Reaction Of HOBr Research Articles

Experimental verification of gas phase bromine enrichment in reactions of HOBr with sea salt doped ice surfaces

AbstractSignificant gas phase bromine enrichment is experimentally verified on flowing gaseous HOBr over ice surfaces doped with sodium halides of sea salt composition. It is argued that formation of Br2Cl− in the condensed phase followed by its dissociation with release of Br2 into the gas phase accounts for this phenomenon.

A Gaskinetic Investigation of HOBr Reactions with CI(2P), O(3P) and OH(2II). The Reaction of BrCl with OH(2II)

AbstractThe reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass‐spectrometric detection. The rate constants based on HOBr consumption have been determined to be k1 = (8.0±0.4)·10−11 and k2 = (3.1±0.2)·10−11. For the reaction with OH radicals k3<5×10−13 was obtained. All rate constants are given in units cm3 molecule−1 s−1.The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCl and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH+BrCl → HOBr+Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr at T = 300 K was evaluated to be ΔH0f (HOBr) = −(60.22±2) kJ · mol−1.

Peroxidase-Mediated Bromination of Unsaturated Fatty Acids to Form Bromohydrins

Eosinophil peroxidase and myeloperoxidase (MPO) catalyze the oxidation of bromide by hydrogen peroxide to produce hypobromous acid (HOBr). Hypochlorous acid, which is also generated by MPO, reacts with unsaturated fatty acids to form chlorohydrins. In this study the equivalent reaction of HOBr, produced from MPO, bromide, and hydrogen peroxide, with oleic (18:1), linoleic (18:2), and arachidonic (20:4) acids has been investigated. Thin-layer chromatography detected one major product of higher polarity than the unmodified fatty acids and additional more polar products with the polyunsaturated fatty acids. Similar results were observed withN-bromosuccinimide-derived HOBr. Gas chromatography–mass spectrometry (GC–MS) and electrospray MS identified the major products of 18:1 as the isomeric 9,10-bromohydrins based on retention time and mass spectrometric isotope and fragmentation patterns. The products of 18:2 and 20:4 were too unstable for analysis by GC–MS. Electrospray MS identified the mono- and bisbromohydrins formed from 18:2 and 20:4 based on mass/charge ratios of the molecular ions and the presence of bromine isotope patterns. Other oxidation products not containing bromine, such as dihydroxy derivatives, were detected as well. Fatty acid bromohydrins could contribute to the antimicrobial activity and inflammatory tissue damage by eosinophils and neutrophils, and could potentially be useful specific markers for HOBr productionin vivo.

Equilibrium and Kinetics of Bromine Hydrolysis.

Equilibrium constants for bromine hydrolysis, K(1) = [HOBr][H(+)][Br(-)]/[Br(2)(aq)], are determined as a function of ionic strength (&mgr;) at 25.0 degrees C and as a function of temperature at &mgr; approximately 0 M. At &mgr; approximately 0 M and 25.0 degrees C, K(1) = (3.5 +/- 0.1) x 10(-)(9) M(2) and DeltaH degrees = 62 +/- 1 kJ mol(-)(1). At &mgr; = 0.50 M and 25.0 degrees C, K(1) = (6.1 +/- 0.1) x 10(-)(9) M(2) and the rate constant (k(-)(1)) for the reverse reaction of HOBr + H(+) + Br(-) equals (1.6 +/- 0.2) x 10(10) M(-)(2) s(-)(1). This reaction is general-acid-assisted with a Brønsted alpha value of 0.2. The corresponding Br(2)(aq) hydrolysis rate constant, k(1), equals 97 s(-)(1), and the reaction is general-base-assisted (beta = 0.8).

Heterogeneous atmospheric bromine chemistry

This paper considers the effect of heterogeneous bromine reactions on stratospheric photochemistry. We have considered reactions on both sulfate aerosols and on polar stratospheric clouds (PSCs). It is shown that the hydrolysis of BrONO2 on sulfate aerosols enhances the HOBr concentration, which in turn enhances the OH and HO2 concentrations, thereby reducing the HCl lifetime and concentration. The hydrolysis of BrONO2 leads to a nighttime production of HOBr, making HOBr a major nighttime bromine reservoir. The photolysis of HOBr gives a rapid increase in the OH and HO2 concentration at dawn, as was recently observed by Salawitch et al. [1994]. The increase in the OH and HO2 concentration, and the decrease in the HCl concentration, leads to additional ozone depletion at all latitudes and for all season. At temperatures below 210 K the bulk phase reaction of HOBr with HCl in sulfate aerosols becomes important. The most important heterogeneous bromine reactions on polar stratospheric clouds are the mixed halogen reactions of HCl with HOBr and BrONO2 and of HBr with HOCl and ClONO2.

The reaction O(³P) + HOBr: Temperature dependence of the rate constant and importance of the reaction as an HOBr stratospheric loss process

The absolute rate constant for the reaction O(³P) + HOBr has been measured between T=233K and 423K using the discharge‐flow kinetic technique coupled to mass spectrometric detection. The value of the rate coefficient at room temperature is (2.5±0.6) × 10−11 cm³ molecule−1 s−1 and the derived Arrhenius expression is (1.4±0.5) × 10−10 exp[(−430±260)/T] cm³ molecule−1 s−1. From these rate data the atmospheric lifetime of HOBr with respect to reaction with O(³P) is about 0.6h at z = 25 km which is comparable to the photolysis lifetime based on recent measurements of the UV cross section for HOBr. Implications for HOBr loss in the stratosphere have been tested using a 1D photochemical box model. With the inclusion of the rate parameters and products for the O + HOBr reaction, calculated concentration profiles of BrO increase by up to 33% around z = 35 km. This result indicates that the inclusion of the O + HOBr reaction in global atmospheric chemistry models may have an an impact on bromine partitioning in the middle atmosphere.

Heterogeneous reaction of HOBr with HBr and HCl on ice surfaces at 228 K

Motivated by the recent observations of springtime ozone loss in the Arctic boundary layer, we have studied the heterogeneous reactions HOBr + HBr → Br2 + H2O and HOBr + HCl → BrCl + H2O using a low temperature flow tube coupled to a mass spectrometer. By monitoring the decay of HOBr in an excess of either HBr or HCl, both reactions have been shown to occur readily on ice surfaces at 228 K with reaction probabilities of 0.12 (±0.03) and 0.25 (+0.10/−0.05), respectively. The gasphase reaction products, Br2 and BrCl, have been observed. Also, it has been shown that HOBr interacts strongly with supercooled 60 wt % sulfuric acid solutions, being taken up with a sticking coefficient of greater than 0.06. The atmospheric implications of the heterogeneous reactivity of HOBr and HBr are discussed.

Organometallic Catalysis in Aqueous Solution: Oxygen Transfer to Bromide

The reaction between hydrogen peroxide and bromide ions in aqueous acidic solutions, ordinarily very slow, is strongly catalyzed by CH[sub 3]ReO[sub 3], a water-soluble organometallic oxide. The complex catalytic kinetics showed that the rate-controlling process consists of two steps: (1) reversible formation of the independently-known 1:1 and 2:1 adducts of hydrogen peroxide and methylrhenium trioxide (the formulas, including the water that had been shown to be coordinated, are CH[sub 3]Re(O)[sub 2]([eta][sup 2]-O[sub 2])(H[sub 2]O) and CH[sub 3]Re(O)([eta][sup 2]-O[sub 2])[sub 2](H[sub 2]O)) and (2) their reactions with bromide ions that yield HOBr. The rate constants for these steps were evaluated by several steady-state kinetic techniques. The HOBr intermediate reacts with Br to yield Br[sub 2]. When hydrogen peroxide was in excess, the reaction yielded oxygen instead of bromine. This can be accounted for by the reaction of HOBr with H[sub 2]O[sub 2]. The 2:1 peroxide-rhenium adduct, formed only at the higher concentrations of hydrogen peroxide, also reacts with bromide ions, but more slowly. Kinetic modeling by numerical techniques was used to provide verification of the reaction scheme. 19 refs., 8 figs., 1 tab.

Mass-spectrometric evidence for the formation of bromochloramine and N-bromo-N-chloromethylamine in aqueous solution

Membrane introduction mass spectrometry (MIMS) is used to confirm the existence of bromochloramine and N-bromo-N-chloromethylamine in aqueous solution, which have been proposed previously from UV-visible spectra. Bromochloramine is detected by mass spectrometry and UV-visible spectroscopy as a product of monochloramine reactions with bromide ion and with hypobromous acid. The reaction of HOBr with NH 2 Cl is at least 3 orders of magnitude faster than the reaction of Br - with NH 2 Cl at pH 6.5

A Simulation of Bromate–Cerium–Oxalic Acid Oscillations

Abstract The oscillation behavior of the bromate–cerium–oxalic acid system was simulated within the FKN framework with bromine-hydrolysis control, where a radical-chain reaction of HOBr with oxalic acid and the formation of HCO2· by the reduction of Ce(IV) were assumed. When [(COOH)2]=0.03 mol dm−3 and k13=0.075 s−1 (k13: the rate constant of bromine removal), the oscillation behavior was qualitatively consistent with the experimental results. Excitability in the reduced and oxidized steady states, induced by a sudden change in the concentration of bromine, was simulated. No bistability was found. When [(COOH)2]=0.03 mol dm−3, no hysteresis near the bifurcation points was observed. However, when [(COOH)2]=0.001 mol dm−3, hysteresis was observed in the transition between the oxidized steady state and the oscillatory state.

Use of a Rotating Ring Disc Electrode to Study Fast Bromine Demand Reactions

Abstract A roatating ring disc electrode (RRDE) was used to study the fast reactions of electrochemically produced bromine with three different model compounds and one natural water sample. One of the three test compounds, ammonia, exhibited slow, pseudo first-order kinetics while two of the test compounds, NaAsO2 and phenyl-arsine oxide, exhibited rapid second-order kinetics. Interpretation of the pseudo first order data yielded a specific rate constant for the reaction of HOBr and NH3 of 8.1 × 107 M−1 s−1, in agreement with published results. Interpretation of the second-order data showed that the minumum detectable concentration of substrate was on the order of 1 × 10−6M and the rate constant for bromine reacting with As(III) approached the upper limit of our RRDE system. The natural water sample collected from the Patuxent River exhibited a rapid second-order bromine demand, similar to As(III). Analysis of the RRDE data suggested a family of naturally occurring reactants with a concentration of 2 × 10...

Etude des petits cycles—XLIII: Reactions d'addition sur les α-cyclopropylidene-cetones et sur les α-cyclopropylidene-aldehydes

α-Cyclopropylidene ketones and aldehydes show high reactivity towards 1,4-addition of methanol in acidic or basic medium, water and hydrochloric acid giving α-(1-methoxy cyclopropyl) ketones and aldehydes α-(1-hydroxy cyclopropyl) ketones and α-(1-chloro cyclopropyl) ketones and aldehydes respectively. The reaction of α-cyclopropylidene-ketones with Grignard reagents gives mainly α-cyclopropyl ketones (the 1,4-addition product) besides α-cyclopropylidene carbinols (the 1,2-addition product). Addition of methyl-lithium and lithium dimethylcuprate lead to the expected 1,2- and 1,4-addition products, respectively. The comparison of these results and those corresponding to α-isopropylidene-ketones confirms the higher tendency of α-cyclopropylidene-ketones to give 1,4-addition products; the measurement of polarographic reduction potentials confirms, in some cases, this difference. The reaction of HOBr (NBS, DMSO, H 2O) with α-cyclopropylidene ketones produces α-hydroxy β-bromo ketones whereas the corresponding α-isopropylidene ketones give β-hydroxy α-bromo ketones.