Reaction Of ClO2 Research Articles

Reaction of Polyamide Membrane Model Monomers with Chlorine Dioxide: Kinetics, Pathways, and Implications.

Aromatic polyamide (PA) based membranes are widely used for reverse osmosis (RO), but they can be degraded by free chlorine used for controlling the biofouling prior to RO treatment. Kinetics and mechanisms for the reactions of PA membrane model monomers, i.e., benzanilide (BA), and acetanilide (AC), with chlorine dioxide (ClO2) were investigated in this study. Rate constants for the reactions of ClO2 with BA and AC at pH 8.3 and 21°C were determined to be (4.1±0.1)×10-1 M-1.24 s-1 and (6.0±0.1)×10-3 M-1 s-1, respectively. These reactions are base assisted with a strong pH dependence. The activation energies of BA and AC degradation by ClO2 were 123.7 and 81.0 kJ mol-1, respectively. This indicates a relatively strong temperature dependence in the studied temperature range of 21-35 °C. The presence of bromide and natural organic matter does not promote the degradation of model monomers by ClO2. BA was degraded by ClO2 via two pathways: (1) the attack on the anilide moiety with the formation of benzamide (major pathway) and (2) oxidative hydrolysis to benzoic acid (minor pathway). A kinetic model was developed to simulate the degradation of BA and formation of byproducts during ClO2 pretreatment, and simulations agree well with the experimental data. Half-lives of BA treated by ClO2 were 1-5 orders of magnitude longer than chlorine under typical seawater treatment conditions. These novel findings suggest the potential application of ClO2 for controlling biofouling ahead of RO treatment at desalination treatments.

Reaction Mechanisms of Chlorine Dioxide with Phenolic Compounds─Influence of Different Substituents on Stoichiometric Ratios and Intrinsic Formation of Free Available Chlorine.

Chlorine dioxide (ClO2) is an oxidant applied in water treatment processes that is very effective for disinfection and abatement of inorganic and organic pollutants. Thereby phenol is the most important reaction partner of ClO2 in reactions of natural organic matter (NOM) and in pollutant degradation. It was previously reported that with specific reaction partners (e.g., phenol), free available chlorine (FAC) could form as another byproduct next to chlorite (ClO2-). This study investigates the impact of different functional groups attached to the aromatic ring of phenol on the formation of inorganic byproducts (i.e., FAC, ClO2-, chloride, and chlorate) and the overall reaction mechanism. The majority of the investigated compounds reacted with a 2:1 stoichiometry and formed 50% ClO2- and 50% FAC, regardless of the position and kind of the groups attached to the aromatic ring. The only functional groups strongly influencing the FAC formation in the ClO2 reaction with phenols were hydroxyl- and amino-substituents in ortho- and para-positions, causing 100% ClO2- and 0% FAC formation. Additionally, this class of compounds showed a pH-dependent stoichiometric ratio due to pH-dependent autoxidation. Overall, FAC is an important secondary oxidant in ClO2 based treatment processes. Synergetic effects in pollutant control and disinfection might be observable; however, the formation of halogenated byproducts needs to be considered as well.

Simultaneous removal of chlorite and coexisting emerging organic contaminants by sulfite: Kinetics and mechanisms

The inevitable formation of chlorite (ClO2–) and the ineffective degradation of some emerging organic contaminants (EOCs) during chlorine dioxide disinfection have aroused increasing concern about their adverse effects on human health. In this study, the kinetics and mechanisms of simultaneous removal of ClO2– and coexisting EOCs by sulfite (S(IV)) were investigated. Under aerobic conditions, ClO2– and coexisting EOCs could be effectively removed by S(IV) at pH 6.5–7.5, and their removal rates decreased as pH increased. ClO3– was generated in this process but its amount decreased with increasing pH. Many lines of evidence verified that the reaction of ClO2– with HSO3– and H+ generated SO3•− and ClO•, and the generated ClO• was rapidly quenched by S(IV) to form OCl– and SO3•−. Subsequently, SO3•− quickly reacted with O2 to form SO5•−, which was further transformed into SO4•−. SO4•− was the dominant reactive oxidant contributing to the degradation of coexisting EOCs and the formation of ClO3–. Using S(IV) to simultaneously control ClO2– and coexisting EOCs in water treatment is a promising approach because its performance was slightly affected by the water matrix.

Reaction of Chlorine Dioxide with Saturated Nitrogen-Containing Heterocycles and Comparison with the Micropollutant Behavior in a Real Water Matrix.

Chlorine dioxide (ClO2) is a very selective oxidant that reacts with electron-rich moieties such as activated amines and thus can degrade specific N-containing micropollutants. N-containing heterocycles (NCHs) are among the most frequent moieties of pharmaceuticals. In this study, the reactions of ClO2 with ritalinic acid and cetirizine, two abundant micropollutants, and model compounds representing their NCH moiety were investigated. The pH-dependent apparent reaction rates of all NCHs with ClO2 were measured and modeled. This model showed that neutral amines are the most important species having reaction rates between 800 and 3200 M-1 s-1, while cationic amines are not reactive. Ritalinic acid, cetirizine, and their representative model compounds showed a high stoichiometric ratio of ≈5 moles ClO2 consumption per degraded ritalinic acid and ≈4 moles ClO2 consumption per degraded cetirizine, respectively. Investigation of chlorine-containing byproducts of ClO2 showed that all investigated NCHs mostly react by electron transfer and form above 80% chlorite. The reactions of the model compounds were well comparable with cetirizine and ritalinic acid, indicating that the model compounds indeed represented the reaction centers of cetirizine and ritalinic acid. Using the calculated apparent reaction rate constants, micropollutant degradation during ClO2 treatment of surface water was predicted for ritalinic acid and cetirizine with -8 to -15% and 13 to -22% error, respectively. The results indicate that in ClO2-based treatment, piperidine-containing micropollutants such as ritalinic acid can be considered not degradable, while piperazine-containing compounds such as cetirizine can be moderately degraded. This shows that NCH model compounds could be used to predict micropollutant degradation.

Kinetic and mechanistic understanding of chlorite oxidation during chlorination: Optimization of ClO2 pre-oxidation for disinfection byproduct control

Chlorine dioxide (ClO2) applications to drinking water are limited by the formation of chlorite (ClO2–) which is regulated in many countries. However, when ClO2 is used as a pre-oxidant, ClO2– can be oxidized by chlorine during subsequent disinfection. In this study, a kinetic model for the reaction of chlorine with ClO2– was developed to predict the fate of ClO2– during chlorine disinfection. The reaction of ClO2– with chlorine was found to be highly pH-dependent with formation of ClO3– and ClO2 in ultrapure water. In presence of dissolved organic matter (DOM), 60-70% of the ClO2– was transformed to ClO3– during chlorination, while the in situ regenerated ClO2 was quickly consumed by reaction with DOM. The remaining 30-40% of the ClO2– first reacted to ClO2 which then formed chlorine from the DOM-ClO2 reaction. Since only part of the ClO2– was transformed to ClO3–, the sum of the molar concentrations of oxychlorine species (ClO2– + ClO3–) decreased during chlorination. By kinetic modelling, the ClO2– concentration after 24 h of chlorination was accurately predicted in synthetic waters but was largely overestimated in natural waters, possibly due to a ClO2– decay enhanced by high concentrations of chloride and in situ formed bromine from bromide. Understanding the chlorine-ClO2– reaction mechanism and the corresponding kinetics allows to potentially apply higher ClO2 doses during the pre-oxidation step, thus improving disinfection byproduct mitigation while keeping ClO2–, and if required, ClO3– below the regulatory limits. In addition, ClO2 was demonstrated to efficiently degrade haloacetonitrile precursors, either when used as pre-oxidant or when regenerated in situ during chlorination.

Ultrasonic role to activate persulfate/chlorite with foamed zero-valent-iron: Sonochemical applications and induced mechanisms

The novel system, consisting of composite oxidants (persulfate/chlorite, S2O82−/ClO2−) and stationary phase activator (zero-valent-iron foam, Fe0f) driven by ultrasonic (US) field, was applied to treat the triphenylmethane derivative effectively even at low temperature (≈ 289 K). By comparisons of sub-systems, the US roles to S2O82−, ClO2−, and Fe0f were seriatim analyzed. US made the reaction order of multi-component system tend to within 1 (leading to de-order reaction), and widened pH activating range of the Fe0f by sonicate-polishing during the process of ClO2− co-activating S2O82−. US and Fe0f were affected by fluid eddy on activating S2O82−/ClO2−. The Fe0f had slight effect on the temperature of US bubble-water interface but the addition of ClO2− lowered it. The partitioning capacity of the above US reactive zone increased during the reaction. US and ClO2− could enrich the kinds of degradation intermediates. The contributions of free radicals (ClOx-based radicals, sulfate radicals (SO4−), and hydroxyl radicals (OH)) and non-free radicals (ClO2, and O = FeIV/V from ionic Fe under “-O-O-” of S2O82− and cyclic adjustment reaction of ClO2−) processes by sonochemical induction were equally important by corresponding detection means. Especially, real-time and online high-resolution mass spectrum by self-developing further confirmed the chain transfers of different free radicals due to US role. The findings expanded the application of sono-persulfate-based systems and improved understanding on activation mechanism.

Volatile organic chloramines formation during ClO2 treatment

Volatile organic chloramines are reported as the disinfection byproducts during chlorination or chloramination. However, ClO2, as an important alternative disinfectant for chlorine, was not considered to produce halogenated amines. In the present work, volatile organic chloramines including (CH3)2NCl and CH3NCl2 were found to be generated during the reaction of ClO2 and the dye pollutants. (CH3)2NCl was the dominant volatile DBP to result from ClO2 treated all four dye pollutants including Methyl Orange, Methyl Red, Methylene Blue and Malachite Green, with molar yields ranging from 2.6% to 38.5% at a ClO2 to precursor (ClO2/P) molar ratio of 10. HOCl was identified and proved to be the reactive species for the formation of (CH3)2NCl, which implied (CH3)2NCl was transformed by a combined oxidation of ClO2 and hypochlorous acid. (CH3)2NCl concentrations in the ppb range were observed when real water samples were treated by ClO2 in the presence of the dye pollutants. The results suggest that these azo dyes are one of the significant precursors for the formation of HOCl during ClO2 treatment and that organic chloramines should be considered in ClO2 disinfection chemistry and water treatment.

Chlorite formation during ClO2 oxidation of model compounds having various functional groups and humic substances

Chlorine dioxide (ClO2) has been used as an alternative to chlorine in water purification to reduce the formation of halogenated by-products and give superior inactivation of microorganisms. However, the formation of chlorite (ClO2−) is a major consideration in the application of ClO2. In order to improve understanding in ClO2− formation kinetics and mechanisms, this study investigated the reactions of ClO2 with 30 model compounds, 10 humic substances and 2 surface waters. ClO2− yields were found to be dependent on the distribution of functional groups. ClO2 oxidation of amines, di- and tri-hydroxybenzenes at pH 7.0 had ClO2− yields >50%, while oxidation of olefins, thiols and benzoquinones had ClO2− yields <50%. ClO2− yields from humic substances depended on the ClO2 dose, pH and varied with different reaction intervals, which mirrored the behavior of the model compounds. Phenolic moieties served as dominant fast-reacting precursors (during the first 5 min of disinfection). Aromatic precursors (e.g., non-phenolic lignins or benzoquinones) contributed to ClO2− formation over longer reaction time (up to 24 h). The total antioxidant capacity (indication of the amount of electron-donating moieties) determined by the Folin-Ciocalteu method was a good indicator of ClO2-reactive precursors in waters, which correlated with the ClO2 demand of waters. Waters bearing high total antioxidant capacity tended to generate more ClO2− at equivalent ClO2 exposure, but the prediction in natural water should be conservative.

Accelerated aging of polyethylene pipe grades in aqueous chlorine dioxide at constant concentration

The impact of disinfected water on the degradation of polyethylene (PE) was investigated with immersion tests of two PE pipe materials in 10 and 5 ppm chlorine dioxide (ClO2) medium at 60 °C. Aging experiments in 1 ppm ClO2 at 60, 50 and 40 °C were also carried out to study the effect of different aging temperatures. During conditioning, the pH was kept at 6.8. A specific exposure device with continuous concentration control and adjustment has been applied in order to generate reliable and reproducible aging conditions. Sample characterization applying scanning electron microscopy (SEM), tensile test, dynamic oxidation tests as well as FTIR-spectroscopy indicated accelerated antioxidant consumption and polymer degradation. Material aging at 50 °C and above was found to be much faster than at 40 °C applying 1 ppm ClO2 concentration. An optimized testing condition for fast material characterization in case of 1 mm thick specimens was found to be a concentration of 1 ppm ClO2 at 50 °C. The simultaneously increasing material embrittlement and the consumption of active antioxidant molecules imply an apparent unselective reaction of ClO2 with the polymer and the stabilizers molecules. Moreover, the radical nature and the high reactivity of ClO2 led to the formation of carbon-chlorine species, which are assumed to originate from degraded antioxidant molecules.

Deactivation of wastewater-derived N-nitrosodimethylamine precursors with chlorine dioxide oxidation and the effect of pH

In this study, the effect of chlorine dioxide (ClO2) oxidation on the deactivation of wastewater (WW)-derived N-nitrosodimethylamine (NDMA) precursors was investigated under various conditions (i.e., ClO2 application pH, dose and contact time). At pH 6.0, decreases in NDMA formation potentials (FPs) or occurrences (under uniform formation conditions [UFC]) were relatively low (<25%) with ClO2 oxidation regardless of WW-impact. A negative removal was also observed after ClO2 oxidation in some of the non-impacted waters. However, NDMA FP removals were significant (up to ~85%) under the same oxidation conditions in WW-impacted waters at pH 7.8. This indicates that the majority of WW-derived NDMA precursors can be deactivated with ClO2 oxidation above neutral pH. This was attributed to the better oxidative reaction of ClO2 with amines that have lone pair electrons to be shared at higher oxidation pH conditions. In addition, relatively short oxidation periods with ClO2 (i.e., ≤10 min) or low Ct (concentration × time, ~10 mg ∗ min/L) values were sufficient for the deactivation of WW-derived NDMA precursors. ClO2 oxidation was effective in freshly WW-impacted waters. Natural attenuation processes (e.g., sorption, biodegradation, etc.) can change the reactivity of WW-derived NDMA precursors for oxidation with ClO2. The effect of ClO2 on the removal of THM precursors was low (<25%) and independent of oxidation conditions. Given the low formation of regulated THMs and HAAs, ClO2 oxidation presents a viable option for the simultaneous control of NDMA and regulated DBP formation during water treatment, especially for utilities treating WW-impacted water sources.

Kinetics of the Benzaldehyde-Inhibited Oxidation of Sulfite by Chlorine Dioxide.

There has been steady interest in the aqueous reaction of ClO2• with sulfur(IV) since the 1950s, and a wide variety of rate laws and mechanisms have been proposed. In neutral-to-alkaline media, the reaction is challenging to study because of its great rate. Here it is shown that benzaldehyde can be used as an additive to slow the reaction and make its rates more amenable to study. The rates can be quantitatively modeled by a mechanism that includes reversible binding of sulfur(IV) by benzaldehyde and a rate-limiting mixed second-order reaction of ClO2• with SO3(2-). The latter reaction occurs through parallel electron transfer from SO3(2-) to ClO2• and oxygen-atom transfer from ClO2• to SO3(2-).

Kinetics of the initial steps in the aqueous oxidation of thiosulfate by chlorine dioxide.

The reaction of ClO2(•) with S2O3(2-) in aqueous solution is a component of the "crazy clock" reaction of ClO2(-) with S2O3(2-), and under conditions of excess S2O3(2-) the absorbance at 360 nm due to ClO2(•) decays with sigmoidal kinetics. A chain reaction mechanism is inferred on the basis that very small concentrations of SO3(2-) accelerate the reaction, and methionine inhibits the reaction. Pseudo-first-order kinetics is observed in the presence of relatively large methionine concentrations, leading to the simple rate law -d[ClO2]/dt = (ka[S2O3(2-)] + kb[S2O3(2-)](2))[ClO2], with ka = 452 ± 16 M(-1) s(-1) and kb = (5.7 ± 0.2) × 10(5) M(-2) s(-1) at 25 °C and pH 7.6. Under these conditions, the initial products are ClO2(-) and S4O6(2-). A classical electron-transfer mechanism is assigned to the reaction that occurs under conditions of methionine inhibition.

Aldehydes formation during water disinfection by ozonation and chlorination process

The goal of this paper is an investigation into the influence of disinfection with ozone, chlorine (Cl2) and chlorine dioxide (ClO2) on the aldehydes formation. Three types of waters were treated with different doses of these disinfectants. The results obtained indicate that the level of carbonyls concentration can significantly increase with the time of Cl2 and ClO2 reaction with aldehyde precursors in treated water. There is no noticeable correlation between quantity of aldehydes and total organic carbon (TOC) value of disinfected water, but potential of organic by-products formation is evidently connected with the nature of organic material. The range of productivity of aldehydes in water treated with ClO2 or Cl2 is very similar. The productivities of aldehydes were calculated for all investigated waters treated with different doses of oxidant and were 2 – 10 μg of aldehydes per 1 mg TOC. Formaldehyde and acetaldehyde were the dominant carbonyl compounds identified in water before as well as after the reaction with disinfectants.

Selective Degradation of Lignin Polymer by Chlorine Dioxide During Chemical Pulp Delignification in Flow Through Reactor

The delignification of pulp in a conventional batch reactor provides convenient conditions for inutile secondary reactions in which ClO2 reacts with oxidized aromatic units of lignin. In this study the flow-through reactor was applied to minimize secondary reactions. The obtained results showed that the removal of oxidized lignin from the reaction zone significantly enhanced the ClO2 reaction toward non-oxidized units of lignin. Application of an organic solvent-water solution, bleaching liquor, significantly increased the removal of oxidized lignin and decreased considerably the secondary reactions. Although this technique considerably improved ClO2 effective efficiency, large amounts of chlorate formation decreased the overall effect of improved ClO2 global efficiency.

Kinetics and Mechanisms of Chlorine Dioxide and Chlorite Oxidations of Cysteine and Glutathione

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.

S-Oxygenation of Thiocarbamides I: Oxidation of Phenylthiourea by Chlorite in Acidic Media

The oxidation of 1-phenyl-2-thiourea (PTU) by chlorite was studied in aqueous acidic media. The reaction is extremely complex with reaction dynamics strongly influenced by the pH of reaction medium. In excess chlorite concentrations the reaction stoichiometry involves the complete desulfurization of PTU to yield a urea residue and sulfate: 2ClO2- + PhN(H)CSNH2 + H2O --> SO4(2-) + PhN(H)CONH2 + 2Cl- + 2H+. In excess PTU, mixtures of sulfinic and sulfonic acids are formed. The reaction was followed spectrophotometrically by observing the formation of chlorine dioxide which is formed from the reaction of the reactive intermediate HOCl and chlorite: 2ClO2- + HOCl + H+ --> 2ClO2(aq) + Cl- + H2O. The complexity of the ClO2- - PTU reaction arises from the fact that the reaction of ClO2 with PTU is slow enough to allow the accumulation of ClO2 in the presence of PTU. Hence the formation of ClO2 was observed to be oligooscillatory with transient formation of ClO2 even in conditions of excess oxidant. The reaction showed complex acid dependence with acid catalysis in pH conditions higher than pKa of HClO2 and acid retardation in pH conditions of less than 2.0. The rate of oxidation of PTU was given by -d[PTU]/dt = k1[ClO2-][PTU] + k2[HClO2][PTU] with the rate law: -d[PTU]/dt = [Cl(III)](T)[PTU]0/K(a1) + [H+] [k1K(a1) + k2[H+]]; where [Cl(III)]T is the sum of chlorite and chlorous acid and K(a1) is the acid dissociation constant for chlorous acid. The following bimolecular rate constants were evaluated; k1 = 31.5+/-2.3 M(-1) s(-1) and k2 = 114+/-7 M(-1) s(-1). The direct reaction of ClO2 with PTU was autocatalytic in low acid concentrations with a stoichiometric ratio of 8:5; 8ClO2 + 5PhN(H)CSNH2 + 9H2O --> 5SO4(2-) + 5PhN(H)CONH2 + 8Cl- + 18H+. The proposed mechanism implicates HOCl as a major intermediate whose autocatalytic production determined the observed global dynamics of the reaction. A comprehensive 29-reaction scheme is evoked to describe the complex reaction dynamics.

Effect of pH and Temperature on the Kinetics of Odor Oxidation Using Chlorine Dioxide

Increasing public concerns over odors and air regulations in nonattainment zones necessitate the remediation of a wide range of volatile organic compounds (VOCs) generated in the poultry-rendering industry. Currently, wet scrubbers using oxidizing chemicals such as chlorine dioxide (ClO2) are utilized to treat VOCs. However, little information is available on the kinetics of ClO2 reaction with rendering air pollutants, limiting wet scrubber design and optimization. Kinetic analysis indicated that ClO2 does not react with hexanal and 2-methylbutanal regardless of pH and temperature and implied that alde-hyde removal occurs primarily via mass transfer. Contrary to the aldehydes, ethanethiol or ethyl mercaptan (a model compound for methanethiol or methyl mercaptan) and dimethyl disulfide (DMDS) rapidly reacted with ClO2. The overall reaction was found to be second and third order for ethanethiol and DMDS, respectively. Moreover, an increase in pH from 3.6 to 5.1 exponentially increased the reaction rate of ethanethiol (e.g., k 2 = 25– 4200 L/mol/sec from pH 3.6 to 5.1) and significantly increased the reaction rate of DMDS if increased to pH 9 (k 3 = 1.4 × 106 L2/mol2/sec). Thus, a small increase in pH could significantly improve wet scrubber operations for removal of odor-causing compounds. However, an increase in pH did not improve aldehyde removal. The results explain why aldehyde removal efficiencies are much lower than methanethiol and DMDS in wet scrub-bers using ClO2.

Hypohalite ion catalysis of the disproportionation of chlorine dioxide.

The disproportionation of chlorine dioxide in basic solution to give ClO2- and ClO3- is catalyzed by OBr- and OCl-. The reactions have a first-order dependence in both [ClO2] and [OX-] (X = Br, Cl) when the ClO2- concentrations are low. However, the reactions become second-order in [ClO2] with the addition of excess ClO2-, and the observed rates become inversely proportional to [ClO2-]. In the proposed mechanisms, electron transfer from OX- to ClO2(k1OBr- = 2.05 +/- 0.03 M(-1) x s(-1) for OBr(-)/ClO2 and k1OCl-= 0.91 +/- 0.04 M(-1) x s(-1) for OCl-/ClO2) occurs in the first step to give OX and ClO2-. This reversible step (k1OBr-/k(-1)OBr = 1.3 x 10(-7) for OBr-/ClO2, / = 5.1 x 10(-10) for OCl-/ClO2) accounts for the observed suppression by ClO2-. The second step is the reaction between two free radicals (XO and ClO2) to form XOClO2. These rate constants are = 1.0 x 10(8) M(-1) x s(-1) for OBr/ClO2 and = 7 x 10(9) M(-1) x s(-1) for OCl/ClO2. The XOClO2 adduct hydrolyzes rapidly in the basic solution to give ClO3- and to regenerate OX-. The activation parameters for the first step are DeltaH1(++) = 55 +/- 1 kJ x mol(-1), DeltaS1(++) = - 49 +/- 2 J x mol(-1) x K(-1) for the OBr-/ClO2 reaction and DeltaH1(++) = 61 +/- 3 kJ x mol(-1), DeltaS1(++) = - 43 +/- 2 J x mol(-1) x K(-1) for the OCl-/ClO2 reaction.

Minimizing chlorate ion formation

Storage tanks that contain liquod bleach should be periodically flushed and cleaned to minimize buildup of a residual chlorate ion concentration.The treatment of drinking water with either NaOCl or Ca(OCl)2 is a source of chlorate ion (ClO3−) in finished water. In basic solution, liquid bleach (NaOCl) decomposition is a second‐order process. The decomposition of OCl− involves chlorite ion (ClO2−) as a low‐concentration intermediate. The reaction of ClO2− to form ClO3− is a fast process, and the ClO2− in liquid bleach is at a concentration at least 200 times less than the OCl− concentration. The formation of oxygen from decomposing OCl− is a slower side reaction (&lt;10 percent).

ChemInform Abstract: Physicochemical Properties of Chlorine Oxides. Part 1. Composition, Ultraviolet Spectrum, and Kinetics of the Thermolysis of Gaseous Dichlorine Hexoxide.

AbstractCl2O6 is synthesized by reaction of ClO2 with excess ozone (diluted with O2) at 0 °C. Vapor pressure measurements of liquid Cl2O6 are carried out at 5‐45 °C. The absorption cross section values of gaseous Cl2O6 are ∼3 times higher than those previously assigned to ClO3.