Reaction Of Bromate Research Articles

Bromide Ion Impurity-Induced Reaction between Selenium(IV) and Acidic Bromate: Prototype of a Cycle with Autocatalytic Behavior.

The selenium(IV)-bromate reaction in an acidic medium using phosphoric acid/phosphate buffer was investigated by UV-vis spectroscopy monitoring the formation of bromine. In an excess of bromate, the absorbance-time curves measured at 450 nm display a characteristic sigmoidal shape having a fairly long induction period, while in the opposite case, when selenium(IV) species is used in excess, the measured data follow the rise and fall behavior. Depending on the excess of Se(IV) the final bromine-containing product is either an elementary bromine or bromide ion. Simultaneous evaluation of the measured kinetic traces clearly indicated that, surprisingly, no direct reaction takes place between the reactants. Instead of that, a trace amount of bromide ion impurity in the stock bromate solution is sufficient to drive the system via the oxidation of the bromide ion by bromate producing elementary bromine followed by the subsequent selenite-bromine reaction reestablishing the bromide ion to open a new cycle. As a result, the concentration of bromide ions increases in a sigmoidal fashion during the course of the reaction unless enough selenium(IV) species is present; hence, the overall synergetic effect observed is the autocatalytic rise of bromide ions. Therefore, the cycle mentioned above may be considered as a prototype of autocatalytic cycles. This observation prompted us to clarify the explicit difference between an autocatalytic cycle and an autocatalytic reaction.

Spectrophotometric determination of bromate with 2-bromo-N,N-dimethylaniline

International Association for Cancer Research included bromates in the group of carcinogenic chemicals. Therefore, it is important to determine the content of bromates in different objects. The purpose of this study is to develop a simple, express and sensitive method for the determination of bromates. We propose the method of spectrophotometric determination of bromate in the concentration range of 0.5 to 45 mg L–1, this technique being based on the reaction of bromate with 2-bromo-N,N-dimethylaniline in the presence of an excess of KBr in the medium of sulfuric acid, followed by photometry of 2,4-dibromo-N,N-dimethylaniline at 240 nm. The optimal concentrations of reagents are determined and the influence of some other conditions on the sensitivity of determination is established. The detection limit of bromate (in compliance with 3s-criterion) is 0.39 mg L–1. The relative error of determination does not exceed 0.10. The influence of foreign ions is studied when determining bromate (5.010–5 mol L–1). Such components of natural water as phosphates, fluorides, chlorides and NH4+ ions have no effect on the bromide determination. Fe3+ ions in comparable quantities impede the determination of bromates. The developed method was tested for the determination of bromate in standard solutions and waters of different categories. The used reagents are stable over time and the proposed method is simple and suitable as an alternative for the determination of bromates in different objects.

Determination of Lorazepam in Drug Formulation and Biofluids Using a Spectrophotometric Method and Response Surface Methodology

A novel, simple, sensitive, and selective kinetic spectrophotometric method has been developed for the determination of lorazepam in pharmaceutical and bioloical samples. The procedure is based on the catalytic effect of lorazepam on the Janus Green–bromate reaction system. The change in absorbance was followed spectrophotometrically at 618 nm. To obtain the maximum sensitivity, the reagents concentration, temperature, and time were optimized by one at the time method. Under optimum experimental conditions, the calibration curve was linear over the range 0.3–19.5 μg/mL of lorazepam, including two linear segments. The relative standard deviations (n = 5) for 1.0, 5.0, and 15.0 μmol/L of lorazepam were 1.09, 1.03, and 0.97%, respectively. The limit of detection was 0.08 μg/mL of lorazepam. An experimental check under these optimal conditions confirmed good agreement in the RSM results. The developed method was successfully applied for the determination of lorazepam in real samples, and the obtained results are in a good agreement with those using HPLC.

Redox-Mediated Bromate Based Electrochemical Energy System

A promising redox-mediated bromate-ion (BrO3 -) based system was investigated through research combined with mathematical modeling and full-cell test to understand the characteristic effect of electrochemical reaction coupled with chemical reaction on the cell behaviors. This system has a unique feature of the reaction mechanism in which the reactant (Br2) is not provided externally, but is kept regenerated by a coupled chemical reaction of bromate in the cell, which may lead to “no limiting current” condition (i.e. non-zero concentration of the reactant species at the electrode surface for any current conditions) by eliminating mass transfer (i.e. concentration) over-potential, and thus this system is estimated to achieve the ultra-high performance [1-4]. From the full-cell based test, a unique behavior induced by this auto-catalytic reaction was found for the first time, and to understand the underlying physics and nature of the system, theoretical study was conducted through mathematical modeling and analytic analysis. Three reaction mechanisms (E, EC, and EC’) were compared in their characteristic reaction behaviors to understand the nature of each reaction mechanism, and the results were analyzed with respect to reaction time and species concentration at the electrode surface. Furthermore, the effect of actual condition of bromate system (i.e. non-unity stoichiometry and limited amount of bromate) was analyzed at unsteady condition for the first time to understand its characteristic behavior in the actual battery condition. As a final step, the effect of catalytic reaction was analyzed analytically to define the parameters to control the catalytic reaction, and especially, the effect of relative rate of electrochemical reaction and coupled chemical reaction on the autocatalytic reaction was compared through a zone diagram where conditions for pure diffusion controlled and pure kinetic controlled cases were defined.

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide-Bromate Substrate-Depletive Clock Reaction.

The thiourea dioxide (TDO)-bromate reaction has been reinvestigated spectrophotometrically under acidic conditions using phosphoric acid-dihydrogen-phosphate buffer within the pH range of 1.1-1.8 at 1.0 M ionic strength adjusted by sodium perchlorate and at 25 °C. The title system shows a remarkable resemblance to the classical Landolt reaction, namely, the clock species (bromine) may only appear after the substrate TDO is completely consumed. Thus, the title system can be classified as substrate-depletive clock reaction. Despite the well-known slow rearrangement characteristic of TDO in acidic solution, it is surprisingly found that the Landolt time of the title reaction does not depend at all on the age of TDO solution applied. It is, however, shown experimentally that the inverse of Landolt time linearly depends on the initial bromate concentration as well as on the square of the hydrogen ion concentration. In addition to this, it is also noticed that dihydrogen phosphate markedly affects the Landolt time as well, and this feature may easily be taken into consideration by the H2PO4- dependence of the rate of bromate-bromide reaction quantitatively. Based on the experiments, a simple three-step kinetic model is proposed from which a complex formula is derived to indicate the exact concentration dependence of the Landolt time.

Kinetic-Spectrophotometric Determination of Thiocyanate in Human Saliva Based on Landolt Effect in Presence of Astrafloxine FF

In the present study a kinetic-spectrophotometric method for thiocyanate determination is described. The suggested method for the determination of thiocyanate is based on its "Landolt effect" on the reaction of bromate with hydrobromic acid, which leads to the formation of only one halogen bromine. The reaction was monitored spectrophotometrically at the maximum wavelength of astrafloxine FF light absorption at 535 nm. The absorbance of reactants mixture decreased with an increase of the reaction time. The calibration curve for thiocyanate determination was obtained in the concentration range of 0.03-2.0 μg mLμ1 under the optimal conditions (pH 1.5; CBrO3 - = 7.6 × 10-4 mol L-1; Castrafloxine FF = 1 × 10-5 mol L-1). The limit of detection was 0.01 μg mLμ1. The method was successfully applied to the determination of thiocyanate in human saliva samples with satisfactory results.

Bromate Reaction on a Rotating Disc Electrode: A New Method of Obtaining Approximate Analytical Solutions for Stationary Regime

A new method (AA approximation) is proposed for obtaining approximate analytical solutions of a system of equations describing the transport of the basic reagents for the electroreduction process of the BrO $$_{3}^{ - }$$ anion on a rotating disc electrode in an acid medium in the presence of very small additions of molecular bromine. This process is of significant interest both from the fundamental point of view (as an example of a new electrochemical EC'' mechanism with autocatalytic properties) and from the applied point of view in the context of prospects to create, on its basis, innovation power sources—bromate redox flow batteries. Since the previously proposed method for solving the system of kinetic transport equations for this system turned out to be inapplicable for very large diffusion layer thicknesses and very strong currents, here a new method of obtaining approximate analytical expressions for concentration profiles and maximum current is proposed. It has been shown that its predictions are in good agreement with the results of the numerical solution of the same problem in a wide range of system parameters, including the region of very large diffusion layer thicknesses, which confirms the validity of the used analytical approximations.

Bromate Reaction on the Rotating Electric Electrode: a New Method of Obtaining Approximate Analytical Solutions for Stationary Regime

Bromate Reaction on the Rotating Electric Electrode: a New Method of Obtaining Approximate Analytical Solutions for Stationary Regime

Kinetic Determination of Thiocyanate by the Reaction of Bromate with Crystal Violet Immobilized in a Polymethacrylate Matrix

A procedure is proposed for the kinetic solid-phase spectrophotometric determination of thiocyanate using a polymethacrylate matrix. The procedure is based on the Landolt reaction between Crystal Violet immobilized in a polymethacrylate matrix and a bromate oxidizer, accompanied by the discoloration of the indicator in the matrix. During some induction period after the introduction of thiocyanate into the test solution, the dye in the matrix is not discolored. The duration of the induction period is proportional to the concentration of thiocyanate in the solution. The change in the color of the polymethacrylate matrix was recorded by measuring its absorbance at 600 nm. The developed procedure ensures the determination of thiocyanate in the concentration range 0.025–12 mg/L, depending on the Crystal Violet concentration in the matrix. The limit of detection calculated according to the 3s-test is 0.02 mg/L with the indicator concentration in the matrix of 0.06 mg/g. A possibility of using the proposed procedure for the determination of thiocyanate in near-wellbore water is shown.

Bromate electroreduction from acidic solution at spherical microelectrode under steady-state conditions: Theory for the redox-mediator autocatalytic (EC″) mechanism

Process of bromate reduction from aqueous acidic medium at (hemi)spherical microelectrode under steady-state conditions has been analyzed theoretically. Since bromate anion is non-electroactive within the potential range under consideration its transformation is based on the electroreduction of bromine which is present in bulk solution in small (even trace) amounts while the bromine reduction product, bromide anion, reacts irreversibly in acidic conditions with bromate anion, with regeneration of bromine, thus forming a redox mediator cycle. Similar to our previous studies of this process at rotating disk electrode it has been shown that this process possesses autocatalytic features, which may under certain conditions leads to considerable accumulation of the redox-couple components, Br2 and Br−, near the electrode surface. As a result the rate of the bromate transformation by the catalytic cycle becomes so rapid that the rate of the whole process is controlled by the bromate transport from the bulk solution to the kinetic layer near the electrode surface, i.e. the current becomes comparable to a very high BrO3− diffusion limited one. For such an autocatalytic passage of the process the radius of the microelectrode has to exceed a critical value which depends on the solution composition. This peculiarity of the system leads to the anomalous dependence of the maximal current density of the bromate reaction on the electrode size: if the electrode radius is under its critical value the current density is very small since it is determined by the discharge of bromine species from the bulk solution, with no significant transformation of bromate. On the contrary, for larger electrodes the autocatalytic EC″ mechanism becomes efficient and the passing current density can exceed the bromate diffusion limited one, i.e. it is a very strong one. The theory also predicts a complicated dependence of the maximal current on the bulk solution concentrations of bromate and protons.

Electroreduction of bromate anion on inactive RDE under steady-state conditions: Numerical study of ion transport processes and comproportionation reaction

The study is devoted to analyzing the electroreduction of bromate anion BrO 3 - on catalytically inactive (e.g., carbon) electrodes by numerical methods. This process is realized due to the combination of the reversible mediator pair Br2/Br- and the process of comproportionation (reaction of bromate and bromide anions) in solution phase. These reactions increase the concentration of bromine and bromide near the electrode surface; hence, this process is autocatalytic (EC″ mechanism). Within the framework of this study, a numerical algorithm which allows the system of diffusion-kinetic equations to be solved for this system is proposed for one-dimensional transport and the process under steady-state conditions. The results are compared with the conclusions of the approximate analytical theory published in Electrochim. Acta, 2015, vol. 173, p. 779, which allows inferring that both approaches are correct. The deviation between the latter is observed only in the cases of violation of approximations lying in the basis of the corresponding analytical relationships. Thus, the predictions of the analytical theory of practical interest can be considered as reliably confirmed by numerical calculations, particularly, the prediction on the nonmonotonous dependence of the maximum current on the diffusion layer thickness (or the RDE rotation rate) including the anomalous region of this dependence in which the current increases with the increase in the diffusion layer thickness.

Bromate removal from water by polypyrrole tailored activated carbon

Bromate adsorption behavior and mechanism were examined on a novel adsorbent devised via depositing polypyrrole (Ppy) into the pores of nut shell-based activated carbon (NAC). This Ppy-tailored activated carbon (Ppy-NAC) hosted positively charged polypyrrole functionality that offered considerable sorption capacity for bromate. Specifically, the Ppy-NAC achieved a bromate loading of 62.5mg/g in the adsorption isotherm, 8.3 times higher than the pristine NAC. The adsorption isotherm data were fitted well by the Langmuir model, and the adsorption kinetics were described well by the pseudo-second-order equation. The occurrence of chloride ions in solution showed that Cl− exchanged with BrO3− during the adsorption process. The X-ray photoelectron spectroscopy (XPS) analysis and the detection of bromide in solution indicated that some of BrO3− were reduced to Br−, and the produced bromide ions were released to the solution and adsorbed on the Ppy-NAC. The increase of oxygen-containing functional groups on Ppy-NAC after adsorption verified that the redox reaction occurred during the adsorption process. The mechanisms of bromate removal by the Ppy-NAC included ion exchange and reduction reaction of bromate on the Ppy-NAC surfaces.

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Tiopronin by Acidified Bromate and Aqueous Bromine

N-2-(Mercaptopropionyl)glycine (MPG) is a free-radical scavenger, a detoxicating synthetic aminothiol which also acts as an antioxidant with a wide range of clinical applications. The oxidation of MPG by aqueous bromine and acidified bromate has been studied by spectrophotometric techniques. The stoichiometry for the reaction of acidic bromate with MPG is 1 : 1, HS(CH3)CH(=O)N(H)CH2COOH + BrO3– → HO3S(CH3)CH(=O)N(H)CH2COOH + Br–, with reaction occurring only at the thiol centre. The involvement of thiyl radicals in the oxidation of MPG competes with a non-radical pathway involving two-electron oxidations of the sulfur centre. A bimolecular rate constant of 5.68 (±0.94) × 103 M–1 s–1 for the direct reaction of MPG with bromine was determined. Electrospray ionization spectral data show that MPG is oxidized through its sulfinic acid, by-passing the unstable sulfenic acid. A simplified reaction network consisting of 19 reactions was simulated and it gave a very good fit to the experimental data.

Spectrophotometric determination of trace carbaryl in water and grain samples by inhibition of the rhodamine-B oxidation

A novel, sensitive, selective and simple kinetic spectrophotometric method has been developed for determination of trace levels of carbaryl based on its inhibitory effect on the oxidation of rhodamine-B by chlorine and bromine released from reaction of potassium bromate with hydrochloric acid in micellar medium. A linear relationship was observed between the inhibitory effect and the concentration of the compound. The absorbance was monitored at the maximum wavelength of 555nm. The effect of different parameters such as pH, temperature and concentration of rhodamine-B, potassium bromate and surfactant on the reaction were investigated and optimum conditions were established. Under the selected experimental conditions, carbaryl was determined in the range of 0.04–0.4μgmL−1. Sandell’s sensitivity and molar absorptivity were found to be 0.00055μgcm−2 and 3.658×105Lmol−1cm−1 respectively. The proposed method was applied satisfactorily for the determination of carbaryl in water and different grain samples. The results were compared with those obtained by reference method and were found to be in agreement.

Appropriate Conditions of Oxidation By-Product Bromate Removal from Drinking Water by Nanoparticle Zero-Valent Iron

AbstractThis study is focused on operating conditions for maximizing reduction efficiency of bromate from drinking water. Batch experiments were conducted with prepared nanoparticle zero-valent iron (NZVI) under various operating conditions. It has been found that NZVI prepared by the liquid-phase-reduction method has the characteristics of small diameter, high specific surface area to mass ratios, and great surface reactivity. Bromate can be reduced by NZVI more effectively than commercial iron powder, and bromate-removal efficiency is influenced by the amount of NZVI, initial bromate concentration, pH, dissolved oxygen (DO), mixing rate, and reaction temperature. The reduction efficiency increases with the increase in the amount of NZVI, reaction temperature, and mixing rate. The pH has dual influence on bromate-reduction rate, and appropriate pH can lead to enhanced bromate-reduction rate. Moreover, the bromate reduction over NZVI can be described by pseudo-first-order reaction kinetics. Appropriate op...

Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Captopril by Acidified Bromate and Aqueous Bromine

By nature of their nucleophilicity, all thiol-based drugs are oxidatively metabolized in the physiological environment. The key to understanding the physiological role of a hypertension drug, (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid, medically known as captopril is through studying its oxidation pathway: its reactive intermediates and oxidation products. The oxidation of captopril by aqueous bromine and acidified bromate has been studied by spectrophotometric and electrospray ionization techniques. The stoichiometry for the reaction of acidic bromate with captopril is 1:1, BrO3(-) + (C4H6N)(COOH)(COCHCH3CH2)-SH → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + Br(-), with reaction occurring only at the thiol center. For the direct reaction of bromine with captopril, the ratio is 3:1; 3Br2 + (C4H6N)(COOH)(COCHCH3CH2)-SH + 3H2O → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + 6HBr. In excess acidic bromate conditions the reaction displays an initial induction period followed by a sharp rise in absorbance at 390 nm due to rapid formation of bromine. The direct reaction of aqueous bromine with captopril was much faster than oxidation of the thiol by acidified bromate, with a bimolecular rate constant of (1.046 (±0.08) × 10(5) M(-1) s(-1). The detection of thiyl radicals confirms the involvement of radicals as intermediates in the oxidation of Captopril by acidified BrO3(-). The involvement of thiyl radicals in oxidation of captopril competes with a nonradical pathway involving 2-electron oxidations of the sulfur center. The oxidation product of captopril under these strong oxidizing conditions is a sulfonic acid as confirmed by electrospray ionization mass spectrometry (ESI-MS), iodometric titrations, and proton nuclear magnetic resonance ((1)H NMR) results. There was no evidence from ESI-MS for the formation of the sulfenic and sulfinic acids in the oxidation pathway as the thiol group is rapidly oxidized to the sulfonic acid. A computer simulation analysis of this mechanism gave a reasonably good fit to the experimental data.

Bisulfite-Driven Autocatalysis in the Bromate–Thiosulfate Reaction in a Slightly Acidic Medium

The thiosulfate-bromate reaction has been studied by high-performance liquid chromatography, monitoring the concentrations of thiosulfate and tetrathionate simultaneously. It is found that concentration-time curves of both species display a sigmoidal shape in a slightly acidic, well-buffered medium. Unlike the previously reported complex reaction systems involving bromate, this nonlinear dynamical behavior originates from neither proton nor bromine(III) autocatalysis under our experimental conditions. We demonstrated that sulfur(IV) species significantly accelerates the reaction; therefore, it acts as an autocatalyst. To the best of our knowledge, no reaction system has yet been reported among the pH-driven oxysulfur-oxyhalogen systems, where sulfur(IV) has such a remarkable role. On the basis of the simultaneous evaluation of [S2O3(2-)] and [S4O6(2-)] time series, an eight-step kinetic model is proposed to account for the experimental observations. The model employed here may serve as a solid starting point to extend it for other oxysulfur-oxyhalogen systems where such a seemingly general phenomenon may become observable.

Speciative determination of total V and dissolved inorganic vanadium species in environmental waters by catalytic–kinetic spectrophotometric method

A kinetic determination of V(V) as a catalyst was spectrophotometrically performed by using the indicator reaction of Gallamine blue (GB+) and bromate at pH 2.0. The reaction was followed by measuring absorbance change for a fixed-time of 3min at 537nm. The variables such as reagent concentration, pH, buffer concentration, ionic strength and temperature were optimized to improve the selectivity and sensitivity. Under the optimized conditions, the determination of V(V) was performed in the range 1–100μgL−1 with limits of detection and quantification of 0.31 and 0.94μgL−1. The developed kinetic method is sufficiently sensitive, selective and simple. It was successfully applied to the speciative determination of total V and inorganic dissolved vanadium species, V(V) and V(IV) in environmental water samples. The oxidizing property of permanganate is used to differentiate between V(IV) and V(V) species. The V(IV) content was found by subtracting the V(V) content from those of total V. The recovery is above 95% for V(V) spiked samples. Additionally, the accuracy was validated by analysis of a certified water sample, CRM TMDA-53.3, and the results were in good agreement with the certified value.

Kinetic spectrophotometric method as a new strategy for the determination of vitamin B 9 in pharmaceutical and biological samples

In this study, a new method is proposed for the determination of trace amounts of folic acid (vitamin B 9). This method is based on the inhibitory effect of folic acid on the reaction of Thionine and bromate in sulfuric acid media. The reaction can be monitored spectrophotometrically by measuring the decrease in absorbance at 601 nm ( λ max). The effective variables on the reaction rate were investigated. Under optimum experimental conditions, the method allows to determine of the folic acid in a wide linear range with two linear segments. The limit of detection was 0.36 μg mL −1 of folic acid. Relative standard deviations of six replicate determinations of 5.0 and 50.0 μg mL −1 of folic acid were 1.18 and 1.02%, respectively. The interfering effect of the different species was also investigated. The method was evaluated by quantifying of folic acid in biological and pharmaceutical samples with satisfactory assay results.

A method for the detection of bromate in brackish water

The objective of this study was to develop a simple yet accurate method for the detection of bromate in brackish water. Typically, bromate is measured by ion chromatography; however, the presence of chloride ions complicates bromate detection using this technique. Where bromide ions are naturally present in the source water to be ozonated, either for drinking water or aquacultural purposes, bromate is formed as a disinfection by-product. As such, the need to measure bromate in brackish water is complicated due to the naturally present chloride ions. The study was carried out in a laboratory setting using a UV-spectrophotometer and an ion chromatograph to verify the results. To examine the robustness of the UV-based method, seven water matrices were used to test the bromate detection method. The bromate method presented herein utilizes a reaction of bromate with iodide followed by detection at a UV absorbance at 352 nm. A key finding from the study was that the concentration of bromate was quickly and accurately determined using spectrophotometry. This method successfully measured bromate in waters containing a broad range of conductivity and avoided interference from other anions. The method detection limit reported for all seven water matrices tested was greater than 0.14 mg L −1, which limits the methods utility to saline solutions.