Neutral hydrolyses of carbon disulfide: Anab initiostudy of water catalysis

Abstract

The water-catalyzed hydrolysis reaction of carbon disulfide (CS(2)) has been investigated at the levels of HF and MP2 with the basis set of 6-311++G(d,p) using the combined supramolecular/continuum models, in which up to six water molecules are involved in the hydrolysis and the effect of water bulk solvent is taken into account according to the polarizable continuum model (PCM). The activation Gibbs free energies in water solution, DeltaG(sol) (not equal) (298 K), for the rate-determining steps of one up to six water hydrolyses are 247.9, 184.2, 152.3, 141.8, 134.4, and 118.9 kJ/mol, respectively. The most favorable hydrolysis path of CS(2) involves a sort of eight-membered ring transition structure formed by six water molecules, among which three water molecules are not involved in the proton transfer, two near to the nonreactive sulfur atom, and one below the parent carbon disulfide. This suggests that the hydrolysis of CS(2) can be mediated with the water molecule(s) and be significantly facilitated by the cooperative effects of the water molecule(s) in the nonreactive region. The catalytic effects of water molecule(s) due to the alleviation of ring strain in the proton transfer process may result from the synergistic effects of rehybridization and charge reorganization from the prereaction complex to the rate-determining transition state structure induced by water molecule(s). PCM solvation models could significantly lower the rate-determining activation Gibbs free energies by 20-38 kJ/mol when two up to six explicit water molecules involved in the neutral hydrolysis of CS(2).

Density functional theory analysis of carbonyl sulfide hydrolysis: effect of solvation and nucleophile variation

“…As shown in Fig. 3, the activation energy for TS6 is 73.1 kJ mol −1 , which is higher than TS4 and TS5 by 40.8 and 16.5 kJ mol −1 , respectively, indicating that the IM6→P2 step via the transition state TS6 with C-S bond cleavage is the RDS for reaction (2). This is in agreement with the reported experimental results.…”

“…Deng et al [3] have investigated the mechanism for hydrolysis reaction (1) in the presence of up to five water molecules, but, as we shall see, this reaction is somewhat different from those presented in this study. Meanwhile, reaction (2) was not mentioned in the studies of Deng et al In fact, reaction (2) is central to OCS hydrolysis, and our present studies show that reaction (2) is the main reaction path in the OCS hydrolysis. Further, several theoretical studies of the elementary processes and reaction mechanisms associated with reaction (2) are often contradictory.…”

“…Experiments by Leu and Smith [34] detected that SOH was only a minor product of the reaction of OCS and OH. The results calculated above show that CO 2 and SH − are the main products for reaction (2). Moreover, the experiment by Leu and Smith indicated that SH was formed as a major product of the reaction of OCS with OH at 517 K.…”

“…Recently, increasingly stringent emission standards have been introduced around the world in order to reduce emissions of sulfur-containing compounds into the atmosphere [1]. Carbonyl sulfide (OCS), which is the by-product of many chemical processes involved in the conversion of fossil fuels, is thought to be one of the major components of organic sulfur compounds [2]. The hydrolysis of OCS is considered a promising process due to its mild reaction conditions and high conversion efficiency [3].…”

“…In the present work, to complete a comprehensive theoretical study of the hydrolysis mechanism of OCS and to gain a good understanding of the hydrolysis of OCS, we carried out a detailed theoretical investigation of the hydrolysis of OCS by reactions (1) and (2) in the presence of explicitly described OH − and H 2 O. In addition, the effect of the bulk water solvent on the reaction was also investigated using the conductor-like screening model (COSMO).…”