Synthesis, characterization and properties of geminal imidazolium ionic liquids

A novel geminal imidazolium ionic liquid with long hydrocarbon group, 1,4-bis(3-tetradecylimidazolium-1-yl) butane bromide was synthesized and its physicochemical properties were studied. To differentiate the novel ionic liquid with conventional ionic liquid, 1-n-tetradecyl-3-methylimidazolium bromide was also synthesized and their properties were compared. FT-IR, 1H NMR and elemental analysis were applied to identify the molecular structure of two compounds, then the crystal structures was investigate by the X-ray diffraction (XRD). Thermal properties of them were studied with thermogravimetry (TG) and differential scanning calorimetry (DSC). Critical micelle concentration (CMC) and surface tension of two compounds in aqueous solution were determined by maximum bubble pressure method. In this work, we also measured the water content in two compounds by using IR moisture meters, and polarity was studied by the solubility in a series of organic solvents. The results show that the new geminal imidazolium ionic liquid possesses higher thermal stability, lower CMC values and larger d-spacing of crystal structure than corresponding ionic liquid with single long chain.