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.

Excess volumes, excess viscosities, and exess Gibbs energies of activation for viscous flow of binary liquid mixtures of formamide with (C₁–C₅) alkan-1-ols have been calculated from the densities and viscosities measured at 298.15 K over the whole composition range. The viscosity–mole fraction data of the five systems were used to test various empirical laws proposed to describe the viscosity of mixtures: the one-parameter models by Nissan–Grunberg, Hind–McLaughlin–Ubbelohde and Teja–Rice, and the two-parameter models by McAllister, Heric, Lobe, and Cao–Fredenslund–Rasmussen were tested. All correlations were in good agreement except that of Teja–Rice. Deviations with respect to ideal behaviour were interpreted in terms of specific interactions between unlike molecules.