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Kinetic Study of the Reactions of Chlorine Atoms and Cl 2 •- Radical Anions in Aqueous Solutions. 1. Reaction with Benzene

2000; American Chemical Society; Volume: 104; Issue: 14 Linguagem: Inglês

10.1021/jp9929768

1520-5215

María L. Alegre, Mariana Geronés, Janina A. Rosso, Sonia G. Bertolotti, André M. Braun, Daniel O. Mártire, Mónica C. González,

Atmospheric Ozone and Climate

The photolysis of Na2S2O8 aqueous solutions containing Cl- ions is a clean method for kinetic studies of the species Cl•/ Cl2•- in the absence and presence of added aromatic substrates. Laser and conventional flash-photolysis techniques were employed to investigate the aqueous phase reactions of chlorine atoms and Cl2•- (340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl2•- in aqueous solutions containing chloride ion concentrations in the range 1 × 10-4 to 0.6 M, total radical (Cl• + Cl2•-) 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 × 109 M-1 s-1 ≤ k ≤ 1.2 × 1010 M-1 s-1 and < 1 × 105 M-1 s-1 were determined for the reactions of Cl• and Cl2•- 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 O2 and Cl−CHD. A reaction mechanism leading to the formation of chlorobenzene is proposed.