The photolysis of Na 2 S 2 O8 aqueous solutions containing Cl -ions is a clean method for kinetic studies of the species Cl • / Cl 2 •-in the absence and presence of added aromatic substrates. Laser and conventional flashphotolysis techniques were employed to investigate the aqueous phase reactions of chlorine atoms and Cl 2 •-(340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl 2 •-in aqueous solutions containing chloride ion concentrations in the range 1 × 10 -4 to 0.6 M, total radical (Cl • + Cl 2 •-) concentrations in the range (0.1-1.5) × 10 -5 M, and pH in the range 2.5-3.0. Interpretation of the experimental data is supported by kinetic computer simulations. The rate constants 6 × 10 9 M -1 s -1 e k e 1.2 × 10 10 M -1 s -1 and < 1 × 10 5 M -1 s -1 were determined for the reactions of Cl • and Cl 2 •-with benzene, respectively, in the aqueous phase. The organic radicals produced from these reactions exhibit an absorption band with maximum at 300 nm, which was assigned to a Cl-cyclohexadienyl radical (Cl-CHD). The kinetic analysis of the traces supports a reversible reaction between O 2 and Cl-CHD. A reaction mechanism leading to the formation of chlorobenzene is proposed.

Laser and conventional flash photolysis of Na 2 S 2 O 8 aqueous solutions containing Clions were employed to investigate the reactions of chlorine atoms and Cl 2 •radical ions with toluene, benzoic acid, and chlorobenzene. A mechanism is proposed which accounts for the faster decay of Cl 2 •in aqueous solutions containing increasing concentrations of the organic substrates. Interpretation of the experimental data is supported by kinetic computer simulations. Chlorine atoms react with the three substituted aromatics studied here almost with diffusioncontrolled rate constants, k ) (1.8 ( 0.3) × 10 10 M -1 s -1 . The high reactivity observed for Cl atoms contrasts with that of the Cl 2 •radical ions, for which the rate constant for its reactions with the substituted benzenes is e 1 × 10 6 M -1 s -1 . The organic radicals produced from these reactions, as well as the nature of the reaction products are discussed. The observed results seem to support an addition mechanism yielding chlorocyclohexadienyl radicals (Cl-CHD) as the most significant reaction channel following reaction of Cl atoms and the organic compounds. In air-saturated solutions, subsequent thermal reactions of Cl-CHD radicals lead both to chlorination and oxidation of the aromatics.

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Dedicated to Prof. Dr. Silvia E. Braslavsky on the occasion of her 60th birthdayThe kinetics and reaction mechanism of phosphate radicals with substituted benzenes, PhX (X OH, Me, H, Cl, MeO, and CHO), were studied by flash photolysis and continuous irradiation of aqueous solutions containing potassium peroxodiphosphate (K 4

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We report mechanistic studies on the reactivity of CO 2 .À 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 .À 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 .À 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 .À 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 .À by both routes, electron transfer and radical addition. Our experimental results indicate that H abstraction by the CO 2 .À radical is negligible under the chosen experimental conditions.

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