Phase behavior of novel functional tropine ionic liquids in binary solvent mixture (water + ethanol): A synergistic effect promoting solubility

Abstract

Phase diagrams for the binary systems ethanol or water+tropine-type ionic liquids including N-benzyl-tropine hexafluorophosphate, N-(3-methoxybenzyl)-tropine hexafluorophosphate, N-(4-nitrobenzyl)-tropine hexafluorophosphate and related ternary systems (ethanol+water+ionic liquid) were measured with equilibrium method at atmospheric pressure in the temperature range of 278.15K to 333.15K. With the increase of temperature, the solubility of these ionic liquids increased obviously and the temperature-sensitive property in binary solvent mixture (water+ethanol) was also proven. On the other side, cosolvency phenomenon was also found in binary system. And it was found that the cosolvency related to the ratio of water and ethanol, as well as the strength of hydrogen bonding between solvent and cationic groups of ILs. The solubility of ionic liquids in the single solvent and certain concentration of binary solvent mixture was correlated by two empirical equations (Apelblat and λh) and two theoretical models (Wilson and NRTL) with good results. This study provides useful information for further research and application of these ionic liquids.