Imidazolium-based protic ionic liquids with perfluorinated anions: Influence of chemical structure on thermal properties

Abstract The influence of the cation chemical structure, namely its side chain, on the thermal properties of imidazolium-based protic ionic liquids (PILs) with different perfluorinated anions (trifluoromethanesulfonimide (TFSI), trifluoromethanesulfonic (TFS), and trifluoroacetic (TFA) acids) was studied. With that purpose, twenty-one PILs with various alkyl (methyl-, ethyl-, butyl- and vinyl-) and fluorinated (-CH2CF3, -CH2CHF2, and -CH2CH2F) side chains were successfully synthesized. Special attention was paid to an optimization of their synthesis conditions. The structure of synthesized fluorinated and alkyl-substituted PILs was confirmed by means of nuclear magnetic resonance (NMR) analysis (1D: 1H, 19F, 13C and 2D: 1H – 19F HOESY experiments) and Fourier transform infrared (FTIR) spectroscopy, while PILs thermal behavior was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in dynamic and isothermal modes. The correlation between the PILs chemical structure and their thermal stability was established. It has been found that an increase of the length of alkyl side chain (methyl-