Synthesis and characterization of Schiff bases from chitosan and salicylaldehyde derivatives

The introduction of salicylaldehyde and derivatives at the C-2 nitrogen position of chitosan with low degree of acetylation has been investigated. Chitosan was reacted with salicylaldehyde and its 5-bromo, 5-chloro, 5-nitro, 5-methyl and 5-methoxy derivatives. The resulting biopolymeric Schiff bases were characterized by elemental analysis (C, H, N), IR spectroscopy, 1H NMR spectroscopy and conductimetric titration. The 1H NMR spectroscopy was used for the determination of degree of acetylation of chitosan. The degree of acetylation was determined from the ratio between the integrated area of the proton signal corresponding to the acetamido group (H-Ac) and that of the proton (H-2) of the GlucN unit. A procedure for the determination of the degree of substitution based on 1H NMR data is proposed. The substitution degree was calculated from the ratio between the integrated area of the proton signal of the imine group and of the proton (H-2) of the GlucN unit. Substitution degrees varying from 4.6 to 68.5% depending on the R group have been measured. No significant change on the acetylation degree during the reaction was observed.