Mechanisms and Energetics for Brønsted Acid-Catalyzed Glucose Condensation, Dehydration and Isomerization Reactions
The mechanisms and energetics for Bronsted acid-catalyzed glucose condensation, dehydration and isomerization reactions were discussed based on our earlier CPMD–MTD simulation results. Glucose condensation reaction is initiated by the protonation of C1–OH, whereas both dehydration and isomerization reactions are initiated by the protonation of C2–OH to form a common 5-member ring intermediate. Glucose dehydration to form HMF occurs via the direct cyclic mechanism, rather than via the open chain mechanism converting glucose to fructose then to HMF. Fructose is formed via a 1,2 hydride shift process following the formation of 5-member ring intermediate. The barriers for Bronsted acid-catalyzed glucose reactions are largely solvent induced due to the competition for proton from the solvent molecules.