Friedel-Crafts sulfonylations

Methanesulfonic and ben2enesulfonic anhydrides are the most frequently used anhydrides ia Friedel-Crafts sulfonylation reactions ... 

Scheme 6.5 Friedel-Crafts sulfonylation of AA-BB and AB types of polycondensations.

Simple ways to catalyze nitrations and sulfonylations of aromatic compounds are of great interest since these reactions are carried out industrially on large scale. Clays and zeolites with defined pore structures and channels as acidic catalysts have been utilized in nitrations [109] and Friedel-Crafts sulfonylations [110]. 

Nara, S. J., Harjani, J. R., and Salunkhe, M. R., Friedel-Crafts sulfonylation in l-butyl-3-methylimidazolium chloroaluminate ionic liquids, /. Org. Chem., 66, 8616, 2001. 

Friedel-Crafts sulfonylation of benzene and its derivatives can also be carried out using iron(III) chloride-based ionic liquids, as was shown by Samant and coworkers [23]. For example, the synthesis of diphenyl sulfone, an important intermediate for the anti-leprosy drug Dapsone, was achieved in 78% yield catalyzed by 1-butyl-3-methylimidazolium chloride combined with FeCl3 (Scheme 6.7). 

Polysulfones can be prepared by Friedel-Crafts sulfonylation reactions [133-150]. The carbenium ion intermediates can be generated from the Lewis acid-catalyzed reaction of involving arene sulfonyl chloride [Eq. 

Lewis acids such as A1C13, AlBr3, FeCl3, and SbCl5 have been used [151]. Friedel-Craft sulfonylation reactions typically require more than one mole equivalent of Lewis acid per sulfonyl halide. This is apparently due to the coordination of one equivalent of the Lewis acid with the sulfonyl group. 

The Friedel-Crafts sulfonylation of aromatics with alkane- and arenesulfonyl halides and anhydrides has been studied (Eq. 9) [23]. In the reaction of pentafluorobenzenesul-fonyl fluoride with pentafluorobenzene, decafluorodiphenyl sulfone is formed with deca-fluorodiphenyl [23c]. Certain phenylacetylenes react with SO2 and benzene in the presence of SbFs to form benzothiophene 5-oxide [24]. (Eq. 10). Sulfinyl fluoride reacts similarly with arenes under SbFs catalysis to give sulfoxides (Eq. 11) [25]. 

Various synthetic approaches have been demonstrated for the synthesis of PAEs since early days [35 0], PAEs were synthesized by Ullmann condensation between bisphenols and aryl fcis-halide monomers using Cu(I) salt/pyridine as catalyst [36], General Electric developed the first commercially successful PAE poly(2,6-dimethyl phenylene oxide) (PPO) [38], It was prepared by oxidative coupling of 2,6-dimethyI phenol. However, this process has its own restrictions, because it does not allow much structural variation or inclusion of any electron-withdrawing group into the polymer main chain. First attempts to synthesize polysulfones (PSF) were successfully done by Friedel-Crafts sulfonylation reaction of arylenedisulfonyl chlorides, for example, diphenyl ether-4,4 -disulfonyl chloride with diaryl ethers, for example, diphenyl ether, or by self-condensation of 4-phenoxy benzene sulfonyl chloride in the presence of FeCls [41], Whereas the former reaction involves side reactions (sulfonylation not only in the para- but also in the ort/io-position), the latter produces only the desired linear all-para products. 

Chloroaluminate ionic liquids were the st reported compounds of this class, and they are still among the best investigated imidazolium ionic liquids [98]. These ILs, specifically the compositions called acidic ([cation]Cl/AlCl3 ratio <1), have been reported as catalysts for alkylation of benzene with dodecene [99], Friedel-Crafts sulfonylation [100], Friedel-Crafts alkylations and acylations [101], and oligomer-izaton of oleflns [102]. 

Fig. 19 Synthesis of poly(ethersulfone)s by A Friedel-Crafts sulfonylation and B by nucleophilic polycondensation in solution using phenolates and C melt polycondensation using trimethylsUyl derivatives of bisphenols... 

FIG. 3.14 Synthesis of poly(ether suIfone)s by (a) Friedel Crafts sulfonylation. (b) nucleophilic polycondensation in solution using phenolates. and (c) melt polycondensalion using trimethylsilyl derivatives of bisphenols. 

The imidazolium chloroaluminate ionic liquid was also found to be effective as an unconventional reaction media and as Lewis acid catalyst for the Friedel-Crafts sulfonylation reaction of benzene and substituted benzene with p-toluenesulfonyl chloride giving rise to the diarylsulfones in high yield (Scheme 6.14) [16]. 

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