CS2 capture in the ionic liquid 1-alkyl-3-methylimidazolium acetate: reaction mechanism and free energeticsElectronic supplementary information (ESI) available: Optimized structures of CS2/COS/CO2 and EMI carbene in the gas and continuum phases, optimized structures of the reactant, product, intermediate and transition states for the conversion of CS2/COS to COS/CO2 and their capture by EMI, comparison of SCRF results for COS-to-CO2 conversion in 1-pentanol and in ethanol, electric dipole moment

Reaction pathways for CS 2 and COS in the ionic liquid, 1-ethyl-3-methylimidazolium (EMI + ) acetate (OAc − ), are studied using the ab initio self-consistent reaction field theory (SCRF) and molecular dynamics (MD) computer simulations. It is found that while CS 2 converts to COS nearly at the 100% level through S/O exchange with acetate, both conversion and capture processes are kinetically possible for COS, yielding CO 2 /thioacetate and 1-ethyl-3-methylimidazole-2-thiocarboxylate (EMI-COS)/acetic acid as reaction products, respectively. These findings are in excellent agreement with recent experimental observations in the closely related 1-butyl-3-methylimidazolium acetate (BMI + OAc − ) ionic liquid system. Constrained ab initio MD indicates that the capture reaction of COS (and CS 2 if allowed) proceeds in a concerted fashion; viz. , proton transfer from EMI + to OAc − and carboxylation of EMI + by COS (and CS 2 ) occur concurrently, analogous to the concerted pathway proposed recently for CO 2 capture in the imidazolium acetate ionic liquid family. As N-heterocyclic carbene (NHC) is not required, the concerted mechanism is fully consistent with the experimental fact that NHC has not been detected directly in this ionic liquid family. Computational analysis further predicts that if NHC would be present in the ionic liquid, it would react with CS 2 and produce 1-ethyl-3-imidazole-2-dithiocarboxylate, prior to the conversion of CS 2 to COS. Since such a dithiocarboxylate compound was not detected experimentally, the present analysis lends support to the view that NHC is not formed in the pure imidazolium acetate ionic liquid family. Reaction pathways for CS 2 and COS in the ionic liquid, 1-ethyl-3-methylimidazolium (EMI + ) acetate (OAc − ), are studied using the ab initio self-consistent reaction field theory (SCRF) and molecular dynamics (MD) computer simulations.