Conversion of Glucose to 5-Hydroxymethylfurfural Using Consortium Catalyst in a Biphasic System and Mechanistic Insights

We found an effective catalytic consortium capable of converting glucose to 5-hydroxymethylfurfural (HMF) in high yields (50%). The reaction consists of a consortium of a Lewis acid (NbCl5) and a Brønsted acid (p-sulfonic acid calix[4]arene (CX4SO3H)), in a microwave-assisted reactor and in a biphasic system. The best result for the conversion of glucose to HMF (yield of 50%) was obtained with CX4SO3H/NbCl5 (5 wt%/7.5 wt%), using water/NaCl and MIBK (1:3), at 150 °C, for 17.5 min. The consortium catalyst recycling was tested, allowing its reuse for up to seven times, while maintaining the HMF yield constant. Additionally, it proposed a catalytic cycle by converting glucose to HMF, highlighting the following two key points: the isomerization of glucose into fructose, in the presence of Lewis acid (NbCl5), and the conversion of fructose into HMF, in the presence of CX4SO3H/NbCl5. A mechanism for the conversion of glucose to HMF was proposed and validated.