Self-sensitised and Methylene Blue-sensitised photo-oxidation of 4-arylazo-1- and 1-arylazo-2-naphthols gives 1,4- and 1,2-naphthoquinone, respectively, via the reaction of singles oxygen with the hydrazone tautomeric forms. The reactivity in both cases decreases with increasing electron-withdrawing strength of substituents in the aryl ring.
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Griffiths et al. (1977) studied this question.