Sulfuric Acid → 6-chloro-7-nitro-1H-indole-2,3-dione

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Reaction Steps

A solution of 2-chloro-2-oxoethane-1,1-diyl diacetate (70.7 g, 363 mmol) in THF (225 mL) was added dropwise to a mixture of 3-chloro-2-nitroaniline (44.7 g, 259 mmol) and potassium hydrogen carbonate (130 g, 1.30 mmol) in THF (450 mL) at 0° C. The resultant mixture was stirred at room temperature for 4 h, filtered and concentrated in vacuo. The residue was diluted with ethanol (450 mL) and a solution of hydroxylammonium chloride (90.0 g, 1.30 mmol) in water (225 mL) was added to the mixture at room temperature. The resultant mixture was refluxed for 2 h and concentrated in vacuo. Water (225 mL) was added to the residue and the resultant mixture was extracted with ethyl acetate. The extract was washed with brine, dried over sodium sulfate, filtered and concentrated in vacuo. The residue was purified by column chromatography on silica gel eluting with ethyl acetate to afford a crude orange solid. The crude solid was added portionwise to conc. sulfuric acid (260 mL) at 50° C., and the resultant mixture was stirred at 70° C. for 2 h, cooled to room temperature and poured into iced water (780 mL). The resultant mixture was extracted with ethyl acetate. The extract was washed with brine, dried over sodium sulfate, filtered through silica gel and concentrated in vacuo. Diisopropyl ether (800 mL) was added to the residue, and the resultant suspension was refluxed for 30 min and cooled to room temperature with stirring. The precipitate was collected by filtration and washed with diisopropyl ether to afford the title compound as a brown solid (33.5 g, 152 mmol 59%).

Provenance & Evidence