Thermodynamic Phase Behavior of Ionic Liquids

The phase diagrams of the following imidazolium ionic liquids, {1-ethyl-3-methylimidazolium tosylate [EMIM][TOS] + hexane or cycloheptane} and {1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO 4 ] + hexane or benzene}, have been measured. The (solid + liquid) (SLE) and (liquid + liquid) (LLE) phase equilibria of binary mixtures containing {hexyl(2-hydroxyethyl)dimethylammonium bromide (C 6 Br) + hexane or benzene or an alcohol (ethanol or dodecan-1-ol)} and the salt with a different anion {hexyl(2-hydroxyethyl)dimethylammonium tetrafluoroborate (C 6 BF 4 ) + hexane or benzene or dodecan-1-ol} have been measured. The effect of anion type (Br - vs BF 4 - ) on the thermophysical properties of the IL and on the phase behavior is dependent on the strength of the cation−anion interaction in the investigated ILs and is noticeable. The phase diagrams for some novel ammonium ionic liquids, (2-decanoyloxyethyl)dimethylpentyloxymethylammonium trifluoro-acetate [C 10 OOEtC 5 OMMMN][CF 3 COO] or (2-methyloyoxyethyl)dimethylpentyloxyammonium acesulfamate [MOOEtC 5 OMMMN][Ace] or (2-hydroxyethyl)dimethylundecyloxymethylammonium dicyanamide [C 11 OMEtOHMMN][(CN) 2 N], with octan-1-ol are reported. The solvents were chosen as representatives of alkanes, cycloalkanes, aromatic hydrocarbons, and alcohols. The interaction between the most commonly studied ionic liquids and those chosen in this work with typical organic solvents was described. The solubilities were measured by a dynamic method from 250 K to the melting point of the ionic liquid or to the boiling point of water in the bath. The immiscibility of the liquid phase in {[EMIM][TOS] + cycloheptane} was observed. The observed upper critical solution temperature (UCST) in binary mixtures of {[EMIM][TOS] + cycloheptane} and {[EMIM][EtSO 4 ] + hexane or benzene} was limited by the boiling temperature of the solvent. The difference between the solubilities of the three ammonium ionic liquids, [C 10 OOEtC 5 OMMMN][CF 3 COO] or [MOOEtC 5 OMMMN][Ace] or [C 11 OMEtOHMMN][(CN) 2 N], in octan-1-ol is significant: a simple eutectic system was observed for [C 10 OOEtC 5 OMMMN][CF 3 COO]; LLE was observed for [MOOEtC 5 OMMMN][Ace]; and an eutectic system with immiscibility in the liquid phase was observed for [C 11 OMEtOHMMN][(CN) 2 N]. For the system {[C 11 OMEtOHMMN][(CN) 2 N] + octan-1-ol}, the upper critical solution temperature was determined to be 312.9 K. Characterization and purity of the compounds were obtained by water content (Fisher method) and differential scanning microcalorimetry (DSC) analysis. From DSC, melting points, enthalpies of fusion, temperatures, and enthalpies of the solid−solid phase transitions and the temperatures of glass transition of all the investigated ionic liquids were measured.