Application of the Extended Hammett Relationship to the Ionization Constants of Substituted Anthranilic Acids

The overlapping ionization constants of the carboxyl and amino groups in 14 substituted anthranilic acids have been determined by a spectrophotometric method. The results have been fitted to the extended Hammett relationship log K1K2/K10K20 = ρ1σA + ρ2σB, where A and B refer to ionization of the carboxyl and amino group, respectively. The values of ρ1 and ρ2 so obtained have been used to estimate Kz0, the equilibrium constant for ionization of neutral anthranilic acid to zwitterion.