Aromatic sulfonation

Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution.

Sulfur trioxide is the electrophile in this electrophilic aromatic substitution generated from concentrated sulfuric acid (or fuming sulfuric acid) when heated. With benzene as substrate the reaction product is benzenesulfonic acid.


In contrast to aromatic nitration and other electrophilic aromatic substitutions this reaction is reversible. Sulfonation takes place in concentrated acidic conditions and desulfonation is the mode of action in a dilute hot aqueous acid. It is very useful in protecting the aromatic system because of this reversibility.

Aromatic sulfonic acids are intermediates in the preparation of dyes and many pharmaceuticals. Sulfonation of aniline produces p-aminobenzenesulfonic acid or sulfanilic acid which is a zwitterion with an unusual high melting point. The amide of this compound and related compounds form a large group of sulfa drugs.
Sulfonation of polystyrene can be used to prepare sodium polystyrene sulfonate.

References

1. March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 .
2. Piria, Ann. 78 31 (1851).
3. THE PIRIA REACTION. I. THE OVER-ALL REACTION W. H. Hunter, Murray M. Sprung J. Am. Chem. Soc., 1931, 53 (4), pp 1432–1443 doi:10.1021/ja01355a037.
4. U.S. Patent 1,210,725
5. Siegfried Hauptmann: Organische Chemie, 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 511, ISBN 3-342-00280-8.

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