Rate constants of chlorine atom reactions with organic molecules in aqueous solutions, an overview
László Wojnárovits, Jianlong Wang, Libing Chu, Erzsébet Takács
Abstract
Abstract Rate constants of chlorine atom (Cl • ) reactions ( k Cl• ) 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 k Cl• values are generally in the 10 8 –10 9 mol −1 dm 3 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 k Cl• values are in the 1 × 10 9 –2 × 10 10 mol −1 dm 3 s −1 range. In the k Cl• = 1 × 10 10 –4 × 10 10 mol −1 dm 3 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 k Cl• measurements are recommended.