[N:1]([O-])=O.[Na+].[NH2:5][C:6]1[CH:10]=[C:9]([S:11][CH3:12])[N:8]([CH3:13])[N:7]=1.O.[Sn](Cl)Cl.[OH-].[Na+]>O.Cl>[NH:5]([C:6]1[CH:10]=[C:9]([S:11][CH3:12])[N:8]([CH3:13])[N:7]=1)[NH2:1]At 0° C., 1.1 g (15.8 mmol) of sodium nitrite in 4 ml of water are added dropwise to 1.9 g (13.1 mmol) of 3-amino-1-methyl-5-methylmercaptopyrazole in 18 ml of concentrated hydrochloric acid, and the mixture is stirred at 0° C. for 2 hours. At −30° C., a solution of 7.4 ml (32.8 mmol) of tin dichloride hydrate in 5.5 ml of conc. hydrochloric acid is added dropwise, and the mixture is stirred at this temperature for 3 hours. The mixture is then made alkaline using 32% strength aqueous sodium hydroxide solution and extracted with methylene chloride. The organic phase is dried (sodium sulfate) and the solvent is stripped off, giving 2.0 g of product which can be used without any further purification.
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