[Br:1][C:2]1[CH:8]=[CH:7][C:5]([NH2:6])=[CH:4][C:3]=1[O:9][CH3:10].[N:11]([O-])=O.[Na+].O.O.[Sn](Cl)Cl>Cl.O>[Br:1][C:2]1[CH:8]=[CH:7][C:5]([NH:6][NH2:11])=[CH:4][C:3]=1[O:9][CH3:10]4-Bromo-3-methoxyaniline (3.0 g, 14.85 mmol) was suspended in concentrated HCl (50 mL) and the mixture was cooled to 0° C. in the ice-water bath. A solution of sodium nitrite (1.23 g, 17.82 mmol) in 10 mL water was added very slowly to the reaction mixture. The mixture turned yellow, then brown with a yellow haze indicating diazotization. The diazonium salt was held at 0° C. for an hour and then a solution of tin(II) chloride dihydrate (10.05 g, 44.5 mmol) in concentrated HCl (20 mL) was added very slowly (caution, extremely exothermic). The reaction was stirred for 2 h at 0° C. then at RT overnight. The reaction was filtered and the filter cake was washed with cold H2O to afford (4-bromo-3-methoxyphenyl)hydrazine as a tan solid (3.1 g, MS: 218 [M+H+]).
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