Effect of the number, position and length of alkyl chains on the physical properties of polysubstituted pyridinium ionic liquids

• Synthesis of five polysubstituted pyridinium based-ionic liquids.
• Physical properties of the pure ionic liquids were measured at several temperatures.
• Thermal analysis of the pure ionic liquids was carried out by DSC and TGA techniques.
• Density, speed of sound, and refractive index were fitted with a linear expression.
• Viscosity data were correlated using the VFT equation.

The knowledge of the physical properties of ionic liquids is of high importance in order to evaluate their potential applicability for a given purpose. In the last few years, ionic liquids have been proposed as promising solvents for extractive desulfurization of fuels. Among them, recent studies have shown that ionic liquids derived from pyridinium affords excellent S-compounds removal capacity. In this work, the thermal analysis of five ionic liquids derived from pyridinium cation polysubstituted with different alkyl chains was carried out by Differencial Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). Furthermore, the density, speed of sound, refractive index and dynamic viscosity for all the pure ionic liquids were also measured from T = (298.15 to 343.15) K. The effect of the number of cation alkyl chains, their length, and their position on the pyridinium ring, on the ionic liquid physical properties is also analyzed and discussed.