Synthesis and thermodynamic properties of a novel pyridinium-based asymmetrical gemini ionic liquid

Abstract

A novel asymmetrical gemini ionic liquid (GIL), [1-(1-pyridinium-yl-hexyl)-6-methylpiperidinium] dihexafluorophosphate ([PyC6MPi][PF6]2) combined with pyridine, 1-methylpiperidine by 1,6-dibromohexane with PF6− as anion, was synthesized and characterized by 1H NMR and IR. The molar heat capacity of the GIL was measured via differential scanning calorimetry from 298.15 K to 448.15 K under atmospheric pressure. No phase transition or other thermal anomaly was observed in the solid-phase region (298.15 K to 358.15 K) and liquid-phase region (403.15 K to 448.15 K). The basic properties and thermodynamic functions of the GIL, such as melting point, molar enthalpy and entropy of fusion, heat capacity, enthalpy HT-H298.15 K, and entropy ST-S298.15 K, were also determined from the experimental data. Thermal decomposition kinetics of [PyC6MPi][PF6]2 were investigated by using non-isothermal thermogravimetric analysis in pure nitrogen atmosphere at various heating rates. Thermal decomposition data were, respectively, correlated with Friedman method, Ozawa-Flynn-Wall equation, and ASTM model. The activation energy (E) and pre-exponential factor (logA) values were obtained by using the above three methods.