Experimental Densities And Calculated Fractional Free Volumes Of Ionic Liquids With Tri- And Tetra-Substituted Imidazolium Cations

Although it has been estimated that there are at least 1 million ionic liquids (ILs) that are accessible using commercially available starting materials, a great portion of the ILs that have been experimentally synthesized, characterized, and studied in a variety of applications are built around the relatively simple 1-n-alkyl-3-methylimidazolium ([C(n)mim]) cation motif. Yet, there is no fundamental limitation or reason as to why tri- or tetra-functionalized imidazolium cations have received far less attention. Scant physical property data exist for just a few trifunctionalized imidazolium-based ILs and there is virtually no data on tetra-functionalized ILs. Thus, there are a broad experimental spaces on the "map" of ILs that are largely unexplored. We have sought to make an initial expedition into these "uncharted waters" and have synthesized imidazolium-based ILs with one more functional group(s) at the C(2), C(4), and/or C(5) positions of the imidazolium ring (as well as N(1) and N(3)). This manuscript reports the synthesis and experimental densities of these tri- and tetra-functionalized ILs as well as calculated densities and fractional free volumes from COSMOTherm. To the best of our knowledge, this is the first report of any detailed experimental measurements or computational studies relating to ILs with substitutions at the C(4) and C(5) positions.