1-octanol/water partition coefficients of 1-alkyl-3-methylimidazolium chloride

The solubilities of 1-alkyl-3-methylimidazolium chloride, [C(n)mim][Cl], where n = 4, 8, 10, and 12, in 1-octanol and water have been measured by a dynamic method in the temperature range from 270 to 370 K. The solubility data was used to calculate the 1-octanol/ water partition coefficients as a function of temperature and alkyl substituent. The melting point, enthalpies of fusion, and enthalpies of solid-solid phase transitions were determined by differential scanning calorimetry, DSC. The solubility of [C(n)mim][Cl], where n = 10 or 12 in 1-octanol is comparable and higher than that of [C(4)mim][Cl] in 1-octanol. Liquid 1-n-octyl-3-methylimidazolium chloride, [C(8)mim][Cl], is not miscible with 1-octanol and water, consequently, the liquid-liquid equilibrium, LLE was measured in this system. The differences between the solubilities in water for n = 4 and 12 are shown only in alpha(1) and gamma(1) solid crystalline phases. Additionally, the immiscibility region was observed for the higher concentration of [C(10)mim][Cl] in water. The intermolecular solute-solvent interaction of 1-butyl-3-methylimidazolium chloride with water is higher than for other 1-alkyl-3-methylimidazolium chlorides. The data was correlated by means of the UNIQUAC ASM and two modified NRTL equations utilizing parameters derived from the solid-liquid equilibrium, SLE. The root-mean-square deviations of the solubility temperatures for all calculated data are from 1.8 to 7 K and depend on the particular equation used. In the calculations, the existence of two solid - solid first-order phase transitions in [C(12)mim][Cl] has also been taken into consideration. Experimental partition coefficients (logP) are negative at three temperatures; this is evidence for the possible use of these ionic liquids as green solvents.