Sulfation of Xylan with Sulfamic Acid in N,N-Dimethylformamide

Sulfation of birch wood xylan by sulfamic acid in N,N-dimethylformamide (DMF) in the presence of urea was studied for the first time. The effect of the duration of sulfation of xylan with a mixture of sulfamic acid-urea in DMF on the yield and substitution degree of xylan sulfates was studied. The sulfur content in the samples was determined using a chemical method. It was found that the degree of substitution in the xylan sulfates was in the range from 1.30 to 1.64 with sulfation for 1-2 h. The structure of initial and sulfated xylan was investigated with the use of FTIR and C-13 NMR spectroscopy methods. The introduction of sulfate groups into the structure of xylan was confirmed by appearance in FTIR spectra new absorption bands characteristic for the stretching vibrations nu (C-O-S) at 804 cm(-1), symmetric stretching vibrations nu(s) (SO2) at 1009 cm(-1), asymmetric stretching vibrations nu(as) (SO2) at 1244 and 1260 cm(-1). Study of the C-13 NMR spectrum of the xylan sulfates showed that there was partial substitution of hydroxyl groups at C(2) and C(3) positions of anhydroxylose units of xylan.