New methylpyridinium ionic liquids – Influence of the position of –CH3 group on physicochemical and structural properties

Abstract

In this work, the three newly synthesized pyridinium based ionic liquids (ILs) are investigated in order to show the structure-property relationship and the possibility of fine-tuning based on a change of –CH3 position on cation heterocycle. Studied ILs are N-hydroxypropyl-n-methylpyridinium chloride, [N-C3OH-n-mpy][Cl] (n is 2, 3 or 4 position of –CH3 on pyridinium ring). The relationship between molecular structure and properties for these pure ILs is explored by a combination of experimentally obtained physicochemical properties, as well as molecular dynamics and quantum chemistry. How the change in the position of the –CH3 group affects the volumetric and viscosimetric properties of aqueous solutions of these ILs is also reported in this work. Density and viscosity measurements were performed in the temperature range from T = (293.15 to 313.15) K at atmospheric pressure and in the molality range from m ~ (0.10000 to 0.50000) mol·kg−1. Based on physicochemical characterization supported with computational simulations for pure ILs and their aqueous solutions, the interactions between these different ILs and water were discussed and more precisely viewed the impact of the position of the methyl substitute on the pyridinium ring.