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General procedure for the synthesis of 3,4-dichloro-5-nitropyridine from 3-chloro-4-hydroxy-5-nitropyridine: 3-chloro-4-hydroxy-5-nitropyridine (35 g, 147.52 mmol) was suspended in toluene (50 mL) at room temperature, followed by the addition of phosphorous trichloride (50 mL). The reaction mixture was slowly heated to 100 °C and the reaction was stirred at this temperature overnight. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated. Ice water was carefully added to the concentrated residue and the reaction mixture was extracted with ethyl acetate. The organic layer was separated, washed sequentially with water and saturated saline, dried over anhydrous sodium sulfate and the solvent was evaporated. The target product 3,4-dichloro-5-nitropyridine (25 g, 90% yield) was finally obtained.

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