At a low flow rate 0.10 mL/min we observe a segregated flow regime, where the two fluids are moving next to each other with a "moving interface", similar to the two-phase system. This results in suppressed hydrolysis and the desired amidation reaction is dominating, giving the observed high yields. When increasing the flow rate to 0.50 mL/min, the two streams begin to mix with the onset of the so-called vortex regime and both, the desired amidation and the undesired hydrolysis reactions, proceed thus decreasing the yield.