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 usef ul ones. Comparing the results, we used both methods for three derivatives of 2-mercapto-5-R-amino-1,3,4-thiadiazole. For the pK(a) determination by t he spectrophotometric method we measured the ratio between the concentratio n of dissociated and undissociated forms. The ratio was calculated from spe ctral data. The potentiometric method for pK(a) consists of measuring the p H values within a potentiometric titration with 0.1 M NaOH. The results pro ved a very low acid character of the derivatives. The pK(a) values were inf luenced by the properties of the amino group substituents, and the results confirm the theoretical considerations. The study confirms the thion-thioli c tautometry of the 2-mercapto-5-R-amino-1,3,4-thiadiazole derivates and th eir property of being ligands for the coordination of the cations of some r epresentative and transitional metals, with application in the preconcentra tion, in the detection and the quantitative determination of polluting and toxic cations in environmental analysis. (C) 1998 Elsevier Science B.V. All rights reserved.