Synthesis of bisimidazolium–ionic liquids: Characterization, thermal stability and application to bentonite intercalation

In this study, a convenient method was developed for the synthesis of bisimidazolium salts and bisimidazolium–ionic liquids. The products were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), mass spectroscopy, elemental analysis and thermogravimetric analyses (TGA). The effect of the counter ion, alkyl chain length and structural isomerism on the thermal stability of the bisimidazolium salts was investigated. Ionic liquid-treated bentonite clays were prepared by ion exchange of the bisimidazolium cations with Na-bentonite. These new organoclays were characterized by X-ray diffraction (XRD), FTIR and TGA. The results show that the ionic liquid-intercalated bentonites have greater thermal stability (450–470 °C) compared with the bisimidazolium- or the diphosphonium-exchanged bentonites.