Liquid Phase Behavior of Ionic Liquids with Water and 1-Octanol and Modeling of 1-Octanol/Water Partition Coefficients

Abstract

This study examines the effect of structural components of an ionic liquid (IL), including the choice of the anion, alkyl chain length on the cation, and substitution on the cation, on the mutual solubility with water and with 1-octanol. This is important because ionic liquids have been shown to be good replacements for organic extraction solvents in some liquid separations. In addition, we use the measured data to predict 1-octanol/water partition coefficients for the ionic liquids using the nonrandom two liquid (NRTL) and electrolyte nonrandom two liquid (eNRTL) excess Gibbs energy models. Specifically, the mutual solubilities of 15 different imidazolium, pyridinium, and quaternary ammonium ionic liquids with water were measured at (23.5 ± 1) °C. An increase in the alkyl chain length or the substitution decreases the mutual solubility with water. The [BF4]- and [B(CN)4]- anions are significantly more hydrophilic than [PF6]-, [(CF3SO2)2N]-, and [(CF3SO2)3C]-. The mutual solubilities of 10 ILs with 1-octanol were measured at (23.5 ± 1) °C. For these systems, the longer the alkyl chain, the more soluble the IL was in the alcohol, while ring substitution has little effect. From this data, 1-octanol/water partition coefficients of 10 ionic liquids were predicted using the NRTL and eNRTL models.

Thermodynamic and thermophysical properties of the reference ionic liquid: 1-Hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide (including mixtures). Part 1. Experimental methods and results (IUPAC Technical Report)

“…The solubility of water in the IUPAC sample of [C 6 Chapeaux et al [26] also reported (at T = 296.6 K) the mass fraction solubility of the IUPAC sample in water determined by coulometric Karl Fischer titration. The estimated uncertainty in w(H 2 O) was 1ؒ10 -4 .…”

Thermodynamic and thermophysical properties of the reference ionic liquid: 1-Hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide (including mixtures). Part 2. Critical evaluation and recommended property values (IUPAC Technical Report)

“…The solubility of water in the IUPAC sample of [C 6 mim][NTf 2 ] was studied by Chapeaux et al [63] and Widegren and Magee [4] using coulometric Karl Fischer titration. Additional results for non-IUPAC samples were published earlier by Fitchett et al [26] and McFarlane et al [64].…”

Mutual Solubility of Hydrophobic Ionic Liquids and Water in Liquid-Liquid Two-phase Systems for Analytical Chemistry

“…For a systematic understanding of the properties of IL-W two-phase systems, the hydrophobicity of ILs and its constituent ions has been experimentally studied through the partition coefficients of ILs between octanol and water, 227,233,234 and reverse-phase high-performance liquid chromatography. [235][236][237][238] These approaches provide a relative magnitude of the hydrophobicity for a series of cations, or that of anions.…”

“…225,233,234,242 . 32,169,242,243 By and large, the linearity also holds for the change in the solubility of W in the ILs with the change in the anionic species.…”