Sulphonamides photolysis

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>. 

On the other hand, thermolysis of ferrocenylsulpkonyl azide (14) in aliphatic solvents may lead to the predominant formation of the amide (16) 17>. A 48.4% yield of (16) was obtained from the thermolysis in cyclohexane while an 85.45% yield of 16 was formed in cyclohexene. Photolysis of 14 in these solvents led to lower yields of sulphonamide 32.2% in cyclohexane, 28.2% in cyclohexene. This suggests again that a metal-nitrene complex is an intermediate in the thermolysis of 14 since hydrogen-abstraction appears to be an important made of reaction for such sulphonyl nitrene-metal complexes. Thus, benzenesulphonamide was the main product (37%) in the copper-catalyzed decomposition of the azide in cyclohexane, and the yield was not decreased (in fact, it increased to 49%) in the presence of hydroquinone 34>. On the other hand, no toluene-sulphonamide was reported from the reaction of dichloramine-T and zinc in cyclohexane. 

Similar results were obtained in the photolysis of ethyl azidofor-mate and in the decomposition of sulphonyl azides, which yielded sulphonamides . ... 

Benzobenzvalene (100) has been shown to add sulphur dioxide to give the sulphone (101) and the 7-sultine (102) both adducts extrude sulphur dioxide on direct photolysis regenerating benzobenzvalene accompanied by naphthalene. Competing homolytic and heterolytic bond cleavages have been observed in singlet excited triarylsulphonium salts, and intramolecular electron transfer is involved in the photodissociation of p-nitrobenzyl 9,10-dimethoxy-anthracene-2-sulphonate.A photochemical method for the detosyl-ation of sulphonamides has been described,and the thermolysis and photolysis of some thiourea derivatives have been compared. 

Forster and coworkers173 report that the sulphonamides 198 undergo loss of sulphur dioxide on excitation, yielding azobenzene and aniline. The former product is thought to arise by an intramolecular path, since the photolysis of the tolyl derivative 199 yields only 3-methylazobenzene and no mixed derivatives. In contrast, N-arylbenzenesulphonamides... 

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