Magnetic Field Effects on and Mechanism of Photoredox Reaction of Aromatic Nitro Group

Article abstract of DOI:10.1246/bcsj.66.920

Photoredox reaction mechanism of a homologous series p-O2NC6H4O(CH2)nNHPh (1) in acetonitrile and benzene is studied.The major products are p-ONC6H4O(CH2)n-1CHO (3) and aniline derived from intramolecular reaction, but the presence of minor amounts of intermolecular reaction products, p-O2NC6H4O(CH2)n-1CHO (4) and p-ONC6H4O(CH2)nNHPh (5) is confirmed in the reaction mixture.In the presence of an external magnetic field, the yield of 3 is suppressed and those of 4 and 5 are correspondingly increased, while the rates of the disappearance of 1 and of the formation of aniline remain unchanged, suggesting the presence of biradical recombination process accompanied by intersystem crossing in a rate-determining step.On the basis of these observations, two reaction schemes are proposed.The magnetic field effects provide strong evidence for the presence of a transient species with (nitro)N(OH)-O-CHN< group generally supposed for nitro oxygen transfer process in this type photoreaction.