Abstract
The photolysis of 4-bromophenol in aqueous solution in the presence of the spin trap 5,5-dimethylpyrroline- N-oxide (DMPO) results in the formation of four distinct electron paramagnetic resonance (EPR) spectra. Three of these have been identified as arising from the DMPO spin adducts of an aryl radical (probably the 4-hydroxyphenyl radical, spectrum A), a hydrated electron plus later protonation (spectrum B) and the hydroxyl radical (spectrum C). Spectrum D is that of the p-benzosemiquinone anion. Spectra A and B appear immediately on initiation of photolysis in both deoxygenated and oxygenated solutions. Spectra C and D arise from secondary products and require the presence of oxygen. The component EPR spectra do not depend on the pH value in the pH range 7.0 × 10.5, but the overall appearance of the spectra changes with increasing pH, showing a larger contribution of both adducts A and B compared with adduct C. The results are compared with those of previous EPR investigations of 4-chlorophenol and with photochemical studies of 4-substituted halogenophenols using conventional sources of irradiation and the flash photolysis technique. The mechanism of aqueous photolysis of the compounds is discussed.
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