Kinetic study of the reactions of chlorine atoms and Cl{sub 2}{sup .-} radical anions in aqueous solutions. 1. Reaction with benzene

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 104; no. 14
• Main Authors: Alegre, M.L., Gerones, M., Rosso, J.A., Bertolotti, S.G., Braun, A.M., Martire, D.O., Gonzalez, M.C.
• Format: Journal Article
• Language: English
• Published: United States 13-04-2000
• Subjects: ATMOSPHERIC CHEMISTRY; BENZENE; CHEMICAL REACTION KINETICS; CHLORINE; CLOUDS; ENVIRONMENTAL SCIENCES; PHOTOLYSIS; RADICALS; TROPOSPHERE
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp9929768

The photolysis of Na{sub 2}S{sub 2}O8 aqueous solutions containing Cl{sup {minus}} ions is a clean method for kinetic studies of the species Cl{sup {sm_bullet}}/Cl{sub 2}{sup {sm_bullet}{minus}} 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 Cl{sub 2}{sup {sm_bullet}{minus}} (340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl{sub 2}{sup {sm_bullet}{minus}} in aqueous solutions containing chloride ion concentrations in the range 1 x 10{sup {minus}4} to 0.6 M, total radical (Cl{sup {sm_bullet}} + Cl{sub 2}{sup {sm_bullet}{minus}}) concentrations in the range (0.1--1.5) x 10{sup {minus}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 x 10{sup 9} M{sup {minus}1} s{sup {minus}1} {le} {kappa} {le} 1.2 x 10{sup 10} M{sup {minus}1} s{sup {minus}1} and <1 x 10{sup 5} M{sup {minus}1} s{sup {minus}1} were determined for the reactions of Cl{sup {sm_bullet}} and Cl{sub 2}{sup {sm_bullet}{minus}} 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{sub 2} and Cl-CHD. A reaction mechanism leading to the formation of chlorobenzene is proposed.