Mechanistic studies on the formation of 5-hydroxymethylfurfural from the sugars fructose and glucose

Abstract In recent years the transformations of fructose and glucose to the platform chemical 5-hydroxymethylfurfural (5-HMF) have been studied extensively, and a variety of mechanisms have been proposed. This review summarizes the varied mechanisms proposed and methods used to study the dehydration of biomass, such as fructose and glucose, to give 5-hydroxymethylfurfural. For fructose dehydration, two main mechanisms have been suggested including a cyclic and an acyclic pathway, of which the cyclic pathway dominates. The conversion of glucose to 5-HMF can proceed either through initial isomerization to fructose or a direct dehydration. For glucose to fructose isomerization, two main reaction pathways have been proposed (1,2-hydride shift and enolization). This review discusses the mechanisms that have been determined based on the evidence from experiments and/or calculations, and briefly introduces the techniques frequently used in such mechanistic studies. Mechanisms in this field are strongly dependent on the nature of the solvent and the catalyst used, so it is important that researchers have a general idea about the existing mechanisms, and the methods and techniques used for investigation, before pursuing their own mechanistic studies.