1. 136 mL (1858 mmol) of anhydrous N,N-dimethylformamide (DMF) was added to 750 mL of toluene, cooled to the appropriate temperature, and 571 g (3716 mmol) of phosphoryl chloride was added dropwise.
2. 137.5 g (929 mmol) of a solution of 3-(difluoromethyl)-1-methyl-1H-pyrazol-5-ol (IX-1) was added dropwise to the above mixture.
3. The reaction mixture was heated to reflux for 3 hours.
4. When the reaction was complete, the reaction mixture was cooled and carefully poured into 4 L of ice water.
5. The aqueous phase was extracted three times with 1500 mL of ethyl acetate and the organic phases were combined.
6. The organic phase was washed twice with saturated sodium bicarbonate solution and once with saturated sodium chloride solution.
7. The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to give 129.2 g (72% yield, GC purity >99%) of 5-chloro-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxaldehyde (II-1) as a reddish brown solid. 8.
8. The product was used in the next step without further purification.
