Nitric Acid → 2-Chloro-6-nitrobenzothiazole

関与物質

反応条件

反応手順

To a solution of 2-chlorobenzothiazole (12.0 g, 70.7 mmol) in concentrated H2SO4 (60 mL) was added HNO3 (69% solution, 6 mL) dropwise at 0° C. for 20 min. The mixture was stirred at 5° C. for 3 h, poured into ice-water (150 mL). The precipitate was collected and washed with 5% sodium bicarbonate and water, dried in vacuo. 1H NMR analysis showed the mixture contained 78% 6-nitro-2-chlorobenzothiazole and 8% 5-nitro-2-chlorobenzothiazole. Recrystallization from ethanol gave 6-nitro-2-chlorobenzothiazole as white crystalline solid (11 g, 72%). 3.5 g of the solid was dissolved in refluxing ethanol-acetic acid (150: 15 mL), Iron powder was added in one portion. The mixture was refluxed for 1.5 h, filtered. The filtrate was concentrated in vacuo to half volume and neutralized with 10% NaOH to pH 7.5, extracted with ethyl acetate. The organic phase was washed with brine, dried over magnesium sulphate and evaporated to give a residue, which was recrystallized from ethanol. Light purple crystals (2.5 g, 83%) were obtained. Mp 160-164° C.; TLC single spot at Rf 0.27 (30% EtOAc/hexane); 1HNMR (270 MHz, DMSO-d6) δ 7.58 (1H, d, J=9.0 Hz, 4-H), 7.03 (1H, d, J=2.0 Hz, 7-H), 6.77 (1H, dd, J=9.0, 2.0 Hz, 5-H), 5.55 (2H, s, NH2). The mother liquor from the recrystallization of nitration product was evaporated and subjected to iron powder reduction as described above. The crude product was purified with flash chromatography (ethyl acetate-DCM gradient elution) to give 2-chloro-benzothiazol-5-yl-amine as yellow solid. Mp 146-149° C.; TLC single spot at Rf 0.52 (10% EtOAc/DCM); 1HNMR (270 MHz, DMSO-d6) δ 7.63 (1H, d, J=8.6 Hz, 7-H), 7.05 (1H, d, J=2.3 Hz, 4-H), 6.78 (1H, dd, J=8.6, 2.3 Hz, 6-H), 5.40 (2H, s, NH2).

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