(51f) Kinetics and Insights into Glucose Dehydration Catalyzed By Homogeneous Lewis Acidic Metal Salts in Water

Dehydration of glucose catalyzed by various Lewis acidic metal salts was studied with water as reaction media. The glucose conversion kinetic profile was used to reflect the Lewis acid character of different metal ions. It was found that the pH value of the aqueous solution played an important role in controlling the Lewis activities. For the lanthanide chlorides, their Lewis acidity was comparable under the pH values studied (from 2.5 to 5.5). However, the Lewis acidity strength of other metal salts, such as aluminum chloride, showed dependence on the pH value of the solution. Activation energies with various Lewis acids were also calculated with both glucose and fructose to obtain more insight about the strength of the catalyst-substrate interaction as well as the dehydration reaction. The kinetic isotope effect with labeled glucose molecules was also studied to explore a more mechanistic understanding of the dehydration, which likely involves the 2-H atom of the glucose molecule in the transition state.