Octanol/water partition coefficients and water solubilities of phthalate esters

Measurements of the octanol/water partition coefficients (K-ow) and water s olubilities of di-n-octyl phthalate (DnOP) and di-n-decyl phthalate (DnDP) by the slow-stirring method are reported. The water solubility was also mea sured for di-n-hexyl phthalate (DnHP). The log K-ow values of dimethyl phth alate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), di-n-pen tyl phthalate (DnPP), and DnHP, determined in a previous study, and the log K-ow values of DnOP determined again in this study were correlated against the number of carbons in the phthalate side chain. The straight line regre ssion equation (log K-ow = 0.979 + 0.615, r(2) = 0.993) was used to extend the estimate for a carbon number 10; that is, log K-ow = 10.41 for DnDP. Th e slow-stirring log K-ow = 8.83 +/- 0.05 reported here for DnDP suggests th at the decrease in solubility of the phthalate in the water layer is nonlin ear when the side chain carbon length increases beyond eight carbons. Simil arly, the straight line regression equation derived from correlation of the measured water solubilities for DnOP and DnHP reported here and the litera ture values for DMP, DEP, and DnBP against side chain carbon number predict ed a 0.005 mu g/L water solubilty for DnDP. The measured water solubility o f DnDP (0.22 +/- 0.05 mu g/L) reported here was 44-fold greater.