The photochemistry of para-substituted phenylsulphamates—photo-fries rearrangements

The photolysis (254 nm) of a series of para-substituted phenylsulphamates, XC₆H₄NHSO₃Na [X=H (1a), CH₃ (1b), F (1c), Cl (Id), Br (1e) and NO₂ (If)] in degassed methanolic solutions has been examined. For 1a and 1b photo-Fries type rearrangements to sulphonic acids and photodegradation to anilines have been observed. The halogenosulphamates 1c–1e do not rearrange but degrade to anilines and are photosolvolysed to p-methoxyphenylsulphamic acid. No notable spectral changes took place during the irradiation of 1f over a relatively long period. Substrate concentration studies, radical scavenging and sensitization and quenching experiments on 1b indicate that, as previously found for 1a, its photolysis involves an intramolecular radical mechanism with the participation of two triplet states.