Studies on the distribution of N-phenylanthranilic acid in two-phase system: Aromatic solvent–water

The detailed description of equilibria of N-phenylanthranilic acid in the aqueous solutions and in the two-phase systems: aromatic solvent–aqueous solution were obtained. The isoelectric point, pHI, the dissociation constants of the protonated form, Ka1, and the neutral form, Ka2, in the aqueous solutions were determined from the apparent ionization constant in methanol–water solutions of various proportions by extrapolation to zero co-solvent using Yasuda–Shedlovsky procedure. On the basis of the spectrophotometric investigations, the values of the distribution ratio, D, of N-phenylanthranilic acid in the two-phase systems: aromatic solvent (benzene, ethylbenzene, toluene, chlorobenzene, bromobenzene)–aqueous solution were obtained. Employing the results of the potentiometric titration in the two-phase systems: aromatic solvent–aqueous solution, and using models of singular and multistep equilibria the values of the distribution constants, KD, dimerization constants, Kdim, were calculated. The significant influence of the polarity of the applied aromatic solvents and pH of the aqueous phase on the percentage of the particular forms of N-phenylanthranilic acid in the two-phase systems was proved.