Ion‐pair association of substituted phenolates with K+ in octanol

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Abstract
The speciation, environmental distribution, and ultimate fate of phenolic compounds, a class of hydrophobic ionizable organic compounds, is influenced by both their hydrophobic and electrostatic characteristics. In this study, electrical conductance measurements were employed to characterize the ion‐pair association properties of a monovalent inorganic cation (K+) with substituted phenolate anions in the model hydrophobic solvent, 1‐octanol. Quantification of such processes is important for characterizing the overall partitioning to and speciation in octanol of phenolic compounds. Data were analyzed and association constants were calculated using a modified form of the Fuoss–Onsager equation for electrical conductivity. Results indicate that the magnitude of ion‐pair association correlates with the electron‐donating and ‐withdrawing characteristics of phenolic ring substituents. A quantitative structure–activity relationship was developed correlating ion‐pair association constants to the sum of Hammett substituent constants for each species. The data suggest that for some phenolate salts, charged triple ion or higher aggregate formation may occur at elevated concentrations. A qualitative interpretation of this phenomenon and the selectivity of its occurrence are discussed.