Kinetics of glucose dehydration catalyzed by homogeneous Lewis acidic metal salts in water

• Different homogeneous Lewis acid salts compared in glucose dehydration.
• Lewis acid activity impacted by solution pH.
• Water compatible Lewis acids active at higher pH values.
• Lewis acid activity correlated with cation size within groups.
• Lewis acids impacted selectivity of fructose dehydration.

Glucose dehydration catalyzed by various Lewis acid metal salts was studied in a biphasic reaction system. The glucose conversion kinetic profile was used to examine the importance of the Lewis acid character for the different metal ions. It was found that the pH value of the aqueous solution played an important role in controlling the Lewis acid activities. For lanthanide chlorides, their Lewis acidities were comparable under the pH values from 2.5 to 5.5. However, the Lewis acid strength of other metal salts, such as aluminum chloride, showed a strong dependence on the solution pH. Apparent activation energies for the Lewis acid salts were calculated for glucose conversion to examine their dependence on the Lewis acid metal salt. Fructose dehydration experiments with the catalyst systems demonstrated that Lewis acids played a role in the dehydration reaction through accelerating fructose conversion but diminishing selectivity to the desired 5-hydroxymethylfurfural (HMF) product.

Homogeneous Lewis acid salt relative activity for glucose conversion.Figure optionsDownload high-quality image (76 K)Download as PowerPoint slide