Characterization of the ionization and spectral properties of mercapto-carboxylic acids Correlation with substituents and structural features.

The ionization constants in aqueous solutions of meso- and dl-dimercaptosuccinic acid and of monomethyl and dimethyl meso-succinates were carefully determined by potentiometric and spectrophotometric methods as a result of the increasing interest in these molecules as heavy metal chelators. In order to explain the influence of various substituents on ionization and (13)C NMR properties, the study was extended to the related oxygen derivatives of succinic acid and to simpler ethanoic derivatives. With the Swain-Lupton dual substituent treatment it was possible to clarify the influence of substituents on both spectral and equilibrium parameters. The differences in pK due to conformation are also discussed.