Carboxymethyl xylan—synthesis and detailed structure characterization

The synthesis of carboxymethyl xylan (CMX) applying different procedures and various slurry media (ethanol/toluene, ethanol, 2-propanol) is studied. The procedures for activation used are (i) suspending of the xylan in the slurry medium followed by the addition of the NaOH solution as usually applied for polysaccharides, and (ii) dissolving the xylan in NaOH solution followed by the addition of the slurry media. The highest DS obtained in a one-step reaction was 1.22 applying activation (ii) and 2-propanol as slurry medium. In any case, the application of 2-propanol gives products of highest DS compared to ethanol and ethanol/toluene as slurry media. The DS values and the pattern of substitution were characterized by 1H NMR spectroscopy and HPLC after acidic depolymerization. The substitution reaction starts at position 2 as revealed by 1H NMR spectroscopic measurements. As indicated by the HPLC studies, a reaction after activation (i) yields products with a non-statistic content of the different repeating units (un-, mono-, and di-substituted), while procedure (ii) give statistically functionalized CMX samples.