THE EFFECT OF SUBSTITUENTS (CH3 AND NH2) IN POSITION-4 AND POSITION-6ON THE ACID-BASE PROPERTIES OF 2(1H)-PYRIMIDINETHIONES

The acid-base properties of 4,6-dimethyl- and 4,6-diamino-2(1H)-pyrimi dinethiones (1 and 2) were investigated by potentiometric titration. D issosiation of 1 and protonation of its anion occur in two steps, the first of which affords the deprotonated dimer [HA(2)](-). The relative stability of the dimer depends on the nature of the solvent. The effe ct of kinetic factors on the acid-base behavior of 1 was elucidated by comparing the results of potentiometric titrations carried out under various kinetic conditions. It was concluded that the difference betwe en the acid-base properties of 1 and 2 results from the electron-donat ing effect of the amino groups.