Primary reactions of sucrose thermal degradation

Abstract

Thermal degradation of sucrose at 185 °C in a closed glassware and presence of air was studied with the help of GC/MS after acetylation of reaction products. Also model compounds were used to support the mechanism of thermolysis. Goal was to identify all the primary reactions of the process. It was observed that already after 5 min of treatment, two glucopyranose isomers were formed as products of sucrose glycosidic bond splitting. The furanose structure is probably transformed to anhydrofructoses, as 2,6-anhydrofructose was identified among the degradation products in much smaller amount than d-glucose. At longer thermolysis times some diastereoisomers of sucrose, anhydrosucroses, and anhydroderivatives of monosaccharides were identified as minor products of parallel primary and secondary reaction. After 30 min at 185 °C there was no sucrose present in the reaction mixture, but some new products with longer retention times (RT) occurred. Also isomers of levoglucosan were observed after 1 h of treatment. This indicates that splitting of glycosidic bond is the most prominent primary reaction. The dehydration towards anhydrosucroses seams to be a minor primary reaction and might proceed via configuration changes on the pyranose ring.