General procedure for the synthesis of 2,4-dichloro-3-fluoronitrobenzene from 2,6-dichlorofluorobenzene: 2,6-dichlorofluorobenzene was dissolved in 20% dichloromethane solution, and nitric acid was introduced through a flat streamer at a flow rate of 11.9 mL/min, which corresponds to a flow rate of nitric acid of 0.27 mL/min. At the same time, sulfuric acid was introduced through a flat streamer at a flow rate of 25.2 mL/min. sulfuric acid, corresponding to a flow rate of sulfuric acid of 0.46 mol/min. sulfuric acid and nitric acid complete mixing in the microchannel reactor 1. Next, 2,6-dichlorofluorobenzene was introduced in dichloromethane via a flat streamer at a flow rate of 38.5 mL/min, which corresponds to a flow rate of 0.27 mol/min of 2,6-dichlorofluorobenzene in microchannel reactor 2. At this point, the reaction of 2,6-dichlorofluorobenzene with the mixed acid was initiated, wherein the molar ratio of 2,6-dichlorofluorobenzene to nitric acid was 1:1. The temperature of the reaction was 40° C. The reaction residence time in each of the microchannel reactors was 0.5 mL/min. The reaction residence time in the microchannel reactor was 33 s and the system pressure was maintained at 0.7 MPa. After the reaction was completed, the product was collected from the outlet. After post-treatment, the conversion of 2,6-dichlorofluorobenzene was 100% and the selectivity of 2,4-dichloro-3-fluoronitrobenzene was 94%. The product was washed and dried in a step to give a pure product.
