Origin and effect of impurities in protic ionic liquids based on 2-methylpyridine and trifluoroacetic acid for applications in electrochemistry

Protic ionic liquids (PILs) based on 2-methylpyridine (2-MPy) and trifluoroacetic acid (TFA) have been synthesized under multiple conditions and with different proportions of their constituents. These PILs present a brown color of variable intensity and the factors responsible for the presence of these impurities have been examined. UV-vis spectroscopy analyses revealed that both TFA and 2-MPy can be thermally degraded during the synthesis process. Distillation of the IL can be used to quickly obtain mixtures without any traces of coloration, but can leads to a severe alteration of the relative proportion of the constituensts. This work shows that high-yield syntheses of PILs obtained with different contents in colored impurities can be compared to evaluate the effect of these impurities not only on the electrochemical behavior (on Pt and on GC) but also on the physicochemical properties of interest for PILs as applications in electrochemistry (conductivity, density, and viscosity). (C) 2009 Elsevier Ltd. All rights reserved.