Physicochemical properties, 1H NMR, ab initio calculations and molecular interactions in a binary mixture of N-methylimidazole with ethyl acetate

Abstract

For a binary mixture of x N-methylimidazole (hereafter abbreviated as N-mim) + (1 − x) ethyl acetate (hereafter abbreviated as EAC), the density, sound velocity, viscosity and refractive index at (288.15, 298.15, 308.15, 318.15, and 328.15) K, mixing enthalpy at 298.15 K, and 1H NMR measurements combined with the ab initio calculations were carried out over a full molar fraction range.The density, sound velocity, isentropic compressibility, refractive index, viscosity, Gibbs energy of activation of viscous flow and the isobaric thermal expansivity were correlated with a polynomial well. The excess molar volume, excess isobaric thermal expansivity, isobaric thermal expansivity deviation, excess sound velocity, sound velocity deviation, excess isentropic compressibility, isentropic compressibility deviation, excess refractive index, refractive index deviation, excess logarithm viscosity, viscosity deviation, excess Gibbs energy of activation of viscous flow and the molar mixing enthalpy, were calculated and fitted to a Redlich-Kister polynomial. The activation parameters of viscous flow of the mixture, chemical shift changes of N-mim and EAC protons, interaction energy and second-order perturbation stabilization energy of 2-CH···OC, 2-CH···N and CH···O H-bonds were calculated.The mixing process of N-mim with EAC is an endothermic process with volume contraction. The energy to break the like molecular interactions is bigger than that to form dislike molecular interactions, and the volume contraction is mainly attributed to both the free volume difference and the more effective steric accommodation of molecules in the mixture.The 2-CH···OC and 2-CH···N H-bonds are approximately equivalent in dimers, 2-CH···OC H-bond in dimer (N-mim + EAC) is stronger and more stable than the CH···O H-bonds in EAC dimer. The amount of 2-CH···OC H-bond reaches a zenith at x ≈ 0.5. The formation of 2-CH···OC H-bond leads to the electron density rearrangement of the N-mim and EAC molecules, where the electron densities of the N-mim and EAC protons decrease and increase, respectively.