The use of safe and sustainable solvents able to solvate reagents and to catalyze their reactions at temperatures below 100 °C is an innovative strategy to develop future lignocellulosic biorefineries. Many low-transition-temperature mixtures (LTTMs) have been investigated for this purpose. Among them, natural deep eutectic solvents (NADESs) have been proposed as cheap and renewable alternatives to ionic liquids for the synthesis of bio-based chemical building blocks. We compare herein the ability of several organic acids/choline chloride/water LTTMs to perform D-fructose dehydration to 5-hydroxymethylfurfural (5-HMF). The addition of chloride salts as well as an increased proportion of choline chloride promotes 5-HMF formation, which seems to indicate a beneficial effect of chloride anions on D-fructose dehydration. Besides improving selectivity by at least 10 %, increasing the choline chloride/acid ratio could enhance the biodegradability of the LTTMs. Unlike other acidic components, maleic and citric acids are especially selective at early D-fructose conversion. Maleic acid was the most selective acidic component among the tested chemicals, achieving an 80 % 5-HMF molar yield in 1 h at 90 °C.

中文翻译：

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在由氯离子和少量有机酸增强的低转变温度混合物中，由D-果糖生产5-羟甲基糠醛。

使用安全且可持续的溶剂能够溶解试剂并在低于100°C的温度下催化其反应是开发未来木质纤维素生物精炼厂的创新策略。为此，已经研究了许多低转变温度的混合物（LTTM）。其中，已提出天然深共晶溶剂（NADES）作为离子液体的廉价且可再生的替代品，用于合成生物基化学构件。我们在本文中比较了几种有机酸/氯化胆碱/水LTTM进行D-果糖脱水成5-羟甲基糠醛（5-HMF）的能力。氯化物盐的添加以及胆碱氯化物比例的增加促进了5-HMF的形成，这似乎表明氯化物阴离子对D-果糖脱水的有益作用。除了将选择性提高至少10％，增加胆碱氯化物/酸的比率还可以增强LTTM的生物降解能力。与其他酸性成分不同，马来酸和柠檬酸在早期D-果糖转化过程中尤其具有选择性。在测试的化学品中，马来酸是最有选择性的酸性组分，在90°C的1小时内达到80％的5-HMF摩尔产率。