Determination of mutual solubilities of ionic liquids and water

Two simple and universal methods for determination of solubility of ionic liquids in water are introduced in this work. The first one, which utilizes negligible vapour pressure of ionic liquids, is based on controlled evaporation of water from a sample of saturated aqueous mixture. The second one utilizes the ionic character of ionic liquids and its principle consists in measurements of electrical conductivity for series of aqueous mixtures. The methods were used for determination of aqueous solubility of five ionic liquids. Namely, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and ethyl-dimethyl-propylammonium bis(trifluoromethylsulfonyl)imide. The aqueous solubility data were completed by the measurement of solubility of water in the studied ionic liquids so that full-valued data on liquid–liquid equilibrium in the temperature range from 288 to 343 K are reported in the article. The obtained experimental data were correlated by the NRTL equation with temperature dependent parameters.