Water → 2-Chloro-4-mercaptophenol

324 mg of said di(3-chloro-4-methoxyphenyl)disulfide was dissolved in 10 ml of ethanol, followed by addition of 106 mg of sodium borohydride. The mixture was stirred over 2 hours at room temperature. The solution thus reacted was made weakly acidic by addition of dilute hydrochloric acid. The product was extracted twice with ethyl acetate. The organic layer was washed with saturated salt water and then dried over sodium sulfate anhydride. The solvent was distilled out under reduced pressure. The resulting crude product was purified by flash column chromatography (hexane: ethyl acetate =15:1), whereby 239 mg of 3-chloro-4-methoxybenzenethiol was obtained. 231 mg of the resulting 3-chloro-4-methoxybenzenethiol was dissolved in 4 ml dichloromethane, followed by cooling to 0° C. 4 ml of boron tribromide in dichloromethane was added dropwise under stirring. The mixture was stirred for 2 hours under cooling on ice and then for 20 hours at room temperature. Subsequently, under cooling on ice, water was added to the solution thus reacted, and the product was extracted twice with chloroform. The organic layer was washed with saturated salt water and dried over sodium sulfate anhydride. The solvent was distilled out, whereby 208 mg of crude 3-chloro-4-hydroxybenzenethiol was obtained.