Polyalkylbenzenes, sulfonation

In the sulfonation of polyalkylbenzenes such as 1,2,4,5-tetramethylbenzene (29) intramolecular migration of an alkyl group (Jacobsen rearrangement, 1886) may occur prior to sulfonation, so that the product is 2,3,4,5-tetramethylbenzenesulfonic acid (30) in which the alkyl groups have moved closer together (Scheme 17). The Jacobsen rearrangement is restricted to tetra- and pentaalkylbenzenes. 

A model reaction of hydrogen transfer has been proposed that describes well the results of kinetic studies of the photoreduction of o- and p-quinones and fluorenone in the presence of p-substituted A,A-dimethylanilines and polyalkylbenzenes/° Photosubstitution of the sulfo group for hydrogen is observed upon irradiation of sulfonated derivatives of hydroquinone. The reaction can be promoted by visible light, with eosin as sensitizer/°°... 

Treatment of polyalkylbenzenes or polyhalobenzenes with concentrated sulfuric acid to give rearranged and sulfonated polyalkylbenzenes or polyhalobenzenes. 

In the sulfonation of polyalkylbenzenes, an intramolecular rearrangement of an alkyl group may occur (see p 9). Similarly during the chlorosulfonation of polyalkylbenzenes, alkyl groups are sometimes displaced from the aromatic nucleus. 

Other examples of the action of chlorosulfonic acid on polyalkylbenzenes include 1-ethyl-2,4,6-trimethylbenzene to give the 3-sulfonic acid 1,2,3,5- and 1,2,4,5-tetraethylbenzenes to give high yields of the 4- and 3-sulfonic acids respectively, also pentaethylbenzene gives the 6-sulfonic acid (89%). ... 

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