General procedure for the synthesis of 4-(methylsulfonyl)phenylhydrazine hydrochloride from 4-methylsulfonylaniline: 100 mL of hydrochloric acid was added to a 500 mL four-necked flask, and the temperature inside the flask was cooled to -10 °C or lower by passing the flask through an ice-water bath and ensuring that the temperature did not exceed -10 °C. Subsequently, 10.27 g (0.06 mol) of 4-(methylsulfonyl)aniline was added and dissolved. After the exothermic reaction ceased, 4.47 g (0.065 mol) of sodium nitrite was slowly added and 30 g of distilled water was added dropwise over a period of 1 hour while keeping the temperature of the flask below -10°C. After completion of the addition, the addition of 67.7 g (0.30 mol) of tin chloride dihydrate dissolved in 60 mL of hydrochloric acid was continued dropwise over 1 h while the reaction temperature was strictly controlled at -10 °C or lower. Upon completion of the reaction, the solid product was collected by filtration and dried at 60 °C for 12 h using a vacuum drier to afford 4-(methylsulfonyl)phenylhydrazine hydrochloride (Intermediate G1). This step was based on a 67.9 mol% yield of 4-(methylsulfonyl)phenylhydrazine.
