Hydrogen Bromide → 2-Bromo-4-chlorobenzothiazole
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N[C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[C:7]([Cl:11])[C:5]=2[N:6]=1.N([O-])=O.[Na+].[BrH:16]>O.[Cu]Br>[Br:16][C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[C:7]([Cl:11])[C:5]=2[N:6]=1N[C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[C:7]([Cl:11])[C:5]=2[N:6]=1.N([O-])=O.[Na+].[BrH:16]>O.[Cu]Br>[Br:16][C:2]1[S:3][C:4]2[CH:10]=[CH:9][CH:8]=[C:7]([Cl:11])[C:5]=2[N:6]=1Slurry 2-amino-4-chlorobenzothiazole (0.255mol) in water (325 mL), heat to reflux and add 48% hydrobromic acid (130 mL). Maintain at reflux for 20 minutes, cool to 0° C. and add a solution of sodium nitrite (17.56g, 0.255mol) in water (90mL), maintaining a temperature of 0° C. Stir at 0° C. for 15 minutes and add by dropwise addition (while keeping cold) to a rapidly stirring mixture of copper (I) bromide (42.03g, 0.293mol) in 48% hydrobromic acid (86mL) and water (225mL). Stir at room temperature for 20 minutes and then heat on a steam bath for an additional 20 minutes. Allow to stand overnight, extract into methylene chloride and dry (MgSO4). Evaporate the solvent in vacuo and purify by chromatography to give 2-bromo-4-chlorobenzothiazole.
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