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.