After 7 hours, there is no big difference when using 10%, 20%, or 40% of K2CO3, while using 5% of K2CO3 only gave benzoin in 80.7% yield. As we can see in the control experiment under a closed system with air, even though 40% amount of K2CO3 was used, only 43.6% of benzil was obtained after 7 hours, this could be due to the co-effect that the high amount of K2CO3 took of the proton from the benzoin and additive AC scrapped byproduct water which promote the reaction equilibrium. Moreover, this clearly shows that the air had a big effect on the oxidation of benzoin. Furthermore, we also evaluated the different water trapper additives like MS 4Å, AC, and MnO2. As shown in the Figure , using MS 4Å, AC, and MnO2 could give the benzil in 84.3%, 86.4%, and 72.9% yield respectively at the beginning of the reaction at 1 hour. While after 7 hours, the benzil yield increased to 94.6%, 99.0%, and 99.0% respectively. As shown in Figure , the co-solvent D2O was also investigated, a small amount of D2O has a slightly lower yield compared to the one only using DMSO. So, in the following experiments, we then decided to do a systematically research of the solvent effect on the K2CO3 catalytic selective oxidation of benzoin.