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In organic chemistry, aromatic sulfonation is a organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid () functional group. Together with nitration and halogenation, aromatic sulfonation is a widely used electrophilic aromatic substitutions.. Aryl group sulfonic acids are used as , dye, and .
To drive the equilibrium, dehydrating agents such as thionyl chloride can be added:
Chlorosulfuric acid is also an effective agent:
In contrast to aromatic nitration and most 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. The reaction is very useful in protection group the aromatic system because of this reversibility. Due to their electron withdrawing effects, sulfonate protecting groups can be used to prevent electrophilic aromatic substitution. They can also be installed as directing groups to affect the position where a substitution may take place.T.W. Graham Solomons: Organic Chemistry, 11th Edition, Wiley, Hoboken, NJ, 2013, p. 676, .
A classic named reaction is the Piria reaction (Raffaele Piria, 1851) in which nitrobenzene is treated with a metal bisulfite forming an aminosulfonic acid as a result of combined nitro group reduction and sulfonation. The Piria Reaction. I. The Overall Reaction W. H. Hunter, Murray M. Sprung J. Am. Chem. Soc., 1931, 53 (4), pp 1432–1443 .
In the Tyrer sulfonation process (1917), 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 and the benzene fed back to the vessel. In this way an 80% yield is obtained.
Sulfonation of polystyrene is used to make sodium polystyrene sulfonate, a common ion exchange resin for water softening.
Historically, mercurous sulfate has been used to catalyze the reaction.
Specialized sulfonation methods
Many method have been developed for introducing sulfonate groups aside from direction sulfonation.
Applications
Aromatic sulfonic acids are intermediates in the preparation of and many pharmaceuticals. Sulfonation of lead to a large group of sulfa drugs.
See also
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