Kinetic study of the reactions of chlorine atoms and Cl-2(center dot-) radical anions in aqueous solutions. 1. Reaction with benzene

The photolysis of Na2S2O8 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 flash-photoly sis techniques were employed to investigate the aqueous phase reactions of chlorine atoms and Cli(340 nm) radical ions in the presence and absence of benzene. A mechanism is proposed which accounts for the decay of Cl-2(.-) i n aqueous solutions containing chloride ion concentrations in the range 1 x 10(-4) to 0.6 M, total radical (Cl-. + Cl-2(.-)) concentrations in the ran ge (0.1-1.5) x 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 c onstants 6 x 10(9) M-1 s(-1) less than or equal to k less than or equal to 1.2 x 10(10) M-1 s(-1) and < 1 x 10(5) M-1 s(-1) were determined for the re actions of Cl-. and Cl-2(.-) with benzene, respectively, in the aqueous pha se. The organic radicals produced from these reactions exhibit an absorptio n band with maximum at 300 nm, which was assigned to a Cl-cyclohexadienyl r adical (Cl-CHD). The kinetic analysis of the traces supports a reversible r eaction between O-2 and Cl-CHD. A reaction mechanism leading to the formati on of chlorobenzene is proposed.