New insights into isopropylthiobenzene decomposition in supercritical water

Abstract

Experiments and quantum chemistry calculations were performed to study the decomposition mechanism of isopropylthiobenzene, the role of supercritical water (SCW) and the effects of alkanes on the decomposition of isopropylthiobenzene. In this study, three possible decomposition paths in SCW were described. The most feasible decomposition path involves four steps. First, hydrocarbon radicals attack the α-H on the isopropyl group of isopropylthiobenzene, leading to cleavage of one C–S bond to form thioacetone. Second, a cycloaddition of water to thioacetone occurs to form a mercaptoalcohol. Third, mercaptoalcohol decomposes into H₂S and acetone either directly or via the catalysis of water. Finally, acetone decomposes into CO₂ via free radical reactions. During the decomposition process, SCW partakes mainly as an H-transfer catalyst and a reactant by forming a n-membered ring transition state (n = 4, 6). The alkanes cause selective cleavage of the C–S bond and promote desulfurization by forming free radicals. In addition, isopropyl from isopropylthiobenzene could act in the same way as an alkane to promote the decomposition of isopropylthiobenzene in SCW.