Differentiation of the Coordination Chemistry of Metal Chlorides in Catalytic Conversion of Glucose in Ionic Liquids

Abstract

Catalytic aldose isomerization to ketose is an important reaction for the utilization of cellulosic biomass. However, a fundamental understanding and knowledge base involved in this reaction remains lacking in the literature. In this chapter, we provide a focused review of the most studied solvent-based catalytic system involving metal halides for glucose isomerization to fructose and further to 5-hydroxymethhylfurfral (5-HMF). Results from studies by different physical techniques are critically reviewed. A differentiation of the coordination chemistry of different metal chlorides obtained by various physical techniques is established to rationalize the drastically different catalytic pathways by the metal chloride catalysts. The performance of metal chloride catalysts for the isomerization of aldose to ketose is found to correlate with their coordination chemistry. Solvents play an important role in determining the coordination structures for the metal ions, which critically affect the catalysis of the metal chloride precursors. Undesired side products are related to the reaction pathways corresponding to the nature of the coordination of metal ions with different oxygen sources in the substrates and the products.