Synthesis, characterization and optimum reaction conditions of oligo-2-amino-3-hydroxypyridine and its Schiff base oligomer

The oxidative polycondensation reaction conditions of 2-amino-3-hydroxypyridine (AHP) and 2-[benzilydeneimino] pyridine-3-ol (BIP) were studied by oxidants such as with air O2, NaOCl and H2O2. Oligo-2-amino-3-hydroxypyridine (OAHP) was synthesized from the oxidative polycondensation of AHP with air O2, NaOCl and H2O2 in an aqueous acidic and alkaline medium at 30–90 °C. BIP was synthesized from condensation of 2-amino-3-hydroxypyridine with benzaldehyde. Oligo-2-[benzilydeneimino] pyridine-3-ol (OBIP) was synthesized from the oxidative polycondensation of BIP with air O2, NaOCl and H2O2 in an aqueous alkaline medium at 40–90 °C. About 95% BIP was converted to OBIP. The number average molecular weight, (Mn) weight average molecular weight (Mw) and polydispersity index (PDI) values of OAHP and OBIP (for air O2 oxidant) were found to be 1433, 1912 g mol−1, 1.33 and 2637, 5106 g mol−1 and 1.94, respectively. At the optimum reaction conditions, the yield of OAHP was found to be 86.0% (for air O2 oxidant), 43.0% (for H2O2 oxidant) and 85.0% (for NaOCl oxidant). At the optimum reaction conditions, the yield of OBIP was found to be 91.0% (for air O2 oxidant), 92.0% (for H2O2 oxidant) and 95.0% (for NaOCl oxidant). The OHAP and OBIP were characterized by FT-IR, UV–Vis, 1H and 13C-NMR elemental analysis. TG and DTA analyses were shown to be unstable of OAHP and OBIP against thermo-oxidative decomposition. According to TG analyses, the weight loss of OAHP and OBIP was found to be 97.35 and 96.60% at 520 and 685 °C, respectively.