Fructose dehydration reactions

Fructose (>99%; Sigma-Aldrich), GVL (>99%; Sigma-Aldrich), HCl (0.5 M; Sigma-Aldrich), and FDCA (>98%; TCI Chemicals) were used as received. Milli-Q water (~18 megohm·cm) was used in all experiments.

Fructose dehydration to produce HMF was carried out in 10-ml thick-walled glass reactors (Alltech Inc.) heated in a temperature-controlled oil bath on a digital stirring hot plate (Thermo Fisher Scientific). The temperature in the oil bath was monitored by a K-type thermocouple (OMEGA Engineering). In a typical experiment, 0.88 g of fructose, along with 2.5 g of GVL, 2.5 g of Milli-Q water, and the required amount of catalyst [HCl (30 μl) or FDCA (31 mg)], was loaded into the glass reactor. The reactor was placed in an oil bath at 453 K for a specified reaction time. The mixture was stirred by a magnetic stir bar in the reactor at 600 rpm. After the desired reaction time had elapsed, the reaction was stopped by cooling the reactor in an ice bath.

The concentrations of the products were measured by high-performance liquid chromatography (HPLC) using a Bio-Rad Aminex HPX-87H column on a Waters 2695 system equipped with RI-2414 and PDA-2998 detectors. An aliquot of the product mixture was diluted 10 times with Milli-Q water and filtered with a 0.2-μm polytetrafluoroethylene (PTFE) filter before analysis. The temperature of the HPLC column was maintained at 338 K, and the flow rate of the mobile phase [water (pH 2), acidified by sulfuric acid] was 0.6 ml/min. Fructose, formic acid, and levulinic acid were analyzed with the refractive index (RI) detector, whereas the concentrations of HMF and furfural were measured with the photodiode array (PDA) detector at 320 and 210 nm, respectively. Yields of HMF, formic acid, and levulinic acid were calculated with respect to the total fructose present in the starting material. Table S1 shows typical product composition, and fig. S1 shows a typical chromatogram for fructose dehydration conducted with 0.53 wt % FDCA as the dehydration catalyst at 453 K for 70 min.