Kinetic Study of the Reactions of Chlorine Atoms and Cl₂^•- Radical Anions in Aqueous Solutions. 1. Reaction with Benzene

Abstract

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.

Photochemistry of 1-Nitronaphthalene: A Potential Source of Singlet Oxygen and Radical Species in Atmospheric Waters

“…ratio is expected to be high and, consequently, the contribution of the chlorine radical to the observed absorption traces can be neglected 25 .…”

“…These radicals are known to be responsible for ozone depletion 24 , and consequently they can alter the oxidant capacity of the atmospheric aqueous and gas phases. They react with organic compounds (R2 -R3) via electron transfer, addition to double bonds and H-abstraction 25 . Although the halogen radicals can initiate a set of catalytic cycles capable of destroying ozone 26 or of oxidizing organic compounds (R2 and R3), to our knowledge only a limited number of studies have investigated their formation via photosensitized reactions of organic compounds in the atmospheric aqueous phase.…”

Photochlorination of aniline in Fe3+-containing saline water under simulated solar light irradiation

“…The small discrepancy indicates that molecular oxygen played a minor role in the formation of CAs. Because O 2 is the effective species for hydrogen abstraction whereas Cl and Cl 2 À are not, [11,12] Photochlorination of aniline in saline water adding directly to the aromatic ring is not supported as one of the effective chlorination mechanisms.…”

“…The polymerisation of aniline is indirect proof of the presence of anilino radical cations during aniline phototransformation. From the viewpoint of thermodynamics, the redox potentials of E(Cl 2 [12] It is evident that aniline can be oxidised by Cl or Cl 2 À to anilino radical cations. Finally, the reaction between Cl or Cl 2 À radicals and anilino radical cations gives rise to the produced CAs, in analogy to the substitution of phenoxyl radicals.…”

“…Finally, the reaction between Cl or Cl 2 À radicals and anilino radical cations gives rise to the produced CAs, in analogy to the substitution of phenoxyl radicals. [12,[17][18][19][20][21] Formation of CA radical cations should be derived from the oxidation of CA because the direct addition of Cl 2 À to the aromatic ring is not supported as discussed above. The observation of CA radical cations in the absorption spectra implies that the photolysis of 4CA occurred under the simulated solar irradiation.…”