To a 100 mL two-necked flask equipped with a stirrer and reflux condenser was added 8.0 g (0.03 mol) of 2,3-dichloro-4-phenylazophenol (CAS: 201656-71-5) and 1 g of sodium hydroxide dissolved in 40 mL of ethanol. The reaction system was cooled in an ice-water bath, followed by the addition of 4.5 g (0.12 mol) of sodium borohydride in one drop. After the dropwise addition was completed, the ice bath was removed and the reaction mixture was gradually warmed up to room temperature and the reaction was continued with stirring for 4 hours. Upon completion of the reaction, the pH of the reaction solution was adjusted to 7 with dilute hydrochloric acid solution and then extracted three times with ethyl acetate. The organic phases were combined, dried with anhydrous sodium sulfate and the solvent was removed by distillation under reduced pressure. The crude product was recrystallized with 20 mL of toluene, and after filtration and drying, 5.08 g of light pink crystalline 4-amino-2,3-dichlorophenol was obtained in 95% yield and 100% purity.
