Insight into the formation of organosulfur compounds from the reaction of methyl vinyl ketone with sulfite radical in atmospheric aqueous phase

Highlights: • SO₃⁻ radical is preferable to be added to C1 site of MVK. • Dissolved O₂ addition to the initial product is more favorable. • The peroxyl radical can be transformed to products through multiple processes. • Bimolecular reaction of peroxyl radical with other species is also important. The formation of organosulfur compounds through the reaction of organic species with sulfoxy radicals produced from the metal-catalyzed oxidation of S(IV) has become of recent concern, but the detailed formation mechanism still remains unanswered. In this work, we studied the mechanism of the initial reaction of methyl vinyl ketone (MVK) by SO₃⁻ radical and the subsequent sulfonate formation processes using DFT calculation. The results show that dissolved O₂ addition to the initial product is more favorable than the addition of MVK to the initial product due to its lower activation free energy (6.19 kcal mol⁻¹). The produced peroxyl radical can undergo bimolecular self-reactions, unimolecular decay and bimolecular reaction with other species (HSO₃⁻ and H₂O) to form alcohols and ketones. Among them, two pathways are most likely to occur: one belongs to bimolecular self-reactions, whose activation free energy is 16.20 kcal mol⁻¹; the other is derived from bimolecular reaction of peroxyl radical with HSO₃⁻, which needs to overcome the activation free energy of 18.47 kcal mol⁻¹. This work displays a complete description of the formation process of sulfonates and thus can provide some insights into the further study on the formation of organosulfur compounds.