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

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.