title: CO2capture in ionic liquid 1-alkyl-3-methylimidazolium acetate: a concerted mechanism without carbene.
abstract: Ionic liquids (ILs) provide a promising medium for CO2capture. Recently, the family of ILs comprising imidazolium-based cations and acetate anions, such as 1-ethyl-3-methylimidazolium acetate (EMI+OAc-), has been found to react with CO2and form carboxylate compounds. N-Heterocyclic carbene (NHC) is widely assumed to be responsible by directly reacting with CO2though NHC has not been detected in these ILs. Herein, a computational analysis of CO2capture in EMI+OAc-is presented. Quantum chemistry calculations predict that NHC is unstable in a polar environment, suggesting that NHC is not formed in EMI+OAc-. Ab initio molecular dynamics simulations indicate that an EMI+ion "activated" by the approach of a CO2molecule can donate its acidic proton to a neighboring OAc-anion and form a carboxylate compound with the CO2molecule. Analysis of this termolecular process indicates that the EMI+-to-OAc-proton transfer and the formation of 1-ethyl-3-methylimidazolium-2-carboxylate occur essentially concurrently. Based on these findings, a novel concerted mechanism that does not involve NHC is proposed for CO2capture.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA. hjkim@cmu.edu.
authors.forename: Fangyong
authors.initials: F
authors.lastname: Yan
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA. hjkim@cmu.edu.
authors.forename: Nilesh R
authors.initials: NR
authors.lastname: Dhumal
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA. hjkim@cmu.edu and School of Computational Sciences, Korea Institute for Advanced Study, Seoul 02455, Korea.
authors.forename: Hyung J
authors.initials: HJ
authors.lastname: Kim