Calculation of partition constants for a series of organic compounds via a novel solubility-parameter-based method

Abstract

A thermodynamic model with additional extrathermodynamic assumptions is presented for the calculation of equilibrium partition constants for a series of organic compounds. Key properties are heat of vaporization, molar liquid volume and Hildebrand–Scatchard solubility parameter of both the compounds and the phases they are partioning over. The heat of vaporization and molar liquid volume of the members of a compound series are thought to be built up from molecular skeleton and interactive substituent contributions. These contributions enable the physical discrimination of isomers within a series. Additional parameters are introduced, which are characteristic constants of an isolated compound series or a compound series solved into a particular phase. They correspond to extensions of existing solubility-parameter-based models. Depending on the availability of data and study objectives the different types of parameters are derived via a non-linear fit to experimental data.Accurate, isomer-specific results are obtained for the heat of vaporization, molar volume, solubility parameter, partition coefficient in octanol–water, chromatographic retention, vapour pressure, aqueous solubility and the Henry's law constant of the 92 methylchlorobenzenes.