2-Chloro-5-nitrobenzenesulfonic Acid, crystallizes as the dihydrate from water (mp 169 ℃, decomp.). The compound undergoes explosive decomposition when heated above 200 ℃, and all reactions, including its production, must be undertaken with great caution.
Amination of 2-Chloro-5-nitrobenzenesulfonic Acid gives 4-nitroaniline- 2-sulfonic acid [96-75-3], which is used as a diazo component or reduced to the important colorant intermediate 2,5-diaminobenzenesulfonic acid [88-45-9]. Chlorination of 2-Chloro-5-nitrobenzenesulfonic Acid in aqueous solution is a more facile route to 2,6- dichloro-4-nitroaniline than chlorination of 4-nitroaniline.
4-Chloronitrobenzene is sulfonated with 65 % oleum at 115 ℃; special precaution must be taken to control temperature. Work-up is by quenching and isolation of the sodium salt after it has been salted out.
[1] J. Appl. Chem. USSR (Engl. Transl.), 1990, vol. 63, # 7.2, p. 1442 - 1445
[2] Zhurnal Prikladnoi Khimii (Sankt-Peterburg, Russian Federation), 1990, vol. 63, # 7, p. 1568 - 1571
[3] European Journal of Medicinal Chemistry, 2012, vol. 50, p. 18 - 26
