Double Salt Ionic Liquids Prepared by Mixing Partially Miscible Ionic Liquids: Tuning the Solubility of Lipophilic Molecules

Double Salt Ionic Liquids (DSILs) were prepared by mixing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl) imide ([P-66614][NTf2]) in their miscible range: [C(2)mim](x)[P-66614]((1-x))[NTf2] (0 <= x <= 0.29). H-1 NMR, F-19 NMR, and FT-IR spectroscopic studies indicated that the [NTf2](-) anions preferentially interact with the [C(2)mim](+) cations. Solubility studies showed that solutes with long alkyl chains (e.g., heptane, methyl palmitate), which have good solubility in [P-66614][NTf2] but are not totally miscible, have tunable solubility in the DSILs and the presence of even minor amounts of [C(2)mim](+) significantly decreases their solubility. However, the solubilities of benzene, toluene, 1-octanol, and poly(ethylene glycol) (PEG-300) in [C(2)mim](x)[P-66614]((1-x))[NTf2] were controlled by their miscibility with [P-66614][NTf2], and can't be tuned by changing the ion concentrations within the miscibility range.