Structure investigations of Schiff bases derived from 3-amino-1H-1,2,4-triazole

In the present paper, twelve Schiff bases derived from 3-amino-1H-1,2,4-triazole (ATz) and various benzaldehydes, and salicylaldehydes were synthesized. The H-1, C-13, and N-15 NMR data are discussed in relation to the structure of ATz and its imine products. In addition, X-ray, ATR-FTIR, and UV-Vis analytical techniques are used for structure elucidation of ATz-based Schiff bases. It was found that the starting material, 3-amino-1H-1,2,4-triazole, exists as tautomeric mixture of three forms (Graphical Abstract) in solution, whereas in the solid state (C-13 and N-15 CPMAS data) potentially tautomeric proton is located on nitrogen atom traditionally marked as N-2 (Graphical Abstract, 2N-H structure). All investigated Schiff bases derived from salicylaldehydes exist in both phases as tautomeric equilibrium mixtures, where enol-imine forms are dominated structures. The positions of those equilibria only very slightly depend on substituents in phenol ring. Generally, the contributions of keto-amine forms in the solid state are higher comparing with DMSO solutions. (C) 2019 Published by Elsevier B.V.