore, the research demonstrates that O₂ and O can directly oxidize HD to form mustard sulfoxide, which can be further oxidized to mustard sulfone – a compound exhibiting comparable toxicity to HD itself. The HD-OH adduct can be converted to mustard sulfoxide in the presence of O₂, and the resulting sulfoxide-OH adduct can subsequently be oxidized to mustard sulfone. Computational analysis of the reaction pathways employing the RS2C method indicates that both steps proceed via substantially high energy barriers. Kinetic simulations show that under typical incineration conditions, OH and O play dominant roles in HD degradation.