Amido Black, a diazo dye, was subjected to UV light in the presence
of H2O2 and the degradation products and intermediates were
analyzed by LC-(+ESI)-MS [37]. It was proposed that the overall photolytic
oxidation of the dye was most likely to have been initiated by
OH radicals. LC-MS/MS studies suggested possible pathways of dye
degradation and revealed a variety of intermediate compounds that
were formed during the course of the reaction (Scheme 3B). Three
different mechanistic pathways were proposed for the degradation
of the dye (radical denitration, radical desulfonation, and radical
diazotization). The study also showed that the dye degradation
started by cleavage of the –N@N group bearing the unsubstituted
phenyl ring. Based on the observations, it was found that, given the
choice of two azo groups, OH radicals preferentially attack the more
electron-rich diazo functionality of the molecule.