SOLVATION IN WEAK COMPLEXING N-OCTYL PHTHALATE AND N-OCTYL TETRACHLOROPHTHALATE SOLVENTS BY GAS-CHROMATOGRAPHY

The solution properties of a varied group of solutes in di-n-octyl pht halate and di-n-octyl tetrachlorophthalate over the temperature range 60 to 120 degrees C were studied by gas chromatography. The solvation parameter model was used to assign the contribution of individual inte rmolecular interactions to the gas-liquid partition coefficients. The dominant interaction was dispersion with only small contributions from dipole-type interactions, n- and pi-electron donor/acceptor interacti ons (for the tetrachlorophthalate ester only), and solvent hydrogen-bo nd base interactions. Neither phthalate eater exhibited solvent hydrog en-bond acid properties. Complexes formed between solutes and these ph thalate eater solvents are likely to be of the Van der Waals type, per haps augmented by dipole-type interactions and hydrogen-bond complexat ion with hydrogen-bond acid solutes. In addition, n- and pi-electron c omplexation interactions, in the temperature range studied, may contri bute to complex formation with the tetrachlorophthalate eater, but are too weak to be the dominant interactions involved. In general, the ra nge of chromatographic selectivity obtainable through exploitation of the phthalate and tetrachlorophthalate nucleus does not warrant their selection as building blocks for new polymer-supported phases with the expectation of providing opportunities to extend the selectivity rang e of existing gas chromatographic stationary phases. In addition, the influence of interfacial adsorption as a retention mechanism for the d etermination of solvent properties and as a potential source of disagr eement between reported solvent properties for the phthalate esters is discussed.