In this work, densities and viscosities for the binary mixtures of 1-hexyl - 3-methylimidazolium tetrafluoroborate, [C6mim][BF4], with butyl acetate, have been determined at 298.15 K. These data were used to calculate the excess molar volumes VEm for the mixtures. It is shown that values of VEm are negative, in the whole concentration range. The VEm values show their minimum at the composition of χIL≈ 0.3, exhibit a maximum at the same mole fraction. For the binary systems, the absolute values of VEm decrease in the butyl acetate. The results are discussed in terms of the ion–dipole interactions between cations of the ionic liquid and the organic molecules and hydrogen bonding interactions between anions of the ionic liquid and the organic compound([C6mim][BF4], butyl acetate).

Keywords: 1-hexyl-3-methylimidazolium tetrafluoroborate, Density, Viscosity, Excess molar volume, butyl acetate, Ionic liquids.