Kinetic study of the reactions of chlorine atoms and Cl(2)(center dot-)radical anions in aqueous solutions. II. Toluene, benzoic acid, and chlorobenzene

Laser and conventional flash photolysis of Na2S2O8 aqueous solutions contai ning Cl- ions 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 aq ueous solutions containing increasing concentrations of the organic substra tes. Interpretation of the experimental data is supported by kinetic comput er simulations. Chlorine atoms react with the three substituted aromatics s tudied here almost with diffusioncontrolled rate constants, k = (1.8 +/- 0. 3) x 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 less than or equal to 1 x 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 se em 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 th ermal reactions of Cl-CHD radicals lead both to chlorination and oxidation of the aromatics.