Electrophilic aromatic substitution, sulfonyl

The reaction exhibits other characteristics typical of an electrophilic aromatic substitution. Examples of electrophiles that can effect substitution for silicon include protons and the halogens, as well as acyl, nitro, and sulfonyl groups. The feet that these reactions occur very rapidly has made them attractive for situations where substitution must be done under very mild conditions. ... 

It has also been known for many years that sulfonyl groups, like carbonyl groups, promote the addition of nucleophilic reagents to carbon- carbon double bonds . The meta-directing properties of the S02Me group in electrophilic aromatic substitution were discovered in the mid-1920s . ... 

Other reactions have been studied for synthesizing these polymers, including the electrophilic aromatic substitution of acyl and sulfonyl halides on aromatic reactants and the nickel-catalyzed aromatic coupling of aromatic dihalides [Yonezawa et al., 2000]. 

Polymers such as polyetherketones and polyethersulfones can be prepared by electrophilic aromatic substitution using aromatic acid chlorides and aromatic sulfonyl chlorides, respectively [Eq. (25)]. However, due to ortho-substitution in addition to the desired para-substitution, it is difficult for these Friedel-Crafts acylations to compete with nucleophilic aromatic substitution of activated aromatic halides which are usually used for their synthesis. 

Acetylation of aniline produces acetanilide (2) and protects the amino group from the reagent to be used next. Treatment of 2 with chlorosulfonic acid brings about an electrophilic aromatic substitution reaction and yields/>-acetamidobenzene-sulfonyl chloride (3). Addition of ammonia or a primary amine gives the diamide, 4 (an amide of both a carboxylic acid and a sulfonic acid). Finally, refluxing 4 with dilute hydrochloric acid selectively hydrolyzes the carboxamide linkage and produces a sulfanilamide. (Hydrolysis of carboxamides is much more rapid than that of sulfonamides.)... 

The functional group transformations are derived from either electrophilic aromatic substitution or nucleophilic aromatic substitution reactions. The electrophilic aromatic substitution functional group transform is shown with a simple X group, where X is chlorine, bromine, nitro, or sulfonyl. The reagents are different, but the basic principle for the formation of such compounds is the same. 

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 ... 

Direct preparation of aryl sulfonyl chlorides from arenes has been achieved through electrophilic aromatic substitution with excess chlorosulfonic acid. ° This method was used in the initial medicinal chemistiy route for the preparation of Viagra, which relied on a penultimate chloro-sulfonylation reaction with chlorosulfonic acid (Scheme 13.3). ... 

The authors note that the scale-up of chlorosulfonylation reactions is difficult due to high toxicity, competitive hydrolysis during the increased quench times, and a high environmental burden. Additionally, the acidic conditions required for electrophilic aromatic substitution for die synthesis of aryl sulfonyl chlorides greatly limits the scope of the arene that can be used, and furthermore, the desired substitution pattern may be inaccessible based on the intrinsic electronic properties of the aromatic ring. Therefore, the discovery of alternative methods for sulfonyl chloride synthesis is a worthy objective. 

PoIysuIfonyIa.tlon, The polysulfonylation route to aromatic sulfone polymers was developed independendy by Minnesota Mining and Manufacturing (3M) and by Imperial Chemical Industries (ICI) at about the same time (81). In the polymerisation step, sulfone links are formed by reaction of an aromatic sulfonyl chloride with a second aromatic ring. The reaction is similar to the Friedel-Crafts acylation reaction. The key to development of sulfonylation as a polymerisation process was the discovery that, unlike the acylation reaction which requires equimolar amounts of aluminum chloride or other strong Lewis acids, sulfonylation can be accompHshed with only catalytic amounts of certain haUdes, eg, FeCl, SbCl, and InCl. The reaction is a typical electrophilic substitution by an arylsulfonium cation (eq. 13). 

In our research, three chemical modification approaches were investigated bromination, sulfonylation, and acylation on the aromatic ring. The specific objective of this paper is to present the chemical modification on the PPO backbone by a variety of electrophilic substitution reactions and to examine the features that distinguish modified PPO from unmodified PPO with respect to gas permeation properties, polymer solubility and thermal behavior. 

The aromatic substrate which undergoes reaction is deactivated by the sulfonyl group toward further electrophilic substitution reactions. Polymers are generally synthesized from monomers having aromatic groups which are separated by some type of spacer that prevents conjugation by resonance between the two rings. 

Synthesis of nitriles (2, 70). Lohaus has published two procedures which illustrate the use of chlorosulfonyl isocyanate for the preparation of nitriles. One, the preparation of 2,4-dimethoxybenzonitrile,8 illustrates the reaction of the reagent with aromatic compounds that readily undergo electrophilic substitution. Thus reaction of resorcinol dimethyl ether (1) with chlorosulfonyl isocyanate in methylene chloride gives the amide N-sulfonyl chloride (2), which on treatment with an amide9 gives 2,4-dimethoxybenzonitrile (3) in 95-96% yield with a purity of 98%. 

The ionic function can be added by (i) electrophilic substitution in ortho-to-ether position on arylene ether segment due to its electron-donating nature or by (ii) aromatic nucleophilic substitution in ortho-to-sulfone position. Due to the electron withdrawing nature of sulfonyl link present in arylene sulfone segment, the acidic character of hydrogen atom present ortho-to-sulfone link is quite high and hence, activated for nucleophilic substitution using lithiation chemistry. 

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