The potentiometric and spectrophotometric determination of dissociation constants for same 2-mercapto-5-R-amino-1,3,4-thiadiazole derivatives.

In order to establish the dissociation constants of organic compounds, the spectrophotometric and potentiometric methods are the most precise and useful ones. Comparing the results, we used both methods for three derivatives of 2-mercapto-5-R-amino-1,3,4-thiadiazole. For the pKa determination by the spectrophotometric method we measured the ratio between the concentration of dissociated and undissociated forms. The ratio was calculated from spectral data. The potentiometric method for pKa consists of measuring the pH values within a potentiometric titration with 0.1 M NaOH. The results proved a very low acid character of the derivatives. The pKa values were influenced by the properties of the amino group substituents, and the results confirm the theoretical considerations. The study confirms the thion-thiolic tautometry of the 2-mercapto-5-R-amino-1,3,4-thiadiazole derivates and their property of being ligands for the coordination of the cations of some representative and transitional metals, with application in the preconcentration, in the detection and the quantitative determination of polluting and toxic cations in environmental analysis.