THERMAL-DECOMPOSITION OF MODEL COMPOUNDS RELATED TO BRANCHED 4-ORTHO-METHYLGLUCURONOXYLANS

Methyl glycosides of xylo-oligosaccharides (linear and branched) and 4-O-methyl-d-glucuronic acid-containing oligomers closely reflecting the main structural features of native xylans were studied by thermal analysis and pyrolysis-gas chromatography. The number of monomeric residues in the oligosaccharides was found to affect markedly the course of active thermal decomposition. The thermal stability increases with increasing number of monomeric residues, but the ratio of the 2-furaldehyde formed to 3-hydroxy-2-penteno-1,5-lactone remains almost constant, the latter compound being formed from both xylopyranosyl and 4-O-methyl-d-glucuronic acid non-reducing residues in the molecule. A considerable difference in the course of thermal decomposition was observed on comparing reducing sugars to their glycosides, and when an ionic dehydrating catalyst was added to the pyrolyzed sample. The results suggest that the 4-O-methyl-α-d-glucopyranosyluronic acid linkage is the most thermally stable linkage in native (4-O-methylglucurono)xylans, and that the acetyl groups do not significantly accelerate the thermal decomposition of the polysaccharide. © 1979.