7343-12-6

39603-24-2

The general procedure for the synthesis of 5,7-dimethylindoline-2,3-dione using (E)-N-(2,4-dimethylphenyl)-2-(hydroxyimino)acetamide as starting material was as follows: concentrated sulfuric acid (20 mL) was added to a 100 mL flask with vigorous stirring at 50°C, and N-2-(hydroxyimino)acetamide derivatives (7.0 g) were added in batches. The reaction temperature was maintained between 50°C and 75°C, followed by the addition of sulfide. After the addition was completed, the reaction mixture was warmed to 80°C and stirring was continued for 30 minutes. After completion of the reaction, the mixture was cooled to room temperature and slowly poured into ice (250 g). The precipitated solid was collected and dried in air to give the crude product. The crude product was dissolved in 5% dilute sodium hydroxide solution (100 mL) and acidified with 4N hydrochloric acid (20 mL). The precipitated solid was filtered and dried thoroughly to give the purified target compound 5,7-dimethylindoline-2,3-dione.