The Role of Salts and Bronsted Acids in Lewis Acid-Catalyzed Aqueous-Phase Glucose Dehydration to 5-Hydroxymethylfurfural

The effect of salts and BrOnsted acids on the Lewis acid (CrCl(3)6H(2)O)-catalyzed glucose dehydration to 5-hydroxymethylfurfural (HMF) in aqueous media are described. We show that the reaction with bromide salts in place of chlorides leads to higher HMF yields. The influence of salts can be attributed to the anions in solution, specifically to the bromide anions enhancing the fructose dehydration step. Additionally, we demonstrate that the reaction kinetics are governed strongly by acidity. Although the fructose dehydration step is accelerated by the addition of BrOnsted acids, even on a catalytic scale, a significant retardation of the glucose conversion rate results in a substantial drop in HMF yields. The suppression in glucose-to-fructose isomerization rate with increasing acidity is ascribed to the restrained formation of the chromium-glucose chelate complex during the reaction.