(231ap) Solvent Properties of Lipidic Ionic Liquids

The discovery of the impact that invisible but harmful gas emissions have on our environment was one of the greatest scientific accomplishments of the 20^th century.  Among the greatest challenges of the 21^st century is to prevent these gasses from being released by industrial processes.  Chemical processes that utilize volatile organic solvents often release harmful emissions into the environment. One solution to this problem is to replace these solvents with ionic liquids, room temperature liquid salts that have vanishingly low vapor pressures, which greatly reduces the possibility of fugitive emissions.   Conventional ionic liquid solvents have poor solubilities for non-polar solutes; however, many industrial processes, including petroleum refining and alternative energy production, require solvents that will dissolve non-polar species.

Recently, our group has synthesized and characterized the pure component properties of a new class of ionic liquids derived from fatty acids.  We have named these novel salts lipidic ionic liquids and they show potential as alternative solvents for non-polar compounds.  A key structural element of lipidic ionic liquids is a long alkyl chain with a “kink” which creates greater asymmetry, frustrating packing and lowering the melting point; most of these species are room temperature liquids.  In the first generation of lipidic ionic liquids, the kink arose from cis unsaturations, inspired by natural lipids.  In the second generation, we have incorporated the kink via a thioether linkage in the chain to provide better oxidative stability.

In this work we present vapor/liquid, liquid/liquid and solid/liquid equilibria along with volumetric measurements for binary mixtures of representative lipidic ionic liquids with model molecular compounds.  The molecular compounds selected represent a broad class of species ranging from polar to non-polar, as well as homologous series to probe the effects of molecular size and shape.  VLE is measured via an intelligent gravimetric analyzer, LLE with a cloud point cell and SLE using differential scanning calorimetry.  In addition to examining homologous series of molecular compounds, the solubilities of the model compounds in lipidic ionic liquids are compared with their solublities in shorter chain, conventional ionic liquids.  The representative lipidic ionic liquids show significantly higher solubilities for non-polar species than do traditional ionic liquids, demonstrating their “non-polar-like” solvent properties and their potential use as environmentally benign replacement solvents for non-polar solutes.