Distribution of hydrophobic ionogenic organic compounds between octanol and water: organic acids

Abstract

The octanol-water distributions of 10 environmentally significant organic acid compounds were determined as a function of aqueous-phase salt concentration (0.05-0.2 M LiCl, NaCl, KCl, CaCl2) or MgCl2) and pH. The compounds were pentachlorophenol, 2,3,4,5-tetrachlorophenol, (2,4,5-trichlorophenoxy)acetic acid, 4-chloro-α-(4-chloro-phenyl)benzeneacetic acid, 2-methyl-4,6-dinitrophenol, (2,4-dichlorophenoxy)acetic acid, 4-(2,4-dichlorophenoxy)butanoic acid, 3,6-dichloro-2-methoxybenzoic acid, 2,3,6-trichlorobenzeneacetic acid, and 2-(2,4,5-trichlorophenoxy)propionic acid. The experimental results were interpreted quantitatively with an equilibrium model that accounts for acid dissociation in the aqueous phase and partitioning into the octanol phase by the neutral organic species, free inorganic and organic ions, and ion pairs. The partition constants for the neutral ion pairs correlate well with the partition constants of the neutral acids. Two experiments address the applicability of these octanol- water distribution data to the distribution of ionogenic compounds in the environment: the distribution of 2- methyl-4,6-dinitrophenol on a natural sorbent as a function of salt concentration (NaCl and CaCl2) and pH, and competitive adsorption of pentachlorophenol and 2,3,4,5-tetrachlorophenol on an environmental sorbent.