Primary stage of the reaction between ozone and chloride ions in aqueous solution: Oxidation of chloride ions with ozone through the mechanism of oxygen atom transfer

Abstract

519Studying how ozone reacts with chloride ions in aqueous solutions is of immediate interest. This reac tion is possible in various manufacturing processes (e.g., water conditioning and purification) involving the use of ozone and in which the presence of Cl -ions is possible. Due to the presence of ozone in the Earth's atmosphere and the great abundance of chloride ions in nature, the reaction between О 3 and Cl -can con siderably affect the environment. The probability of the reaction between these two components must be taken into account when using ozonized saline solu tion in medicine.The question of the nature of the primary stage in the complex reaction between О 3 and Cl -(aq) is of great importance. A mechanism in which the oxida tion of chloride ions with ozone occurs via the transfer of an oxygen atom from the О 3 molecule to the Cl -ion has been recognized in all works devoted to studying the reaction between О 3 and Cl -(aq) since 1949. In 2010, however, a new mechanism for this reaction was proposed: it was claimed that the oxidation of chloride atoms is accompanied by the transfer of an electron from the Cl -ion to the О 3 molecule [2, 3] (see also [4]). The purpose of this work is to clarify via which mechanism the primary stage of the reaction between О 3 and Cl -(aq) actually proceeds.One feature of the complex reaction between О 3 and Cl -(aq) is that its primary stage is a slow process. At the same time, the substances produced during the primary stage are much more reactive than chloride ions and enter into rapid secondary reactions that lead to the formation of the final products. As a result, indi vidual primary reactions (without secondary reac tions) is virtually inaccessible to experimental studies. Consequently, any conclusions as to the nature of the primary stage should be based on information about the final products and the kinetic features of the com plex reaction between О 3 and Cl -(aq) as a whole.The kinetics of the reaction between О 3 and Cl -(aq) in an acid aqueous solution were studied for the first time in [1]. The reaction was found to be catalyzed by Н + ions, and the rate constants were determined to be 0 and 9.5°С. At higher temperatures, determination of the rate constants failed, since the results were dis torted appreciably by the decomposition of ozone. For the same reason, only the upper limit value of the rate constant was determined in [5] for the non catalytic reaction between О 3 and Cl -(aq) at 23°С, k < 3 × 10 -3 l/(mol s) (pH 2). In [6,7], the kinetics of the decomposition of ozone in an aqueous solution containing chloride ions was studied using the same method as in [5]. If we relate the constant of the decomposition of ozone found in the works men tioned above to the concentration of chloride ions, we obtain the upper limit values for the rate constant of the noncatalytic reaction between О 3 and Cl -. These estimates are in agreement with the following data [5]: k < 3 × 10 -3 l/(mol s) (рН 6, 20°С) [6]; k < 6 × 10 -3 l/(mol s) (pH 6, 20°С) [7].The produ...

Solubility of Ozone and Kinetics of Its Decomposition in Aqueous Chloride Solutions

“…The value of the constant k (O 3 +Cl – ), calculated from eq , is approximately 1.5 times larger than the values given in works , , and The presence of hydrogen ion concentration in expressions and reflects the fact that reaction is accelerated by these particles. H + ions can be regarded as catalyst, although they are consumed in the total reaction .…”

“…H + ions can be regarded as catalyst, although they are consumed in the total reaction . Reaction is complex and proceeds through several stages; its mechanism is discussed in ref . The primary rate-determining step is the oxidation of chloride ion by ozone molecule through the mechanism of oxygen atom transfer, with the formation of chlorine compounds in oxidation state +1, ClO – or HOCl.…”

“…For acidic solutions (pH < 2), the agreement is very good, since in them the interaction of chloride ion with ozone proceeds dominantly via the mechanism of oxygen atom transfer, and the total reaction is described by eq 10. 38 In neutral NaCl solutions (pH 5−7), the value of k 2 exceeds that of k(O 3 + Cl − ), calculated from formula 13 using the appropriate H + concentration. This is due to the fact that in such solutions, in addition to the reaction between ozone and chloride ion by the mechanism of oxygen atom transfer from O 3 molecule, other processes of O 3 decay and Cl − oxidation become significant, which involve hydroxyl radicals OHthe intermediates of the chain reaction of ozone self-decomposition in aqueous solution.…”

Mechanism and Kinetic Model of Chlorate and Perchlorate Formation during Ozonation of Aqueous Chloride Solutions

“…The reaction of Cl − with O 3 by the mechanism of oxygen atom transfer is complex and proceeds through several stages. 20,26,43 As the intermediates of this reaction have not been experimentally determined, in the model, it is written as…”

“…The primary oxidation of chloride ion occurs when it interacts with ozone O 3 or hydroxyl radical OH • . The reaction of Cl – with O 3 by the mechanism of oxygen atom transfer is complex and proceeds through several stages. ,, As the intermediates of this reaction have not been experimentally determined, in the model, it is written as and its rate constant is a function of temperature, ionic strength, and concentrations of H + and Cl – , as determined by expression from our work . The value of the constant is k 1 = 2.2 × 10 –3 L mol –1 s –1 at 20 °C, pH > 3, and the concentration of Cl – and ionic strength being equal to 1 M. The stages and rate constants of the complex reaction of chloride ion oxidation by OH • radicals are given in the model according to the literature. − …”