Investigation of the solute-solute and solute-solvent interactions in ternary {saccharide + ionic liquid + water} systems

The aim of this work is to investigate the salt effect resulted by addition of ionic liquids to aqueous saccharide solutions. To achieve this goal, systematic studies have been made on ternary {saccharide + ionic liquid + water} system using the available vapor-liquid equilibrium (VLE) data published recently. Vapor pressure depression, osmotic and activity coefficient data for the ionic liquids and saccharides in the binary solutions are used to investigate ionic liquid-water and saccharide-water interactions. For ternary solutions, the calculated activity coefficient of saccharides in presence of ionic liquids, transfer Gibbs energies, pair and triplet interaction parameters and salting constants are used to investigate saccharide-ionic liquid interactions. The variety of ionic liquids based on imidazolium and pyridinium have been considered. To extent the number of systems considered in this work, we have also included vapor-liquid equilibrium studies on the new systems {d-fructose + 1-butyl-4-methyl pyridinium bromide + H2O} and {sucrose + 1-butyl-4-methyl pyridinium bromide + H2O} from which experimental water activity data are measured. The aforementioned properties were also calculated for these new systems. In this article, the effect of stereochemistry of sugar, cation (imidazolium or pyridinium), chain length and anion of ionic liquids on vapor-liquid equilibrium behavior of these ternary systems and saccharide-ionic liquid interactions have been discussed. Generally, we found that there is a relationship between soluting-in or soluting-out behavior of ionic liquids and their hydration so that soluting-in effect is observed in ionic liquids with longer chain length and with anions having smaller values of osmotic coefficient. Soluting-out effect is observed in ionic liquids with shorter chain length and with anions having larger values of osmotic coefficient. From the VLE results we conclude that soluting-out effect of ionic liquids also depends on the hydration of saccharides and is observed in saccharides with high tendency to interact with water.