(776a) The Influence of Structural Variation On the Thermophysical Properties of Lipid-Inspired Ionic Liquids

Lipid-inspired ionic liquids, first described by our group in a symposium in 2007, and more extensively in a recent publication, are a class of ionic liquids that utilize structural features similar to those of natural lipids to allow the incorporation of long alkyl chains in ionic liquids while preserving low melting points.  Such compounds are of interest as potential separations agents, due to their higher solubility of non-polar compounds relative to other ionic liquids, lubrication applications and as models for lipid membranes.

In the first generation of these compounds we utilized bio-derived fatty alcohols to generate the side chains of 1-methyl-3-alkylimidazolium ions to demonstrate the significant melting point decrease observed for the bistriflimide salts when simple structural features such as a single cis-double bond were introduced into the alkyl chain.  In the second generation of these compounds we demonstrated similar effects with other natural and synthetic asymmetric structural features that introduce either “kinks”, “bumps” or both in the alkyl chain structure.

In the third generation of these materials we have utilized the click chemistry of thio-ene reactions to generate synthetic analogs of the naturally derived side chains.  Asymmetric features are introduced through the inclusion of sulfur atoms and branches in the alkyl chain, both easily facilitated through the use of thiol-ene chemistry.  This synthetic motif has also allowed us to examine the effect of the location of the heteroatom and branches in the alkyl chain on the thermophysical properties of the species providing valuable structure/property information which informs molecular design.  In this work we focus on the effect of structural variation on the melting points and viscosities on homologous series of this new class of compounds and provide insights which may be useful for designing new task-specific ionic liquids.