Liquid-Liquid Equilibria in Aqueous 1-Alkyl-3-methylimidazolium- and 1-Butyl-3-ethylimidazolium-Based Ionic Liquids

In this work, novel phase diagrams for aqueous solutions of 1-alkyl-3-methylimidazolium- and 1-butyl-3-ethylimidazolium-based ILs combined with phosphate-based salts, namely, K3PO4 or K2HPO4, are reported and discussed. To correlate the binodal data, the Merchuk equation is applied. The tie lines and tie-line lengths are also presented. The anion influence on the ability to form aqueous biphasic system (ABS) is investigated for the IL with the same1-butyl-3-methylimidazolium cation, [bmim](+), and various anions, for example, salicylate, [SAL](-); trifluoromethanesulfonate, [TFS](-); dicyanamide, [DCA](-); and chloride, [Cl](-). The order of studied anions to form ABS is [TFS](-) GT [SAL](-) GT [DCA](-) GT [Cl](-). The effect of alkyl chain length on imidazolium ion on liquidliquid equilibrium is discussed in terms of increasing ionic liquid hydrophobicity and poorer affinity for water. It is shown that 1-hexyl-3-methylimidazolium chloride ionic liquid has a better ability to form ABS comparing to ionic liquid with butyl chain and the same anion. Newly synthesized ionic-liquid-containing ethyl group 1-butyl-3-ethylimidazolium bromide was also investigated, showing the influence of both ethyl group and bromide anion on the ability of ABS formation