Chlorosulfonic acid → 2-oxo-2,3-dihydro-1H-indole-5-sulfonyl chloride

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Reaction Steps

To a 100 mL flask charged with 27 mL of chlorosulfonic acid was added slowly 13.3 g of 2-oxindole. The reaction temperature was maintained below 30° C. during the addition. After the addition, the reaction mixture was stirred at room temperature for 1.5 hr, heated to 68° C. for I hr, cooled, and poured into water. The precipitate was washed with water and dried in a vacuum oven to give 11.0 g of 5-chlorosulfonyl-2-oxindole (50% yield) which was used without further purification.

Provenance & Evidence