Synthesis and physico-chemical characterization of binary mixtures of hydroxyl- and ester-functionalized ionic liquids

Abstract

The first binary system of 1-(6-hydroxyhexyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (IL-OH) and 1-(hexyl-4-oxopentanoate)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (IL-Ester) ionic liquids (ILs) was prepared across the entire mole fraction range. Physico-chemical properties such as density, viscosity, thermal stability and refractive index were determined for the binary system at different temperatures. It was found that the density decreases whereas viscosity and refractive index increase as a function of IL-Ester mole fraction. Furthermore, the excess properties (molar volumes, and refractive indices) were calculated which indicated increasing interactions and hence improved packing efficiency by the addition of IL-Ester. The thermal stability was somewhat lowered by the presence of IL-Ester. Hence, this study has provided an insight into the mixing behaviour and interactions among these binary mixtures. A group contribution method was applied to estimate densities from refractive index measurements. Overall, this work forms the basis for developing these types of ionic liquids for reactive extractions of value-added products.