[ClH:1].[NH2:2][C:3]1[N:7]([C:8]2[CH:13]=[CH:12][C:11]([O:14][CH3:15])=[CH:10][CH:9]=2)[N:6]=[CH:5][C:4]=1[N:16]=O.[H][H]>C(O)C.[Pd]>[ClH:1].[ClH:1].[CH3:15][O:14][C:11]1[CH:10]=[CH:9][C:8]([N:7]2[C:3]([NH2:2])=[C:4]([NH2:16])[CH:5]=[N:6]2)=[CH:13][CH:12]=18.0 g (31 mmol) of 5-amino-1-(4-methoxyphenyl)4-nitrosopyrazole hydrochloride from Step 1.2 in 200 mL of ethanol was hydrogenated for 6 hours on 0.8 g of Pd/C (10%) at 8 bar of hydrogen pressure. The catalyst was filtered off, and the reaction mixture was concentrated to a total volume of about 30 mL. After the addition of 40 mL of 3-molar ethanolic hydrochloric acid and agitation in an ice bath, the product crystallized. Suction filtration and washing with 50 mL of ethyl acetate gave 7.4 g (27 mmol), 86% of the theoretical) of 1-(4-methoxyphenyl)-4,5-diamino-1H-pyrazole dihydrochloride.
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