Mass density, sound velocity, mixing enthalpy, 1H NMR, Ab initio calculations and intermolecular interactions in binary mixtures of N-methylimidazole + water, +methanol, +ethanol, +1-propanol, +2-propanol

Abstract

Over a full molar fraction range, for binary mixtures of x N-methylimidazole (hereafter abbreviated to N-mim) + (1 − x) water, +methanol, +ethanol, +1-propanol, +2-propanol, the mass density and sound velocity at (288.15, 298.15, 308.15, 318.15, 328.15) K, the mixing enthalpy at 298.15 K, and 1H NMR measurements, combined with the Ab initio calculations, have been carried out.The excess molar volume, excess average volume expansivity, excess sound velocity, excess isentropic compressibility, and the molar mixing enthalpy were calculated and fitted to a Redlich-Kister equation. The partial molar enthalpy of N-mim, the difference between the partial molar volume and the molar volume of N-mim, and the protons chemical shift changes were calculated and compared. The chemical shifts of N-mim protons, hydroxyl protons, and α-H (proton on the carbon atom next to the –OH group) of alcohols in the mixtures containing alcohols were explained by a model proposed by Gupta et al..The properties indicate that the intermolecular interactions between unlike molecules are stronger than those between like molecules. An increase in temperature has a greater influence on the mixture containing water than on pure components, and has a greater influence on pure components than on mixtures containing alcohols. The predominant interactions between unlike molecules are hydrogen-bonded complexes in the mixture containing water, and are N-mim: alcohols = 1:1 hydrogen-bonded networks in the mixtures containing alcohols, where the alkyl groups of alcohols are electron-withdrawing groups, and the methyl group of N-mim is an electron-donating group. Ab initio calculations proved that the N⋯HO hydrogen bond in the mixtures is more stable and stronger than HO⋯HO in pure water or in pure alcohols and N⋯HC in pure N-mim. The strength sequence of the intermolecular interactions between unlike molecules for the mixtures at 298.15 K is N-mim–water > N-mim–methanol > N-mim–ethanol > N-mim–1-propanol ≥ N-mim–2-propanol.