Synthesis and characterization of Schiff bases from chitosan and salicylaldehyde derivatives Jose ´ E. dos Santos a,1 , Edward R. Dockal a ,E ´ der T.G. Cavalheiro b, * a Departamento de Quı ´mica, Universidade Federal de Sa ˜o Carlos, Via Washington Luiz, Km 235, 13565-905 Sa ˜o Carlos, SP, Brazil b Departamento de Quı ´mica e Fı ´sica Molecular, Instituto de Quı ´mica de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Avenida do Trabalhador Sa ˜o-Carlense, 400, 13566-590 Sa ˜o Carlos, SP, Brazil Received 28 May 2004; revised 14 December 2004; accepted 19 December 2004 Available online 7 April 2005 Abstract 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, 1 H NMR spectroscopy and conductimetric titration. The 1 H 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 1 H 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. q 2005 Elsevier Ltd. All rights reserved. Keywords: Chitosan; Schiff bases; Degree of substitution 1. Introduction Chitosan is the N-deacetylated derivative of chitin, although this N-deacetylation is almost never complete (Matteus, 1997). Chitin is the most important natural polysaccharide after cellulose, and is found in crustacean shells or in fungi cell walls. The term chitosan is usually used when the polymers become soluble in a dilute acid solution. The solubility is also controlled by the distribution of the acetyl groups remaining along the chain (Matteus, 1997). This biopolymer has applications ranging from cosmetics, artificial skin, photography, food and nutrition, ophthalmology and wastewater treatment (Narang,1990; Ravi-Kumar, 2000). The chitosan is insoluble in water, but it dissolves in aqueous solutions of organic acids as acetic, formic, citric, besides inorganic acids, as diluted hydrochloric acid resulting in viscous solutions. (Rinaudo; Pavlov, & Des- brie ´res, 1999). It is well known that some of the structural characteristics such as degree of acetylation (DA) and molecular weight controlled the solubility the in chitosan. The determination of the DA of chitosan has been largely discussed in the literature. The main techniques suggested for this determination are conductimetric titration, infrared spectroscopy, 1 H NMR, HPLC, thermal analysis, and others (Jiang, Chen, & Zhong, 2003; Raymond, Morin & Marchessault, 1993). The presence of amminic groups in the polymeric chain leads to the possibility of a several chemical modifications, including the preparation of Schiff bases by reaction with aldehydes and ketones (Moore & Roberts, 1981; Muzzarelli, Jeunieux, & Gooday, 1985). The reaction of chitosan with aromatic aldehydes in acetic acid to produce the corresponding Schiff bases has 0144-8617/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2004.12.008 Carbohydrate Polymers 60 (2005) 277–282 www.elsevier.com/locate/carbpol * Corresponding author. Tel.: C55162738054; fax: C55162739987. E-mail address: cavalheiro@iqsc.usp.br (E ´ .T.G. Cavalheiro). 1 Permanent address: Universidade Federal de Campina Grande, DCEN, Campus II, Cajazeiras, PB, Brazil.