# Selective and Tunable Routes for Glucose to Fructose Conversion Using MgCl2 Catalysis and Comparison to Other Metal Ions

## TL;DR

This study explores how MgCl2 can efficiently convert glucose to fructose in water, with control over reaction conditions to avoid unwanted side reactions.

## Contribution

The study introduces MgCl2 as a tunable and selective catalyst for glucose isomerization, with insights into competing reaction pathways and effects of pH and oxygen.

## Key findings

- MgCl2 catalyzes glucose to fructose isomerization with high selectivity under controlled pH and oxygen conditions.
- Isotope tracking reveals multiple competing pathways for the isomerization process.
- Mg2+ shows lower stereoselectivity compared to Al3+ and Cr3+ in glucose isomerization.

## Abstract

The conversion of glucose to fructose is an important step for the formation of biofuels, fine chemicals and in the food industries. Mg2+ 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 MgCl2 can be tuned using strategies that limit the presence of basic oxide. Upon calcination and reaction under N2, 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 Al3+ and Cr3+, the stereoselectivity is considerably lower for Mg2+ than for Al3+ and Cr3+. Effects of formic acid on the initial rate of glucose‐to‐fructose isomerization showed a slowing of the reaction catalyzed both by Mg2+, Al3+, and Cr3+. Inhibition decreased in this order, which resembles decreasing pKa 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 Mg2+ and carbohydrate results in a moderate stereoselectivity.

MgCl2 is a cheap catalyst for glucose to fructose conversion in water with excellent selectivity if competing pathways leading to C—C bond breakage avoided by control of pH and oxygen and use of mild temperatures. Both a stereoselective 1,2‐hydride shift and isomerization via an enediol intermediate contribute to the isomerization. Similarities and differences are discussed to Lewis acidic ions that are popular in sustainable chemistry.© 2026 WILEY‐VCH GmbH