1. Add 3-picoline-N-oxide, triethylamine and dichloromethane to the reaction kettle, and add benzoyl chloride dropwise under nitrogen protection. Continue to keep warm for 2 hours after adding. Suction filtration, and the filtrate was desolubilized under reduced pressure to obtain a light brown viscous liquid. Adjust the pH value of this liquid to 6 with 45% NaOH solution under cooling conditions, carry out water distillation, and continue to neutralize it with alkali solution to keep the pH value around 6 during the distillation process. The oil layer was separated from the distillate, and the oil layer was desolvated under reduced pressure to obtain a colorless to light yellow oily liquid with a yield of 60.0%. The liquid was 2-chloro-5-methylpyridine and 2, The mixture of 2-chloro-3-methylpyridine can be obtained by freezing to obtain pure 2-chloro-5-methylpyridine.
2. Add the mixture of 2-chloro-5-methylpyridine and 2-chloro-3-methylpyridine, acetonitrile, and initiator in the reaction kettle, heat up to the reflux temperature, and react with chlorine under ultraviolet light until the conversion rate ≥ 75%, stop the chlorine flow, evaporate the solvent and unreacted raw materials under reduced pressure to obtain a light brown liquid, which is directly used in the next step without purification.
3. Add imidazolidine, dimethylformamide and an appropriate amount of benzene into the reaction kettle, heat up and reflux for dehydration. After the dehydration was completed, it was cooled, anhydrous potassium carbonate was added, and dimethylformamide was added dropwise at about 90°C. After the dropwise addition, the temperature was kept for 1.5 hours. The solid was removed by filtration, the filtrate was poured into ice water, stirred, filtered, washed with water and recrystallized to obtain imidacloprid as a light brown solid with a yield of 75%.