An aqueous medium synthesis and tautomerism study of 3(5)-amino-1,2,4-triazoles

A catalyst-free highly efficient synthesis of 3(5)-amino-5(3)-(het)aryl-1,2,4-triazoles in aqueous medium was performed using conventional heating and microwave irradiation. The tautomerism in the products was investigated using NMR spectroscopy and X-ray crystallography. The effects of the substitution, temperature, solvents, and concentration on the tautomerism were studied. The triazoles were found to exist in I H-forms, the 4H-form was not observed either in solid state or in solution. In general, 5-amino-1,2,4triazoles were electronically preferred in the tautomeric equilibrium, but some exceptions from the established relationship were also identified. (C) 2009 Elsevier Ltd. All rights reserved.