Homogeneous catalyst mediated glucose mutarotation studies using vibrational spectroscopy

The pitfalls of overdependence on fossil fuels are well documented. Current research aims to focus on biomass obtained from renewable cellulose for the production of fuels and chemicals. In that regard, with cellulose as source, 5-hydroxymethylfurfural (HMF) is a versatile platform chemical for the production of chemicals like levulinic acid. The isomerization of glucose to fructose is one of the steps in the synthesis of HMF from cellulose. Glucose exists in several anomeric forms and it has been shown that the isomerization reaction is anomer specific. This work focuses on the study of mutarotation in glucose in the presence of homogeneous Lewis acid catalysts. A combination of spectroscopic tools: ATR-IR and Raman spectroscopy are used to study the vibrational modes of glucose in aqueous solution. At room temperature, changes in vibrational modes can be attributed to the mutarotation reaction. This work compares the rate of mutarotation in different concentrations of AlCl3, CrCl3 and SnCl4. The influence of metal salts in solution, pH and ionic strength were also probed by comparing with the rates obtained in Brönsted acids. The mutarotation in Lewis acid is faster than that in water. It is fastest in SnCl4 and increases with increase in concentration of SnCl4. Results also indicate a lack of glucose-Lewis acid interactions. However, rates vary depending on the nature of metal salts in solution indicating that the mutarotation is influenced by the nature of Lewis acid-water interactions.