Desulfonation reaction

In organic chemistry, the desulfonation reaction is the hydrolysis of sulfonic acids: The reaction applied to aryl and naphthylsulfonic acids. It is the reverse of sulfonation. The temperature of desulfonation correlates with the ease of the sulfonation.
 * RC6H4SO3H + H2O → RC6H5 + H2SO4



Applications in synthesis
This reactivity is exploited in the regiospecific preparation of many di- and tri-substituted aromatic compounds. The approach exploits the meta-directing effect of the sulfonic acid group. 2-Chlorotoluene for example can be prepared by chlorination of p-toluenesulfonic acid, followed by hydrolysis. The method is also useful for the preparation of 2,6-dinitroaniline and 2-bromophenol via phenol-2,4-disulfonic acid.