Isomer effect of propanol on liquid–liquid equilibrium in hydrophobic room-temperature ionic liquids

The cloud-point temperature determined the liquid–liquid phase equilibrium (LLE) of binary systems comprising hydrophobic room-temperature ionic liquids (RTILs) and propanol. The RTILs were 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [Cxmim][TFSI] (2 ≤ x ≤ 10). Upper critical solution temperatures in LLE are inversely proportional to the Cxmim+ cation alkyl chain length, x. The propanol isomer effect indicates the critical alkyl chain length (xcritical = 6–7). UNIQUAC model determined the interaction parameters (with crossing points at x = 6). In pure RTILs, conformation stability of TFSI− by Raman spectroscopy changed between x = 6 and 7, corresponding to the simulation-determined 90°-torsion angle at x = 6.