Synthesis Example 2-2 Synthesis of 4-chloro-3-nitrobenzenesulfonyl chloride: to a reaction vial containing a mixture of 1280 g of potassium 4-chloro-3-nitrobenzenesulfonate, 1150 mL of acetonitrile, 250 mL of sulfoxide, and 30 mL of dimethylacetamide, 1240 mL of phosphinic acid chloride was added dropwise at a slow rate, while controlling the temperature within the reaction system to maintain a temperature of 60°C to 70°C. After the dropwise addition was completed, the reaction mixture was stirred at 73°C for 3 hours. Upon completion of the reaction, the reaction mixture was cooled with water, followed by the slow addition of 400 mL of water. The reaction mixture was poured into 5 L of ice water and the precipitated crystals were separated by filtration, washed with water and dried to give 1060 g of the target product 4-chloro-3-nitrobenzenesulfonyl chloride in 84% yield. The melting point of the product was 55 °C to 56 °C.
