Synthesis of 5-hydroxymethylfurfural from glucose in a biphasic medium with AlCl3 and boric acid as the catalyst

In combination with non-corrosive and low-toxic boric acid, AlCl3 · 6H2O was found to be effective for the synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose. In this work, a 5-HMF yield of ≈ 60 % was obtained at 170°C for 40 min in a H2O/THF biphasic solvent mixture. An addition of NaCl not only improved the partition coefficients but also inhibited by-product formation. THF was identified as an ideal extraction solvent in biphasic systems containing C4 solvents. However, low concentration of ZnCl2, CoCl2 · 6H2O, MnCl2 · 4H2O, NiCl2 · 6H2O, FeCl3 · 6H2O were not suitable for the catalyst system, while ZrOCl2 · 8H2O, InCl3 · 4H2O showed high activity for the reaction. Boric acid increased the amount of Lewis acid sites in the reactive phase and enhanced the isomerization of glucose to fructose. A mechanism of the AlCl3 · 6H2O and boric acid catalyzed glucose dehydration reaction was proposed to proceed through the isomerization of glucose to fructose followed by the transformation of fructose to 5-HMF.