Interactions of Imidazolium Based Ionic Liquids with Water Studied by Density and Speed of Sound Measurements: Effect of the Chain Length of an Alkyl Substituent on the Imidazolium Ion

Abstract

Densities and speeds of sound of three ionic liquids (ILs), 1-ethyl-3-methyl imidazoliumtetrafluoroborate (C2mimBF4), 1-butyl-3-methylimidazoliumtetrafluoroborate (C4mimBF4) and 1-hexyl-3-methylimidazoliumtetrafluoroborate (C6mimBF4) were measured in aqueous solutions at (288.15, 293.15, 298.15, 303.15 and 308.15) K. These data were used to calculate the volumetric properties apparent molar volume and apparent molar isentropic compression as a function of molality. Infinite dilution values for these properties were evaluated by an extrapolation procedure based on Redlich–Meyer type equations. Apparent molar isobaric expansions at infinite dilution were also obtained from the slopes of the apparent molar volume at infinite dilution versus temperature. All these properties are interpreted in terms of IL–water interactions. The hydrolysis of the \( {\text{BF}}_{4}^{ - } \) anion of the ILs and its effects on the results is discussed.