Tricaprylin-water partition coefficients and their temperature dependence for selected chlorobenzenes

Measurements of partition coefficients between tricaprylin (glyceryl tri-n- octanoate) and water are reported for seven chlorobenzenes (1,2-dichloraben zene, 1,4-dichlorobenzene, 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenze ne, 1,2,3,5-tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene) between 5 degrees C and 45 degrees C. The values are compared with reported data on octanol-water and triolein-water partition coefficients. The van't Hoff plots of log K-OW versus T-1 exhibit linearity with values of K-OW in creasing by 5%-8% over this temperature range, and the enthalpy of phase ch ange varies from 9.7 to 16 kJ/mol. Several reasons are suggested why tricap rylin-water partition coefficients may be preferable to octanol-water and t riolein-water partition coefficients when quantifying a substance's hydroph obicity. The mutual solubilities of tricaprylin and water are less than tha t of octanol and water. Tricaprylin is less volatile than octanol and, bein g a triglyceride, is structurally more similar to lipids. Tricaprylin is ea sier to purify than triolein and, because of its lower molecular mass, is e asier to analyze by gas chromatography.