Density functional theory study of the oxidation reaction in the gas and aqueous phase of allyl methyl disulfide with hydroxyl radical

An in silico analysis of the oxidation mechanism of allyl methyl disulfide (AMDS) by hydroxyl radical was achieved at DFT level using B3LYP, CAM-B3LYP, M06-2X, and BMK functionals and 6-311++G(3df,2p) triple-zeta basis set. The calculations were carried out in both gas and aqueous phases using the SMD model (density-based solvation model). Three potential reactions were proposed according to results of Fukui function; in reactions 1 and 2, the hydroxyl radical attacks the sulfur atom breaking the disulfide bond and the reaction 3 is a hydrogen atom subtraction reaction. The respective structures of transition states (TSs) were found. Intrinsic reaction coordinate (IRC) calculations were performed for the three reactions, and their rates and equilibrium constants were calculated. When the solvent effect is taken into account, the four DFT functionals employed designate R3 (a subtraction reaction) as the fastest reaction. Thus, we elucidated the thermodynamic and kinetic feasibility of the proposed oxidation reactions.