Hydrogen Bromide → 2-bromo-5,6-dichloro-1H-benzimidazole

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2-Amino-5,6-dichlorobenzimidazole (3 g, 16 mmole) was suspended in 150 ml of water and brought into solution with 2 ml of HBr. Sodium nitrite (3.3 g, 55 mmole) was then added and the mixture was stirred at room temperature for 1 hr. Excess CuBr2 was then added and the mixture was heated on a steam bath for 1 hr. The aqueous solution was extracted with ethyl acetate (3×100 ml), dried with MgSO4, concentrated, and crystallized from ethyl ether to give 1.13 g (26%) of 2-bromo-5,6-dichlorobenzimidazole (7). 1H NMR (DMSO-d6) δ 7.81 ppm (s, 2H), 13.62 (s, 1H). GC/MS: m/e 266, 185, 158, 150, 133, 124, 107, 97, 88, 73, 62, 52, 37.

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