M. Sarakha et al., SELECTIVE OXIDATION OF META-PHENYLPHENOL AND PARA-PHENYLPHENOL PHOTOSENSITIZED BY [CO(NH3)(5)N-3](2-SOLUTION() IN AQUEOUS), Journal of photochemistry and photobiology. A, Chemistry, 97(1-2), 1996, pp. 81-86
The oxidation of meta-phenylphenol (m-PP) and para-phenylphenol (p-PP)
was photosensitized by excitation at 365 nm in the presence of azidop
entaammine cobalt(III) in neutral aqueous solution. The presence of m-
PP or p-PP did not affect the initial quantum yield of cobalt(III) red
uction, and oxygen had no apparent effect. By electron spin resonance
spectroscopy upon irradiation, it was possible to detect the formation
of both N-3(.) and m-PP. radicals as adducts with the spin trap 5,5-d
imethyl-1-pyrroline-N-oxide. Laser Bash photolysis experiments gave ev
idence of the formation of the corresponding phenylphenoxyl radical by
reaction between N-3(.) and the phenols, and their constants of forma
tion and decay were calculated. The dimers were identified as the majo
r photoproducts. Trimers and tetramers of m-PP and p-PP were also form
ed. It is worth noting that no formation of quinones was observed. Cob
alt appeared to prevent the reaction of oxygen with the phenoxyl radic
als.