Photochemical behavior of the iron(III)/2,6-dimethylphenol system

The photoinduced degradation of 2,6-dimethylphenol (DMP) by iron(lll) in aqueous solution has been investigated under monochromatic excitation (lambda = 365 nm). Depending on the nature of the iron(lll) species (monomeric, dimeric...) present in the solution, there are two different mechanisms that can induce DMP disappearance. When the monomeric species Fe(OH)(2+) is present, an attack by (OH)-O-. radicals coming from an intramolecular photoredox process accounts for half of the degradation; the second process involves a quenching between iron(lll) species in the excited state and DMP leading to 2,6-dimethyl-phenoxyl radical. in the absence of monomeric species only the second mechanism is present. The major photoproduct is 2-hydroxy-3,5-dimethylbenzoquinone, which comes from a further hydroxylation of 2,6-dimethylbenzoquinone, whose formation was evidenced only by Rash photolysis-HPLC experiments. For prolonged irradiations, the total degradation of DMP is observed.