[C:1]1(C)C=CC=CC=1.[F:8][CH:9]([F:20])[C:10]1[C:14]([C:15]([O:17][CH2:18][CH3:19])=[O:16])=[CH:13][NH:12][N:11]=1.[OH-].[Na+].S(OC)(OC)(=O)=O>[Cl-].C[N+](C)(C)C.O>[F:20][CH:9]([F:8])[C:10]1[C:14]([C:15]([O:17][CH2:18][CH3:19])=[O:16])=[CH:13][N:12]([CH3:1])[N:11]=1
The toluene solution of crude ethyl 3-difluoromethylpyrazole-4-carboxylate was stirred and cooled to 20° C. Water (260 ml), tetramethylammonium chloride (10% aqueous solution, 15.0 g), and 25% NaOH solution (36-60 g) were added in sequence. Dimethyl sulphate (99.5%, 94.5 g, 0.75 mol) and additional 25% NaOH were fed simultaneously over 2 hours at 20° C. while maintaining the pH between 10.5 and 12.0. After 2 hours post reaction, the bottom aqueous phase was separated off.
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