Spectroscopic approach to estimation of microequilibrium constants of prototropic reactions of aminobenzoic acids.

The microequilibrium constants of protolytic dissociation of diprotic acids, dihydric bases, or ampholytes such as the aminobenzoic acids, with dissimilar ionizing groups, can be estimated by spectrophotometric titration and measurement of the molar absorptivity at the long wavelength absorption maximum of simple alkylated derivatives. The method is applicable when the long wavelength absorption spectral bands of the tautomeric species are well resolved. Compared to the traditional method of estimating microequilibrium constants using the dissociation constants of alkylated derivatives, the proposed method is simpler, faster, and more accurate.