The Photochemistry of Some Methoxy and Dimethylamino Derivatives of Azoxybenzene

Article abstract of DOI:10.1021/jo00351a018

The photochemistry of the six azoxybenzene derivatives carrying a methoxy and/or a dimethylamino group in positions 4/4' has been examined in alcogols and in benzene and found to lead to different processes.The photo-Wallach rearrangement takes place for all except the disubstituted derivatives.This process involves an intermediate, which either gives back the starting azoxy or is converted to the final o-hydroxy derivative through acid catalysis as well as by the previously reported basic catalysis or via cleavage to diazonium ions, which can be trapped before recombination.Oxygen shift to yield the isomeric azoxy derivative (only one precedent known) is a general, one-way process, leading in every case to the azoxy benzene with the N->O group far from the ring carrying the stronger electron-donating substituent.Differently from the photo-Wallach rearrangement, this process shows little solvent dependence.The dimethylamino derivatives undergo also or exclusively different fragmentations, such as intramolecular hydrogen abstraction and cleavage of either the N=N or the C-N bond.The solvent and substituent effect upon electronic spectra, reaction quantum yield, and product distribution are discussed.The photochemistry is attributed to a ?,?^* state with strong internal charge transfer.