To mitigate this risk, continuous flow synthesis has recently been studied . A compact and closed system should improve the process safety of handling molecular oxygen by eliminating unexpected ignition. However, to maximize this advantage, the gas-liquid biphasic reaction needs to be controlled under continuous flow conditions. This reaction requires high mixing efficiency to assure high mass transfer of the gas to the liquid phase and a consequent high reaction rate . The mechanism for mixing is mainly categorized as active and passive mixing . Active mixing needs an external force and a driving part. In using oxygen, active mixing increases the risk of ignition due to friction from the driving part, making it unsuitable for the continuous system to handle aerobic oxidation. Therefore, we hypothesized that passive mixing would be more suitable for aerobic oxidation. Passive mixing is commonly realized by slug-flow and a static mixer . Slug-flow is the simplest method for passive mixing, but the formation of slug-flow depends on the tube diameter , and the reaction rate decreases as the tube diameter increases . The gas-liquid biphasic reaction also displays the same characteristic, and a static mixer needs to be developed to enable more robust aerobic oxidation under continuous flow conditions.