1968 Volume 41 Issue 9 Pages 2151-2155
The photochemical oxygen migration and cis-trans isomerization of azoxybenzene have been investigated. The direct irradiation of trans-azoxybenzene leads to both rearrangement to 2-hydroxyazobenzene and cis-trans isomerization, whose rate is faster in a polar protic solvent and is never affected by a quencher. Direct irradiation does not afford any azobenzene formed from an excited triplet state of azoxybenzene. On the basis of these observations, the author proposes a mechanism in which 2-hydroxyazobenzene and cis-azoxybenzene are formed directly from an excited singlet state of trans-azoxybenzene. This mechanism is analogous to that for the photochemical rearrangement of nitrone to oxaziridine. Nitro- or dimethylamino-substituted azoxybenzene undergoes neither photochemical rearrangement nor cis-trans isomerization. Oxygen migration is not sterically hindered by a substituent in the 3-position of azoxybenzene.
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