Thermodynamics of the molecular association of tri-n-octylphosphine oxide and haloalkanes using gas-liquid chromatography

Abstract

The gas chromatographic retention behavior of nineteen halogenated hydrocarbons and of seven saturated hydrocarbons was measured at four temperatures from 55 to 65°C in tri-n-octylphosphine oxide (TOPO) and at 60°C in squalane (SQ). Thermodynamic functions of solution in TOPO were computed from these data. Strongly negative deviations from the ideal behavior were interpreted in terms of halogenated hydrocarbon+TOPO association, and the equilibrium constants were calculated by reference to the inert solvent SQ. The larger equilibrium constants correspond to solutes with a definite proton donor capability. The substitution of Cl for Br, however, produces an increase in the association constants suggesting the existence of other interaction mechanisms. Complexing of halogenated hydrocarbons with TOPO is markedly greater than with ethers, thioethers or tertiary amines.