Selective and Tunable Routes for Glucose to Fructose Conversion Using MgCl ₂ Catalysis and Comparison to Other Metal Ions

The conversion of glucose to fructose is an important step for the formation of biofuels, fine chemicals and in the food industries. Mg 2+ is the most abundant divalent cation in living cells and sea water and could be an environmentally friendly biomimetic catalysts for glucose‐to‐fructose isomerization in water, while holding relevance to prebiotic chemistry. Here, we demonstrate that the catalytic performance of MgCl 2 can be tuned using strategies that limit the presence of basic oxide. Upon calcination and reaction under N 2 , glucose isomerization in water at 120°C approached the thermodynamic equilibrium (≈42% fructose) within 30 minutes. Isotope tracking showed that the isomerization proceeds via competing pathways. Compared to Al 3+ and Cr 3+ , the stereoselectivity is considerably lower for Mg 2+ than for Al 3+ and Cr 3+ . Effects of formic acid on the initial rate of glucose‐to‐fructose isomerization showed a slowing of the reaction catalyzed both by Mg 2+ , Al 3+ , and Cr 3+ . Inhibition decreased in this order, which resembles decreasing p K a values of the metal ions in aqueous solution. Hydrolysis of aqua ions appears to generate active species for the 1,2‐hydride shift in all cases, where the formation of transient and non‐specific interactions between Mg 2+ and carbohydrate results in a moderate stereoselectivity.