Hydrogen Bromide → 5-Bromo-2-methylbenzothiazole

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Sodium nitrite (0.9 g, 13 mmol) was added portionwise to a suspension of 2-methyl-5-aminobenzothiazole dihydrochloride (2.0 g, 8 mmol) in hydrobromic acid (24 ml) at 0° C. The resulting mixture was added dropwise to a solution of copper(I) bromide (4.0 g, 14 mmol) in hydrobromic acid (50 ml) at 0° C. After stirring at 0° C. for 2 hours, water was added. The reaction mixture was basified to pH 9 using aqueous ammonium hydroxide and was extracted with ethyl acetate. The combined organic layers were dried over magnesium sulfate to give 2-methyl-5-bromobenzothiazole (1.0 g, 52%, 82% AUC GC) after chromatography (9:1 heptane/ethyl acetate): 1H NMR (300 MHz, DMSO-d6) δ 8.12 (d, J=1.8 Hz, 8.02 (dd, 1H) J=8.4, 1.5 Hz, 1H), 7.56 (dd, J=8.7, 2.1 Hz, 1H), 2.81 (s, 3H).

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