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, (M_n) weight average molecular weight (M_w) 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.