INTRAMOLECULAR PROTON TRANSFER EQUILIBRIUM IN SALICYLIDENE- AND NAPHTHALENE-BASED TETRAIMINE SCHIFF BASES

Abstract

In this work, two nitro-Schiff bases were synthesized by condensation reaction of 4-nitro-benzaldehyde with p-phenylenediamine and 3-amino-2-naphthol in 2:1 and 1:1 ratios, respectively. Then, asymmetric tetraimine Schiff bases (L-1, L-2, L-3) were prepared by the reduction of nitro group to amino group with sodium dithionite and adding aldehyde, such as salicylaldehyde, 2-hydroxy-1-naphthaldehyde or terephthaldehyde. Tetraimines have been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV–vis, and mass spectroscopy techniques in order to study the structure effect on the phenol-keto tautomerism. Solvent, acid and base effects on the tautomeric equilibrium have been also investigated by using UV–vis spectra.