Liquid-liquid equilibria of room-temperature ionic liquids and butan-1-ol

Room-temperature ionic liquids are salts that are liquid at room temperature. Their use as catalysts and catalytic support has been studied extensively. However, there are very few measurements on their solubility and phase equilibria in common organic solvents. In this work, the liquid-liquid phase equilibria of mixtures of room-temperature ionic liquids, 1-alkyl-3-methylimidazolium hexafluorophosphate, [R(n)mim] [PF6] (1) where R-n = butyl, pentyl, hexyl, heptyl, and octyl, with butan-1-ol (2) over a composition range have been measured. The binodal coexistence curves of the mixtures were found to have an upper critical solution temperature (USCT) at x(2) approximate to 0.9. The UCST decreases with increase in the length of the alkyl chain of the ionic liquid, with the UCST of the butyl at 373 K and that of the octyl at 326 K. Both the UCST and the composition at the UCST as a function of the 1-alkyl group chain length can be reasonably well predicted from theory on the basis of unimolecular quantum chemical calculations.