Synthesis, physical, and thermodynamic properties of 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Highlights: ► Synthesis of four 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imides. ► DSC measurements of glass and melting transition properties. ► Heat capacity, density, dynamic viscosity, surface tension measurements. ► Calculations of the isothermal expansion coefficient. ► Calculation of the thermodynamic functions of surface, critical temperature, parachor, and speed of sound. - Abstract: Synthesis of new ionic liquids (ILs) viz. 1-butyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [BCN3Py][NTf2], 1-hexyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN3Py][NTf2], 1-hexyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN4Py][NTf2], and 1-octyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [OCN3Py][NTf2] were performed. The specific basic characterization of new compounds by NMR spectra, elementary analysis, water content and glass transition temperature as well as melting temperature, enthalpy of fusion and decomposition of compounds TG/DTA determined by the differential scanning calorimetry, DSC is presented. The heat capacity was measured at three temperatures (298.15, 323.15, and 353.15) K and at pressure 0.1 MPa. The effect of temperature on the density and viscosity is reported over the temperature range from (293.15 to 363.15) K and at 0.1 MPa. The density and viscosity correlation for these systems was provided by an empirical polynomial. From the density–temperature dependence, the isothermal expansion coefficient (volume expansivity), α, was calculated. The surface tension of pure ionic liquids was measured at 0.1 MPa at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15) K. The surface thermodynamic functions such as surface entropy and enthalpy, critical temperatures according to the Eötvös and Guggenheim definition and the total surface energy of the ILs studied were derived from the temperature dependence of the surface tension values. The parachor and speed of sound for pure ionic liquids were described within a range of temperature from (298.15 to 338.15) K. A qualitative analysis on these quantities in terms of molecular interactions is reported.