Ethylammonium alkanoate-based ionic liquid + water mixtures: a calorimetric and volumetric study at 298.15 K

A systematic study of a series of room-temperature ionic liquids, belonging to the ethylammonium alkanoate family (EAX), was carried out at 298.15 K and 0.1 MPa with the aim of investigating the effect of the anionic chain length on some thermophysical properties and their behaviour in water (W), over the whole mole fraction range. The determination of Gutmann acceptor numbers for the pure EAX by using 31P NMR spectroscopy allowed us to obtain a quantitative measure of Lewis acidity. Experimental densities, ρ, were used to calculate molar volumes, V m, and excess molar volumes, V E. Complementary information was obtained by isothermal titration calorimetry that provided the values of the heat of mixing, H E, and the excess partial molar enthalpies of each component, \( \bar{H}_{1}^{E} \) and \( \bar{H}_{2}^{E} \). The density values of pure EAX samples decrease as the alkyl chain length of the anion increases. Moderate negative V E and H E values were found for each EAX + W system, indicating the presence of attracting interactions between the constituents.