Sulfuric Acid → 5-Fluoroisatin

Participants

Reaction Conditions

Reaction Steps

Concentrated sulfuric acid (200 mL) was heated at 50° C., and N-(4-fluorophenyl)-2-hydroxyiminoacetamide was slowly added. The black solution was carefully heated at 90° C. At this temperature, some slight cooling was necessary to keep the temperature at 90° C. When no more heat had developed, the reaction mixture was heated at 90° C. for an additional half hour. The dark-red solution was cooled to room temperature and poured onto 3 L ice water and 1 L ethyl acetate with vigorous stirring. The layers were separated, and the aqueous layer was extracted with ethyl acetate (1×1 L, 1×0.5 L). The combined organic extracts were dried over sodium sulfate, filtered, and evaporated to dryness. Yield: 35.3 g (52%) of a dark red solid, 5-fluoro-1H-indole-2,3-dione.

Provenance & Evidence