The synthesis and properties of oligosalicylaldehyde and its Schiff base oligomers

The products and oxidative polycondensation reaction conditions of salicylaldehyde (SA) with air oxygen and sodium hypochloride (NaOCl) were studied. In this reaction, NaOCl was observed to be more active than O2 and their optimum reaction conditions were determined. Oligosalicylaldehyde (OSA) was synthesized from the oxidative polycondensation of SA with air and NaOCl in an aqueous alkaline medium between 85 and 100°C. The products were characterized by 1H-NMR, FT-IR, UV–Vis and elemental analysis. The number average molecular weight, mass average molecular weight and polydispersity index values of OSA synthesized at medium NaOCl and O2 were found to be 3700, 5990 g mol−1, 1.62 and 1690, 5150 g mol−1, 3.05, respectively. At the optimum reaction conditions, the yield of the reaction products were found to be 65.5% (O2) and 71.4% (NaOCl). About 80% SA was converted to OSA. TG analyses showed OSA to be resistant to thermo-oxidative decomposition. The weight loss of OSA were found to be 5, 50 and 89% at 217, 587 and 1000°C, respectively. Also, new oligomeric Schiff bases were synthesized from condensation of OSA with aniline, p-toluidine and p-nitroaniline and their the structures and properties were determined.