Selective mono-N-2-carboxyethylation of chitosan in the presence of magnesium halides

The solubility of chitosan in aqueous solutions of lithium and magnesium halides varies in the order: LiCl < LiBr < LiI; MgCl2 < MgBr2 < MgI2. A method for selective production of mono-N-(2-carboxyethyl)chitosan (NCE-chitosan) was developed by synthesis in gel (concentration of chitosan 4–20%) of the magnesium halides solution (1.1–3.5 M) using acrylic acid. Using for reaction of MgI2 or MgBr2 provides relative greater amount of the monosubstituted amino groups (73–87%) in comparison with their absence (50–70%) at the high degree of substitution (DS) more than 0.7. DS of the prepared NCE-chitosan and the ratios mono-:disubstitution of amino groups was determined by 1H NMR spectroscopy. The chemical structure of the obtained NCE-chitosan was characterized by FT-IR and 13C NMR spectroscopies.