Reactions of carbon dioxide radical anion with substituted benzenes

We report mechanistic studies on the reactivity of CO2.- radicals towards s ubstituted benzenes, XPh, with X = NO2, COOH, COH, CH3, H, Cl and HO. Vacuu m ultraviolet (VUV, 172 nm) irradiation of aqueous solutions containing for mate was used as a method of CO2.- radical generation for the study of the reaction products, which were determined by gas chromatography-mass spectro metry and high-performance liquid chromatography. The nature of some of the reaction intermediates was studied by laser flash photolysis of aqueous so lutions of peroxodisulfate in the presence of formate. The observed product s and intermediates of reaction are discussed and rationalized by a dual re activity of the CO2.- radical anion with substituted benzenes: a one-electr on reduction and radical addition to the aromatic ring. For substituted ben zenes with X = NO2, COOH and COH, the observed products support an electron transfer from CO2.- to the substrates as the primary reaction channel, whi le the reactions with toluene follow the channel of radical addition. Benze ne and chlorobenzene react with CO2.- by both routes, electron transfer and radical addition. Our experimental results indicate that H abstraction by the CO2.- radical is negligible under the chosen experimental conditions. C opyright (C) 2001 John Wiley & Sons, Ltd.