(2) Fluorination step: In 800 g of dimethyl sulfoxide (DMSO), 206.5 g of 2,3,6-trichlorobenzonitrile was dissolved, followed by the addition of 145.3 g of potassium fluoride (KF) to the solution. The reaction mixture was heated to 170 °C with continuous stirring and maintained for 1.5 hours. After completion of the reaction, the mixture was poured into water and extracted with dichloromethane (DCM). After removing the solvent by distillation, the reaction mixture was further distilled and the fraction with a boiling point of 95 °C/11 mmHg was collected to give 166.6 g of 3-chloro-2,6-difluorobenzonitrile in 96.0% yield.
