Structural Effect of Potassium Dihydrogen Citrate on the Interactions of Imidazolium Based Ionic Liquids with Water

The main objective of this study is to understand the effect of a bio medically important organic salt on molecular interactions of ionic liquids. Volumetric and ultra-acoustic studies of two immidazolium based ionic liquids, 1-butyl-3 methyl imidazolium chloride and 1-ethyl-3-methyl imidazolium ethyl sulphate are carried out in presence of potassium dihydrogen citrate. Experimentally obtained and derived parameters are analysed in the light of ionic, hydrophilic, and hydrophobic interactions taking place between different ionic, polar, and nonpolar segments of the ILs and the citrate salt. The effect of the said salt on the interactions of the ILs with water are explored in terms of apparent molar volume \({(V}_{\phi })\), partial molar volume \(({V}_{\phi }^{0}\)), and partial molar expansibility \({(E}_{\phi }^{0})\), compressibility and apparent compressibility behaviour of solution at different concentrations \({{(K}_{s} \text{and} K}_{\phi ,s})\) and at infinite dilution \(({{K}_{s }^{0} \text{and} K}_{\phi ,s}^{0}\)). Transfer values are calculated to understand the solute–co-solute interactions and overlapping of hydration co-spheres. Hydration numbers are calculated to reinforce the compressibility data. Structural changes of water induced by the solute–co-solute and solute–solvent interactions are determined by the magnitude and sign of well-known Hepler’s constant.

Graphical Abstract