Understanding the effect of molecular solvents on the microscopic network of DBU imidazole ionic liquid

Abstract

In order to uncover the microscopic structure of ionic liquids (ILs) in solutions of organic solvents, a protic ionic liquid, prepared from superbase 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with imidazole, which is so-called [HDBU]IM, has been synthesized. And the 1H NMR chemical shifts of binary mixtures, namely [HDBU]IM/ dimethyl sulfoxide (DMSO), [HDBU]IM/dimethylformamide (DMF) and [HDBU]IM/ethanol were measured at 298.15 K within whole concentrations range, which were correlated using the local composition (LC) model to obtain the local mole fractions. In addition the excess molar volumes VE and excess Gibbs energy of activation for viscous flow ΔG⁎E were calculated from experimental data of densities ρ and viscosities η of mixtures. Moreover electrical conductivities κ of all solutions were measured and correlated using empirical Casteel-Amis equation. LC analysis deduced from 1H NMR chemical shifts shows that the ability of organic solvents to destroy the network of [HDBU] IM could follow this order: ethanol>DMF > DMSO, which is consistent with the variation of VE, κ and ΔG⁎E values.