Synthesis
General procedure for the synthesis of 3,5-dichlorobenzaldehyde from 3,5-dichloro-1-methylbenzene: (1) Apparatus: a tubular reactor was installed with reference to Fig. 2, and the type of tubing was a combination of (3a + 3d) DC channels and reinforced mixed-cake rectangular flat tubes, with the diameter and volume determined according to the flow rate and reaction conditions. (2) A mixed solution was prepared by dissolving 6.06 g of cobalt acetate and 6.06 g of sodium molybdate in 200 ml of 3,5-dichlorotoluene and 200 ml of acetic acid, respectively, where n (cobalt acetate): n (3,5-dichlorotoluene) = 0.015: 1. An H2O2-acetic acid solution was prepared by dissolving 6.06 g of sodium bromide in 20% H2O2, where n (sodium bromide): n (3, 5-dichlorotoluene) = 0.015: 1. The 3,5-dichlorotoluene-acetic acid solution and H2O2-acetic acid solution were injected into a tubular reactor at a flow rate of 8.33 ml/min and 16.67 ml/min, respectively. The reactor was subjected to continuous heat exchange via a thermostatic pump maintaining n(H2O2):n(3,5-dichlorotoluene) = 2:1. A microchannel reactor shown in Fig. 2 was used, with a controlled reaction temperature of 105 °C and a residence time of 600 s. The reaction was carried out at the outlet of the tubular reactor at a flow rate of 8.33 ml/min and 8.67 ml/min, respectively. After completion of the reaction, the outlet was cooled to 0 °C and the reaction was quenched with dichloromethane. The conversion of 3,5-dichlorotoluene was analyzed by GC to be 60.8% and the yield of 3,5-dichlorobenzaldehyde was 39.2%.
