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.
Preparations are reported for an extensive series of phosphate salts of polyammonium species from the corresponding halide salts. The phosphate salts, as anhydrous materials, are liquid at or near room temperature. Three approaches for the preparation of these materials are noted, including treatment with aqueous hexafluorophosphoric acid, classical ion exchange methods, and treatment with 85% phosphoric acid. The last of these provides the most desirable results. Several monocationic phosphate salts have also been prepared for comparison with other types of ionic liquids.
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