Tautomerism of aminothiazoles. pKBH+ Values of 2-aminothiazoles and of some model imines

Abstract

pK_BH⁺ Values of a number of 2-aminothiazoles, of their methiodides and of some fixed model imines have been measured in water at 25 °C. In favourable cases this allows the determination of the tautomeric constant K_T([amine]/[imine]). Comparison of the results shows that 2-aminothiazoles generally exist in the aminoaromatic form. 2-p-Tosylaminothiazole exists predominantly in the imino-form. 2-Aminothiazoles are generally protonated at the aza-nitrogen while the model imines are protonated at the exocyclic nitrogen. 2-p-Tosyliminothiazoles protonate at the aza-nitrogen as a consequence of the large substituent effect of the tosyl group.