Phase behaviour of 1-hexyloxymethyl-3-methyl-imidazolium and 1,3-dihexyloxymethyl-imidazolium based ionic liquids with alcohols, water, ketones and hydrocarbons: The effect of cation and anion on solubility

Abstract

The liquid–liquid equilibrium (LLE), or solid–liquid equilibrium (SLE) of more than 20 binary systems containing 1-hexyloxymethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide [C 6H 13OCH 2MIM][Tf 2N] with alcohol (butan-1-ol, or hexan-1-ol, or octan-1-ol), water and ketone (3-pentanone, or cyclopentanone) and of 1-hexyloxymethyl-3-methyl-imidazolium tetrafluoroborate [C 6H 13OCH 2MIM][BF 4] with alcohol (methanol, or ethanol, or butan-1-ol, or hexan-1-ol, or octan-1-ol), water and ketone (3-pentanone, or cyclopentanone) have been measured. The solubility of dialkoxy-imidazolium salts: (1) 1,3-dihexyloxymethyl-imidazolium bis(trifluoromethylsulfonyl)-imide [(C 6H 13OCH 2) 2IM][Tf 2N] in alcohol (butan-1-ol, or hexan-1-ol, or octan-1-ol, or decan-1-ol), in water and hydrocarbon (benzene, hexane and cyclohexane); (2) 1,3-dihexyloxymethyl-imidazolium tetrafluoroborate [(C 6H 13OCH 2) 2IM][BF 4] in alcohol (hexan-1-ol, or octan-1-ol, or decan-1-ol) and water have been measured. Measurements were carried out by using a dynamic method from T = 275 K to the boiling point of the solvent. In this work a systematic study of the impact of different factors on the phase behaviour of hexyloxy-imidazolium-based ionic liquids with polar and nonpolar solvents has been presented. Most of the examined systems showed immiscibility in the liquid phase with an upper critical solution temperature (UCST), or complete solubility of the ionic liquid at room temperature in many solvents. An increase in the alkyl chain length of alcohol resulted in an increase in the UCST. The choice of anion was shown to have large impact on the solubility: by changing the anion [Tf 2N] − to [BF 4] −, the solubility dramatically decreased and the UCST increased. By contrast, increasing hydrogen bonding opportunities with the solvent by replacing a methyl group with the second alkoxy-group on the imidazolium ring results in an increase of the solubility. The paper includes also a thermophysical basic characterization of pure ionic liquids obtained via differential scanning calorimetry (TG/DSC), temperatures of decomposition and melting, enthalpies of fusion, enthalpies of solid–solid phase transitions and temperatures of the glass transition. The experimental results of LLE and SLE have been correlated using the NRTL, or Wilson equations. The average root-mean square deviation of the equilibrium mole fraction for all the LLE data was 0.010 and average mean square deviation of temperature for SLE was 1.06 K. From the solubility results the partition coefficient of ionic liquids in binary system octan-1-ol/water mixtures has been calculated. Experimental partition coefficients (log P) at the temperature 298.15 K were negative.