Synthesis of Birch Wood Xylan Sulfate in the Sulfamic Acid–Urea Melt

A green method for the synthesis of xylan sulfates in the sulfamic acid–urea melt has been proposed for the first time. This method excludes the use of harmful and dangerous solvents (pyridine and DMSO) and aggressive reagents (chlorosulfonic acid and SO₃-pyridine complexes) in the reaction process. The synthesis time is reduced to 30 min.

Abstract

The synthesis of polysaccharide sulfates without harmful solvents used is a serious environmental problem. A method for the synthesis of xylan sulfate using the sulfamic acid–urea melt as a sulfating agent without solvents is proposed. The melt is prepared by heating the sulfamic acid–urea mixture with a molar ratio of 1 : 1 at a temperature of 110 °C. This ratio allows significant reduction of side reactions, in particular, carbamation of xylan. Sulfation is carried out at temperatures of 110,115, 120, 125, and 130 °C. The maximum yield and degree of substitution (DSsulfate 1.40) are attained at atemperature of 115 °C. The proposed method makes it possible to synthesize xylan sulfate rapidly (for 0.5 h) and without contamination of the obtained product with toxic solvents, e. g., dimethyl sulfoxide, pyridine, etc. The composition and structure of initial and sulfated xylan are confirmed by FTIR, NMR, GC, and elemental analysis.

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