A New Category of Liquid Salt--Liquid Ionic Phosphates (LIPs)

Abstract

Starting with polycationic ammonium and phosphonium salts bearing halide anions previously synthesized in our laboratory, we have prepared a new category of nonaqueous ionic liquids. These new nonaqueous ionic liquids bear either free phosphate anions or partially esterified phosphate anions as the counterions to the ammonium or phosphonium cations. We generally refer to these new species as LIPs (liquid ionic phosphates). We have developed three approaches toward the syntheses of these materials from the halide salts: one using hexafluorophosphoric acid;; a classical ion exchange method; and treatment with the free phosphorus-containing acid under vacuum. The new LIPs, although highly viscous, exhibit significantly high specific conductivities. Unlike ionic liquids bearing tetrafluoroborate of tetrachloroaluminate anions, the LIPs are unreactive toward water. Further, the LIPs bearing simple phosphate anions are soluble in water, unlike their corresponding hexafluorophosphate salts. We have also examined the UV/Vis, fluorescence, and mobility characteristics of the new LIPs.