Suchergebnisse

AbstractNatural waters, water droplets in the air at coastal regions and wastewaters usually contain chloride ions (Cl-) in relatively high concentrations in the milimolar range. In the reactions of highly oxidizing radicals (e.g.,•OH,•NO3, or SO4•-) in the nature or during wastewater treatment in advanced oxidation processes the chloride ions easily transform to chlorine containing radicals, such as Cl•, Cl2•-, and ClO•. This transformation basically affects the degradation of organic molecules. In this review about 400 rate constants of the dichloride radical anion (Cl2•-) with about 300 organic molecules is discussed together with the reaction mechanisms. The reactions with phenols, anilines, sulfur compounds (with sulfur atom in lower oxidation state), and molecules with conjugated electron systems are suggested to take place with electron transfer mechanism. The rate constant is high (107–109M-1s-1) when the reduction potential the one-electron oxidized species/molecule couple is well below that of the Cl2•-/2Cl-couple.

AbstractRate constants of chlorine atom (Cl•) reactions (kCl•) determined using a large variation of experimental methods, including transient measurements, steady-state and computation techniques, were collected from the literature and were discussed together with the reaction mechanisms. The kCl• values are generally in the 108–109 mol−1 dm3 s−1 range when the basic reaction between the Cl• and the target molecule is H-atom abstraction. When Cl• addition to double bonds dominates the interaction, the kCl• values are in the 1 × 109–2 × 1010 mol−1 dm3 s−1 range. In the kCl• = 1 × 1010–4 × 1010 mol−1 dm3 s−1 range, single-electron-transfer reactions may also contribute to the mechanism. The Cl• reactions with organic molecules in many respects are similar to those of •OH, albeit Cl• seems to be less selective as •OH. However, there is an important difference, as opposed to Cl• in the case of •OH single-electron-transfer reactions have minor importance. The uncertainty of Cl• rate constant determinations is much higher than those of •OH. Since Cl• reactions play very important role in the emerging UV/chlorine water purification technology, some standardization of the rate constant measuring techniques and more kCl• measurements are recommended.