Fluorosulfonic acid, reaction with benzene

In 1927 Steinkopf reported the preparation of several aromatic sulfonyl fluorides (287). For example, he obtained benzene sulfonyl fluoride, C6H6S02F, by the slow addition of fluorosulfonic acid to benzene at about 20°. The crude product was poured over ice and was then extracted in ether. After evaporating the ether, the benzene sulfonyl fluoride was refined by steam distillation. Another method for preparing aromatic sulfonyl fluorides is by the reaction of an aromatic sulfonic acid, such as C6H6S03H, with fluorosulfonic acid (202). By boiling a mixture of an aromatic sulfonyl chloride with a concentrated solution of potassium fluoride in water, the chloride is converted to a fluoride (62). 

Benzene (Table I, p. 165). Some of the factors involved in the industrial sulfonation of benzene have been discussed. In the small-scale, laboratory preparation, where the difference in cost between sulfuric acid and oleum is negligible, oleum is the preferred reagent. Benzene is added gradually to ice-cold sulfuric acid containing 5-8% of the anhydride the reaction is complete after ten to fifteen minutes. Benzensul-fonic acid is isolated readily as the sodium salt by the addition of the reaction mixture to a saturated sodium chloride solution. The reaction of benzene with chlorosulfonic acid is not used for the preparation of benzenesulfonic acid because, under conditions that limit the formation of the sulfonyl chloride, the acid is always accompanied by phenyl sulfone. Benzenesulfonyl chloride can be obtained in a yield of 75-77% by the addition of benzene to an excess of chlorosulfonic acid (room temperature). Fluorosulfonic acid reacts less vigorously the addi-... 

To 225 g. (2.25 moles) of -fluorosulfonic acid in an iron container is added 55 g. (0.7 mole) of benzene with stirring during six hours at 16-20°. After an additional nine hours at the same temperature, with continued stirring, the reaction mixture is poured on ice and extracted with ether the ether layer is washed with water to which sufficient calcium carbonate is added to neutralize the acid, the ether solution is separated and concentrated, and the residue is distilled with steam. There is obtained 77.5 g. (62% yield) of an oil that distils at 90-91°/14 mm. and 203-204°/ 760 mm. 4°° 1.3286 and nif 1.4932. The residue from the steam distillation contains 9.5 g. of phenyl sulfone. Benzenesulfonyl fluoride may be obtained also by allowing benzenesulfonyl chloride to stand with four times its weight of fluorosulfonic acid at room temperature for twenty-four hours. 

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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