Aromatic substitution reactions sulphonylation

Some aromatic compounds have been shown to be substituted in the ring by sulphonyl peroxides421,422 to give 50-70% yields of the sulphonate ester, as shown in equation 96. The experimental evidence from this reaction is apparently consistent with an electrophilic aromatic substitution reaction. 

The success of this reaction was ascribed to the solubility of the chlorozinc intermediate, whereas other chloramine-T derivatives (e.g. the sodium salt) are insoluble. An alternative non-nitrene pathway was not eliminated from consideration. On the other hand, no aromatic substitution or addition, characteristic of a free sulphonyl nitrene (see below), took place on treatment of jV,lV-dichloromethanesulphonamides with zinc powder in benzene in the cold or on heating. The only product isolated was that of hydrogen-abstraction, methanesulphonamide 42>, which appears to be more characteristic of the behaviour of a sulphonyl nitrene-metal complex 36,37). Photolysis of iV.iV-dichloromethanesulphonamide, or dichloramine-B, or dichloramine-T in benzene solution led to the formation of some unsubstituted sulphonamide and some chlorobenzene but no product of addition of a nitrene to benzene 19>. 

The chemical reactions of sulphonyl nitrenes include hydrogen abstraction, insertion into aliphatic C—H bonds, aromatic substitution , addition to olefinic double bonds, trapping reactions with suitable nucleophiles, and Wolff-type rearrangement. Hydrogen-abstraction from saturated carbon atoms is usually considered to be a reaction typical of triplet... 

Aromatic sulphonyl chlorides have been synthesized from unsubstituted sulphona-mides by reaction with PC15639. On the other hand, AT-alkyl substituted sulphonamides undergo a rather surprising reaction with the same reagent, as shown in equation 160640. Sulphonyl fluorides may be prepared from unsubstituted sulphonamides by reaction of the latter with HF and sodium nitrite641. 

This is a typical electrophilic aronatic substitution in which the aromatic substrate is attacked by some form of the arylsulphonylium cation and hydrogen displaced as a proton. The attacking reagent is formed by interaction of the sulphonyl chloride with a Friedel Crafts catalyst the catalyst should be selected from Fed, SbCl or Ind, since with these halides only catalytic quantities are requiredf in contrast to the equimolar quantities usually recommended for Friedel Crafts condensations %d.th acid halides (9). This choice of catalyst is important as it eliminates side reactions and helps considerably with the problem of catalyst removal from the polymers. 

The migration of methyl to sulphur observed in reactions of o-mercapto-benzoic acid methyl ester with primary aliphatic amines, possibly via an S i mechanism, contributes another example to an extensive list of interactions of aromatic or/Ao-substituents. More conventional nucleophilic substitution processes include syntheses of L-selenomethionine, MeSeCH2 -CHa CH(NH2) C02H, and its c-ethyl and S e-benzyl analogues by treatment of O-toIuene-p-sulphonyl-L-homoserine with appropriate organo-selenium nucleophiles also, analogous reactions of hydroxy-acid... 

Miscellaneous reactions of cr-sulphonyl carbanions with electrophiles include processes involving arylsulphonylmethyl methyl ether anions, cr-sulphinyl sulphone anions, perfluorobutylsulphonylmethylmagnesium halides, nucleophilic substitution in aromatic nitro-compounds by cr-halogenosulphonyl... 

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