Scaled-particle theory and salting constant of tetrahydrofuran in various aqueous electrolyte solutions at 298.15 K

Abstract

The vapour pressure change upon addition of electrolytes to dilute aqueous tetrahydrofuran (THF) solutions has been determined at 298.15 K. From these data the salting constants k_s(Setchenov constant) have been calculated for THF in aqueous electrolyte solutions with: NaCl, NaNO₃, NaClO₄, NaBr, CsBr, CsNO₃, AgNO₃, Ni(NO₃)₂, NiCl₂, CaCl₂, BaCl₂, Na₂SO₄, CdSO₄, CuSO₄, LaCl₃, Me₄NBr, Et₄NBr, Pr₄NBr, Bu₄NBr, NaPh₄B and Ph₄AsCl. Using classical extra-thermodynamic assumptions single-ion k_s values are calculated. It is shown, using the scaled-particle theory (SPT) that a Lennard-Jones 6–12 potential can describe the interaction of the THF molecule with all the inorganic cations. This may be considered as evidence that collisions occur between the THF molecule and the inorganic cations studied, although the ions should be considered as preferentially hydrated. Comparison of the behaviour of dilute THF and benzene aqueous inorganic electrolyte solutions suggests that under these conditions, THF behaves as a non-polar molecule. In the case of the interaction with organic ions, the THF molecule induces, unlike benzene, an additional repulsion term.