Reaction Of Bromine Atoms Research Articles

A theoretical kinetic study on the reaction of atomic bromine with toluene

AbstractThe reaction of Br atoms with toluene was investigated by employing various quantum chemical methods and statistical rate theory calculations. Various composite methods such as CBS‐QB3, G3, and G4 were used to obtain the energy profiles of the Br + toluene reaction. Further single‐point calculations of the stationary points were performed at the CCSD(T)/cc‐pV(D,T)Z level of theory using B3LYP/cc‐pVTZ and MP2/aug‐cc‐pVDZ optimized geometries. Our calculations revealed several reaction pathways in the potential energy surface of the Br + toluene reaction. However, the reaction pathway that abstracts hydrogen atoms from the methyl site of toluene was found to be energetically the most favorable. This reaction pathway appears to proceed via a complex forming mechanism, similar to that seen in the reactions of cyclic ethers with Br atoms. Our calculations reveal that the reaction of a Br atom with toluene proceeds exclusively via intermediate complexes in an overall endothermic addition‐elimination mechanism. Based on the ab initio results, the standard enthalpies of formation of the product radicals and the rate coefficients for the relevant reaction pathways are computed. The calculated values of the enthalpy of formation are found to match excellently with the available literature data. Lowering the barrier height of hydrogen abstraction reaction at the methyl site by less than 4 kJ/mol, the calculated rate coefficients, kov(T) = 1.36 × 10–23 T3.687 exp(−4.57 K/T) cm3 molecule–1 s–1, reproduced the experimental data excellently from 200 to 500 K.

Kinetics of Elementary Steps in the Reactions of Atomic Bromine with Isoprene and 1,3-Butadiene under Atmospheric Conditions

Laser flash photolysis of CF(2)Br(2) has been coupled with time-resolved detection of atomic bromine by resonance fluorescence spectroscopy to investigate the gas-phase kinetics of early elementary steps in the Br-initiated oxidations of isoprene (2-methyl-1,3-butadiene, Iso) and 1,3-butadiene (Bu) under atmospheric conditions. At T ≥ 526 K, measured rate coefficients for Br + isoprene are independent of pressure, suggesting that hydrogen transfer (1a) is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 526 K ≤ T ≤ 673 K: k(1a)(T) = (1.22 ± 0.57) × 10(-11) exp[(-2100 ± 280)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2σ and represent precision of the Arrhenius parameters). At 271 K ≤ T ≤ 357 K, kinetic evidence for the reversible addition reactions Br + Iso ↔ Br-Iso (k(1b), k(-1b)) and Br + Bu ↔ Br-Bu (k(3b), k(-3b)) is observed. Analysis of the approach to equilibrium data allows the temperature- and pressure-dependent rate coefficients k(1b), k(-1b), k(3b), and k(-3b) to be evaluated. At atmospheric pressure, addition of Br to each conjugated diene occurs with a near-gas-kinetic rate coefficient. Equilibrium constants for the addition/dissociation reactions are obtained from k(1b)/k(-1b) and k(3b)/k(-3b), respectively. Combining the experimental equilibrium data with electronic structure calculations allows both second- and third-law analyses of thermochemistry to be carried out. The following thermochemical parameters for the addition reactions 1b and 3b at 0 and 298 K are obtained (units are kJ mol(-1) for Δ(r)H and J mol(-1) K(-1) for Δ(r)S; uncertainties are accuracy estimates at the 95% confidence level): Δ(r)H(0)(1b) = -66.6 ± 7.1, Δ(r)H(298)(1b) = -67.5 ± 6.6, and Δ(r)S(298)(3b) = -93 ± 16; Δ(r)H(0)(3b) = -62.4 ± 9.0, Δ(r)H(298)(3b) = -64.5 ± 8.5, and Δ(r)S(298)(3b) = -94 ± 20. Examination of the effect of added O(2) on Br kinetics under conditions where reversible adduct formation is observed allows the rate coefficients for the Br-Iso + O(2) (k(2)) and Br-Bu + O(2) (k(4)) reactions to be determined. At 298 K, we find that k(2) = (3.2 ± 1.0) × 10(-13) cm(3) molecule(-1) s(-1) independent of pressure (uncertainty is 2σ, precision only; pressure range is 25-700 Torr) whereas k(4) increases from 3.2 to 4.7 × 10(-13) cm(3) molecule(-1) s(-1) as the pressure increases from 25 to 700 Torr. Our results suggest that under atmospheric conditions, Br-Iso and Br-Bu react with O(2) to produce peroxy radicals considerably more rapidly than they undergo unimolecular decomposition. Hence, the very fast addition reactions appear to control the rates of Br-initiated formation of Br-Iso-OO and Br-Bu-OO radicals under atmospheric conditions. The peroxy radicals are relatively weakly bound, so conjugated diene regeneration via unimolecular decomposition reactions, though unimportant on the time scale of the reported experiments (milliseconds), is likely to compete effectively with bimolecular reactions of peroxy radicals under relatively warm atmospheric conditions as well as in 298 K competitive kinetics experiments carried out in large chambers.

Kinetics of elementary steps in the reaction of atomic bromine with 2,3‐dimethyl‐2‐butene under atmospheric conditions

AbstractWe have employed the laser flash photolysis–resonance fluorescence technique to investigate the gas‐phase kinetics of elementary steps in the Br‐initiated oxidation of 2,3‐dimethyl‐2‐butene (TME) under atmospheric conditions. At T⩾ 274 K, measured rate coefficients are independent of pressure suggesting hydrogen abstraction as the dominant pathway. The following Arrhenius expression adequately describes all kinetic data at 274 K ⩽T⩽ 420 K: k1a(T) = (3.84 ± 0.84) × 10− 11 exp[(−169 ± 61)/T] cm3 molecule−1s−1 (uncertainties are 2σ, precision only). At 203 K ⩽T⩽ 241 K, kinetic evidence for reversible addition, Br + TME ↔ Br−TME (k1b, k−1b), is observed. Analysis of the approach to equilibrium data allows evaluation of the rate coefficients k1b and k−1b. At atmospheric pressure addition of Br to TME occurs at a near gas kinetic rate. Equilibrium constants are obtained from k1b/k−1b. Combining the experimental results with electronic structure calculations allows third‐law analyses of the equilibrium data. The following thermochemical parameters for the addition reaction (1b) at 0 and 298 K are obtained (standard state = 1 atm): ΔrH0= −47.1 ± 3.0 kJ mol−1, ΔrH298=−47.3 ± 3.0 kJ mol−1, and ΔrS298=−101.5 ± 10.0 J mol−1 K−1. Examination of the effect of added O2 on Br atom kinetics under conditions where reversible adduct formation is observed allows determination of the rate coefficient for the Br–TME + O2 reaction (k2). At 223 K, we find that k2 increases from 3.9 to 5.5 × 10−12 cm3 molecule−1s−1 as pressure increases from 25 to 200 Torr. Our results suggest that under most atmospheric conditions the Br–TME reaction with O2 occurs more rapidly than the Br–TME unimolecular decomposition. Hence, the fast addition reaction appears to control the rate of TME loss by reaction with Br in the atmosphere. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 13–26, 2012

Rate constant for the reaction of bromine atoms with ethane: Kinetic and thermochemical implications

Relative-rate kinetic experiments were carried-out at T = 310 ± 3 K to determine rate constant ratios for the reactions of Br atoms with C2H6(1), CH2ClBr(2) and neo-C5H12(3). Br atoms were produced by stationary photolysis of Br2 and the consumption of the reactants was determined by gas-chromatography. k2/k1 = 1.174 ± 0.053 and k3/k1 = 0.458 ± 0.027 were determined (with 1σ precision given). The rate constant ratios were resolved to absolute k1 values, and k1(310 K) = (2.27 ± 0.30) × 105 cm3 mol−1 s−1 was recommended. The recommended k1 was applied in a third law analysis providing ΔfHo298(C2H5) = (122.0 ± 1.9) kJ mol−1.

Pulse radiolysis studies of the reactions of bromine atoms and dimethyl sulfoxide–bromine atom complexes with alcohols

Dimethylsulfoxide (DMSO)–Br complexes were generated by pulse radiolysis of DMSO/bromomethane mixtures and the formation mechanism and spectral characteristics of the formed complexes were investigated in detail. The rate constant for the reaction of bromine atoms with DMSO and the extinction coefficient of the complex were obtained to be 4.6×10 9 M −1 s −1 and 6300 M −1 cm −1 at the absorption maximum of 430 nm. Rate constants for the reaction of bromine atoms with a series of alcohols were determined in CBrCl 3 solutions applying a competitive kinetic method using the DMSO–Br complex as the reference system. The obtained rate constants were ∼10 8 M −1 s −1, one or two orders larger than those reported for highly polar solvents. Rate constants of DMSO–Br complexes with alcohols were determined to be ∼ 10 7 M −1 s −1. A comparison of the reactivities of Br atoms and DMSO–Br complexes with those of chlorine atoms and chlorine atom complexes which are ascribed to hydrogen abstracting reactants strongly indicates that hydrogen abstraction from alcohols is not the rate determining step in the case of Br atoms and DMSO–Br complexes.

Temperature-dependent rate coefficient measurements for the reaction of bromine atoms with trichloroethene, ethene, acetylene, and tetrachloroethene in air

Temperature-dependent rate coefficient measurements for the reaction of bromine atoms with trichloroethene, ethene, acetylene, and tetrachloroethene in air

Temperature-dependent rate coefficient measurements for the reaction of bromine atoms with a series of aldehydes

Relative rate coefficient data have been obtained for the reactions Br + RCHO → RCO + HBr for a series of aldehydes: HCHO, reaction (1); CH3CHO, reaction (2); CH3CH2CHO, reaction (3); CH3CH2CH2CHO, reaction (4). Measurements were made over the temperature range 240–300 K in an environmental chamber/FTIR spectrometer system, using standard relative rate techniques. All measured rate coefficient ratios were found to be independent of temperature over the range studied (k2/k1 = 3.60 ± 0.29, k3/k1 = 6.65 ± 0.53, k4/k1 = 8.62 ± 0.69, and k3/k2 = 1.80 ± 0.14), implying that the activation barriers for all four reactions are essentially identical with the A-factors increasing with the size of the aldehyde. Relative rate coefficients for k1 and k2 agree well with currently recommended data at room temperature, but inconsistencies on the order of 20% arise at lower temperatures. The entire set of relative rate coefficient measurements is put on an absolute scale using a combination of currently recommended values for k1 and k2. The following expressions (all in units of cm3 molecule−1 s−1) are obtained: k1 = (0.79 ± 0.10) × 10−11 exp(−580 ± 200/T), k2 = (2.7 ± 0.4) × 10−11 exp(−567 ± 200/T), k3 = (5.75 ± 0.75) × 10−11 exp(−610 ± 200/T), k4 = (5.75 ± 0.75) × 10−11 exp(−540 ± 200/T), where uncertainties quoted for the A-factor reflect the uncertainty in the room temperature value. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 460–465, 2000

Kinetics of the reactions of bromine atoms with a series of aliphatic aldehydes at 298 K

AbstractThe kinetics of the reactions of Br(2P3/2) with selected aldehydes, i.e. ethanal (l), propanal (2). 2‐methyl‐pro‐panal (3), 2,2‐dhethyl‐propanal (4) and trichloroacetaldehyde (5) were studied at 298±2 K. Rate constants for overall reactions were measured using the fast flow technique with resonance fluorescence detection of Br. Complementary determinations were carried out by the laser flash photolysis method. The following rate constants were obtained in the kinetic measurements (±2σ): k1=(2.1±0.2)×1012, k2=(4.3±0.4)×1012, k3=(6.3±1.4)×1012, k4=(8.5±0.8)×1012, k5≤1×109 all in cm3 mol−1 s−1 units.The probable mechanism for the reactions of bromine atoms with aliphatic aldehydes has been discussed.

Soluble polymer-bound phase-transfer catalysts

New soluble polymer-bound phase-transfer catalysts (PTCs) were synthesized using commercially available oxidized polyethylene as the substrate polymer. These new polymeric compounds are bifunctional catalysts containing I ether and quaternary ammonium groups attached to a polyethylene skeleton. They were prepared by direct amidation of oxidized polyethylene with diamino Jeffamines — diamino derivatives of poly(alkene) glycols — followed by a quaternization reaction. Their catalytic activity was studied in the nucleophilic substitution reaction of bromine atoms in 1,6-dibromohexane by cyanide and iodide anions. The activity of the PTCs was dependent on the nature of the starting reagents (oxidized polyethylene and polyglycol diamine), the procedure by which catalysts were synthesized, and the conditions of the substitution reaction. The temperature-dependent solubility of the PTC facilitates their use as homogeneous catalysts, since they can be separated out by filtration at the end of the reaction. The new catalysts can then easily be separate from the products and recovered without loss of activity.

Laser flash photolysis determination of absolute rate constants for reactions of bromine atoms in solution

The photodecomposition of vicinal dibromides at 266 nm produces bromine atoms with a quantum yield of ∼2.0. This results from an efficient primary photocleavage of a C-Br bond, followed by rapid elimination of a second bromine atom from radicalsofthe type RCH-CH 2 Br. This cleavage occurs with a lifetime of <20 ns at room temperature. Bromine atoms react with bromine ions with a rate constant of 1.6×10 10 M -1 s -1 to yield Br 2 .- , an easily detectable and long-lived radical ion. This reaction can be used as a probe in order to determine absolute rate constants for other reactions of bromine atoms

Free Radical Reductive Degradation of vic-Dibromoalkanes and Reaction of Bromine Atoms with Polyunsaturated Fatty Acids: Possible Involvement of Br . in the 1,2-Dibromoethane-Induced Lipid-Peroxidation

Bromine atoms generated upon reductive degradation of 1,2-dibromoethane and various other vic-dibromoalkanes have been shown to react with polyunsaturated fatty acids via both abstraction of bisallylic hydrogen and addition to the double bonds. The abstraction process occurs with 53, 68, and 77% efficiency from linoleic (18:2), linolenic (18:3), and arachidonic acid (20:4), respectively. The corresponding absolute rate constants have been evaluated to be 1.2 × 10 9, 1.8 × 10 9, and 5.1 × 10 9 M −1 s −1 for these three polyunsaturated fatty acids (PUFAs). The rate constants for the bromine atom addition reaction appear to be very similar for all PUFAs and have been determined to (1.2 ± 0.3) × 10 9 M −1 s −1. Absolute rate constants in the order of 10 5-10 6 s −1 have also been measured for the bromine atom elimination from various β-bromoalkyl radicals. The results render bromine atoms a potential initiator for lipid peroxidation, and their reactions may well provide an important chemical basis for the overall toxic action of 1,2-dibromoethane and related substrates.

Kinetics and thermochemistry of R + hydrogen bromide .dblarw. RH + bromine atom reactions: determinations of the heat of formation of ethyl, isopropyl, sec-butyl and tert-butyl radicals

The reactions of alkyl radicals (R = CH{sub 3}, C{sub 2}H{sub 5}, i-C{sub 3}H{sub 7}, and t-C{sub 4}H{sub 9}) with HBr have been studied by excimer laser flash photolysis coupled with photoionization mass spectrometry. R + HBr rate constants are approximately a factor of 2 higher than previously reported. The source of this disparity is explained. The kinetics of reverse reactions, Br + RH (R = C{sub 2}H{sub 6}, C{sub 3}H{sub 8}, n-C{sub 4}H{sub 10}, i-C{sub 4}H{sub 10}), have also been investigated using laser flash photolysis/resonance fluorescence methods. These results, combined with previously obtained kinetic information, were used in second- and third-law thermochemical calculations to obtain accurate determinations of the heats of formation of the C{sub 2}-C{sub 4} alkyl radicals involved. Second- and third-law determinations agreed extremely closely (differences were under 1.3 kJ mol{sup {minus}1}). The heats of formation of the radicals thus obtained are in excellent agreement with values obtained from studies of dissociation/association equilibria, within 2.6 kJ mol{sup {minus}1}. Recommended alkyl-radical heats of formation (with uncertainties) at 298 K are provided that are based on an assessment of all the results of the current study and a review of other recent determination (kJ mol{sup {minus}1}): C{sub 2}H{sub 5},more » 121.0 {+-} 1.5; i-C{sub 3}H{sub 7}, 90.0 {+-} 1.7; sec-C{sub 4}H{sub 9}, 67.5 {+-}2.2; t-C{sub 4}H{sub 9}, 51.3 {+-} 1.8. Accurate determination of carbon-hydrogen bond enthalpies (298 K) are provided that are based on these heats of formation (kJ mol{sup {minus}1}): primary C-H in C{sub 2}H{sub 6} (422.8 {+-} 1.5); secondary C-H in C{sub 3}H{sub 8} (412.7 {+-} 1.7) and n-C{sub 4}H{sub 10} (411.1 {+-} 2.2); tertiary C-H in i-C{sub 4}H{sub 10} (403.5 {+-} 1.8). 44 refs., 4 figs., 8 tabs.« less

Reaction of atomic bromine with difluorochloromethane: the heat of formation of the CClF2 radical and the D.degree.(CClF2-H) bond dissociation energy

The gas-phase photobromination of CHClF 2 (1) in the presence of CH 3 Cl (2) as competitor has been studied in the temperature range 80-150 o C at halomethane pressures of ∼35 Torr and a Br 2 pressure of ∼2.3 Torr. The temperature dependence of the rate constant ratio is found to obey the Arrhenius expression ln (k 1 /k 2 )=(-0.0885±0.0580)-(1144±20)/T

Rate constants for the etching of intrinsic and doped polycrystalline silicon by bromine atoms

The rate constants for the reaction of bromine atoms with intrinsic and heavily doped n+-type polycrystalline silicon, as well as their temperature dependencies, are reported for the first time. The rate constant for intrinsic silicon is given as k=(4±2)×107 nm min−1 Torr−1e−(62±2kJ/mol)/RT and for n+-type silicon with a phosphorus number density of 5×1018 cm−3, k=(1±1)×1011 nm min−1 Torr−1e−(62±2kJ/mol)/RT. Although the etch rates for the n+-type silicon are 2–3 orders of magnitude larger than for intrinsic silicon at the same temperature and atom concentration, the difference in the two rate constants is due to a change in the pre-exponential Arrhenius factor and not in the activation energy.

A relative rate study of the reaction of bromine atoms with a variety of organic compounds at 295 K

AbstractThe relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i‐butane or acetaldehyde or both. Using rate constants of 1.74 × 10−15 and 3.5 × 10−12 cm3 molecule−1 s−1 for the reaction of Br with i−butane and acetaldehyde respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: 2, 3−dimethylbutane, (6.40 ± 0.77) × 10−15; cyclopentane, (1.16 ± 0.18) × 10−15, ethene, (≤2.3 × 10−13); propene, (3.85 ± 0.41) × 10−12; trans‐2‐butene, (9.50 ± 0.76) × 10−12, acetylene, (5.15 ± 0.19) × 10−15; and propionaldehyde, (9.73 ± 0.91) × 10−12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals.

Reaction of atomic bromine with ethyl bromide. The heat of formation of the 1-bromoethyl radical and the .alpha.-carbon-hydrogen bond dissociation energy

Reaction of atomic bromine with ethyl bromide. The heat of formation of the 1-bromoethyl radical and the .alpha.-carbon-hydrogen bond dissociation energy

Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

Acetylene (C2H2) is an important hydrocarbon species which is present in trace quantities in the troposphere and lower stratosphere. Potential loss processes for atmospheric C2H2 include reactions with OH, Cl, O, and Br as well as photodissociation. Rate data for the first three reactions are available in the literature, but the latter reaction has not been the subject of any previous studies. We have measured the rate constant for the reaction at four temperatures over the range 210–393 K and at pressures between 15 and 100 torr Ar. The technique employed was flash photolysis combined with time‐resolved detection of atomic bromine via Br resonance radiation. The reaction was shown to be independent of total pressure (Ar) and temperature over the indicated ranges. The average of all experiments gives the value k = (4.0 ± 0.8) × 10−15 cm3 s−1, where the error is 2 standard deviations. The result is compared with previous data from our laboratory for reactions of H, Cl, OH, and NH2 with C2H2. Loss rates for atmospheric C2H2 have been calculated as a function of altitude for reactions with OH, Cl, O, and Br.

Structure of the bromovinyl radical: a matrix isolation study

The bromovinyl radical has been prepared by the reaction of bromine atoms with acetylene in an argon matrix at 17 K and its i.r. spectrum has been studied. The spectrum of C2H DBr˙ shows the presence of two isomers, indicating that the radical has an unsymmetric structure.

Photodissociation of bromine azide. II. Production of Br2(D′ 3Π2g)

The quenching of N2(A 3Σ+u) metastables by Br2(X 1Σ+g) results in the generation of Br2(D′ 3Π2g)→A′(3Π2u) emission. Although this energy exchange is near resonant, its rate constant is only (5±2)×10−13 cm3 molecule−1 s−1. Comparison of this result with the known rate for N2(A 3Σ+u) quenching by I2 indicates the importance of Franck–Condon factors in these energy transfer processes. In light of this result, the generation of intense Br2 D′→A′ emission from the UV photolysis of BrN3 is modeled as a Franck–Condon favored process in which Br2(A′ 3Π2u or A 3Π1u) is excited to the D′(3Π2g) state by collisions with N2(A 3Σ+u) metastables. Br2 (A or A′) is generated as a product of the reaction of bromine atoms, produced as a photodissociation fragment, with BrN3. The rate constant for this process is k5=(3.0±0.5)×10−11 cm3 molecule−1 s−1. The rate constant of the energy transfer process is inferred to be k6≥1.5×10−10 cm3 molecule−1 s−1. A second mechanism producing Br2(D′ 3Π2g) is evident in the time profile of the D′→A′ emission. This mechanism, which produces prompt D′→A′ emission, does not involve excitation by collisions with N2(A).

Matrix reactions of bromine atoms and nitrogen dioxide molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMatrix reactions of bromine atoms and nitrogen dioxide moleculesDavid E. TevaultCite this: J. Phys. Chem. 1979, 83, 17, 2217–2221Publication Date (Print):August 1, 1979Publication History Published online1 May 2002Published inissue 1 August 1979https://doi.org/10.1021/j100480a007RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (658 KB) Get e-Alerts