Halobenzenes, sulfonation

Many variations of the reaction can be carried out, including halogenation, nitration, and sulfonation. Friedel-Crafts alkylation and acylation reactions, which involve reaction of an aromatic ling with carbocation electrophiles, are particularly useful. They are limited, however, by the fact that the aromatic ring must be at least as reactive as a halobenzene. In addition, polyalkylation and carbocation rearrangements often occur in Friedel-Crafts alkylation. 

Much of the research on the SbCls-catalyzed halogenation of arenes has focused on the chlorination and bromination of perfluoroalkyl-substituted aromatics [14]. The reaction of organic disulfides with electron-rich aromatic compounds under catalysis with SbCls and AgSbFg affords unsymmetrical aryl sulfides in modest yields [15a]. Electrophilic sulfinylation and sulfonation can be similarly effected by SbCls [15a-c]. Alkyl- and halobenzenes give thiocyano derivatives when treated with a mixture of SbCls and Pb(SCN)2 in CCI4 [16],... 

The sulfonation of halobenzenes is anomalous because although the halogen atom exerts a strong (-1) inductive (electronic withdrawal) effect with deactivation, sulfonation occurs in the ortho-position and para-position owing to the electron donation involving the electromeric effect (+E) from the lone electron pairs on the halogen atom in the presence of the reagent. 

Uses. Tetramethylene sulfone has high solvent power for aromatics and has been used extensively by Olah and co-workers for Friedel-Crafts type nitrations and for studies of the mechanism of nitronium tetrafluoroborate nitration of alkyl-benzenes and halobenzenes in homogeneous solution. It is a superior solvent for quaternization of tertiary amines with alkyl halides, since it has a high dielectric constant and does not enter into side reactions observed with nitrobenzene and dimethylformamide. For example in the synthesis of the acridizinium salt (3), Bradsher and Parham effected quaternization of (1) with benzyl bromide in tetramethylene sulfone at room temperature in excellent yield. Several other salts analagous to (2) were obtained in good yield and in crystalline form with use of tetramethylene sulfone, whereas with other solvents the products were colored... 

Toluenesulfonyl perchlorate (which is formed from 5-10% solutions of /Koluenesulfonyl bromide and silver perchlorate in nitromethane at 0°) is the strongest sulfonylating agent known.231 For instance, it sulfonylates the relatively unreactive halobenzenes in satisfactory yield at room temperature / -bromo- and / -chloro-phenyl p-tolyl sulfone were obtained in 66.5% and 63% yield, respectively 231... 

In practical terms, it is usually possible to get high yields of para products from electrophilic substitution reactions of halobenzenes. Both nitration and sulfonation of bromobenzene give enough material to make the synthesis worthwhile. Although mixtures of products are always bad in a synthesis, electrophilic aromatic substitution is usually simple to carry out on a large enough scale to make separation of the major product, ideally by crystallization, a workable method. A 68% yield of sodium p-bromobenzenesulfonate can be achieved by recrystallization of the sodium salt from water and a 70% yield of p-bromonitrobenzene by separation from the ortho isomer by recrystallization from EtOH. 

Formylation and Carboj lation. Formylatlon of aromatic compounds such as benzene, toluene, xylenes, mesltylene, Indan, tetralin, and halobenzenes Is achieved In HSOsF-SbFs under atmospheric CO pressure at 0 °C (eq 19). However, In the cases of alkylbenzenes, both formylatlon and sulfonation took place under these reaction conditions to give alkylbenzaldehydes and formylalkylbenzenesulfonyl fluorides, as well as small amounts of alkylbenzenesulfonyl fluorides and bis (alkyIphenyl) sulfones. With benzene and halobenzenes, because of their lower reactivity only aldehydes were produced. 

Studies by Kiersznicki and co-workers demonstrated that chlorosulfonic acid is an effective catalyst in the alkylation of arenes by reaction with alkenes. Benzene, toluene and ethylbenzene were alkylated by propene, elhene and 2-butene in the presence of chlorosulfonic acid which strongly catalysed the alkylations and inhibited polyalkylation. Increasing the concentration of the catalyst enhanced the proportion of /7-isomers in the products. Fluoro-, chloro-and bromobenzenes were similarly alkylated by reaction with C2-C4 alkenes using chlorosulfonic acid as catalyst. The optimum alkylation conditions were with a halobenzene alkene ratio of 1 0.25, a catalyst concentration of 0.33 mol mol" of fluorobenzene and 0.5 mol mol of the other halobenzenes, a temperature of 70 C and a reaction time of 2 hours. Alkylation with propene gave haloisopropylbenzenes the monoalkyl products were obtained as o-, m- and p- mixtures, the relative amounts depended on the quantity of catalyst used and the by-products were dialkyl derivatives, sulfonic acids and sulfones. In the reaction of benzene with propene, fluorosulfonic acid was a more potent alkylation catalyst than chlorosulfonic acid. ... 

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