Thermophysical properties of N-phenyl-N-ethanol ammonium carboxylate based ionic liquids: Measurements, correlations and COSMO-RS study

Abstract In this work, a series of four protic ionic liquids were synthesized by an exothermic neutralization process between N -phenyl- N -ethanolamine and stoichiometric quantity of different acids, namely, propionic acid, butyric acid, pentanoic acid and hexanoic acid. After characterization by 1 H NMR and 13 C NMR spectroscopic methods, density ( ρ ), speed of sound ( u ), viscosity ( η ) and conductivity ( σ ) of neat ionic liquids have been measured 293.15 to 343.15 K and the refractive index ( n D ) was measured only at 303.15 K. The density and refractive index data were correlated by Gardas-Coutinho model and Lorentz-Lorenz mathematical equation, respectively, whereas viscosity and electrical conductivity were estimated by Vogel-Tammann-Fulcher (VTF) equation. Further experimental data used to calculate several derived thermodynamic properties such as thermal expansion coefficient ( α ), isentropic compressibility ( β S ), molar volume ( V m ), standard entropy ( S °), intermolecular free length ( L f ), molar refraction ( R m ) and free volume ( f V ). The decomposition temperature ( T d ) of synthesized ILs was investigated using TGA analysis. Finally, Conductor-like Screening Model for Real Solvents (COSMO-RS) computational method was also studied to understand the structural variations of the ionic liquids.