The experimental physicochemical properties, ¹H NMR, and COSMO-RS model calculations for the binary system containing water and 1-ethylimidazole

In order to explore the properties and molecular interactions in the binary systems of 1-alkylimidazole with molecular solvents, the system of x 1-ethylimidazole (herein referred to as 1-Eim) + (1-x) water, in the temperature range (288.15–328.15) K, the density ρ, sound velocity u, viscosity η, refractive index n_D, pH and conductivity κ, and the ¹H NMR δ_H, were measured at atmospheric pressure; the excess molar enthalpy H_m^E, the excess molar Gibbs free energy G_m^E, and the excess molar entropy S_m^E were predicted from the COSMO-RS model. The experimental and predicted properties indicate that the H-bonded interactions are the predominant interactions over the whole composition range. 1-Eim protons share more electron densities than water protons via the H-bonds, which are stronger between dissimilar molecules than between similar ones. The stable H-bonded structure of water molecules breaks when x is about 0.1, while the stable H-bonded structure of 1-Eim molecules forms when x is about 0.9. Temperature affects the H-bonded interactions more in the case of dissimilar molecules than similar molecules, especially in the water-rich region. The real mixing process is an enthalpy-driving spontaneous process with the liquid structure more ordered. A lower temperature more greatly benefits spontaneous mixing.