Synthesis and Characterization of Chitosan-based Schiff Base Compounds with Aromatic Substituent Groups

Chitosan is the product of N-deacetylation of chitin. For its innocuous, renewable, biocompatible property chitosan is applied in many fields e.g., pharmaceutical, food, catalysis, material. In this work, three chitosan-based Schiff-based (CSB) compounds with aromatic substituent groups were synthesized from the reaction of chitosan with different aromatic aldehydes i.e., salicylaldehyde, 4-hexadecyloxy-2-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde. The chitosan-based Schiffbase copper (II) complexes (CSBCu) were subsequently obtained through the reaction of relative Schiff bases with copper acetate. These products were characterized by elementary analysis (EA), Fourier transform infrared (FTIR) spectroscopy, thermal analysis (TG-DSC, TG-DTA), and X-ray diffraction (XRD) spectra, respectively. Generally, elemental analysis data may confirm the formation of chitosan-Schiff base as well as the coordination reaction of CSB with copper ions. FTIR analysis indicated that Schiff base and coordination reaction take place in Schiff base skeleton. Moreover,with the difference in substituent groups and spacer, FTIR spectra showed the clear variety. Thermal analysis showed that the thermal stability of CSB increased slightly, while that of the copper complexes was reduced significantly in comparison with chitosan. The XRD results demonstrated the appearance of a new crystallization peak of CSB in the vicinity of five degree and the lower crystallinity of CSBCu. The differences in crystallinity and thermal stability are mainly attributed to the formation of Schiff base group and complexation with copper ions, as well as spatially partial hindrance and hydrophobic forces in the aromatic substituent groups. The present results show that the specific properties of chitosan-based Schiff base derivatives can be altered by modifying the molecular structures of objective compounds with proper substituent groups.