Abstract
The synthesis of 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) by hexoses and pentoses dehydration is considered as a promising path to produce materials from renewable resources. Low-transition-temperature mixtures (LTTMs) enable selective (>80%) dehydration of ketoses to furanic derivatives at moderate temperature (<100°C). However, aldoses dehydration generally requires higher temperatures and an isomerization catalyst. Chromium trichloride has been reported as one of the most efficient catalyst but its kinetic inertness could limit its performances below 100°C. Consequently, we investigate herein boric acid catalysis of aldoses dehydration in LTTMs based on choline halides and organic acids at 90°C. The limited activity of boric acid regarding furanic compounds synthesis (e.g., 5% 5-HMF yield and 23% glucose conversion after 1 h at 90°C with maleic acid) can be enhanced through tetrahydroxyborate esters (THBE) formation with α-hydroxyacids (e.g., 19% 5-HMF yield and 61% glucose conversion after 1 h at 90°C). THBE formation is however associated with H3O+ generation favoring the appearance of side products (humins). We demonstrate that boric acid catalysis is not straightforward and that the use of THBE under moderate acidity should be further investigated to limit humins formation and promote furanic derivatives synthesis.
Highlights
Synthesis of renewable platform chemicals from biomass carbohydrates is considered as a milestone in the development of an efficient use of renewable resources
Maleic acid is known to efficiently dehydrate D-fructose to 5-HMF (Istasse et al, 2018), this attempt did not lead to the appearance of 5-HMF from Dglucose and D-mannose or 2-F from D-arabinose
A similar reaction with monosaccharides seems likely to occur in mixtures of organic acids and choline chloride
Summary
Synthesis of renewable platform chemicals from biomass carbohydrates is considered as a milestone in the development of an efficient use of renewable resources Among these chemicals, 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F), resulting from the dehydration of hexoses (e.g., D-fructose, D-glucose) and pentoses (D-xylulose, D-xylose) respectively, receive particular attention (Rosatella et al, 2011; Van Putten et al, 2013b). 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F), resulting from the dehydration of hexoses (e.g., D-fructose, D-glucose) and pentoses (D-xylulose, D-xylose) respectively, receive particular attention (Rosatella et al, 2011; Van Putten et al, 2013b) Both platform chemicals possess numerous applications in material synthesis including plastics, thermoset resins, pharmaceuticals, and fuels (Rosatella et al, 2011; Eseyin and Steele, 2015). The use of ionic liquids (ILs) was studied in order to perform dehydration of monosaccharides to 5-HMF and 2-F at moderate temperature (100◦C) with high selectivity (>80%) (Moreau et al, 2006; Qi et al, 2008; Simeonov et al, 2012)
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