Carboxyalkylation of chitosan in the gel state

This study presents a new approach for direct carboxyalkylation of chitosan in the gel state by using aza-Michael addition and substitution reactions. Various reagents were applied including acrylic and crotonic acids, and alpha-, beta-, gamma-, delta-, and epsilon-halocarboxylic acids. The reaction of chitosan with gamma- and delta-halocarboxylic acids showed no target product formation either in solution or in the gel state. In the case of acrylic, crotonic, alpha- and beta-halocarboxylic acids, the reaction performed in the gel state (concentration of chitosan 20-40%) shows higher degree of substitution at lower reaction time and temperature than in diluted solutions (concentration of chitosan 0.5-2%). The results were discussed in terms of kinetics of the target and side reactions. H-1 and C-13 NMR confirmed that in all cases the carboxyalkylation of chitosan proceeds exclusively at the amino groups. (C) 2012 Elsevier Ltd. All rights reserved.