Synthesis and characterization of oligo‐2‐hydroxy‐1‐naphthaldehyde and its Schiff base oligomers

Abstract

AbstractIn this study, oligo‐2‐hydroxy‐1‐naphthaldehyde (OHNA) was synthesized from the oxidative polycondensation of 2‐hydroxy‐1‐naphthaldehyde (HNA) with air oxygen, NaOCl, and H2O2 in an aqueous alkaline medium at 50–95°C. We determined the products and the oxidative polycondensation reaction conditions of HNA with oxidants such as air oxygen, NaOCl, and H2O2. In these reactions, H2O2 was more active than air oxygen and NaOCl and their optimum reaction conditions were studied. The products were characterized by 1H‐NMR, FTIR, UV–visible, and elemental analysis. The respective number‐average molecular weight, mass‐average molecular weight, and polydispersity index values of OHNA and its Schiff base oligomers (compounds 1, 2, and 3) were found to be 500 g mol−1, 1880 g mol−1, and 3.75 for OHNA; 670 g mol−1, 2490 g mol−1, and 3.71 for compound 1; 390 g mol−1, 1080 g mol−1, and 2.77 for compound 2; and 320 g mol−1, 670 g mol−1, and 1.85 for compound 3. At the optimum reaction conditions, the yields of the reaction products were found to be 77.0% O2, 78.0% H2O2, and 75.4% NaOCl. About 80% of the HNA was converted into OHNA. In addition, new Schiff based oligomers were synthesized from the condensation reaction of OHNA with p‐aminophenol, triethyleneglycol bis(4‐aminophenyl ether), and aniline and their structures and properties were determined. Thermogravimetric and dynamic thermal analyses showed OHNA and its Schiff base oligomers to be stable against thermooxidative decomposition. The weight losses of OHNA and its Schiff base oligomer compounds 1, 2, and 3 were found to be 5% at 175, 225, 190, and 230°C, respectively; 50% at 900, 590, 650, and 620°C, respectively; and 60, 80, 85, and 82%, respectively, at 1000°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 442–450, 2003