References to Chlorosulfonic Acid

The appendix contains a selection of the most recent references to chlorosulfonic acid together with details of the relevant chapters in the main text for cross-reference. The literature has been covered up to December 2001. 

A refers to concentrated sulfuric acid B, to oleum C, to chlorosulfonic acid and D, to fluoro-sulfonic acids... 

As shown here, the sulfonyl chloride group (—SO2CI) can be conveniently introduced to an aromatic ring via an electrophilic aromatic substitution reaction using chlorosulfonic acid. The reaction is usually referred fo as chlorosul-fonation. It has been determined that two equivalents of fhe acid are required per equivalent of the aromatic compound. In the initial attack the system first forms the corresponding sulfonic acid, which in turn is converted to the sulfonyl chloride. If is believed fhat the initial stage of the reaction involves SO3 as the electrophile. It is likely that this reagent results from the establishment of fhe equilibrium reaction shown here ... 

The sulfonation of 2-tert-butylphenol with chlorosulfonic acid has been studied kinetically the reaction mixture was demonstrated to contain 13 acids (derivatives of phenol, 2-tert-butylphenol, 4-tert-butylphenol and 2,4-ditert-butylphenol). The majority of the reactions gave first order rate constants and the operation of a two-phase reaction mechanism was discussed with reference to direct sulfonation, sulfate ester rearrangement and ipso sulfonation. 

The early work on the sulfonation of aliphatic compounds is described in Suter s book there are also several general references " which include the use of chlorosulfonic acid in the sulfonation of aliphatic compounds. Aliphatic compounds are generally less reactive towards sulfonating reagents than aromatic species, because they are less nucleophilic in character and so are less susceptible to attack by an electrophilic reagent like chlorosulfonic acid. 

Poly-/>-phenylene (PPP), after doping with a mixture of antimony pentachloride and chlorosulfonic acid, had a greatly increased electrical conductivity due to the formation of a charge-transfer complex. The term doping refers to the addition of an impurity to a material to enhance its physical properties. 

The industrial chemist will find several references to the direct sulfonation of polymers to produce ion exchange resins and water-soluble materials. For example, chlorosulfonic acid is used to treat polystyrene to give an ion exchange resin. In addition phenol formaldehyde resins can also be sulfonated. 

Sulfonic acid groups (SO3H) are both bulky and electron-withdrawing consequently once one sulfonic acid group has been introduced into the aromatic nucleus, the resultant arylsulfonic acid will be more resistant towards further sulfonation. The latter will require more drastic conditions and the product will contain the two sulfonic acid groups in the 1,3-position with respect to each other. With reactive substrates, e.g. aromatic hydrocarbons, halides or ethers, mono-chlorosulfonation is often best achieved at low temperature in ftie presence of chloroform, dichloromethane or 1,2-dichloroethane to moderate the reaction and avoid disulfonation. Suter and Weston S described the experimental procedures for the sulfonation of aromatic hydrocarbons, halides and ethers and many early references and details of the synthesis of sulfonic acids and sulfonyl chlorides are included in Suter s comprehensive text." ... 

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