5-Hydroxymethylfurfural (HMF) has become a benchmark chemical as it can be obtained by the processing of renewable biomass, making its downstream modification an important topic both in industry and academia. Finding catalytic processes for the selective derivatization of HMF is challenging due to its reactivity, hence mild conditions are needed. Here we report the selective oxidative esterification of HMF to methyl 5-(hydroxymethyl)furan-2-carboxylate and to dimethyl furan-2,5-dicarboxylate (FDCM) under mild conditions using oxygen (from air) as oxidant. A synergetic effect between the used catalysts, cobalt oxide over nitrogen-doped carbon, and ruthenium over carbon catalysts was observed by catalytic and electron paramagnetic resonance measurements. Kinetic analysis revealed a first order dependence on substrate for the cobalt catalyst and an apparent zero order for the ruthenium catalysts. The conversion rates were improved by the use of perfluoroether as solvent, proving that the oxygen diffusion is the limiting factor in the system.

中文翻译：

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温和条件下5-羟甲基糠醛的协同双金属氧化酯化

5-羟甲基糠醛（HMF）已成为基准化学品，因为它可以通过加工可再生生物质来获得，使其下游修饰成为工业界和学术界的重要课题。由于其反应性，寻找用于HMF选择性衍生化的催化方法是具有挑战性的，因此需要温和的条件。在这里，我们报道了在温和的条件下，使用氧气（来自空气）作为氧化剂，将HMF选择性氧化成5-（羟甲基）呋喃-2-甲酸甲酯和呋喃-2,5-二羧酸二甲酯（FDCM）的选择性氧化酯化反应。通过催化和电子顺磁共振测量，观察到了所用催化剂，氮掺杂碳上的氧化钴和碳催化剂上的钌之间的协同作用。动力学分析显示钴催化剂对底物的第一级依赖性和钌催化剂的表观零级依赖性。通过使用全氟醚作为溶剂提高了转化率，证明了氧扩散是系统中的限制因素。