Thermally-Stable Imidazolium Dicationic Ionic Liquids with Pyridine Functional Groups

Abstract

Thermally-stable ionic liquids (ILs) have limited structural possibilities and lack coordinating anions or functional groups. Thermal stability effectively incurs a tunability penalty, limiting ionic liquid function to render them as simple heat-stable fluids. In this work, a series of new thermally-stable dicationic ionic liquids with pyridine functional groups, abbreviated [(C8ImC1)2Py][A]2, are presented and compared to nonfunctional geminal dicationic ILs. All ILs have been thermally characterized to understand their elevated temperature stabilities and the processes that lead to their decomposition. Importantly, functional [(C8ImC1)2Py][A]2 with noncoordinating anions (i.e., [NTf2]−) have thermal stabilities comparable to those of geminal dicationic ILs, with the added advantage of a functional pyridine moiety. Dissolution of Zn[NTf2]2 in [(C8ImC1)2Py][NTf2]2 is demonstrated, and the resulting solutions are characterized to show their liquid properties, high thermal stabilities, and the coordination of the metal center to the functional group. This is the first example of a thermally-stable functional IL with the potential to reclaim the tunable, task-specific nature of ILs at elevated temperatures. Importantly, these properties open new avenues for high-temperature applications of IL by extending their operational ranges; catalysis, metal remediation, and separation-based applications are potential key areas of improvement.