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.

中文翻译：

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由果糖和葡萄糖形成5-羟甲基糠醛的机理研究

近年来，已经对果糖和葡萄糖向平台化学5-羟甲基糠醛（5-HMF）的转化进行了广泛的研究，并提出了多种机理。这篇综述总结了提出的各种机制以及用于研究生物质（例如果糖和葡萄糖）脱水以生成5-羟甲基糠醛的方法。对于果糖脱水，已经提出了两种主要机制，包括循环和非循环途径，其中循环途径占主导。葡萄糖向5-HMF的转化可以通过初始异构化为果糖或直接脱水进行。对于葡萄糖到果糖的异构化，已经提出了两个主要的反应途径（1,2-氢化物转移和烯醇化）。这篇综述讨论了基于实验和/或计算的证据所确定的机制，并简要介绍了此类机理研究中经常使用的技术。该领域的机理在很大程度上取决于所用溶剂和催化剂的性质，因此重要的是，在进行自身的机理研究之前，研究人员必须对现有的机理以及用于研究的方法和技术有一个总体的认识。