3,4-Dichloroisothiazole-5-carbonitrile

In a 1 liter four-necked flask, 500 ml of dimethylformamide was added, 49 g (1 mole) of sodium cyanide was added with stirring, and the reaction solution was cooled with a water bath so that the temperature of the reaction solution was lowered to 20 , and the addition of 79.8 g (1.05 mole) of carbon disulfide was started dropwise, and the acceleration of dropwise addition was controlled so as to keep the temperature of the reaction solution between 20 and 30 . After dropwise addition, the reaction solution was stirred for 1 hour at room temperature, heated to 60, and held at 60 for 3 hours. A large amount of solid was precipitated after 12 hours or more; stirring, the solid was dispersed in the reaction solution, cooled with ice brine, 31 g of chlorine was introduced, and during the introduction of chlorine, the color of the reaction solution changed in the same way as in Example 1. The reaction was heated to 50C with a heating jacket, kept warm with stirring for 1 hour, and 50 g of chlorine gas was introduced with stirring. The temperature was increased to 60C, and the reaction was held with stirring for 3 hours. At 60-70 C, 440 ml of dimethylformamide was recovered under reduced pressure and 500 ml of ethyl acetate was added to the residue. The residue was refluxed with stirring for 10 min, cooled to room temperature, filtered, and the filter cake was washed with ethyl acetate, drained, and the dark brown filter cake was discarded. The filtrate at 60 under reduced pressure to recover ethyl acetate to dry, cooled precipitation crystal, filtration, drying, to obtain a brown solid 41 g. The mother liquor was added 200 ml of water. Add 200 ml of water to the mother liquor, distillation at atmospheric pressure, the product with the water evaporated, steamed to no product to bring out, stop distillation. After cooling, filtration, air-drying, to obtain a white solid 7 grams. The total product 3,4-dichloro-5-cyanoisothiazole 48 g, yield 53.6%.