Article

Effect of Chloride Ion on the Kinetics and Mechanism of the Reaction between Chlorite Ion and Hypochlorous Acid

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The effect of chloride ion on the chlorine dioxide formation in the ClO 2 (-)-HOCl reaction was studied by following .ClO 2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of .ClO 2 formation. At the same time, the .ClO 2 yield is increased in HOCl but decreased in ClO 2 (-) excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl 2 + H 2O left harpoon over right harpoon Cl 2OH (-) + H (+) and Cl 2OH (-) left harpoon over right harpoon HOCl + Cl (-) and the increased reactivity of Cl 2OH (-) compared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2O 2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to approximately 90% conversion. The advantage of this method of evaluation is briefly outlined.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... ClO 2 • concentrations were standardized using an extinction coefficient of 1250 M −1 cm −1 at 359 nm [59]. HOCl stock solutions were prepared as reported [60] and standardized by iodometric titration. ...
... A plot of k′ 4 (k′ 4 corresponds to the slope of dependence of k obs.4 on ClO 2 − concentration) is shown in Fig. 5, i.e., the reaction rate decreases upon alkalinization of the medium, but does not tend to zero. To explain this pH dependence, a kinetically active species of the oxidant can be suggested, viz., ClO 2 − and HClO 2 (reaction 1; pK a = 1.74, 25 °C [60]). Using Eq. (2), the following values for the corresponding rate constants were found: k 4 [53] is substantially higher than our data. ...
... On the basis of the experimental and published [60] data, the following mechanism of reduction of chlorite by cob(II)alamin can be proposed. In the first step, one electron reduction of ClO 2 − or HClO 2 proceeds (reaction 3). ...
Article
Reactions of aquacobalamin (H2O-Cbl(III)) and its one-electron reduced form (cob(II)alamin, Cbl(II)) with chlorite (ClO2(-)) and chlorine dioxide (ClO 2(•) ) were studied by conventional and stopped-flow UV-Vis spectroscopies and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ClO2(-) does not react with H2O-Cbl(III), but oxidizes Cbl(II) to H2O-Cbl(III) as a major product and corrin-modified species as minor products. The proposed mechanism of chlorite reduction involves formation of OCl(-) that modifies the corrin ring during the course of reaction with Cbl(II). H2O-Cbl(III) undergoes relatively slow destruction by ClO 2(•) via transient formation of oxygenated species, whereas reaction between Cbl(II) and ClO 2(•) proceeds extremely rapidly and leads to the oxidation of the Co(II)-center.
... Stock solutions of HOCl were prepared according to published procedure (Kormányos et al. 2008) and standardized by iodometric titration. ...
... Dependence of the slopes of concentration dependencies (k 0 ) on pH (Fig. 7) indicates a substantial increase in a reaction rate upon acidification of the medium. This can be explained by an increase in the concentration of hypochlorous acid (pK a (-HOCl) = 7.40 at 25°C (Kormányos et al. 2008; reaction 1) at less basic solutions, that possesses stronger oxidizing properties than hypochlorite (Cho et al. 2014). Protonation of sulfur atom in glutathionyl ligand occurs only in strongly acidic medium (Schumacher et al. 2011) and does not affect the reaction kinetics. ...
Article
Full-text available
Glutathionylcobalamin (GSCbl), a tight complex of glutathione (GSH) with cobalamin(III), is readily oxidized to aquacobalamin by hypochlorite. Corrin macrocycle remains unmodified in the presence of threefold excess of hypochlorite, whereas aqua- and cyanocobalamins are partially transformed to chlorinated species under the same conditions. The suggested mechanism of reaction between GSCbl and hypochlorite involves subsequent oxidation of thiol and amino groups and dissociation of oxidized glutathione from Co(III)-ion.
... Therefore, it seemed to be important to reinvestigate the HOCl À ClO À 2 system in presence of 0-0.01 M chloride concentration range. 13 The result of these studies clearly indicated that chloride ion has a sound effect on this reaction as well, i.e., the chloride ion is in fact an autocatalyst in the HOCl À ClO À 2 reaction. Within the concentration range used in the original work, 4 however, the autocatalytic feature of the reaction was not manifested. ...
... • In presence of excess chloride, the chlorine dioxide concentration slightly decreases in the later phase of the reaction, as it was shown in Figure 1 of Ref. 13. • The basic stoichiometry of the tetrathionate-chlorine dioxide system in both excesses (see Table II ...
Article
Individually proposed kinetic models of the key subsystems of the chlorite-thiosulfate reaction, such as the hypochlorous acid-chlorite, tetrathionate-chlorite, and tetrathionate-chlorine dioxide reactions, have been unified to be able to describe all the main characteristics of these systems simultaneously. A complex 38-step kinetic model is composed in which the subsystems are coupled by the necessary short-lived intermediates and such species that is products or reactants in one system but transients in the other. Such a cross-coupling between the individual systems as well as the sound agreement between the measured and calculated absorbance-time profiles in 367 experimental curves strongly validates the proposed kinetic model.
... Considering the complexity of the chemical composition of HOCl solution, the effects of other active electrophiles should not be overlooked. Previous experimental studies have shown that the main chlorinating agents in HOCl solution are affected by many factors, such as pH, chloride ion [32,33], and chlorite concentration [57]. In recent decades, evidence from multiple reports has quantified the influence of electrophilic species in HOCl solution, including HOCl, Cl 2 O, Cl 2 , and H 2 OCl + [58]. ...
Article
Full-text available
Although hypochlorous acid (HOCl) solution has become a popular electrophilic reagent for industrial uses, the question of which molecule (HOCl or Cl2) undergoes electrophilic addition with olefins remains a controversial issue in some literature and textbooks, and this problem has been largely underexplored in theoretical studies. In this work, we computationally studied the electrophilic addition mechanism of olefins using three experimentally predicted effective electrophilic chlorinating agents, i.e., HOCl, Cl2, and Cl2O molecules. Our results demonstrate that Cl2 and Cl2O are the main electrophilic agents in HOCl solution, whereas the HOCl molecule cannot be the electrophile since the energy barrier when directly adding HOCl molecule to olefins is too high to overcome and the “anti-Markovnikov” regioselectivity for tri-substituted olefin is not consistent with experiments. Notably, the HOCl molecule prefers to form oxonium ion intermediate with a double bond, rather than the generally believed chlorium ion intermediate. This work could benefit mechanistic studies of critical biological and chemical processes with HOCl solution and may be used to update textbooks.
... This relationship can be explained by the effect of acid-base properties of HOCl (Eq. 2; pK a = 7.4 at 25.0 °C [33]) on the reaction rate, i.e. CNCbl reacted with HOCl but not with ClO -. ...
Article
Full-text available
Hypochlorous acid (HOCl) is a strong oxidant produced by myeloperoxidase. Previous work suggested that HOCl modifies the corrin ring of cobalamins to yield chlorinated species via mechanisms that are incompletely understood. Herein, we report a mechanistic study on the reaction between cyanocobalamin (CNCbl, vitamin B12) and HOCl. Under weakly acidic, neutral and weakly alkaline conditions, the reaction produces the c-lactone derivative of CNCbl chlorinated at the C10-position of corrin ring (C10–Cl–CNCbl-c-lactone). Formation of C10–Cl–CNCbl-c-lactone was not observed at pH ≥ 9.9. The chlorination of CNCbl by HOCl proceeds via two pathways involving one and two HOCl molecules: the reaction is initiated by the very fast formation of a complex between CNCbl and HOCl, which either undergoes slow transformation to chlorinated species, or rapidly reacts with a second HOCl molecule to produce C10–Cl–CNCbl. Subsequent reaction of C10–Cl–CNCbl with HOCl proceeds rapidly toward lactone ring formation by H-atom abstraction at position C8. This work uncovered mechanisms and products of the reaction of a biologically active and therapeutically used cobalamin, CNCbl and the endogenous oxidant HOCl. Binding and reactivity studies of C10–Cl–CNCbl and C10–Cl–CNCbl-c-lactone with relevant proteins of the cobalamin pathway and with cultured cells are necessary to elucidate the potential physiological effects of these species.Graphic abstract
... Furthermore, Cl 2 addition did not affect the formation of ClO 2 -. Therefore, these increases in ClO 3 are mainly attributed to the reaction of hypochlorous acid with ClO 2 , Kormanyos et al. 2008, Csordas et al. 2001). Overall, simultaneous use of Cl 2 and ClO 2 ...
Article
A long-term (>18 months), systematic investigation was conducted to examine (1) the removal of N-nitrosodimethylamine (NDMA) formation potential (FP) by different treatment processes under various operational conditions at nine water treatment plants in South Carolina, and (2) the occurrence of NDMA in their distributions systems. Average NDMA FP removal by alum clarification ranged from 12 to 30% during different seasons and weather conditions. Powdered activated carbon addition improved the removal of NDMA FP, especially at high doses (>4 mg/L). The use of oxidants (i.e., chlorine [Cl2] and chlorine dioxide [ClO2]), especially simultaneous application, enhanced the removal of NDMA FP and lowered the NDMA concentration in the distribution systems to <10 ng/L. However, simultaneous application of ClO2 and Cl2 led to the formation of elevated levels of chlorate. The average NDMA FP reduction by reverse osmosis and microfiltration was 81 and 7%, respectively. The overall NDMA FP removal efficiencies between raw and finished water ranged between 40 and 59%.
... We represent the chlorite-bromide and chlorite-chloride reactions with the −cv term. This term is used to simplify the detailed kinetics of the bromide-related [21][22][23][24]24] and chloride-related [25][26][27][28][29] mechanisms into a reaction rate law that is first order in v and first order in halide concentration. Since in our study we use a large excess of bromide and chloride compared to chlorite, we further simplify the expression to a pseudofirst order form. ...
Article
Turing patterns in the chlorine dioxide-iodine-malonic acid reaction were modified through additions of sodium halide salt solutions. The range of wavelengths obtained is several times larger than in the previously reported literature. Pattern wavelength was observed to significantly increase with sodium bromide or sodium chloride. A transition to a uniform state was found at high halide concentrations. The observed experimental results are qualitatively well reproduced in numerical simulations with the Lengyel-Epstein model with an additional chemically realistic kinetic term to account for the added halide and an adjustment of the activator diffusion rate to allow for interhalogen formation.
Article
The first asymmetric total synthesis of (–)-arbophyllidine, an unusual pentacyclic monoterpenoid indole alkaloid, has been achieved.
Article
In this article, a complex oxidant (CO) composed of NaClO and NaClO 2 was employed to remove arsenic from flue gas. Experiments were conducted to evaluate the effects of several influencing parameters on arsenic removal efficiency in a bench-scale reactor, such as molar ratio of NaClO to NaClO 2 , solution pH, solution temperature and various flue gas components including O 2 , SO 2 , NO, CO 2 . The results indicated that the arsenic removal efficiency could reach 100%, under the optimum experimental conditions, in which molar ratio of NaClO to NaClO 2 was 1.0, solution pH was 5.5–6.0, solution temperature was 50 ℃. Besides, it was also observed that O 2 and CO 2 did not affect the removal of arsenic while both SO 2 and NO concentrations in flue gas could significantly inhibit the removal of arsenic. Furthermore, the final reaction products in the solution were analyzed by high-performance liquid chromatography coupled with a hydride-generation atomic fluorescence spectrometer (HPLC-HG-AFS), the reaction mechanism and pathways of arsenic removal using complex absorbent were proposed.
Article
The chlorate-nitrous acid reaction was investigated in acid media, using a high concentration of reagents. It was followed via ultraviolet-visible light (UV-vis) spectroscopy and presented a complex behavior. The order of reagents, and the products formed by this reaction, are dependent on the concentration of reagents. For the high concentration set we used, the reaction has shown a first-order behavior for H(+) and HNO2, and an order equal to 0.79 for chlorate. In this case, chlorine dioxide is formed. Moreover, chlorine dioxide starts to form only after all HNO2 has been consumed. This is the first time chlorine dioxide was observed to be formed by this reaction. Reduction of the concentration of reagents decreases the order of HNO2 to 0.91 and no chlorine dioxide is formed. An isosbestic point was found at 312 nm, which indicates a 1:1 ratio between nitrate ion and nitrous acid species. A model, with 14 independent species and 12 reactions is presented, which is able to simulate the experimental behavior for the low and high concentrations sets of reagents and it is a significant improvement in the understanding of the complex nitrogen and chlorine aqueous chemistry.
Chapter
Redox reactions of simple inorganic species exhibit an amazingly rich variety of complex kinetic phenomena. Typically, these reactions are interpreted on the basis of multistep kinetic models which postulate the formation and subsequent fast reactions of reactive intermediates. The main purpose of this chapter is to demonstrate the challenges associated with mechanistic studies on complex redox reactions, and to offer selected examples how the complexities can be handled with currently available experimental and computational methods. Clear arguments are presented to demonstrate that the stoichiometries of these reactions are kinetically controlled. It is shown that in order to understand the intimate details of these systems, the stoichiometry as a function of reaction time, the final stoichiometry and the kinetic properties need to be studied under as broad experimental conditions as possible. Furthermore, thorough characterization of the reactive intermediates is the key to in-depth understanding of the mechanism. The importance of photoinitiation and kinetic coupling between photochemical and thermally activated reaction steps is also demonstrated in several systems. The survey of the literature results confirms that simultaneous and critical evaluation of all available experimental results is essential to validate the mechanistic conclusions. Finally, it is shown that adapting the methodology of homogeneous reaction kinetics for studying nonhomogeneous physicochemical processes leads to unique kinetic information regarding the kinetics of adsorption and desorption processes.
Article
The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H2O2 contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate and chlorate with hydrogen-peroxide in acidic medium at 60 oC is investigated using electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate and chlorate in their reactions with hydrogen-peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO3 and H2O2 is supposed to be the source of IO2• radicals. The KBrO3 and H2O2 reaction did not produce any EPR signal, while the KClO3-H2O2 system was found to be a source of HO• radical. Moreover, KClO3 dissolved in sulfuric acid without hydrogen-peroxide produced HO• radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO2• and HOO• radicals, and ClO2• and HO• radicals in the particular kinetic models of iodate–hydrogen-peroxide and chlorate–hydrogen-peroxide systems, as well as possible exclusion of BrO2• radical from the kinetic scheme of the bromate–hydrogen-peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen containing species.
Article
A waste heat recovery and denitrification system was developed for improving energy conservation and emissions control especially for control of PM2.5 particles and haze. The system uses enhanced heat and mass transfer techniques in a packed heat exchange tower with self-rotation and zero-pressure spraying, low temperature NO oxidation by ozone, and neutralization with an alkali solution. Operating data in a test project gave NOx in the exhaust flue gas of less than 30 mg/Nm³ with an ozone addition rate of 8 kg/h and spray water pH of 7.5–8, an average heat recovery of 3 MW, and an average heat supply of 7.2 MW.
Article
Full-text available
The kinetics and mechanism of the oxidation of methimazole (1-methyl-3H-imidazole), MMI, by chlorite in mildly acidic environments was studied. It is a complex reaction which gives oligooscillations in chlorine dioxide concentrations in excess chlorite conditions. The stoichiometry is strictly 2:1, with the sulfur center being oxidized to sulfate and the organic moiety being hydrolyzed to several indeterminate species. In excess MMI conditions over chlorite, the sulfinic acid and sulfonic acid were observed as major intermediates. The sulfenic acid, which was observed in the electrochemical oxidation of MMI, was not observed with chlorite oxidations. Initial reduction of chlorite produced HOCl, an autocatalytic species in the chlorite oxidations. HOCl rapidly reacts with chlorite to produce chlorine dioxide, which, in turn, reacts rapidly with MMI to produce more chlorite. The reaction of chlorine dioxide with MMI is competitive, in rate, with the chlorite-MMI and HOCl - ClO2- reactions. This explains the oligooscillations in ClO2 concentrations.
Article
Experiments on simultaneous absorption of SO2 and NOX from sintering flue gas via a composite absorbent NaClO2/NaClO were carried out, The effects of various operating parameters such as NaClO2 concentration (ms), NaClO concentration (mp), molar ratio of NaClO2/NaClO (M), solution temperature (TR), initial solution pH, gas flow (Vg) and inlet concentration of SO2 (CS) and NO (CN) on the removal efficiencies of SO2 and NO were discussed. The optimal experimental conditions were determined to be initial solution pH = 6, TR = 55 °C and M = 1.3 under which the average efficiencies of desulfurization and denitrification could reach 99.7% and 90.8%, respectively. Moreover, according to the analysis of reaction products, it was found that adding NaClO to NaClO2 aqueous solution is favorable for the generation of ClO2 and Cl2 which have significant effect on desulfurization and denitrification. Finally, engineering experiments were performed and obtained good results demonstrated that this method is practicable and promising.
Article
Full-text available
Role of added chloride ions on the shift of reaction pathway of oxidation of aromatic ketones (acetophenone, desoxybenzoin) by dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Participation of enolic and protonated forms of ketones in the rate determining steps is manifested from zero and first orders with respect to the oxidant in absence and presence of added chloride ions, respectively. Positive and negative effects of acid and dielectric constant on the reaction rate were observed. The observations deduce plausible mechanisms involving (i) rate-determining formation of enol from the conjugate acid of the ketone (SH+) in the absence of added chloride ions and (ii) rapid formation of molecular chlorine species from HOCl (hydrolytic species of DCICA) in the presence of added chloride ions, which then interacts with SH+ in a rate-determining step prior to the rapid steps of product formation. The order of Arrhenius parameters substantiate the proposed plausible mechanisms based on order of reactants both in presence and absence of added chloride ions.
Article
Sulfur-contained nonlinear reaction system is a significant branch of nonlinear chemistry, which can display complicated dynamics both in the homogeneous and reaction-diffusion medium. In particular, it also plays a critical role in the aspect of fronts interaction, labyrinthic pattern, self-replication pattern and systematical design of pattern formation in recent years. According to the number of oscillatory components, sulfur-contained oscillatory systems are mainly divided into two-component systems and three-component systems. The progress on sulfur-contained compound oscillators and pattern formation during the past three decades are introduced in the review. Furthermore, the potential application of the sulfur-contained oscillators and the involved reaction systems in biological field and responsive gel medium are systematically summarized. The difficulties existed in this active field are discussed in detail and the future directions are prospected.
Article
The combination of chlorine dioxide (ClO2) and chlorine (NaOCl) or monochloramine (NH2Cl) was used to degrade the formation of ClO2-, when ClO2 was used as an effective oxidant which could form undesirable oxidation by-products, i.e. ClO2-. In this article, Mill-Q water was used, and the impact of NaOCl or NH2Cl combined with ClO2or ClO2-on the yield of ClO2-and ClO2 were investigated by monitoring the residual of NaOCl, NH2Cl, ClO2 and ClO2-. It was proved that when NaOCl or NH2Cl combined with ClO2, hypochlorousacid (HOCl) formed by NaOCl or NH2Cl could react with ClO2-, which was the reason that ClO2-yield reduced and ClO2yield increased, and the increase in ClO2yield exceeded the decrease in ClO2-yield. For the purpose of the highest reaction rate, the optimal ratio between NaOCl and ClO2 was 3:1, while it was 1:1 between NH2Cl and ClO2. The appropriate ratios of residual NaOCl/NH2Cl and ClO2-for ClO2-complete removal were found to be close to the value of 1 and 0.5 respectively. Furthermore, compared with NaOCl, equivalent yield of NH2Cl had much more ClO2 residual yield when reacted with ClO2, and had faster reaction rate in any ratio. It can be concluded that the generation of ClO2-is typically much lower and the residual of ClO2 is much higher with combination of ClO2and NaOCl or NH2Cl when compared to the use of ClO2alone. And the minimum ratio between NaOCl and ClO2, NH2Cl and ClO2are 3:1 and 1:1 respectively when used in micro-polluted water.
Article
Full-text available
A flow battery employing H2 as the fuel and one or more of highly soluble halate salts (such as 50 %w/wLiBrO3aq.) as the oxidant presents a viable opportunity as a power source for fully electric vehicles which meets the specific energy, specific power, energy efficiency, cost, safety, and refill time requirements. We further disclose a process of regeneration of the fuel and the oxidant from the discharged halide salt and water using electric (or solar) energy as the only input and generating no chemical waste. The cycle of discharge and re-generation takes advantage of pH-driven comproportionation and disproportionation reactions, respectively, and of pH manipulation using an orthogonal ion migration across laminar flow (OIMALF™) reactor.
Article
Full-text available
Effect of added chloride ions on kinetics and pathway of reaction between cyclic ketones (five to eight membered rings) and dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchlo� ric acid medium. Formation of aliphatic dicarboxylic acids as the end products demonstrates the ring cleav� age oxidation. Positive effect of acid and negative effect of dielectric constant on the reaction rate reveals a interaction between positive ion (oxidant in the form of H2OCl+) and dipolar substrate molecule. Zero and first orders by oxidant in absence and presence of added chloride ions illustrates the participation of substrate as enolic form of ketone and protonated ketone, respectively, in the rate determining steps. The observed order of reactivity of cyclic ketones (cyclohexanone > cyclooctanone > cyclopentanone > cycloheptanone) was explained on the bases of ring strain, change of hybridization and conformational considerations. The envisaged plausible mechanism based on order of reactants in presence and absence of added chloride ions was substantiated by the order of Arrhenius parameters.
Article
A multicomposite active absorbent was prepared using the liquid-phase complex of NaClO2 and NaClO as well as solid-phase slake lime to simultaneous desulfurization and denitrification at a flue gas circulating fluidized bed (CFB). The effects of influencing factors on the removal efficiencies of SO2 and NO were investigated. Removal efficiencies of 96.5% for SO2 and 73.5% for NO were obtained, respectively, under the optimal experimental conditions. The characterization of the spent absorbent was carried out by using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and chemical analysis methods, from which the simultaneous removal mechanism of SO2 and NO based on this absorbent was proposed.
Article
Full-text available
An investigation of the kinetics and mechanism for epoxidation of styrene and para-substituted styrenes by chlorite at 25 °C in the pH range of 5-6 is described. The proposed mechanism in water and water/acetonitrile includes seven oxidation states of chlorine (-I, 0, I, II, III, IV, and V) to account for the observed kinetics and product distributions. The model provides an unusually detailed quantitative mechanism for the complex reactions that occur in mixtures of chlorine species and organic substrates, particularly when the strong oxidant chlorite is employed. Kinetic control of the reaction is achieved by the addition of chlorine dioxide to the reaction mixture, thereby eliminating a substantial induction period observed when chlorite is used alone. The epoxidation agent is identified as chlorine dioxide, which is continually formed by the reaction of chlorite with hypochlorous acid that results from ClO produced by the epoxidation reaction. The overall stoichiometry is the result of two competing chain reactions in which the reactive intermediate ClO reacts with either chlorine dioxide or chlorite ion to produce hypochlorous acid and chlorate or chloride, respectively. At high chlorite ion concentrations, HOCl is rapidly eliminated by reaction with chlorite, minimizing side reactions between HOCl and Cl2 with the starting material. Epoxide selectivity (>90% under optimal conditions) is accurately predicted by the kinetic model. The model rate constant for direct reaction of styrene with ClO2(aq) to produce epoxide is (1.16 ± 0.07) × 10(-2) M(-1) s(-1) for 60:40 water/acetonitrile with 0.20 M acetate buffer. Rate constants for para substituted styrenes (R = -SO3(-), -OMe, -Me, -Cl, -H, and -NO2) with ClO2 were determined. The results support the radical addition/elimination mechanism originally proposed by Kolar and Lindgren to account for the formation of styrene oxide in the reaction of styrene with chlorine dioxide.
Article
Full-text available
The kinetics of chlorate-chloride reaction was studied following the formation of ClO2• by UV-Vis spectroscopy. For comparison with other results in the literature, the initial rate was measured after small induction period. The results show a special effect of a saturation profile for the initial chloride concentration, suggesting the formation of the intermediate Cl2O32-. At low chloride concentration, the reaction orders for chlorate, chloride and H+ were 1.03 ± 0.05, 1.02 ± 0.03 and 2.80 ± 0.03, respectively. These order values must be considered with care because they were calculated using the maximum rate values after induction period. In fact, the presence of this induction period indicates that the system is complex. Then, a mechanism was proposed to explain the experimental results, and includes the reaction between two ClOClO to form ClO2•. It was able to model the experimental curves at different [H+]0 and at low and high [Cl-]0.
Data
Full-text available
A multicomposite active absorbent was prepared using the liquid-phase complex of NaClO 2 and NaClO as well as solid-phase slake lime to simultaneous desulfurization and denitrification at a flue gas circulating fluidized bed (CFB). The effects of influencing factors on the removal efficiencies of SO 2 and NO were investigated. Removal efficiencies of 96.5% for SO 2 and 73.5% for NO were obtained, respectively, under the optimal experimental conditions. The characterization of the spent absorbent was carried out by using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and chemical analysis methods, from which the simultaneous removal mechanism of SO 2 and NO based on this absorbent was proposed.
Article
Performance of simultaneous desulfurization and dinitration using the solution of NaClO2 and NaClO as new-style complex absorbent was investigated experimentally in self-designed bench scale bubbling reactor. The effects of main parameters, such as the concentrations of NaClO2 and of NaClO, solution pH and reaction temperature and so on, on removal efficiencies of SO2 and NOx, were examined, then the optimal conditions were established, in which the molar ratio of NaClO to NaClO2 was 1:1, the reaction temperature was 50°C and the solution pH was 5.5. The removal efficiencies of SO2 and NO under the optimal conditions were 100% and 89.2%, respectively. The mechanism of simultaneous removal based on complex absorbent was proposed by analyzing the removal products and the electrode potentials of related species, namely SO2 and NO are oxidized by chlorite anion, hypochlorite, chlorine dioxide and chlorine contained in complex absorbent. In thermodynamic aspect, simultaneous desulfurization and denitration reactions in liquid phase can happen spontaneously and completely, and are all exothermic reactions. It was confirmed by kinetics that for simultaneous desulfurization and dinitration, the reaction order and average activation energy of SO2 were 1 and 21.6 kJ·mol−1, respectively, and those of NO were 1 and 8.2 kJ·mol−1, respectively.
Article
Full-text available
A new-style complex absorbent was prepared for simultaneous desulfurization and denitrification in this paper. The performance of the absorbent was tested in fixed bed. On the basis of the experimental results in fixed bed, the M substances were selected as the optimal additive. Furthermore the effects of various factors, such as additive content, flue gas temperature, humidity, Ca/(S+N), and NOx inlet concentration et al, on the removal efficiencies of SO2 and NOx were investigated. According to our simultaneous flue gas desulfurization and denitrification experiment results using the new-style absorbent in a circulating fluidized bed (CFB) system, High simultaneous removal efficiency, 94.9% of SO2 and 68.3% of NO, was achieved under the optimal experimental conditions. The work would offer important basic data for industrial application of simultaneous removal SO2 and NOx based on flue gas circulating fluidized bed.
Article
An improved method is described for selective room temperature epoxidation of alkenes by sodium chlorite in a solvent mixture of ethanol, acetonitrile, and water buffered at pH 7. In addition, the use of aldehydes as promoters in chlorite oxidations is described for the first time. The amount of sodium chlorite, the solvent mixture, and the addition of formaldehyde as a practical promoter were optimized. Styrene was used as a test substrate in the optimization studies and the generality of the method was assessed by using a variety of nucleophilic and electrophilic substrates. Yields up to 89% were obtained with styrene and other nucleophilic alkenes are readily converted into epoxides.
Article
This study investigated the effects of temperature, chlorine dioxide dosage, and filtrate circulation on various filtrate and pulp properties in chlorine dioxide prebleaching of birch kraft pulp. Also the effect of a preceding A-stage was examined. Kappa number, delignification, and hexenuronic acid removal were unaffected by the used dilution media and temperature. Increasing ClO2 charge resulted in a lower kappa number, increased hexenuronic acid removal, and more efficient delignification. With a preceding A-stage the kappa number was lower throughout the D0-stage, but the kappa number reduction and the removal of hexenuronic acid were slightly decreased. Chlorine dioxide consumption was practically independent of the tested variables; only dosage had an effect. The formation of chlorate and chloride was increased with higher dosages of ClO2, but the stoichiometry remained unchanged. The concentration of chlorite + chlorous acid during bleaching depended on temperature, used dilution medium, and the presence of an A-stage.
Article
A complex absorbent containing NaClO (M) and NaClO2 was used to investigate simultaneous removal of SO2 and NO from flue gas. The various influencing factors, such as molar ratio of M to NaClO2, solution pH, reaction temperature, SO2 concentration and NO concentration on removal efficiencies of SO2 and NO were studied experimentally, and the optimal conditions were established, in which molar ratio of M to NaClO2 was 4.0, solution pH was 5.5, reaction temperature was 50 °C. Under the optimal conditions, the removal efficiencies of SO2 and NO reached 100% and 85%, respectively. In addition, the reaction mechanism of simultaneous desulfurization and denitration using complex absorbent was proposed.
Article
Chlorite-thiosulfate reaction was studied by high performance liquid chromatography under slightly alkaline solution by monitoring the concentration of thiosulfate and tetrathionate simultaneously during the course of reaction. It is demonstrated that various polythionates are formed and the composition of polythionates mainly depends on pH. Initial rate studies have revealed that the formal kinetic order of hydrogen ion is unambiguously unity but that of chlorite ion is significantly larger, while that of thiosulfate is lower than one. A 10-step kinetic model is proposed with seven fitted and three fixed parameters by simultaneous evaluation of kinetic data taking all the important characteristics of the measured kinetic curves into account. It is also enlightened that higher formal kinetic order of chlorite and lower kinetic order of thiosulfate than unity is an inherent feature of the system and may explain the systematic deviation between the measured and the calculated data encountered in previous studies.
Article
The tetrathionate-hypochlorous acid reaction has been investigated in nearly neutral medium at I = 0.5 M ionic strength and T = 25.0 +/- 0.1 degrees C in dihydrogen-phosphate-hydrogen-phosphate buffer by UV-vis spectrophotometry. In excess of hypochlorous acid, the stoichiometry was found to be S(4)O(6)(2-) + 7HOCl + 3H(2)O --> 4SO(4)(2-) + 7Cl(-) + 13H(+), but in excess of tetrathionate colloidal sulfur precipitates. On the basis of the simultaneous evaluation of the kinetic curves, a nine-step kinetic model with four fitted and five fixed rate coefficients is proposed. Analogous oxidation reactions of tetrathionate are also compared and discussed.
Article
A mechanism is proposed for the reaction of chlorite and iodide ions. This scheme, which involves eight elementary steps and six principal species, is considerably simpler and yields better agreement with experiment than the mechanism proposed earlier by Epstein and Kustin. Our new mechanism successfully simulates the observed clock reaction behavior and recovery of [I2] under batch conditions and the bistability and oscillation found in a CSTR. It also sheds light on some of the effects observed in this reaction on varying the extent of mixing. Because of the relative simplicity of the mechanism, it should be possible to combine it with models of other reactions such as bromate-iodide, or of other processes such as stirring, to yield insights into more complex dynamical phenomena.
Article
By means of the temperature jump relaxation technique, the kinetics of hydrolysis of the halogens Cl2, Br2 and I2 have been studied. The over-all process is fastest for Br2 and slowest for Cl2. Numerical values for the rate constants of the over-all reaction mechanism X2 + H2O⇄k↼k⇀X- + H+ + XOH could be determined. The measured values for the over-all hydrolysis rate constant k⇀ are: k⇀cl2, = 11.0 sec.-1, k⇀Br2 = 110 sec.-1, k⇀I2 = 3.0 sec.-1. A general mechanism, in which hydrolysis occurs via the intermediate X2OH-, is proposed. From studies of pH and concentration dependence individual rate constants could be determined or estimated. General trends exhibited by the measured or estimated values are discussed.
Article
Kombination der bistabilen, durch I" autokatalysierten Reaktion A mit der durch I2 autokatalysierten Rückkopplungsreaktion Bliefert, wie spektrophotometrische Messungen der I′-Absorption und des Potentials einer I′-empfindlichen Elektrode in einem Durchfluß-Rührkessel-Reaktor zeigen, ein dauernd oszillierendes System.
Article
On the basis of elementary chemical considerations, it is shown that proton-producing redox reactions of oxyanions are expected to be autocatalytic and to manifest propagating acidity fronts. The conditions of proton production in redox reactions are established and verified experimentally by the reaction of S 2 O 3 2− , S 4 O 6 2− , S 2 O 4 2− , SO 3 2− , S 2 O 6 2− , and N 2 H 5 + with BrO 3 − , IO 3 − , ClO 3 − , ClO 2 , and S 2 O 8 2− . Twenty new propagating acidity front reactions have been discovered among the possible combinations of these reactions
Article
The reaction between ClO2•- and HOCl has been studied by spectrophotometrically monitoring the production of ClO2 at pH 5-6. In excess ClO2-, the reaction is first order in ClO2-, HOCl, and H+, and the stoichiometry is given by HOCl + 2ClO2- + H+ → 2ClO2 + Cl- + H2O. In excess HOCl and at higher pH's, ClO3- is produced, and the order of the reaction is between 1 and 2 for HOCl and between 0 and 1 for H+. By combining computer simulation and least-squares analysis, we obtain a mechanism in which the reaction 2HOCl + ClO2- → ClO3- + Cl2 + H2O (k = (2.1 ± 0.1) × 10-3 M-2 s-1) plays a key role in explaining the behavior at high [HOCl]/[ClO2-].
Article
The reaction of bromate, chlorite, and iodide ions in a stirred tank reactor involves two independently oscillatory reactions (BrO3--I- and ClO2--I-) chemically coupled through common iodine-containing species. A 20-step mechanism, constructed by combining and slightly modifying the mechanisms of the component oscillators, is proposed for the coupled system. Numerical simulations give good agreement not only with the behavior of the bromate-iodide and chlorite-iodide reactions but also with the new dynamical behavior, i.e., birhythmicity and compound oscillation, found in the full bromate-chlorite-iodide system. Several new regions, which should be accessible by appropriately designed experiments, are predicted to exist in the phase diagram of the coupled system.
Article
Commercial chlorine dioxide generators are operated in an about 4.5-mol/L sulfuric acid solution. The chlorous acid disproportionation may be an important pathway to generate chlorine dioxide under such a condition. On the basis of the product determination, we found that, in the absence of a chloride ion, chloric acid, hypochlorous acid, and chlorine, rather than chlorine dioxide, are the products from the chlorous acid disproportionation. However, chloride addition to the chlorous acid solution under otherwise the same condition results in the generation of chlorine dioxide. The underlying mechanism of the chloride effect on the chlorous acid disproportionation is discussed.
Article
Oxidation of NiII(CN)42- by aqueous chlorine proceeds by three parallel pathways via Cl2O, Cl2, and HOCl to yield trans-NiIII(CN)4(H2O)2-: d[Ni(III)]/dt = 2(kCl2O[Cl2O] + kCl2[Cl2] + kHOCl[HOCl])[NiII(CN)42-]. The values of the second-order rate constants (M-1 s-1; 25.0°C; μ = 0.10 M) for oxidations by Cl2O, Cl2, and HOCl are 1.3 × 107, 3.2 × 105, and 0.5, respectively. The proposed mechanism involves the formation of a nickel(IV) intermediate by Cl+ transfer to nickel(II) in the rate-determining step. This is followed by a rapid electron transfer between the nickel(IV) intermediate and NiII(CN)42- to give the final nickel(III) product. When the Cl2O path predominates and higher concentrations of NiII(CN)42- are used, the formation of Cl2O (catalyzed by acetic acid) becomes rate limiting: d[Cl2O]/dt = (k2 + k5[HOAc])[HOCl]2 where k2 is 0.12 M-1 s-1 and k5 is 280 M-2 s-1. Under these conditions the direct HOCl oxidation of NiII(CN)42- also contributes to the appearance of nickel(III).
Article
The kinetics and mechanism of the iron(III)-catalyzed decomposition of the chlorite ion have been investigated by using conventional batch, stopped-flow, stopped-flow-rapid-scan spectrophotometric, and quenched stopped-flow methods at 25-degrees-C and in 1.0 M NaClO4. The concentration vs time profiles were determined for chlorite ion, chlorine dioxide, and, in a few cases, chloride ion in the 40 ms-several minute interval. It was confirmed that the stoichiometry can be given as the appropriate combination of the following reactions: 4HClO2 = 2ClO2 + ClO3- + Cl- + 2H+ + H2O; 5HClO2 = 4ClO2 + Cl- + H+ + 2H2O. The proposed mechanism postulates that the catalytic decomposition is initiated by the formation of the FeClO22+ complex and the rate-determining step is the redox decomposition of this species. The mechanism was validated by model calculations based on the GEAR algorithm. The measured and calculated kinetic curves are in excellent agreement under a variety of experimental conditions. It was shown that the overall stoichiometry is kinetically controlled and ultimately determined by fast secondary reactions between various chlorine species. This work represents the first totally inorganic application of the quenched stopped-flow method. Several aspects of this technique are discussed.
Article
The reaction between free chlorine (HOCl/OCl⁻) and chlorite ion (ClOâ⁻) has been studied in the pH 6.4-10.0 region. The reaction proceeds through the ClâOâ intermediate followed by a direct reaction of the intermediate with hypochlorous acid to form chlorate ion. Time-concentration profiles were measured for each chlorine species, resulting in both total chlorine and redox balance. Negligibly small amounts of chlorine dioxide are formed above pH 7. Indirect evidence suggests that, in this pH region, the formation of any chlorine dioxide is primarily due to the presence of concentration gradients or because of the adventitious presence of catalytic metal ion impurities. Details of the overall reaction mechanism for the formation of chlorate ion are presented.
Article
The generation of chlorine dioxide from the reaction between hypochlorous acid and chlorite with or without an initial chloride addition has been studied under slightly acidic conditions. Chloride (Cl-), one of the products from the reaction, not only changes the reaction stoichiometry, but also alters the rate law. It was found that the formation of chlorine dioxide from the HOCI-ClO2- system consists of two distinct parts, one is promoted by chloride, the other is independent of chloride. The overall kinetics of the chlorine dioxide generation from the reaction is: This model can very well predict the reaction under the following conditions: La production de bioxyde de chlore à partir de la réaction entre l'acide hypochloreux et la chlorite avec ou sanc ajout initial de chlorure a été étudiée dans des conditions légèrement acides. Le chlorure (CL), l'un des produits de la réaction, non seulement modifie la stoechiométrie de la réaction, mais altère également la loi de vitesse. On a trouvé que la formation de bioxyde de chlore avec le système H0C1-C102∼ comprend deux parties distinctes, l'une due au chlorure, l'autre étant indépendante du chlorure. La cinétique globale de la production de bioxyde de chlore à partir de la réaction est: Ce modèle peut parfaitement prédire la réaction dans les conditions suivantes:
Article
The kinetics of decomposition of aqueous chlorous acid has been reinvestigated at pH 0.7-1.9, ionic strength 1.0 M (HSO 4 -/SO 4 2-), and temperature 25.0 (0.1 °C. Optical absorbances were collected in the 240-450 nm wavelength range for up to ∼90% decomposition for time series lasting as long as 2 days. The number of absorbing species was investigated by matrix rank analysis; no absorbing intermediate was formed in significant concentration during the decomposition. Of the many mechanistic models tested, the one that fit best included the following reactive intermediates: HOCl, Cl 2 O 2 , Cl 2 O 3 , • ClO, • OH. The stoichiometric ratio of ClO 2 produced to Cl(III) consumed varies with pH and [Cl -]. Reaction of Cl 2 O 3 with Cl(III) yields chlorate exclusively. Reaction of Cl 2 O 3 with Cl -favors ClO 2 over chlorate, but does not entirely exclude chlorate, because it is produced by hydrolysis of Cl 2 O 2 . Invoking Cl 2 O 3 explains the variation in stoichiometric ratio as well as the maximum observed in the initial rate of ClO 2 formation as a function of pH. The kinetics of chlorous acid decomposition cannot be quantitatively fit through the last stages of the reaction without postulating a first-order decomposition. Scission of chlorous acid to give short-lived hydroxyl and chlorine-(II) monoxide is a plausible route for this process. A set of best-fit and literature-derived parameters is presented for the complete mechanism.
Chapter
Decomposition of Chlorite Ion and Chlorous Acid SolutionsReactions of Chlorine (O) and Chlorine (I) with Chlorine (III)Reaction of Chlorine (O) and Chlorine (I) with Chlorine (IV) and the Reaction of Chlorate Ion with Chloride IonChlorine Dioxide–Properties, Preparation, Disproportionation, and Decomposition Reactions.
Article
The kinetics of the aqueous phase reaction between molecular chlorine and chlorite ion was studied experimentally by measuring the enhancement of chlorine transfer from the gas phase. The results were interpreted by using the penetration theory of mass transfer, in conjunction with the assumption that the reaction is second order overall, being first order with respect to both chlorine and chlorite. The second-order rate constant was determined as a function of temperature and solution ionic strength. These experiments indicated that the reaction rate constant at 293 K and zero ionic strength is 1.62 × 104 M-1·s-1. The reaction rate constant increased with increasing temperature, having an activation energy of 39.9 kJ·mol-1, and decreased with increasing ionic strength. A collision theory interpretation of the observed rate indicates that the steric factor is on the order of unity, suggesting that nearly every collision of sufficient energy results in reaction, regardless of the relative orientation.
Article
The availability of an improved analytical method allowed a preliminary study of the stoichiometry of the reaction between chlorite ion and hypochlorous acid at pH 5. The stoichiometry varies with the initial concentration ratio of the reactants, suggesting parallel pathways for the reaction mechanisms. The yield of chlorine dioxide is shown to vary with the initial concentration ratio of hypochlorous acid to chlorite ion as well as the contact time between reactants. The formation of molecular oxygen is postulated as a byproduct.
Article
The rate of oxidation of ClO2- by HOCl is first order in each reactant and is general-acid catalyzed. In the initial steps of the proposed mechanism, a steady-state intermediate, HOClOClO-, forms (k1 = 1.6 M-1 s-1) and undergoes general-acid (HA)-catalyzed reactions (k2HA) to generate a metastable intermediate, ClOClO. Values of k2HA/k-1 are 1.6 x 10(4) M-1 (H3O+), 20 M-1 (HOAc), and 8.5 M-1 (H2PO4-). Subsequent competitive reactions of ClOClO with ClO2- (k3) to give 2ClO2 and with OH- (k4OH) and other bases (k5B) to give ClO3- are very rapid. The relative yields of these products give k4OH/k3 = 1.3 x 10(5), k5HPO4/k3 = 0.20, and k5OAc/k3 = 0.06. At low pH and low buffer concentrations, the apparent yield of ClO2, based on 2ClO2 per initial HOCl, reaches 140%. This anomaly is attributed to the induced disproportionation of ClO2- by ClOClO to give ClO3- and additional HOCl. A highly reactive intermediate, ClOCl(O)OClO-, is proposed that can undergo Cl-O bond cleavage to give 2ClO2 + Cl- via one path and ClO3- + 2HOCl via another path. The additional HOCl recycles in the presence of excess ClO2- to give more ClO2. Ab initio calculations show feasible structures for the proposed reaction intermediates. Acetic acid has a second catalytic role through the formation of acetyl hypochlorite, which is much more reactive than HOCl in the transfer of Cl+ to ClO2- to form ClOClO.
Article
The oxidation of ClO(2) by OCl(-)is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO(2)]/dt = 2k(OCl)[ClO(2)][OCl(-)]. The rate constant (T = 298 K, mu = 1.0 M NaClO(4)) and activation parameters are k(OCl) = 0.91 +/- 0.02 M(-1) s(-1), DeltaH = 66.5 +/- 0.9 kJ/mol, and DeltaS(++) = -22.3 +/- 2.9 J/(mol K). In alkaline solution, pH > 9, the primary products of the reaction are the chlorite and chlorate ions and consumption of the hypochlorite ion is not observed. The hypochlorite ion is consumed in increasing amounts, and the production of the chlorite ion ceases when the pH is decreased. The stoichiometry is kinetically controlled, and the reactants/products ratios are determined by the relative rates of the production and consumption of the chlorite ion in the ClO(2)/OCl(-) and HOCl/ClO(2)(-) reactions, respectively.
Article
The kinetics and mechanism of the reaction between Cl(2) and ClO(2)(-) are studied in acetate buffer by stopped-flow spectrometric observation of ClO(2) formation. The reaction is first-order in [Cl(2)] and [ClO(2)(-)], with a rate constant of k(1) = (5.7 +/- 0.2) x 10(5) M(-)(1) s(-)(1) at 25.0 degrees C. Nucleophilic attack by ClO(2)(-) on Cl(2), with Cl(+) transfer to form ClOClO and Cl(-), is proposed as the rate-determining step. A possible two-step electron-transfer mechanism for Cl(2) and ClO(2)(-) is refuted by the lack of ClO(2) suppression. The yield of ClO(2) is much less than 100%, due to the rapid reactions of the metastable ClOClO intermediate via two competing pathways. In one path, ClOClO reacts with ClO(2)(-) to form 2ClO(2) and Cl(-), while in the other path it hydrolyzes to give ClO(3)(-) and Cl(-). The observed rate constant also is affected by acetate-assisted hydrolysis of Cl(2). The rate of Cl(2) loss is suppressed as the concentration of Cl(-) increases, due to the formation of Cl(3)(-). In excess ClO(2)(-), a much slower formation of ClO(2) is observed after the initial Cl(2) reaction, due to the presence of HOCl, which reacts with H(+) and Cl(-) to re-form steady-state levels of Cl(2).
Article
The initial rate of formation of chlorine dioxide in the chlorite-tetrathionate reaction changes in an unusual fashion. The formal kinetic order of both reactants varies over a very wide range. Moreover, chlorite ion behaves not just as a simple reactant, but also as a self-inhibitor. A five-step scheme, derived from an eight-step mechanism, is proposed in which the autocatalytic formation of HOCl plays a central role in accounting for this kinetic behavior.
Article
The chlorite-tetrathionate reaction has been studied spectrophotometrically in the pH range of 4.65-5.35 at T = 25.0 +/- 0.2 degrees C with an ionic strength of 0.5 M, adjusted with sodium acetate as a buffer component. The reaction is unique in that it demonstrates autocatalysis with respect to the hydrogen and chloride ion products and the key intermediate, HOCl. The thermodynamically most-favorable stoichiometry, 2S(4)O(6)2- + 7ClO2- + 6H2O --> 8SO(4)2- + 7Cl- + 12H+, is not found. Under our experimental conditions, chlorine dioxide, the chlorate ion, or both are detected in appreciable amounts among the products. Initial rate studies reveal that the formation of chlorine dioxide varies in an unusual way, with the chlorite ion acting as a self-inhibitor. The reaction is supercatalytic (i.e., second order with respect to autocatalyst H+). The autocatalytic behavior with respect to Cl- comes from chloride catalysis of the chlorite-hypochlorous acid and hypochlorous acid-tetrathionate subsystems. A detailed kinetic study and a model that explains this unusual kinetic behavior are presented.
Article
It is shown and explained in detail by four examples generated from known kinetic models that simplified evaluation procedures--initial rate studies, individual exponential curve fitting method--may inherently lead to inappropriate chemical conclusions, even in the case of relatively simple kinetic systems. It is also shown that in the case of all four examples the simultaneous curve fitting immediately reveals the defectiveness of the kinetic model obtained from the simplified evaluation procedures. We therefore propose the extensive usage of the simultaneous curve fitting of all the kinetic traces to avoid these pitfalls and to find the appropriate kinetic models.
InEncyclopedia of Chemical Technology
  • T W Clapper
  • W A Gale
InThe Bleaching of Pulp
  • W Howard
  • G B Strumila