Reductive N-alkylation of chitosan with acetone and levulinic acid in aqueous media
1Graduate School of Agricultural and Life Sciences, The University of Tokyo, Biomaterial Sciences, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Abstract:
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, NaBH(3)CN 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 72h. No depolymerization occurred on chitosan molecules under the reductive N-alkylation conditions used.
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