Influence of the number, position and length of the alkyl-substituents on the solubility of water in pyridinium-based ionic liquids

In this work, the solubility of water in eight pyridinium-based ionic liquids were experimentally determined at several temperatures and atmospheric pressure, and the temperature-composition phase diagrams are reported. From these data, the effect of the number, position (positional isomers) and length of the substituents of the cation was analyzed and discussed. The obtained results indicate that water content in the studied ionic liquids increases with temperature and, in general, it decreases as the number and length of the substituents increase. As regards the position of the alkyl groups, the solubility of water decreases with the proximity of the substituents. Finally, the miscibility of water in the studied ionic liquids was satisfactorily described with the Non-Random Two-Liquid (NRTL) thermodynamic model.