Iron-catalytic photochemical reactions of benzoic acid: Product identification and reaction mechanisms

Iron-catalyzed photochemical oxidation of benzoic acid, one of the major photodegradation products of petroleum hydrocarbons, with sunlight and monochromatic light in a wavelength range of 254-419 nm was studied. The photochemical degradation of benzoic acid occurred at 245 nm either in the presence or in the absence of iron(III). Addition of iron(III) enhanced greatly the photodegradation of benzoic acid at 350 nm, 419 nm, and under solar irradiation. The major reaction products were monohydroxybenzoic acids and ferrous iron species. The proposed reaction mechanism includes the photoexcitation of iron(III) hydroxide complexes to form iron(II) species and corresponding hydroxyl radicals (OH·) that attack ortho, meta, and para positions of benzoic acid to form monohydroxybenzoic acids and hydrogen peroxide. The monohydroxybenzoic acids were attacked further by hydroxyl and superhydroxyl radicals (HO ₂ ^-/O ₂ ^-) to yield dihydroxybenzoic acids. This is an abstract of a paper presented at the 229th ACS National Meeting (San Diego, CA 3/13-17/2005).