Biobased Chemicals\nfrom d‑Galactose:\nAn Efficient Route to 5‑Hydroxymethylfurfural Using a Water/MIBK\nSystem in Combination with an HCl/AlCl<sub>3</sub> Catalyst

5-Hydroxymethylfurfural\n(HMF) is an attractive building block for\nbiobased chemicals. Typically, ketoses like d-fructose (FRC)\nare suitable starting materials and give good yields of HMF in a simple\naqueous phase process with a Bro̷nsted acid catalyst. With aldoses,\nsuch as d-glucose (GLU), much lower yields were reported\nin the literature. Here, we report an experimental and modeling study\non the use of d-galactose (GAL) for HMF synthesis, using\na liquid–liquid system (water/MIBK) in combination with an\nHCl/AlCl<sub>3</sub> catalyst. Experiments were conducted in a batch\nsystem with temperatures between 112 and 153 °C, HCl and AlCl<sub>3</sub> concentrations ranging from 0.02 to 0.04 M, and initial GAL\nconcentrations between 0.1 and 1.0 M. The highest HMF yield was 49\nmol % obtained for a batch time of 90 min at 135 °C. This value\nis much higher than in experiments with GAL in a monophasic aqueous\nsystem with HCl as the catalyst (2 mol % HMF yield) under similar\nreaction conditions. Based on detailed product analyses, a reaction\nscheme is proposed in which the isomerization of GAL to tagatose (TAG),\ncatalyzed by the Lewis acid AlCl<sub>3,</sub> is the first and key\nstep. TAG is then converted to HMF by Bro̷nsted acid HCl. The\nexperimental data were modeled using a statistical approach as well\nas a kinetic approach. The kinetic model demonstrates a good agreement\nbetween the experimental and modeled data. Our findings reveal that\ntemperature is the reaction variable with the most significant influence\non the HMF yield. The use of a biphasic system appears to be a promising\nmethod for HMF production from GAL.