Influence of pH and ionic strength on the aqueous-nonaqueous distribution of chlorinated phenols

Abstract

The distribution ratio of hydrophobic ionizable organic compounds (HIOC's) between aqueous and nonaqueous phases is shown to depend on the pH and ionic strength of the aqueous phase. Four models are presented to describe the association of the HIOC with the nonaqueous phase: (i) transfer of the neutral organic species from the bulk of the aqueous phase to the bulk of the nonaqueous phase; (ii) transfer of the ionic organic species with inorganic counterions to the bulk of the nonaqueous phase; (iii) transfer of the ionic organic species to the aqueous-non-aqueous interface with inorganic counterions in the aqueous phase; (iv) association of the organic species with specific functional groups of the nonaqueous phase. The distribution of 2,3,4,5-tetrachlorophenol and pentachlorophenol in the two-phase system composed of KOH, KG, H₂O, octanol, and the chlorophenol was determined as a function of ionic strength and interpreted quantitatively in terms of models i and ii. For aqueous phases with high pH values and ionic strengths, the dominant species of the chlorophenols in the octanol phase were the chlo-rophenolate ions in association with K⁺ counterions.