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

Area of Science:

• Biomimetic catalysis
• Green chemistry
• Carbohydrate chemistry

Background:

• Glucose-to-fructose isomerization is crucial for biofuels, fine chemicals, and food industries.
• Magnesium (Mg2+) is abundant and a potential environmentally friendly biomimetic catalyst for this reaction in water.
• Understanding Mg2+ catalysis is relevant to prebiotic chemistry and sustainable chemical synthesis.

Purpose of the Study:

• To investigate and optimize the catalytic performance of magnesium chloride (MgCl2) for glucose isomerization to fructose in water.
• To explore the reaction pathways and stereoselectivity of Mg2+ catalysis compared to other metal ions.
• To understand the role of metal ion hydrolysis and interactions in the catalytic mechanism.

Main Methods:

• Catalytic conversion of glucose to fructose in water using MgCl2 under optimized conditions (calcination, N2 atmosphere).
• Isotope tracking to elucidate reaction pathways.
• Comparative studies with Al3+ and Cr3+ to assess stereoselectivity.
• Kinetic analysis using formic acid to probe the catalytic mechanism and active species.

Main Results:

• Optimized MgCl2 catalysis achieved near-thermodynamic equilibrium (≈42% fructose) within 30 minutes at 120°C in water.
• Isotope tracking revealed competing pathways for glucose isomerization.
• Mg2+ exhibited lower stereoselectivity compared to Al3+ and Cr3+.
• Formic acid inhibited the reaction catalyzed by Mg2+, Al3+, and Cr3+, with inhibition decreasing in order of decreasing pKa values, suggesting hydrolysis generates active species.

Conclusions:

• Tuned MgCl2 demonstrates efficient and rapid glucose isomerization to fructose in water, offering a sustainable catalytic approach.
• The catalytic mechanism involves metal ion hydrolysis generating active species and transient carbohydrate interactions, leading to moderate stereoselectivity for Mg2+.
• Mg2+ catalysis provides a viable, environmentally friendly alternative for industrial glucose-fructose conversion.