Octanol/Water Partition Coefficients and Water Solubilities of Phthalate Esters

Abstract

Measurements of the octanol/water partition coefficients (Kow) and water solubilities of di-n-octyl phthalate (DnOP) and di-n-decyl phthalate (DnDP) by the slow-stirring method are reported. The water solubility was also measured for di-n-hexyl phthalate (DnHP). The log Kow values of dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), di-n-pentyl phthalate (DnPP), and DnHP, determined in a previous study, and the log Kow values of DnOP determined again in this study were correlated against the number of carbons in the phthalate side chain. The straight line regression equation (log Kow = 0.979 + 0.615, r2 = 0.993) was used to extend the estimate for a carbon number 10; that is, log Kow = 10. 41 for DnDP. The slow-stirring log Kow = 8.83 ± 0.05 reported here for DnDP suggests that the decrease in solubility of the phthalate in the water layer is nonlinear when the side chain carbon length increases beyond eight carbons. Similarly, the straight line regression equation derived from correlation of the measured water solubilities for DnOP and DnHP reported here and the literature values for DMP, DEP, and DnBP against side chain carbon number predicted a 0.005 μg/L water solubilty for DnDP. The measured water solubility of DnDP (0.22 ± 0.05 μg/L) reported here was 44-fold greater.