Evaluation of the Conductor-like Screening Model for Real Solvents for the Prediction of the Water Activity Coefficient at Infinite Dilution in Ionic Liquids

Ionic liquids (ILs) have attracted great attention, from both industry and academia, as alternative fluids for very different types of applications. The large number of cations and anions allow a wide range of physical and chemical characteristics to be designed. However, the exhaustive measurement of all these systems is impractical, thus requiring the use of a predictive model for their study. In this work, the predictive capability of the conductor-like screening model for real solvents (COSMO-RS), a model based on unimolecular quantum chemistry calculations, was evaluated for the prediction water activity coefficient at infinite dilution, gamma(infinity)(w), in several classes of ILs. A critical evaluation of the experimental and predicted data using COSMO-RS was carried out. The global average relative deviation was found to be 27.2%, indicating that the model presents a satisfactory prediction ability to estimate gamma(infinity)(w) in a broad range of ILs. The results also showed that the basicity of the ILs anions plays an important role in their interaction with water, and it considerably determines the enthalpic behavior of the binary mixtures composed by Its and water. Concerning the cation effect, it is possible to state that generally gamma(infinity)(w) increases with the cation size, but it is shown that the cation-anion interaction strength is also important and is strongly correlated to the anion ability to interact with water. The results here reported are relevant in the understanding of ILs-water interactions and the impact of the various structural features of its on the gamma(infinity)(w) as these allow the development of guidelines for the choice of the most suitable lLs with enhanced interaction with water

Mutual solubilities between water and non-aromatic sulfonium-, ammonium- and phosphonium-hydrophobic ionic liquids

Although previous studies attempted to characterize the liquidliquid phase behaviour between water and ionic liquids (ILs), the impact of non-cyclic cations on the solubilities is poorly studied and yet to be understood. In this work, the mutual solubilities between water and ILs containing the anion bis(trifluoromethylsulfonyl)imide, [NTf2]-, combined with the cations diethylmethylsulfonium, [S-221][NTf2], triethylsulfonium, [S-222][NTf2], butyltrimethylammonium, [N-4111][NTf2], tributylmethylammonium, [N-4441][NTf2], methyltrioctylammonium, [N-1888][NTf2], and methyltrioctylphosphonium, [P-1888][NTf2], from (288.15 to 318.15) K and at 0.1 MPa, were experimentally measured and further compared with predictions from the COnductor-like Screening MOdel for Real Solvents (COSMO-RS). All the studied phase diagrams display an upper critical solution temperature (UCST). The binary system composed of [P-1888][NTf2] exhibits the widest immiscibility gap, followed by [N-18888][NTf2], [N-4441][NTf2], [S-222][NTf2], [N-4111][NTf2], and [S-221][NTf2]. The COSMO-RS is able to correctly predict the experimental UCST behaviour and the cation impact on the immiscibility regimes observed. Natural Population Analysis (NPA) calculations were additionally performed for the isolated cations in the gas phase indicating that the differences in the water-IL mutual miscibilities might not result only from the hydrophobicity of the cation (derived from the increase of the alkyl chains length) but also from the charge distribution of the central atom and attached methylene groups. This fact explains the enhanced solubility of ammonium-based ILs in water here identifie