The synthesis and characterization of oligo-N-4-aminopyridine, oligo-2-[(pyridine-4-yl-imino) methyl] phenol and its some oligomer–metal complexes

Abstract

The product and the oxidative polycondensation reaction conditions of oligo-4-aminopyridine were studied by using NaOCl as oxidant. Oligo-4-aminopyridine (4-OAP) was synthesized from the oxidative polycondensation of 4-aminopyridine (4-AP) in an aqueous solution medium acidic and neutral between 25 and 60 °C by using NaOCl as oxidant. About 85% of 4-AP was converted to 4-OAP. The number average molecular weight, ( M n) mass average molecular weight ( M w) and polydispersity index (PDI) values of 4-OAP synthesized were found to be 270, 850 g mol −1 and 3.15, respectively, using NaOCl. The respective values of the Schiff base were 1721, 2256 g mol −1 and 1.31, respectively, using air oxygen and 2173, 2372 g mol −1 and 1.09, respectively, using NaOCl and 2749, 6432 g mol −1 and 2.33, respectively, using H 2O 2. At the optimum reaction conditions, the yield of oligo-2-[(pyridine-4-yl-imino) methyl] phenol (OPMP) were found to be 86% (H 2O 2) and 89% (NaOCl) and 95% (air oxygen). The 4-OAP and OPMP were characterized by 1H NMR, FT-IR, UV–Vis and elemental analysis. TG analysis showed to be stable of 4-OAP against thermo-oxidative decomposition. The weight loss of 4-OAP and its Schiff base oligomer was found to be 50, 86.39 and 71.78% at 525, 625 and 1000 °C, respectively. Also, new oligomeric Schiff base was synthesized from condensation of 4-AP with salicylaldehyde and their structures and properties were determined. During polycondensation reaction, a part of the azomethine (–CHN–) groups oxidized to carboxylic (–COOH) group. Thus, soluble fraction in water of oligo-2-[(pyridine-4-yl-imino) methyl] phenol involved in carboxylic (–COOH) (11%) group. Besides, the structure and properties of oligomer–metal complexes of oligo-2-[(pyridine-4-yl-imino) methyl] phenol (OPMP) with Cu(II), Ni(II) and Co(II) were studied.