Synthesis
Chloral hydrate (8.93 g, 0.054 mol), anhydrous sodium sulfate (130 g, 0.40 mol), m-chloroaniline (0.05 mol), hydroxylammonium chloride (10.98 g, 0.158 mol), and concentrated hydrochloric acid (43 mL) were added to 120 mL of water in sequence. The resulting suspension was heated to 90 °C, maintained for 5 minutes and cooled to room temperature. The reaction mixture was filtered and washed with water (2 x 20 mL) to obtain the crude product. The crude product was added in batches to a 250 mL three-necked flask pre-filled with concentrated sulfuric acid (32.6 mL) and preheated to 65 °C, after which the mixture was heated to 80 °C and maintained for 20 minutes. After completion of the reaction, the solution was cooled to room temperature and slowly poured into 500 g of ice water with vigorous stirring for 4 hours. The intermediate 4-chloroindoline-2,3-dione was isolated by filtration, washed with water and recrystallized from ethanol in a final yield of 25.7% to 73.2%.
References
[1] Chinese Chemical Letters, 2013, vol. 24, # 10, p. 929 - 933
