N[C:2]1[C:6]([C:7]([O:9][CH2:10][CH3:11])=[O:8])=[CH:5][N:4]([CH3:12])[N:3]=1.P(=O)(O)(O)O.N([O-])=O.[Na+].[Cl-:22].[Na+]>Cl.O>[Cl:22][C:2]1[C:6]([C:7]([O:9][CH2:10][CH3:11])=[O:8])=[CH:5][N:4]([CH3:12])[N:3]=1A solution of 41.4 g (267 mmol) of ethyl 3-amino-1-methylpyrazole-4-carboxylate in a mixture of 150 mL of concentrated hydrochloric acid, 50 mL of 85 percent phosphoric acid, and 100 mL of water was prepared and cooled to about 0° C. A solution of 18.6 g (270 mmol) of sodium nitrite in 50 mL of water was added to this dropwise with cooling and stirring. After a short time the reaction mixture was added dropwise with stirring at ambient temperature to a solution of 46.5 g (484 mmol) of cupric sulfate and 60.0 g (1.03 mol) of sodium chloride in 200 mL of water. When the addition was complete, the mixture was heated to 50° C. with stirring for 1 hr. A solid formed. The mixture was extracted with methylene chloride and the extract was washed with water, dried over magnesium sulfate, and concentrated by evaporation under reduced pressure to obtain an impure solid. This was dried and recrystallized from ethanol to obtain 24.8 g of the title compound as a white solid melting at 76°-77° C.
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