Proximity Effects in Diaryl Derivatives. Part 7. Mechanism of Base-catalysed Rearrangement of 2-(Hydroxyamino)aryl Phenyl Sulphones to 2-Hydroxy-2'-(phenylsulphonyl)azoxybenzenes

Article abstract of DOI:10.1039/P29830000105

Base-catalysed rearrangement of a 2-(hydroxyamino)aryl phenyl sulphone (1b) to the 2-hydroxy-2'-(phenylsulphonyl)azoxybenzene (4b) was shown by isolation and kinetic studies to be a rapid reaction requiring oxygen; in the absence of oxygen the sulphur-free azoxybenzene (3; R=Cl) was the only product isolated from the reaction of (1c).A mechanism for the formation of 2-hydroxyazoxybenzenes (4) is proposed (Scheme 2) involving dimerization of a nitrosoaryl radical anion (9) to the dianion of an NN-diol (10), and displacement of a phenylsulphonyl group by intramolecular transfer of oxygen from a nitrogen atom.A similar study of the base-catalysed reactions of a 2-(hydroxyamino)aryl phenyl sulphide (12) in the presence of oxygen showed that with a poorer leaving group the bis(phenylthio)azoxybenzene (11; R=SPh) is formed.An improved procedure for the preparation of N-arylhydroxylamines from nitrobenzenes is described.