DHMF under an open-air system in water. As shown in the Figure , the amount of MS 4Å had a great effect on the DHMF oxidation. Without using any MS 4Å, only a 15% yield of BHMF was obtained after 9 hours. While increasing the MS 4Å ratio from 0.1 to 0.2, 0.5, and 1, the BHMF yield gradually increased. Surprisingly, an excellent BHMF yield of 97% could be observed after 9 hours at 80°C under the K2CO3 catalytic oxidation of DHMF in an open-air system. Based on the control experiments, when the reaction was carried out in a closed system without air, only 5% of BHMF could be obtained. Furthermore, when no MS 4Å was used, the oxidation of DHMF did not occur which showed that air and MS 4Å are both necessary for the reaction. As shown in Figure , when the reaction temperature increased from 80 °C to 100 °C, there was no significant increase in the BHMF yield under the 0.5 MS 4Å, open-air system. Interestingly, unlike the oxidation of benzoin, the organic solvent THF did not give good results, and only a 5% yield of BHMF was obtained. That is maybe the DHMF is soluble in H2O while did not dissolve efficiency in THF. The BHMF yield was analyzed and calculated using HPLC method. Then we further explore the amount of base effect on the oxidation process. As shown in Figure and Figure , the oxidation of DHMF undergoes slowly to give 10% of BHMF in 5 hours without using K2CO3. When the K2CO3 ratio increased from 0.05 to 0.1, 0.2, and 0.5, the BHMF yield increased gradually from 60% to 98% after 2 hours.