Phosphorus oxychloride → 2,3-Dioxoindoline-5-sulfonyl chloride

A suspension of sodium 2,3-dioxoindoline-5-sulfonate dihydrate (5.0 g, 17.53 mmol) and POCl3 (8.17 ml, 88 mmol) in sulfolane (25 ml, 264 mmol) was heated at 60° C. for 3 hours. The solution was cooled to 0° C. and water (60 ml) was added drop wise; the green precipitate was filtered and washed with a small amount of water. The solid was dissolved in ethyl acetate and washed three times with water; the organic phase was then dried over sodium sulfate and evaporated to give a crude solid that was purified by crystallization from hexane/ethyl acetate 1:1 to give 2,3-dioxoindoline-5-sulfonyl chloride (3.52 g, 14.33 mmol, 82% yield).