Experimental and Computational Study of the Properties of Imidazole Compounds with Branched and Cycloalkyl Substituents

Abstract

N-functionalized imidazole compounds with linear alkyl groups have been widely utilized precursors for imidazolium ionic liquids (ILs) while the effects of branched and cycloalkyl substituents on properties of imidazole compounds have not been studied; however, such compounds are just as synthetically accessible as those with linear alkyl groups. In this work, two fundamental properties, density and viscosity, of selected N-functionalized imidazoles bearing iso-propyl, iso-butyl, sec-butyl methylcyclopropyl, cyclopentyl, and methylcyclohexyl groups have been measured in the temperature range of 293.15–353.15 K for the guidance of molecular design for future applications. A linear and parabolic model were used for temperature-density correlation while temperature dependence of viscosity was summarized using the Andrade Equation and the Vogel-Fulcher-Tammann equation. In addition to experimental data, density, viscosity, vapor pressure and vaporization of enthalpies of target imidazole compounds were predicted using COSMOtherm calculations and compared with experimental data. It was found that the calculated densities were quite close to the experimental data, while viscosity data, obtained from COSMOtherm, underestimated experimental measurements and a scaling factor provided agreement with experiments. Predictions of vapor pressure were relatively reliable at low temperature, although the difference between experiment and prediction tended to expand with increasing temperature. Variances of vaporization enthalpies were small upon temperature change and a maximum error of ~12.3% was observed for all compounds studied.