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the substitution of a sulfo group (—SO3H) for a hydrogen atom attached to a carbon atom in an organic compound under the action of sulfuric acid or oleum. Sulfonation of aromatic compounds is most common—for example,
C6H6 + H2SO4 → C6H5SO3H + H2O
In the case of aliphatic compounds, the sulfo group is usually introduced indirectly, for example, by the exchange of a halogen atom in halide derivatives (1) or by the action of sulfur dioxide and chlorine on hydrocarbons upon irradiation with ultraviolet light (sulfochlorination), with subsequent hydrolysis (2):
(1) CH2═CH—CH2Cl + NaHSO3 → CH2═CH—CH2SO3H + NaCl
(In these formulas R represents a hydrocarbon radical—for example, an alkyl.)
Compounds that are not resistant to acids are sulfonated by sulfur trioxide bound in a complex—for example, in sulfur trioxide-dioxane:
Sulfonation and sulfochlorination are important industrial processes that are widely used in the production of sulfonic acids and ion-exchange resins.
B. L. DIATKIN