On the properties of 1-butyl-3-methylimidazolium octylsulfate ionic liquid

Abstract

This work reports on a theoretical and experimental study on the ionic liquid 1-butyl-3-methylimidazolium octylsulfate ([BMIM]OS). The halogen-free ionic liquid [BMIM]OS is a stable solvent regarding hydrolysis, whose availability, toxicologically favourable features and well documented biodegradability turns it into a suitable candidate for different multiton-scale industrial applications. The pressure–volume–temperature behaviour of this fluid has been evaluated accurately over wide ranges of temperature and pressure, and correlated successfully with the empirical TRIDEN equation. From the measured data the relevant derived coefficients, isothermal compressibility, isobaric expansibility and internal pressure have been calculated. Other valuable properties such as isobaric heat capacity, speed of sound and refractive index were measured at several temperatures and atmospheric pressure. The molecular structure was looked into by quantum computations at the B3LYP/6-31 + g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS–AA forcefield. Both macroscopic and microscopic studies concur in a complex structure involving microheterogenous polar and non-polar domains, brought about by the aggregation of the non-polar anionic chains.