N-Alkylations of chitosan promoted with sodium hydrogen carbonate under aqueous conditions

Chitosan was reacted with four alkyl halides, monobromoacetic acid, benzyl bromide, 2-bromoethanol, and monochloroacetic acid, in the presence of NaHCO3 in water. Chemical structures, degrees of substitution, and degrees of polymerization of reaction products were studied by FT-IR, NMR, SEC-MALLS, and elementary analyses. All alkyl groups were introduced selectively into the C2-amine groups of chitosan, and the yields of the N-alkyl chitosans were >90% by this method. N-Carboxymethyl chitosan (N-CMCh) and N-benzyl chitosan (N-BnCh) with high degrees of substitution (DS) up to 200% and 164% of the C2-amine groups, respectively, were obtained; N,N-dicarboxymethyl and N,N-dibenzyl chitosans were obtained in high yields. Degrees of polymerization (DP) of N-CMCh decreased during the reaction. The greater the amount of monobromoacetic acid added, the lower the DP of N-CMCh.