Dicationic imidazolium based ionic liquids: Synthesis and properties

In the present work, four dicationic ionic liquids (DILs) having 1,1-Bis(3-methylimidazolium-1-yl) butylene ([C4(Mim)2]) cation with counter anions namely hydrogensulfate, methanesulfonate, trifluoromethanesulfonate, and paratoluene sulfonate were synthesized and characterized. The structures of ILs were confirmed by 1H NMR, 13C and elemental analysis (CHNS). The effect of temperature and anion type on thermophysical properties such as refractive index, density and viscosity were studied. Density and viscosity values were measured within the temperature range of 293.15-273.15 K. Moreover, thermal expansion coefficient, molecular volume, molar volume, free volume, standard entropy, and lattice energy were derived from the density and viscosity values. Viscosity values were used for calculation of activation energy using the Arrhenius equation. Refractive index values were measured in the temperature range of 293.15-323.15 K and the values of refractive index were used further to estimate the electronic polarizability using Lorenz-Lorentz equation. Thermal properties of the synthesized DILs were determined using thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC).