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The general procedure for the synthesis of 2,4-dichloro-5-pyrimidinecarbonyl chloride from uracil-5-carboxylic acid is as follows: 9.1 Preparation of 2,4-dihydroxypyrimidine-5-carbonyl chloride In a 250 mL round bottom flask, 10.0 g (64.0 mmol) of 2,4-dihydroxypyrimidine-5-carboxylic acid was dissolved in 46 mL (500.0 mmol) of phosphorus oxychloride (POCl3) under nitrogen protection. The reaction mixture was cooled to 0°C via an ice bath, followed by the batch addition of 47.7 g (230 mmol) phosphorus pentachloride (PCl5). The reaction solution was heated and stirred at reflux for 16 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was dissolved in 100 mL of toluene and ground, followed by filtration. After this operation was repeated three times, the filtrate was evaporated under reduced pressure to give 13.5 g (64.0 mmol) of the yellow oily product 2,4-dichloro-5-pyrimidinecarbonyl chloride, which was used directly in the next step of the reaction. Yield = 100%.

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