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

Abstract

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 ¹³C 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 ν (C–O–S) at 804 cm^–1, symmetric stretching vibrations ν_s (SO₂) at 1009 cm^–1, asymmetric stretching vibrations ν_as (SO₂) at 1244 and 1260 cm^–1. Study of the ¹³C NMR spectrum of the xylan sulfates showed that there was partial substitution of hydroxyl groups at С(2) and С(3) positions of anhydroxylose units of xylan.