An Overview of Mutual Solubility of Ionic Liquids and Water Predicted by COSMO-RS

Abstract

To properly screen and use ionic liquids (ILs) as environmental-friendly solvents in chemical reactors and separation processes, the knowledge of their solubilities with water is essential. In the present work, mutual solubilities of 1500 ILs (50 cations, 30 anions) with water at 298.15 K were predicted by using the conductor-like screening model for real solvents (COSMO-RS) as a thermodynamic model. On the basis of the COSMO-RS calculations, the influence of the types of anion and cation, side chain modifications and substituent groups on the mutual solubility with water was extensively analyzed. The data obtained can be used for the prescreening of ILs as solvent candidates. Moreover, to understand the intrinsic solubility behavior in detail, different types of molecular interactions between ILs and water in solution were compared on the basis of the determination of multiple water–IL interaction energies from COSMO-RS computation. The results confirm that hydrogen bonding interactions between anions and water molecules have the dominant influence on the solubility. Finally, for the purpose of fast solubility estimation and solvent selection, COSMO-RS derived molecular descriptors which indicate the strength of anionic HB acceptors were calculated for typical anions and anion families.