Aromatic sulfonation

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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.[1]

Sulfonation of Benzene to benzene sulfonic acid


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.

generation of sulfur trioxide from sulfuric 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.

Piria reaction[edit]

A classic named reaction is the Piria reaction (R. Piria, 1851) in which nitrobenzene is reacted with a metal bisulfite forming an aminosulfonic acid as a result of combined nitro group reduction and sulfonation.[2][3]

The Piria Reaction

Tyre sulfonation process[edit]

In the Tyrer sulfonation process (1917),[4] at some time of technological importance, benzene vapor is led through a vessel containing 90% sulfuric acid the temperature of which is increased from 100 to 180°C. Water and benzene are continuously removed in a condenser and the benzene layer fed back to the vessel. In this way an 80% yield is obtained.

Synthesis of sulfanilic acid from aniline and sulfuric acid.[5]


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.

See also[edit]


  1. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 .
  2. ^ Piria, Raffaele (1851). "Über einige Produkte der Einwirkung des schwefligsäuren Ammoniaks auf Nitronaphtalin". Annalen der Chemie und Pharmacie 78: 31–68. doi:10.1002/jlac.18510780103. ISSN 0075-4617. 
  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.