Autoxidation and photochromism of aryl aldehyde arylhydrazones

Abstract

Aerial oxidation of aldehyde arylhydrazones has been shown to result in the formation of bright red formazans in varying yields. A mechanism proposed for this reaction involves the decomposition of an intermediate arylazo hydroperoxide to an aryldiazonium ion and subsequent coupling of the latter with another molecule of the arylhydrazone.��� The irreversible formation of 1,3,5-triphenylformazan from benzaldehyde phenylhydrazone satisfactorily accounts for the ?photochromism? (light-induced coloration) of the latter compound; the apparent reversibility of the photochromism is attributed to the subsequent aerial oxidation of the red formazan to the corresponding colourless tetrazolium ion.