Partitioning of Alkylbenzenes and Aliphatic Alcohols between Hexadecane and Methanol- Water Mixtures

Partition coefficients between n-hexadecane and methanol-water mixtures are reported and analyzed for a series of alkylbenzenes and aliphatic alcohols. A custom-designed flask which has a side arm attached near the bottom was used for the measurements. The hexadecane layer was sampled from the top of the flask, and the aqueous layer was sampled through the side arm of the flask. Both phases were analyzed by an appropriate analytical technique, either gas or liquid chromatography, to determine concentrations. A lattice-model theory suggests a correlation between the hexadecane/methanol-water partition coefficients and the solute molar volume for each solute group type and between the hexadecane/methanol-water partition coefficients and the volume fraction of water in the aqueous phase. The mole-fraction-based activity coefficients calculated from the partition coefficients compare favorably to those determined by a headspace gas chromatographic method. Finally, based upon the data contained herein, the retention mechanism in reversed phase liquid chromatography appears to involve the stationary phase as more than just a passive receptor.