Reactions of carbon dioxide radical anion with substituted benzenes

We report mechanistic studies on the reactivity of CO(2)(.-) radicals towards substituted benzenes, XPh, with X = NO(2), COOH, COH, CH(3), H, Cl and HO. Vacuum ultraviolet (VUV, 172 nm) irradiation of aqueous solutions containing formate was used as a method of CO(2)(.-) radical generation for the study of the reaction products, which were determined by gas chromatography-mass spectrometry and high-performance liquid chromatography. The nature of some of the reaction intermediates was studied by laser flash photolysis of aqueous solutions of peroxodisulfate in the presence of formate. The observed products and intermediates of reaction are discussed and rationalized by a dual reactivity of the CO(2)(.-) radical anion with substituted benzenes: a one-electron reduction and radical addition to the aromatic ring. For substituted benzenes with X = NO(2), COOH and COH, the observed products support an electron transfer from CO(2)(.-) to the substrates as the primary reaction channel, while the reactions with toluene follow the channel of radical addition. Benzene and chlorobenzene react with CO(2)(.-) by both routes, electron transfer and radical addition. Our experimental results indicate that H abstraction by the CO(2)(.-) radical is negligible under the chosen experimental conditions. Copyright (C) 2001 John Wiley & Sons, Ltd.