title: Concerted or stepwise mechanism? New insight into the water-mediated neutral hydrolysis of carbonyl sulfide.
abstract: The water-mediated neutral hydrolysis mechanism of carbonyl sulfide (OCS) has been re-examined using the hybrid supramolecule/continuum models with n = 2-8 explicit water cluster at the level of MP2(fc)(CPCM)/6-311++G(d,p)//MP2(fc)(CPCM)/6-31+G(d). Present calculations indicate that the potential energy surface in water solution is different from the one in the gas-phase, and only stepwise mechanism is observed in aqueous solution, i.e., monothiocarbonic acid (H2CO2S) is formed via monothiocarbonate (OCSOH(-), MTC) and its counterion, protonated water cluster, (H2O)nH3O(+). The predicted rate-determining step (RDS) barrier for the stepwise mechanism in water solution, about 90 kJ/mol, shows good agreement with the experimental values, 83.7-96.2 kJ/mol using six- or eight-water model including two cooperative water molecules. Moreover, two reaction pathways, the nucleophilic addition of water molecule across the C═O or the C═S bond of OCS are competitive.
authors.affiliation: College of Chemistry and Key State Laboratory of Biotherapy, Sichuan University , Chengdu 610064, China.
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Li
authors.forename: Si-Jia
authors.initials: SJ
authors.lastname: Ren
authors.forename: Xi-Guang
authors.initials: XG
authors.lastname: Wei
authors.forename: Yi
authors.initials: Y
authors.lastname: Zeng
authors.forename: Guo-Wei
authors.initials: GW
authors.lastname: Gao
authors.forename: Yi
authors.initials: Y
authors.lastname: Ren
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu
authors.forename: Kai-Chung
authors.initials: KC
authors.lastname: Lau
authors.forename: Wai-Kee
authors.initials: WK
authors.lastname: Li
mesh_terms: D006868:Hydrolysis; D015394:Molecular Structure; D011789:Quantum Theory; D013461:Sulfur Oxides / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D013461:Sulfur Oxides; D014867:Water; C010063:carbonyl sulfide