Thermal decomposition mechanism of O-acetyl-4-O-methylglucurono-xylan

O-acetyl-4-O-methylglucurono-xylan is selected as a model compound because of its abundant O-acetyl and 4-O-methylglucuronic acid groups as side chains of hemicellulose. The detailed decomposition pathways of O-acetyl-4-O-methylglucurono-xylan are investigated by using density functional theory (DFT) and transition state theory. In addition, the possible pyrolysis pathways of 4-O-methylglucuronic acid, based on the Mayer bond order values, are predicted. The results indicate that the most energetically favored initial reaction of O-acetyl-4-O-methylglucurono-xylan is the cleavage of the 4-O-methylglucuronic acid unit. Furfural can be obtained through the ring-opening of 4-O-methylglucuronic acid in three different pathways. The O-methyl group is predominantly responsible for the generation of CH3OH. In addition, the formation pathways of a special furan-derived product 2-hydroxymethylene-tetrahydrofuran-3-one are first validated by DFT calculation. The rate-determining steps to form 2-hydroxymethylene-tetrahydrofuran-3-one are the cyclization reaction and enol–keto tautomerization. Anhydroxylopyranose and dianhydroxylopyranose can be produced through intramolecular dehydration and glycosidic bond cleavage reactions.