Liquid-liquid equilibria of aqueous biphasic systems containing 1-alkyl-3-methylimidazolium amino acid ionic liquids with different anions (L-Leucine, L-Valine, L-Lysine) and inorganic salt (tripotassium phosphate, potassium carbonate)

Abstract

Aqueous biphasic systems containing water-miscible ionic liquids (ILs) and inorganic salt are considered as an effective media for liquid-liquid extraction of bioactive materials. One of the important advantages of ILs is the possibility for a modification of their chemical structure and, as a result, their properties, i.e. their multifunctionality. Among the modified ILs, the amino acid ILs (AAILs) attract much attention due to their low toxicity and biodegradability. In the present work, new experimental data on phase behavior (binodal curves and tie lines) were obtained at 298.15 K for the systems containing 1-alkyl-3-methylmidazolium AAILs, [Cnmim]Х, with different hydrocarbon chain length (n = 4, 8), and with the amino acid anions: X = [Leu] (L-Leucine), [Val] (L-Valine), [Lys] (L-Lysine), and inorganic salts (K3PO4, K2CO3). AAILs under investigation were synthesized and characterized by means of thermogravimetric analysis, 1H- and 13C-NMR spectra. The ability of the studied systems to phase separation, the lengths and the slopes of the tie lines were discussed in terms of AAIL's structure. Systems containing [C8mim][Lys] show stronger tendency for phase separation. The slopes of the tie lines increase with the length of alkyl chain of IL's cation. For the aqueous systems [Сnmim]X + inorganic salt, the slopes of the tie lines increase in the sequence: [Lys] < [Val] < [Leu] < Cl < Br. Phase behavior of the investigated ternary systems favors their use for the extraction of bio-solutes.