Ionic Liquids Stable At High Temps

Ionic liquids—essentially liquid salts—can be used in all sorts of ways, including as solvents and electrically conducting fluids. Researchers have been tinkering with various properties of ionic liquids, in particular their stability at high temperatures, to make them useful as heat-transfer fluids. James H. Davis Jr. of the University of South Alabama and colleagues have now developed what may be the most thermally stable ionic liquids yet. The group synthesized a suite of new tetraarylphosphonium cations that pair with the anion Tf₂N^– [bis(trifluoromethylsulfonyl)imide] to form ionic liquids that are stable at temperatures of up to 350 °C. The researchers found that even after heating at that temperature for 96 hours, the material remained colorless and less than 10% had evaporated (Chem. Commun. 2013, DOI: 10.1039/c3cc44118k). In contrast, other popular ionic liquids with cations such as imidazolium, quaternary ammonium, or tetraalkylphosphonium thoroughly decomposed when subjected to those conditions and left dark solids at the bottom of the dish. The researchers are now working to expand the ionic liquids’ capabilities by decreasing their melting points yet maintaining their thermal stability.