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Metal-Free Dehydration of Glucose to 5-(Hydroxymethyl)furfural in Ionic Liquids with Boric Acid as a Promoter

Authors

  • Tim Ståhlberg,

    1. Centre for Catalysis and Sustainable Chemistry, Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
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  • Dr. Sergio Rodriguez-Rodriguez,

    1. Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
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  • Prof. Peter Fristrup,

    Corresponding author
    1. Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
    • Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
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  • Prof. Anders Riisager

    Corresponding author
    1. Centre for Catalysis and Sustainable Chemistry, Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
    • Centre for Catalysis and Sustainable Chemistry, Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark)
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Abstract

The dehydration of glucose and other hexose carbohydrates to 5-(hydroxymethyl)furfural (HMF) was investigated in imidazolium-based ionic liquids with boric acid as a promoter. A yield of up to 42 % from glucose and as much as 66 % from sucrose was obtained. The yield of HMF decreased as the concentration of boric acid exceeded one equivalent, most likely as a consequence of stronger fructose–borate chelate complexes being formed. Computational modeling with DFT calculations confirmed that the formation of 1:1 glucose–borate complexes facilitated the conversion pathway from glucose to fructose. Deuterium-labeling studies elucidated that the isomerization proceeded via an ene–diol mechanism, which is different to that of the enzyme-catalyzed isomerization of glucose to fructose. The introduced non-metal system containing boric acid provides a new direction in the search for catalyst systems allowing efficient HMF formation from biorenewable sources.

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