Hydrogen Bromide → 2-Bromo-6-nitrobenzothiazole

Participants

Reaction Conditions

Reaction Steps

Into a 150 mL beaker, 2-amino-6-nitrobenzothiazole (5.1089 g, 25.39 mmol, 1 eq) was mixed vigorously with phosphoric acid, 85 wt. % (22.6 mL, 13 eq) at 50° C. The solution was then cooled to −20° C., using an acetone/dry ice bath. To this, a solution of NaNO2 (1.943 g, 28.16 mmol, 1.1 eq) in water (5.0 mL), also cooled to −20° C., was added slowly over the course of 15 min. After 1 h, the resulting suspension was poured over a solution of CuBr (4.593 g, 32.02 mmol, 1.3 eq) in 48% HBr (25.3 mL) at rt and was stirred. Additional HBr (≈35 mL) aided in transfer. After 1 h, the mixture was heated at 40° C. for 2 h. After 2 h, the heat was turned off and the reaction continued to stir at rt for 16 h. The crude mixture was diluted with water to a final volume of 200 mL and was extracted with DCM (3×). The organics were dried over anhydrousmg2SO4, filtered, and concentrated under reduced pressure. The crude material was adsorbed onto silica gel, dry loaded, and purified by chromatography on silica gel [Jones Flashmaster, 50 g/150 mL cartridge, eluting with DCM/Hex 1:1→2:1→neat DCM]. Fractions containing product were combined, concentrated in vacuo, and re-chromatographed to give the title compound as an orange solid. 1H NMR (400 MHz, CDCl3): δ=8.11 (d, J=9.2 Hz, 1H), 8.38 (dd, J=9.2, 2.4 Hz, 1H), 8.78 (d, J=2.0 Hz, 1H). MS (ES+): m/z 258.95/260.96 (100/96) [MH+]. HPLC: tR=3.43 min (ZQ2000, polar—5 min).

Provenance & Evidence