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]− > [SAL]− > [DCA]− > [Cl]−. The effect of alkyl chain length on imidazolium ion on liquid–liquid 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.