Reductive N-alkylation of chitosan with acetone and levulinic acid in aqueous media

Reductive N-alkylation with acetone and levulinic acid in the presence of sodium cyanoborohydride was applied to chitosan to prepare N-isopropyl and 5-methyl-pyrrolidinone chitosans, respectively. These chitosan derivatives were obtained quantitatively, and the highest degrees of substitution (DS) were achieved for chitosan solutions at the initial pH 4.5–5.0. When the molar ratio of the primary amino groups of chitosan, NaBH3CN and either acetone or levulinic acid was 1:10:3, reaction ratios at the primary amino groups reached about 100% and 41% for N-isopropyl and 5-methyl-pyrrolidinone chitosans, respectively, after the reaction at room temperature for 72 h. No depolymerization occurred on chitosan molecules under the reductive N-alkylation conditions used.