Hydrolysis of 2-Chloro-3,5-dinitrobenzenesulfonic Acid with aqueous alkali readily yields 2,4-dinitrophenol-6-sulfonic acid, which is reduced with sodium sulfide to 4-nitro- 2-aminophenol-6-sulfonic acid [96-67-3], a diazo component of metallizable azo dyes. Under very mild conditions, 2-Chloro-3,5-dinitrobenzenesulfonic Acid is aminated to 2,4-dinitroaniline-6-sulfonic acid, and 2-Chloro-3,5-dinitrobenzenesulfonic Acid reacts with sodium sulfite to give 3,5-dinitrobenzene- 1,2-disulfonic acid.
4-Chloronitrobenzene is sulfonated by gradual addition of 25 % oleum at 60 ℃; the temperature is raised slowly to 125 ℃, and held there for 8 h. The sulfonation mixture is cooled to 70 ℃, nitric acid is added over 5 h, and the reaction is completed by heating for 12 h at 70 ℃ followed by 4 h at 100 ℃. After cooling and quenching, the sodium salt of the product is salted out by addition of sodium sulfate and isolated in 80 % yield.
