Aromatic sulphonamides

Aromatic peroxides and per-acids, 807 Aromatic substitution, 524, 525 Aromatic sulphonamides, 553... 

Aromatic sulphonamides have been particularly exhaustively studied. The substituent-... 

N spectra have been recorded for many sulphonamides, and some 15N NMR chemical shifts are given in Table 32. The aromatic sulphonamides in particular have... 

Sulphonic acids may also be prepared by the pyrolysis of mixed sulphonic-carboxylic anhydrides above 130 °C. In addition, ketenes are formed which presumably undergo further reaction, depending on the reaction conditions317. A series of aromatic sulphonic acids have been prepared by reaction of aromatic sulphonamides with nitrosonium tetrafluoroborate318, as shown in equation 67. 

Sulphonamides have also been prepared from sulphamoyl chlorides by a different procedure. In this method, sulphamoyl chlorides are reacted with a tertiary amine to produce an azasulphene, which is then used in situ for the formation of sulphonamides. A wide structural variety of sulphonamides may be obtained by reaction of azasulphenes with different substrates. Reaction with some substituted alkenes proceeds via either a [2 + 2] cycloaddition reaction as exemplified in equation 102433 or a [2 + 4] cycloaddition reaction as shown in equation 103434,435. Azasulphenes also react with aromatic compounds that are highly activated towards electrophilic substitution as shown in equation 104436. If carboxyethyl azasulphene is used in this reaction, then the unsubstituted aromatic sulphonamide may be obtained in high yield, simply by hydrolysis436 (equation 105). 

Arenesulphonamides may be cathodically cleaved in alkaline as well as acidic media27,60. The electrochemical hydrogenolysis of sulphonamides at mercury cathodes using tetramethylammonium salts as supporting electrolytes was first investigated2. It was then established that aromatic sulphonamides were cleaved to yield amines in high yields and therefore this cathodic reaction appeared to present an important route in the deprotection... 

The latter reaction occurs with all types of substituents R1 and R2 (aliphatic or/and aromatic) since the presence of an aromatic moiety associated with the —S02— group renders the whole class of aromatic sulphonamides electroactive. On the other hand, anilides of aliphatic sulfonic acids are not reduced under similar experimental conditions (aqueous electrolyte) as given in Reference 2. Thus the presence of the arenesulphonyl group appears then to be a necessary condition to permit the preliminary electron transfer and therefore to allow the deprotection of amines. 

Biochemical Aspects. The zinc-containing metalloenzyme carbonic anhydrase (carbonic hydro-lyase, EC 4.2.1,1) is specifically inhibited by univalent anions and by aromatic sulphonamides. AfT (25 for the binding reactions between bovine carbonic anhydrase and 3-methyl-2-acetylimino-l,3,4-thiadiazoline-5-sulphonamide (Methazolamide) is — 59.0kJmol and that for 5-phenyl-sulphonamido-l,3,4-thiadiazole-2-sulphonamide (CL 11366) is — 57.7kJmol" The thermodynamic quantities did not correlate with the assumed structural features of the binding process. ... 

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