Kinetic and Mechanistic Study of Glucose Isomerization Using Homogeneous Organic Brønsted Base Catalysts in Water,ACS Catalysis

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Kinetic and Mechanistic Study of Glucose Isomerization Using Homogeneous Organic Brønsted Base Catalysts in Water
ACS Catalysis ( IF 11.3 ) Pub Date : 2015-04-23 00:00:00 , DOI: 10.1021/acscatal.5b00316
Jack M. Carraher _{1,

2} , Chelsea N. Fleitman _{1,

2} , Jean-Philippe Tessonnier _{1,

2}

Affiliation

The isomerization of glucose to fructose represents a key intermediate step in the conversion of cellulosic biomass to fuels and renewable platform chemicals, namely, 5-hydroxymethyl furfural (HMF), 2,5-furandicarboxylic acid (FDCA), and levulinic acid (LA). Although both Lewis acids and Brønsted bases catalyze this reaction, the base-catalyzed pathway received significantly less attention due to its lower selectivity to fructose and the poor yields achieved (<10%). However, we recently demonstrated that homogeneous organic Brønsted bases present a similar performance (∼31% yield) as Sn-containing beta zeolite, a reference catalyst for this reaction. Herein, we report on the first extensive kinetic and mechanistic study on the organic Brønsted base-catalyzed isomerization of glucose to fructose. Specifically, we combine kinetic experiments performed over a broad range of conditions (temperature: 80–120 °C; pH 9.5–11.5; reactant: glucose, fructose) with isotopic studies and in situ ¹H NMR spectroscopy. Pathways leading to isomerization and degradation of the monosaccharides have been identified through careful experimentation and comparison with previously published data. Kinetic isotope effect experiments were carried out with labeled glucose to validate the rate-limiting step. The ex situ characterization of the reaction products was confirmed using in situ ¹H NMR studies. It is shown that unimolecular (thermal) and bimolecular (alkaline) degradation of fructose can be minimized independently by carefully controlling the reaction conditions. Fructose was produced with 32% yield and 64% selectivity within 7 min.

中文翻译：

均相有机布朗斯台德碱催化剂在水中进行葡萄糖异构化的动力学和机理研究

葡萄糖异构化为果糖代表了纤维素生物质向燃料和可再生平台化学品（即5-羟甲基糠醛（HMF），2,5-呋喃二甲酸（FDCA）和乙酰丙酸（LA））转化过程中的关键中间步骤。。尽管路易斯酸和布朗斯台德碱均催化该反应，但由于其对果糖的选择性较低且收率较低（<10％），因此碱催化的途径受到的关注明显较少。但是，我们最近证明，均匀的有机布朗斯台德碱具有与含锡β沸石（该反应的参考催化剂）相似的性能（约31％的收率）。在本文中，我们报道了有机布朗斯台德碱催化葡萄糖异构化为果糖的首次广泛的动力学和机理研究。具体来说，¹ H NMR光谱。通过仔细的实验并与先前发表的数据进行比较，已经确定了导致单糖异构化和降解的途径。用标记的葡萄糖进行了动力学同位素效应实验，以验证限速步骤。使用原位¹ H NMR研究证实了反应产物的异位表征。结果表明，通过小心地控制反应条件，可以独立地使果糖的单分子（热）和双分子（碱性）降解最小化。在7分钟内以32％的收率和64％的选择性产生果糖。

更新日期：2015-04-23

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