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The general procedure for the synthesis of 2,4-dichloropyrimidine-5-carboxylic acid from uracil-5-carboxylic acid was as follows: 10.0 g (64.06 mmol) of uracil-5-carboxylic acid (purchased from Aldrich Chemical Company), which was partially dissolved in 20 mL of N,N-dimethylformamide (DMF), was placed in a reaction vial under the cooling condition in an ice bath. Subsequently, 59.7 mL (0.64 mol) of phosphoryl chloride and 10.3 mL (64.7 mmol) of N,N-diethylaniline were slowly added to the reaction system. The reaction mixture was heated and refluxed in an oil bath at 90°C for 2 hours and 40 minutes. Upon completion of the reaction, the system was cooled to room temperature and the excess phosphoryl chloride was removed by distillation under reduced pressure (about half the volume was evaporated). The remaining reaction solution was slowly poured into crushed ice to quench the reaction and then extracted with ether. The organic phases were combined, dried over anhydrous sodium sulfate, filtered to remove the desiccant, and the filtrate was concentrated under reduced pressure by rotary evaporator to afford 8.1 g (41.97 mmol) of the white solid product 2,4-dichloropyrimidine-5-carboxylic acid in 65% yield.

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