Quantum Chemical Study of Mechanisms of the Reaction of Cyclohexyl Phenyl Sulfide with Water

Theoretical Insights into the Catalytic Effect of Transition-Metal Ions on the Aquathermal Degradation of Sulfur-Containing Heavy Oil: A DFT Study of Cyclohexyl Phenyl Sulfide Cleavage

“…Although the calculated energy barriers of the homolytic cleavage of C−S bonds in CPS at ambient temperatures (about 190 kJ/mol) were shown to be somewhat lower than the energy barriers of the heterolytic cleavage (about 290 kJ/mol) and be able further lowered under conditions of aquathermal treatment. 24 First, we have studied the hydrolysis of cyclohexyl phenyl sulfide in the uncatalyzed process and under conditions of catalysis with Fe 2+ ions using the DFT method within the PRIRODA software package. 23 The relevant reaction routes are given in Scheme 1.…”

“…Several reaction mechanisms were considered in previous ab initio theoretical studies of the reaction of aquathermolysis of cyclohexyl phenyl sulfide, namely, homolytic cleavage with formation of radical species, proton-catalyzed heterolytic cleavage, and hydrolysis . On the basis of these results and the results of experimental studies of the reaction products in the laboratory aquathermolysis process, we suggest that the heterolytic cleavage via ionic routes is also the most preferable mechanism involved in the transition-metal-catalyzed aquathermolysis processes of heavy oils, which we have studied recently under laboratory conditions. − Even if the hydrolysis routes also involve ionic reaction schemes, they are characterized by rather high energy barriers according to the published results of ab initio calculations . To compare these two possible mechanisms, i.e., heterolytic cleavage and hydrolysis, which are most likely involved in the processes of aquathermolysis of CPS under conditions of catalysis by transition-metal ions, we have calculated thermodynamic characteristics of these processes using rigorous quantum-chemical approaches.…”

“… 25 − 27 Even if the hydrolysis routes also involve ionic reaction schemes, they are characterized by rather high energy barriers according to the published results of ab initio calculations. 24 To compare these two possible mechanisms, i.e., heterolytic cleavage and hydrolysis, which are most likely involved in the processes of aquathermolysis of CPS under conditions of catalysis by transition-metal ions, we have calculated thermodynamic characteristics of these processes using rigorous quantum-chemical approaches. The homolytic cleavage in this study was not considered since transition-metal ions hardly have catalytic effects on this process.…”

“…Although the calculated energy barriers of the homolytic cleavage of C–S bonds in CPS at ambient temperatures (about 190 kJ/mol) were shown to be somewhat lower than the energy barriers of the heterolytic cleavage (about 290 kJ/mol) and be able further lowered under conditions of aquathermal treatment. 24 …”

“…Hence, it can be considered as a rate-limiting step in the entire sequence of reactions. The obtained energy barrier values of the heterolytic cleavage of a prereaction complex of CPS with H 3 O + are close to the published values . At the same time, this step is a barrierless reaction followed by subsequent rearrangement of the generated cyclohexyl cation into the more stable methylcyclopentyl cation in the third exothermic reaction step.…”