Synthesis and properties of l-valine based chiral long alkyl chain appended 1,2,3-triazolium ionic liquids

Abstract

The increasing importance of ionic liquids (ILs) in various strata of chemical sciences is largely due to the fact that modification in the architecture of the cation and/or the anion imparts favorable and specific properties to an IL. Consequently, there is a need to develop new ILs with different functionalities. A series of L-valine based alkyl chain-appended 1,2,3-triazolium ILs (alkyl = hexyl, octyl, dodecyl, cetyl and octadecyl) with iodide and hexafluorophosphate anions, respectively, are synthesized and characterized. These new ILs show optical activity and hence are termed chiral ILs (CILs). All ten CILs are room temperature ILs (RTILs) as their melting points, obtained from differential scanning calorimetry (DSC), are found to be below ambient temperature. Thermogravimetric analysis indicates these CILs to have adequate thermal stability. The longer alkyl chain containing CILs exhibit facile self-aggregation when dissolved in ethanol. There is a hint of pre-micellar aggregation by short alkyl chain possessing CILs along with the long alkyl chain containing ones. These CILs demonstrate weak absorbance and emission of UV-Vis radiation and hence can be considered ideal solvents for photochemical applications. These CILs, consisting of different functionalities, possess interesting properties and have potential to be used in many areas of chemistry.