[F:1][C:2]1[CH:8]=[C:7]([F:9])[CH:6]=[CH:5][C:3]=1[NH2:4].[N:10]([O-])=O.[Na+].O.O.[Sn](Cl)Cl.[C:19]([OH:24])(=[O:23])[C:20]([CH3:22])=O>Cl.O>[F:1][C:2]1[CH:8]=[C:7]([F:9])[CH:6]=[CH:5][C:3]=1[NH:4][N:10]=[C:20]([CH3:22])[C:19]([OH:24])=[O:23]Under a dry nitrogen atmosphere, a stirred solution of 25.8 g (0.20 mol) of 2,4-difluoroaniline in 235 ml of concentrated hydrochloric acid was cooled to -10° C. While maintaining this temperature, a solution of 13.8 g (0.20 mol) of sodium nitrite in 80 mol of water was added dropwise. After complete addition, the mixture was stirred at -10° C. for one hour. A solution of 101.5 g (0.450 mol) of tin (II) chloride dihydrate in 115 ml of concentrated hydrochloric acid was added dropwise to the cold reaction mixture. The resultant mixture was stirred for two hours, allowing the reaction temperature to rise to room temperature. Water (200 ml) was added to the mixture followed by the dropwise addition of 17.6 g (0.020 mol) of pyruvic acid in 200 ml of water. The resultant suspension was stirred vigorously for 45 minutes, and was filtered. The filter cake was dried to yield 40.4 g of 2-(2,4-difluorophenylhydrazono)propionic acid as a solid.
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