Wallach rearrangement photochemical

A photochemical Wallach rearrangement is also known The product is the o-hydroxy azo compound, the OH group is found in the farther ring, and the rearrangement is intramolecular. ... 

There are only a relatively small number of examples of this rearrangement in the chemical literature nevertheless, both a thermal and photochemical Wallach rearrangement of azoxybenzene has been achieved in zeolite cages [89] and an ortho-selective rearrangement has been developed on azoxybenzene-SbClj complexes [90]. 

In some way formally similar to the benzidine rearrangement is the Wallach rearrangement of azoxybenzene 23 to give 4-hydroxyazobenzene 24 in concentrated (typically 95%) H2SO4. The 2-hydroxy isomer is sometimes formed in low yield with some substituted azoxybenzenes, and it is the main product in the photochemically induced reaction. Much of what is known about the reaction has been covered in earlier review articles28-30. This contribution will report work published since 1981. 

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