The field of ionic liquids (ILs) is dominated by binary salts, which are valued for being tunable by changing the ions. However, the tunability of ILs can be further enhanced by combining two ILs or dissolving a solid salt in an IL to give a homogeneous ionic fluid with three or more ions. We have adopted the term Double Salt Ionic Liquid (DSIL) to describe these systems, which are molten analogs of crystalline double salts (salts with three or more ions in a single crystal lattice). While combining molten ILs tends to resemble ideal mixing in some ways, ILs also have a microstructure not commonly found in molecular compounds which would be expected to change upon combination with another ionic compound. Here we present a study of the physical and spectroscopic properties of DSILs composed of 1-ethyl-3-methylimidazolium ([C2mim]+) cation and two anions, the hydrophilic acetate ([OAc]-) and the hydrophobic bis(trifluoromethane)sulfonimide ([NTf2]-). The high basicity of [OAc]- allows it to draw [C2mim]+ cations away from the [NTf2]- anions, creating ionic clusters which are not possible in either of the parent ILs. The solubility of solvent molecules (ethyl acetate and water) and active pharmaceutical ingredients with different acidities (ibuprofen and diphenhydramine) were found to be finely tunable by varying the ratio of [OAc]- to [C2mim]+. This study points the possibility that DSILs can provide systems with tunable and unique solubilities which might find use in many new separation processes.

Double salt ionic liquids with unique chemical environments for separations

249th National Meeting (2015)

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