Formation Of Bromine Research Articles

Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetyl Homocysteine Thiolactone by Acidified Bromate and Aqueous Bromine

N-acetyl homocysteine thiolactone (NAHT), medically known as citiolone, can be used as a mucolytic agent and for the treatment of certain hepatic disorders. We have studied the kinetics and mechanisms of its oxidation by acidic bromate and aqueous bromine. In acidic bromate conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of bromine and N-acetyl homocysteine sulfonic acid. The stoichiometry of the bromate-NAHT reaction was deduced to be: BrO3(-) + H2O + CH3CONHCHCH2CH2SCO → CH3CONHCHCH2CH2(SO3H)COOH + Br(-) (S1) while in excess bromate it was deduced to be: 6BrO3(-) + 5CH3CONHCHCH2CH2SCO + 6H(+) → 3Br2 + 5CH3CONHCHCH2CH2(SO3H)COOH + 2H2O (S2). For the reaction of NAHT with bromine, a 3:1 stoichiometric ratio of bromine to NAHT was obtained: 3Br2 + CH3CONHCHCH2CH2SCO + 4H2O → 6Br(-) + CH3CONHCHCH2CH2(SO3H)COOH + 6H(+) (S3). Oxidation occurred only on the sulfur center where it was oxidized to the sulfonic acid. No sulfate formation was observed. The mechanism involved an initial oxidation to a relatively stable sulfoxide without ring-opening. Further oxidation of the sulfoxide involved two pathways: one which involved intermediate formation of an unstable sulfone and the other involves ring-opening coupled with oxidation through to the sulfonic acid. There was oligooscillatory production of aqueous bromine. Bromide produced in S1 reacts with excess bromate to produce aqueous bromine. The special stability associated with the sulfoxide allowed it to coexist with aqueous bromine since its further oxidation to the sulfone was not as facile. The direct reaction of aqueous bromine with NAHT was fast with an estimated lower limit bimolecular rate constant of 2.94 ± 0.03 × 10(2) M(-1) s(-1).

Cloud Point Extraction of Plutonium in Environmental Matrixes Coupled to ICPMS and α Spectrometry in Highly Acidic Conditions

A new cloud point extraction procedure has been developed for the quantification of plutonium(IV) in environmental samples. The separation procedure can be either coupled to inductively coupled plasma mass spectrometry (ICPMS) or α spectrometry for plutonium quantification. The method uses a combination of selective ligand (P,P'-di(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP])) and micelle shielding by bromine formation to enable quantitative extraction of Pu in highly acidic solutions. Cross-optimization of all parameters (nonionic and ionic surfactant, chelating agent, bromate, bromide, and pH) led to optimal of the extraction conditions. Figures of merit of the method for the detection using α spectrometry and ICPMS are reported (limit of detection, limit of quantification, minimal detectable activity, and recovery). Quantitative extractions (>95%) were obtained for a wide variety of aqueous and digested samples (synthetic urine, wastewater, drinking water, seawater, and soil samples). The method features the first successful coupling between α spectrometry and cloud point extraction and is the first demonstration of CPE suitability with metaborate fusion as a sample preparation approach, techniques used extensively in nuclear industries.

Oxidative treatment of bromide-containing waters: Formation of bromine and its reactions with inorganic and organic compounds — A critical review

Bromide (Br−) is present in all water sources at concentrations ranging from ∼10 to >1000μgL−1 in fresh waters and about 67mgL−1 in seawater. During oxidative water treatment bromide is oxidized to hypobromous acid/hypobromite (HOBr/OBr−) and other bromine species. A systematic and critical literature review has been conducted on the reactivity of HOBr/OBr− and other bromine species with inorganic and organic compounds, including micropollutants.The speciation of bromine in the absence and presence of chloride and chlorine has been calculated and it could be shown that HOBr/OBr− are the dominant species in fresh waters. In ocean waters, other bromine species such as Br2, BrCl, and Br2O gain importance and may have to be considered under certain conditions.HOBr reacts fast with many inorganic compounds such as ammonia, iodide, sulfite, nitrite, cyanide and thiocyanide with apparent second-order rate constants in the order of 104–109M−1s−1 at pH 7. No rate constants for the reactions with Fe(II) and As(III) are available. Mn(II) oxidation by bromine is controlled by a Mn(III,IV) oxide-catalyzed process involving Br2O and BrCl.Bromine shows a very high reactivity toward phenolic groups (apparent second-order rate constants kapp≈103–105M−1s−1 at pH 7), amines and sulfamides (kapp≈105–106M−1s−1 at pH 7) and S-containing compounds (kapp≈105–107M−1s−1 at pH 7). For phenolic moieties, it is possible to derive second-order rate constants with a Hammett-σ-based QSAR approach with log(k(HOBr/PhO−))=7.8−3.5Σσ. A negative slope is typical for electrophilic substitution reactions.In general, kapp of bromine reactions at pH 7 are up to three orders of magnitude greater than for chlorine. In the case of amines, these rate constants are even higher than for ozone. Model calculations show that depending on the bromide concentration and the pH, the high reactivity of bromine may outweigh the reactions of chlorine during chlorination of bromide-containing waters.

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.

A comparative study of anodic oxidation of bromide and chloride ions on platinum electrodes in 1-butyl-3-methylimidazolium hexafluorophosphate

The anodic processes of bromide and chloride ions on platinum electrodes were investigated in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, under the same conditions. The halide anions were added to the ionic liquid as their 1-butyl-3-metylimidazolium salts or tetrabutylammonium salts to high concentrations (up to 1.1molL−1). Analysis and comparison of the electrode reactions were made through cyclic voltammetry, chronoamperometry, and double potential step chronocoulometry with a platinum micro-disk electrode, and bulk potentiostatic electrolysis and UV–Vis spectroscopy. Both halide anions exhibited anodic oxidation. The main difference as revealed by cyclic voltammetry was that the chloride ion exhibited only one anodic current peak, whilst the bromide ion underwent clearly distinguished two oxidation steps. This difference is attributed to different electrode kinetics and stabilities of the two tri-halide ions. Bulk electrolysis and UV–Vis spectroscopy confirmed that the tri-bromide ion was the main product from the overall oxidation of the bromide ion, although bromine formation was indicated by cyclic voltammetry at potentials of the second anodic peak.

Iodate and Iodo-Trihalomethane Formation during Chlorination of Iodide-Containing Waters: Role of Bromide

The kinetics of iodate formation is a critical factor in mitigation of the formation of potentially toxic and off flavor causing iodoorganic compounds during chlorination. This study demonstrates that the formation of bromine through the oxidation of bromide by chlorine significantly enhances the oxidation of iodide to iodate in a bromide-catalyzed process. The pH-dependent kinetics revealed species specific rate constants of k(HOBr + IO(-)) = 1.9 × 10(6) M(-1) s(-1), k(BrO(-) + IO(-)) = 1.8 × 10(3) M(-1) s(-1), and k(HOBr + HOI) < 1 M(-1) s(-1). The kinetics and the yield of iodate formation in natural waters depend mainly on the naturally occurring bromide and the type and concentration of dissolved organic matter (DOM). The process of free chlorine exposure followed by ammonia addition revealed that the formation of iodo-trihalomethanes (I-THMs), especially iodoform, was greatly reduced by an increase of free chlorine exposure and an increase of the Br(-)/I(-) ratio. In water from the Great Southern River (with a bromide concentration of 200 μg/L), the relative I-incorporation in I-THMs decreased from 18 to 2% when the free chlorine contact time was increased from 2 to 20 min (chlorine dose of 1 mg Cl(2)/L). This observation is inversely correlated with the conversion of iodide to iodate, which increased from 10 to nearly 90%. Increasing bromide concentration also increased the conversion of iodide to iodate: from 45 to nearly 90% with a bromide concentration of 40 and 200 μg/L, respectively, and a prechlorination time of 20 min, while the I-incorporation in I-THMs decreased from 10 to 2%.

Longpath DOAS observations of surface BrO at Summit, Greenland

Abstract. Reactive halogens, and in particular bromine oxide (BrO), have frequently been observed in regions with large halide reservoirs, for example during bromine catalyzed coastal polar ozone depletion events. Much less is known about the presence and impact of reactive halogens in areas without obvious halide reservoirs, such as the polar ice sheets or continental snow. We report the first LP-DOAS measurements of BrO at Summit research station in the center of the Greenland ice sheet at an altitude of 3200 m. BrO mixing ratios in May 2007 and June 2008 were typically between 1–3 pmol mol−1, with maxima of up to 5 pmol mol−1. These measurements unequivocally show that halogen chemistry is occurring in the remote Arctic, far from known bromine reservoirs, such as the ocean. During periods when FLEXPART retroplumes show that airmasses resided on the Greenland ice sheet for 3 or more days, BrO exhibits a clear diurnal variation, with peak mixing ratios of up to 3 pmol mol−1 in the morning and at night. The diurnal cycle of BrO can be explained by a changing boundary layer height combined with photochemical formation of reactive bromine driven by solar radiation at the snow surface. The shallow stable boundary layer in the morning and night leads to an accumulation of BrO at the surface, leading to elevated BrO despite the expected smaller release from the snowpack during these times of low solar radiation. During the day when photolytic formation of reactive bromine is expected to be highest, efficient mixing into a deeper neutral boundary layer leads to lower BrO mixing ratios than during mornings and nights. The extended period of contact with the Greenland snowpack combined with the diurnal profile of BrO, modulated by boundary layer height, suggests that photochemistry in the snow is a significant source of BrO measured at Summit during the 2008 experiment. In addition, a rapid transport event on 4 July 2008, during which marine air from the Greenland east coast was rapidly transported to Summit, led to enhanced mixing ratios of BrO and a number of marine tracers. However, rapid transport of marine air from the Greenland east coast is rare and most likely not the main source of bromide in surface snow at Summit. The observed levels of BrO are predicted to influence NOx chemistry as well as impact HOx partitioning. However, impact of local snow photochemistry on HOx is smaller than previously suggested for Summit.

S-Oxygenation of Thiocarbamides IV: Kinetics of Oxidation of Tetramethylthiourea by Aqueous Bromine and Acidic Bromate

The kinetics and mechanism of oxidation of tetramethylthiourea (TTTU) by bromine and acidic bromate has been studied in aqueous media. The kinetics of reaction of bromate with TTTU was characterized by an induction period followed by formation of bromine. The reaction stoichiometry was determined to be 4BrO(3)(-) + 3(R)(2)C═S + 3H(2)O → 4Br(-) + 3(R)(2)C═O + 3SO(4)(2-) + 6H(+). For the reaction of TTTU with bromine, a 4:1 stoichiometric ratio of bromine to TTTU was obtained with 4Br(2) + (R)(2)C═S + 5H(2)O → 8Br(-) + SO(4)(2-) + (R)(2)C═O + 10H(+). The oxidation pathway went through the formation of tetramethythiourea sulfenic acid as evidenced by the electrospray ionization mass spectrum of the dynamic reaction solution. This S-oxide was then oxidized to produce tetramethylurea and sulfate as final products of reaction. There was no evidence for the formation of the sulfinic and sulfonic acids in the oxidation pathway. This implicates the sulfoxylate anion as a precursor to formation of sulfate. In aerobic conditions, this anion can unleash a series of genotoxic reactive oxygen species which can explain TTTU's observed toxicity. A bimolecular rate constant of 5.33 ± 0.32 M(-1) s(-1) for the direct reaction of TTTU with bromine was obtained.

Formation of Gas-Phase Bromine from Interaction of Ozone with Frozen and Liquid NaCl/NaBr Solutions: Quantitative Separation of Surficial Chemistry from Bulk-Phase Reaction

The formation kinetics of gas-phase bromine (Br(2)) from interaction of gas-phase ozone (O(3)) with frozen and liquid solutions of NaCl (0.55 M) and NaBr (largely from 1.7 to 8.5 mM) have been studied from -40 to 0 °C in a coated-wall flow tube coupled to a chemical ionization mass spectrometer. The reactive uptake coefficient for O(3) is deduced from the product formation rate and then studied as a function of experimental conditions. In particular, for both the liquid and frozen solutions, we find that the uptake coefficient is inversely dependent on the gas-phase O(3) concentration in a manner that is quantitatively consistent with both surface- and bulk-phase kinetics. The reaction is fastest on acidic media (pH of the starting solution down to 2) but also proceeds at an appreciable rate on neutral substrates. Above 253 K, the uptake coefficient increases with increasing temperature on frozen solutions, consistent with an increasing brine content. The similarity of the absolute magnitude and form of the kinetics on the frozen and liquid substrates suggests that the reaction on the frozen solution is occurring with the associated brine, and not with the ice bulk or a quasi-liquid layer existing on the ice. The implications of these results to bromine activation in the tropospheric boundary layer are made.

Probing the sensitivity of gaseous Br 2 production from the oxidation of aqueous bromide-containing aerosols and atmospheric implications

This paper presents a global sensitivity and uncertainty analysis of the bromine chemistry included in the Model of Aqueous, Gaseous and Interfacial Chemistry (MAGIC) in dark and photolytic conditions. Uncertainty ranges are established for input parameters (e.g. chemical rate constants, Henry's law constants, etc.) and are used in conjunction with Latin hypercube sampling and multiple linear regression to conduct a sensitivity analysis that determines the correlation between each input parameter and model output. The contribution of each input parameter to the uncertainty in the model output is calculated by combining results of the sensitivity analysis with input parameters' uncertainty ranges. Model runs are compared using the predicted concentrations of molecular bromine since Br 2(g) has been shown in previous studies to be generated via an interface reaction between O 3(g) and Br (surface) − during dark conditions [Hunt et al., 2004]. Formation of molecular bromine from the reaction of ozone with deliquesced NaBr aerosol: evidence for interface chemistry. Journal of Physical Chemistry A 108, 11559–11572]. This study also examines the influence of an interface reaction between OH (g) and Br (surface) − in the production of Br 2(g) under photolytic conditions where OH (g) is present in significant concentrations. Results indicate that the interface reaction between O 3(g) and Br (surface) − is significant and is most responsible for the uncertainty in MAGICs ability to calculate precisely Br 2(g) under dark conditions. However, under photolytic conditions the majority of Br 2(g) is produced from a complex mechanism involving gas-phase chemistry, aqueous-phase chemistry, and mass transport.

Disinfection by-product formation from chloramination of clarified water after prechlorination and preozonation

The formation of disinfection by-products (DBPs) was evaluated from a chloraminated water after coagulation with and without prechlorination or preozonation. Prechlorination enhanced formation of trihalomethane (THM), 1,1,1-trichloro-2-propanone (1,1,1-TCP) and total organic chlorine (TOCl) and the concentrations of most DBPs increased with increasing chlorine dosages. Preozonation reduced dichloroacetonitrile (DCAN) and TOCl formation but increasing ozone (O3) dosages did not necessarily reduce the formation of THM, 1,1-dichloro-2-propanone (1,1-DCP) and total organic bromine (TOBr). Increasing coagulant doses reduced the formation of most DBPs and TOCl. However, the formation of TOBr cannot be readily controlled by coagulation in most cases except the case involving prechlorination.

Kinetics and Mechanism of Oxidation of N, N′-Dimethylaminoiminomethanesulfinic Acid by Acidic Bromate

The major metabolites of the physiologically active compound dimethylthiourea (DMTU), dimethylaminoiminomethansesulfinic acid (DMAIMSA), and dimethylaminoiminomethanesulfonic acid (DMAIMSOA) were synthesized, and their kinetics and mechanisms of oxidation by acidic bromate and aqueous bromine was determined. The oxidation of DMAIMSA is much more facile and rapid as compared to a comparable oxidation by the same reagents of the parent compound, DMTU. The stoichiometry of the bromate-DMAIMSA reaction was determined to be 2BrO 3 (-) + 3NHCH 3(NCH 3)CSO 2H + 3H 2O --> 3SO 4 (2) (-) + 2Br (-) + 3CO(NHCH 3) 2 + 6H (+), with quantitative formation of sulfate. In excess bromate conditions, the stoichiometry was 4BrO 3 (-) + 5NHCH 3(NCH 3)CSO 2H + 3H 2O --> 5SO 4 (2) (-) + 2Br 2 + 5CO(NHCH 3) 2 + 6H (+). The direct bromine-DMAIMSA reaction gave an expected stoichiometric ratio of 2:1 with no further oxidation of product dimethylurea (DMU) by aqueous bromine. The bromine-DMAIMSA reaction was so fast that it was close to diffusion-controlled. Excess bromate conditions delivered a clock reaction behavior with the formation of bromine after an initial quiescent period. DMAIMSOA, on the other hand, was extremely inert to further oxidation in the acidic conditions used for this study. Rate of consumption of DMAIMSA showed a sigmoidal autocatalytic decay. The postulated mechanism involves an initial autocatalytic build-up of bromide that fuels the formation of the reactive oxidizing species HBrO 2 and HOBr through standard oxybromine reactions. The long and weak C-S bond in DMAIMSA ensures that its oxidation goes directly to DMU and sulfate, bypassing inert DMAIMSOA.

S-Oxygenation of Thiocarbamides. 3. Nonlinear Kinetics in the Oxidation of Trimethylthiourea by Acidic Bromate

The oxidation of trimethylthiourea (TMTU) by acidic bromate has been studied. The reaction mimics the dynamics observed in the oxidation of unsubstituted thiourea by bromate with an induction period before formation of bromine. The stoichiometry of the reaction was determined to be 4:3, thus 4BrO(3)- + 3R(1)R(2)C=S+ 3H(2)O --> 4Br- + 3R(1)R(2)C=O + 3SO(4)(2-) + 6H+. This substituted thiourea is oxidized at a much faster rate than the unsubstituted thiourea. The oxidation mechanism of TMTU involves initial oxidations through sulfenic and sulfinic acids. At the sulfinic acid stage, the major oxidation pathway is through the cleavage of the C-S bond to form a reducing sulfur leaving group, which is easily oxidized to sulfate. The minor pathway through the sulfonic acid produces a very stable intermediate that is oxidized only very slowly to urea and sulfate. The direct reaction of aqueous bromine with TMTU was faster than reactions that form bromine, with a bimolecular rate constant of (1.50 +/- 0.04) x 10(2) M(-1) s(-1). This rapid reaction ensured that no oligooscillatory bromine formation was observed. The oxidation of TMTU was modeled by a simple reaction scheme containing 20 reactions.

Bromide Oxidation and Formation of Dihaloacetic Acids in Chloraminated Water

A comprehensive reaction model was developed that incorporates the effect of bromide on monochloramine loss and formation of bromine and chlorine containing dihaloacetic acids (DHAAs) in the presence of natural organic matter (NOM). Reaction pathways accounted for the oxidation of bromide to active bromine (Br(l)) species, catalyzed monochloramine autodecomposition, NOM oxidation, and halogen incorporation into DHAAs. The reaction scheme incorporates a simplified reaction pathway describing the formation and termination of Br(l). In the absence of NOM, the model adequately predicted bromide catalyzed monochloramine autodecomposition. The Br(l) reaction rate coefficients are 4 orders of magnitude greater than HOCl for the same NOM sources under chloramination conditions. Surprisingly, the rate of NOM oxidation by Br(l) was faster than bromide catalyzed monochloramine autodecomposition by Br(l) so that the latter reactions could largely be ignored in the presence of NOM. Incorporation of bromine and chlorine into DHAAs was proportional to the amount of NOM oxidized by each halogen and modeled using simple bromine (alpha(Br)) and chlorine (alpha(Cl)) incorporation coefficients. Both coefficients were found to be independent of each other and alpha(Br) was one-half the value of alpha(Cl). This indicates that chlorine incorporates itself into DHAA precursors more effectivelythan bromine. Model predictions compared well with DHAA measurements in the presence of increasing bromide concentrations and is attributable to the increased rate of NOM oxidation, which is rate limited by the oxidation of bromide ion in chloraminated systems.

Characterizing the Emissions of Polybrominated Dibenzo-p-dioxins and Dibenzofurans from Municipal and Industrial Waste Incinerators

As yet, very little is known about the polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) characteristics in the stack flue gases of incinerators. In this study, nine large-scale continuous municipal solid waste incinerators (MSWIs), two small-scale batch MSWls, and nine industrial waste incinerators (IWIs) were investigated for 2,3,7,8-substituted PBDD/Fs. The elevated PBDD/F concentrations (18.2 pg/Nm3, 4.17 pg TEQ/Nm3) of the IWIs, which were eight times higher than those of MSWIs (2.28 pg/Nm3, 0.557 pg TEQ/Nm3), are accompanied by PCDD/ Fs that are in the same range as those measured from MSWIs (0.0171-1.98 ng I-TEQ/Nm3). The obtained TEQ ratios (in percentage) of the PBDD/F to the PCDD/F concentration in the stack flue gases of the MSWls (0.72%), batch MWIs (0.18%), and IWIs (5.4%) are useful for the future estimate of PBDD/F emission quantity based on the well-established PCDD/F inventory. In addition, a significantly high correlation was found between the PBDD/F and PCDD/F concentrations, and the PBDD/F and PCDD/F congener profiles of the same emission source were similar, indicating a similar formation and substitution mechanism of bromine and chlorine in the combustion system.

Transformation of Bromine Species During Decomposition of Bromate under UV Light from Low Pressure Mercury Vapor Lamps

Bromate decomposition with low pressure mercury vapor lamps (LPMVL) was studied in buffer-free and buffered Milli-Q water by following the fate of bromine species BrO3 −, Br−, and free bromine. BrO3 − was converted over time to Br− with total free bromine (TFBr) as secondary reaction product. BrO3 − decay followed pseudo-first-order kinetics and was independent of [BrO3 −]o (0.06–0.6 mM), pHo (6.9–9.5) and HCO3 − (0.05–1.0 mM), slightly dependent on acetate (0.06–0.27 mM), highly dependent on and adversely affected by humic acids (HA) and an increasing function of photon flux I as measured by potassium ferrioxalate actinometry. Reaction pH dropped by as much as 2.2 units at pHo ≤ 8.5 in the buffer-free experiments, while it remained within 0.5 unit at pHo > 9. TFBr decay due to exposure to LPMVL resulted in formation of Br− (major) and BrO3 − (minor). Decay of HA in the presence of BrO3 − was highly augmented by photon emission of LPMVL at 185 nm and was found to substantially contribute to BrO3 − decay in the presence of HA. Correlations on the dependency of bromine species decay or formation rates as a function of photon flux are presented.

Bromate formation on the non-porous TiO 2 photoanode in the photoelectrocatalytic system

The increasing use of ozone in water disinfection processes has been the focus of considerable concern in regards to inorganic disinfection by product formation of bromate in waters containing bromide. Due to the public health risk caused by the presence of bromate as a suspected carcinogen, attention had been addressed to the conditions under which bromate is formed. In this study, photoanodic bromine generation and bromate ( BrO 3 - ) formation were investigated using a TiO 2 electrode in a photoelectrocatalytic (PEC) treatment process. The separation of anodic and cathodic reactions in the PEC system resulted in a pH decrease from 9.3 to 3.0 in the photoanode compartment and an increase to 11.0 in the cathode compartment. Under a photo-illumination intensity of 5.7 mW cm −2 UV, a biasing potential of +1.0 V vs SCE, a pH of 6.0 and at a NaBr concentration of 1.0 × 10 −2 M, active bromine formation increased over time with 2.4 × 10 −6 M min −6 rate and reached a steady-state concentration of 1.44 × 10 −4 M in 60 min. Bromate formation was detected after a lag-period of 15 min and exhibited a continuous increasing trend with respect to irradiation time. No bromate formation was observed below pH 6.5 whereas an increasing bromate concentrations and pH up to pH = 8.5 were noted.

Synergy between nanocomposite formation and low levels of bromine on fire retardancy in polystyrenes

An organically-modified clay has been prepared using ammonium salts which contain an oligomeric material consisting of vinylbenzyl chloride, styrene and dibromostyrene. The presence of dibromostyrene enhances the flame retardancy of polystyrene nanocomposites compared to both the virgin polymer and polystyrene nanocomposites prepared from non-halogen-containing organically-modified clays. The nanocomposites were prepared both by bulk polymerization and melt blending and they were evaluated by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry measurements. Bulk polymerization produced nanocomposites with reduced peak heat release rate, reduced total heat release and improved thermal stability. It is noteworthy that all these improvements were obtained with clay loading as low as 3% and bromine content less than 4%.

Oxyhalogen−Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Guanylthiourea by Acidified Bromate

This article reports on the kinetics and mechanism of oxidation of the biologically active molecule guanylthiourea (GTU) by acidic bromate. This was a follow-up of a previous study in which mild oxidizing agents acidic iodate and molecular iodine oxidized GTU to a ring-cyclized product: 3,5-diamino-1,2,4-thiadiazole. In contrast, acidic bromate and molecular bromine, as stronger oxidizing agents, were able to oxidize GTU all the way to a complete desulfurization to yield guanylurea. No N-bromination was observed on any of the amino groups on guanylurea. The stoichiometry of the reaction was deduced to be 4BrO3- + 3H2N(NH)CNH(CS)NH2 + 3H2O → 4Br- + 3H2N(NH)CNH(CO)NH2 + 3SO42- + 6H+. In excess bromate conditions in which the ratio of oxidant to reductant R = [BrO3-]0/[GTU]0 > 1.6, the stoichiometry of the reaction was 8BrO3- + 5H2N(NH)CNH(CS)NH2 + H2O → 4Br2(aq) + 5H2N(NH)CNH(CO)NH2 + 5SO42- + 2H+. The direct reaction of aqueous bromine with GTU was extremely fast with an estimated lower limit bimolecular rate constant of 7.5 ± 1.2 × 104 M-1 s-1. This rapid reaction with bromine produced reaction dynamics which involved bromine formation after a short induction period which was determined by the time it took for the complete oxidation of GTU and its oxidation intermediates. The mechanism of the reaction involved the initial formation of the ring-cyclized 3,5-diamino-1,2,4-thiadiazole which was later successively oxidized through the sulfoxide and sulfone, followed by the opening of the ring to yield sulfate and guanylurea. All the observed global reaction dynamics were satisfactorily modeled by a simple mechanism involving 14 elementary reactions.

Formation of Molecular Bromine from the Reaction of Ozone with Deliquesced NaBr Aerosol: Evidence for Interface Chemistry

The reaction of ozone with aqueous sodium bromide particles is investigated with a combination of aerosol chamber experiments, kinetics modeling, and molecular dynamics simulations. The molecular bromine production in the chamber experiments is approximately an order of magnitude greater than that predicted by known chemistry in the gas and bulk aqueous phases with use of a comprehensive computer kinetics model. Molecular dynamics simulations indicate that ozone has significant residence time at the air−solution interface, while making frequent contacts with bromide ions for as long as 50 ps in the surface layer of a 6.1 M NaBr solution. The formation of a complex between ozone and bromide ion, [O3···Br-], which can lead to production of Br2 by reaction at the air−water interface, is therefore feasible. Experimentally observed Br2 is well predicted by including an interface process with a reaction probability of [1.9 ± 0.8] × 10-6 (1 s) as the first step in a surface mechanism to produce additional gas-ph...