Production of 5‐hydroxymethylfurfural from D‐fructose in low‐transition‐temperature mixtures enhanced by chloride anions and low amounts of organic acids

The research for 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 promote 5‐HMF formation which seem 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 LTTMs biodegradability. 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 allowing to achieve an 80% 5‐HMF molar yield in 1h at 90°C.