Previous work in our group discovered that incorporating unsaturation into long, lipid-like aliphatic side chains grafted onto imidazolium cations dramatically reduces the temperatures at which ionic liquids (ILs) containing those ions liquefy relative to counterparts bearing saturated side chains of equal length.  In addition, we recently reported that incorporation of a thioether linkage within the long alkyl chain at various locations dramatically reduces the melting points of these ionic liquids.  In continuation of our work with lipid-like ionic liquids, we investigated the thiol-ene reaction with different ene-functionalized pyridinium-based ionic liquids by reacting them photochemically with alkylthiols, yielding structurally diverse ionic liquids in a single step. Differential scanning calorimetry (DSC) was utilized to study the effects of both long and branched substituents upon ionic liquid melting points.4-Methyl and 3-methyl substituted pyridinium-based cations precursors were employed as ene substrates for the study. Pyridinium-based cations with N-allyl moieties were chosen to assess the effect, if any, of having the sulfur moiety at the fourth position from the center of the cationic charge.  All of the pyridinium-based ionic liquids contained a thioether linkage with alkyl chain lengths ranging from C3 to C18. The synthetic methodology will be discussed, as well as the impact of these structural modifications upon ionic liquid melting points.

Thiol-ene “click” reactions as an efficient approach to synthesize structurally diverse pyridinium-based ionic liquids

243rd National Meeting (2012)

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