We investigated this phenomenon further with four solvents at different flow rates using acetic anhydride (Figure ). In terms of the two-phase system (toluene and EtOAc), the yields of the desired amide 4 were decreased as flow rates were increased. When increasing the flow rates, the drop sizes were observed to be larger, and flow became irregular. It was hypothesized that the decrease of the interfacial area of mass transfer between the two phases resulted in lower yields. Higher yields were observed when using EtOAc compared to toluene as a solvent. It is considered the interfacial tension of EtOAc-water system (6.8 mN/m) is smaller than of the toluene-water system (35.4 mN/m), therefore smaller drop sizes were generated, resulting in larger interfacial areas.