To a dry three-necked flask was added 98.0 kg of 4-bromoindole, 307.0 kg of aluminum trichloride and 500 L of methylene chloride, and 79.0 kg of acetyl chloride was added slowly and dropwise to the three-necked flask. The reaction mixture was heated to 40 °C and kept for 8 hours. Upon completion of the reaction, the mixture was poured into 800 L of ice water, the organic phase was separated and the solvent was recovered to give 1,3-diacetyl-4-bromoindole. Subsequently, 161 kg of morpholine and 40.0 kg of sulfur were added directly to the reaction system, heated to 120 °C and kept for 5 hours. After the rearrangement reaction was completed, 500 L of methanol was added, heated to dissolve, decolorized with activated carbon, filtered and cooled. To the filtrate, 300 L of 70% ethanol and 200 L of 15% sodium hydroxide solution were added and heated to reflux for 4 hours. After completion of the reaction, filter and recover the solvent under vacuum. To the residue, appropriate amount of water was added and the pH was adjusted to 1-2 with dilute hydrochloric acid to precipitate a solid. It was filtered, washed with water to neutral, and finally recrystallized with 60% ethanol to obtain 102.2 kg of 4-bromoindole-3-acetic acid in 85.2% yield.
