Comprehensive study on the impact of the cation alkyl side chain length on the solubility of water in ionic liquids
authors Kurnia, KA; Neves, CMSS; Freire, MG; Santos, LMNBF; Coutinho, JAP
nationality International
journal JOURNAL OF MOLECULAR LIQUIDS
author keywords Water solubility; Ionic liquid; Imidazolium-based; Trend shift; Symmetry; Asymmetry; COSMO-RS; Ab initio
keywords MUTUAL SOLUBILITIES; COSMO-RS; THERMOPHYSICAL PROPERTIES; MOLECULAR-DYNAMICS; BINARY-SYSTEMS; SYMMETRY; PREDICTION; BIS(TRIFLUOROMETHYLSULFONYL)IMIDE; EXTRACTION; MIXTURES
abstract A comprehensive study on the phase behaviour of two sets of ionic liquids (ILs) and their interactions with water is here presented through combining experimental and theoretical approaches. The impact of the alkyl side chain length and the cation symmetry on the water solubility in the asymmetric [C-N (-) (1)C(1)im][NTf2] and symmetric [C-N (-) (1)C(1)im][NTf2] series of Rs (N up to 22), from 288.15 K to 318.15 K and at atmospheric pressure, was studied. The experimental data reveal that the solubility of water in ILs with an asymmetric cation is higher than in those with the symmetric isomer. Several trend shifts on the water solubility as a function of the alkyl side chain length were identified, namely at [C(6)C(1)im][NTf2] for asymmetric ILs and at [C(4)C(4)im][NTf2] and [C(7)C(7)im]INTf2] for the symmetric ILs. To complement the experimental data and to further investigate the molecular-level mechanisms behind the dissolution process, density functional theory calculations, using the Conductor-like Screening Model for Real Solvents (COSMO-RS) and the electrostatic potential-derived CHelpG, were performed. The COSMO-RS model is able to qualitatively predict water solubility as a function of temperature and alkyl chain lengths of both symmetric and asymmetric cations. Furthermore, the model is also capable to predict the somewhat higher water solubility in the asymmetric cation, as well as the trend shift as a function of alkyl chain lengths experimentally observed. Both COSMO-RS and the electrostatic potential-derived CHelpG show that the interactions of water and the IL cation take place on the IL polar region, namely on the aromatic head and adjacent methylene groups that explains the differences in water solubility observed for cations with different chain lengths. Furthermore, the CHelpG calculations for the isolated cations in the gas phase indicates that the trend shift of water solubility as a function of alkyl chain lengths and the difference of water solubility in symmetric may also result from the partial positive charge distribution/contribution of the cation. (C) 2015 Elsevier B.V. All rights reserved.
publisher ELSEVIER SCIENCE BV
issn 0167-7322
year published 2015
volume 210
beginning page 264
ending page 271
digital object identifier (doi) 10.1016/j.molliq.2015.03.040
web of science category Chemistry, Physical; Physics, Atomic, Molecular & Chemical
subject category Chemistry; Physics
unique article identifier WOS:000363346800014
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journal analysis (jcr 2017):
journal impact factor 4.513
5 year journal impact factor 3.929
category normalized journal impact factor percentile 80.153
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