Showing papers in "International Journal of Chemical Kinetics in 2000"

The reaction kinetics of dimethyl ether. I: High‐temperature pyrolysis and oxidation in flow reactors

Abstract: Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions. Pyrolysis of dimethyl ether was studied in a variable-pressure flow reactor at 2.5 atm and 1118 K. Studies were also conducted in an atmospheric pressure flow reactor at about 1085 K. These experiments included trace-oxygen-assisted pyrolysis, as well as full oxidation experiments, with the equivalence ratio (ϕ) varying from 0.32 ≤ ϕ ≤ 3.4. On-line, continuous, extractive sampling in conjunction with Fourier Transform Infra-Red, Non-Dispersive Infra-Red (for CO and CO2) and electrochemical (for O2) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactors. Species concentrations were correlated against residence time in the reactor and species evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism. Some changes were made to the model in order to improve agreement with the present experimental data. However, the revised model continues to reproduce previously reported high-temperature jet-stirred reactor and shock tube results. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet: 32: 713–740, 2000

The reaction kinetics of dimethyl ether. II: Low-temperature oxidation in flow reactors

Abstract: Dimethyl ether oxidation has been studied in a variable-pressure flow reactor over an initial reactor temperature range of 550–850 K, in the pressure range 12–18 atm, at equivalence ratios of 0.7 ≤ ϕ ≤ 4.2, with nitrogen diluent of approximately 98.5%. On-line extraction sampling in conjunction with FTIR, NDIR (for CO and CO2), and electrochemical (for O2) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactor. Product species concentrations were correlated against residence time (at constant inlet temperature) and against temperature (at fixed mean residence time) in the reactor. Formic acid was observed as a major intermediate of dimethyl ether oxidation at low temperatures. The experimental species-evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism [1]. This mechanism did not predict the formation of formic acid. In the current study we have included chemistry leading to formic acid formation (and oxidation). This new chemistry is discussed and is able to reproduce the experimental observations with good accuracy. In addition, this model is able to reproduce low-temperature kinetic data obtained in a jet-stirred reactor [2] and the shock-tube results of Pfahl et al. [3] © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 741–759, 2000

Detailed kinetic modeling of 1,3‐butadiene oxidation at high temperatures

Abstract: The high-temperature kinetics of 1,3-butadiene oxidation was examined with detailed kinetic modeling. To facilitate model validation, flow reactor experiments were carried out for 1,3-butadiene pyrolysis and oxidation over the temperature range 1035–1185 K and at atmospheric pressure, extending similar experiments found in the literature to a wider range of equivalence ratio and temperature. The kinetic model was compiled on the basis of an extensive review of literature data and thermochemical considerations. The model was critically validated against a range of experimental data. It is shown that the kinetic model compiled in this study is capable of closely predicting a wide range of high-temperature oxidation and combustion responses. Based on this model, three separate pathways were identified for 1,3-butadiene oxidation, with the chemically activated reaction of H· and 1,3-butadiene to produce ethylene and the vinyl radical being the most important channel over all experimental conditions. The remaining uncertainty in the butadiene chemistry is also discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 589–614, 2000

Experimental and kinetic modeling study of the oxidation of benzene

Abstract: The oxidation of benzene under flow-reactor conditions has been studied experimentally and in terms of a detailed chemical kinetic model. The experiments were performed under plug-flow conditions, at excess air ratios ranging from close to stoichiometric to very lean. The temperature range was 900–1450 K and the residence time of the order of 150 ms. The radical pool was perturbed by means of varying the concentration of water vapor and by adding NO. Furthermore, a few experiments were conducted on pyrolysis and oxidation of phenol. Benzene oxidation is initiated at ∼1000 K; the temperature for complete oxidation depends on stoichiometry, ranging from 1100 K (very lean conditions) to 1300 K (close to stoichiometric). The water vapor level and the presence of NO have only a minor impact on the temperature regime for oxidation. The proposed chemical kinetic model was validated by comparison with the present experimental data as well as flow reactor and mixed reactor data from literature. The model provides a reasonably good description of the overall oxidation behavior of benzene over the range of conditions investigated. However, before details of the oxidation behavior can be predicted satisfactorily, a number of kinetic issues need to be resolved. These include product channels and rates for the reactions of phenyl and cyclopentadienyl with molecular oxygen as well as reaction chemistry for the oxygenated cyclic compounds formed as intermediates in the oxidation process. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 498–522, 2000

Kinetic modeling of the CO/H2O/O2/NO/SO2 system: Implications for high-pressure fall-off in the SO2 + O(+M) = SO3(+M) reaction

Abstract: Flow reactor experiments were performed to study moist CO oxidation in the presence of trace quantities of NO (0–400 ppm) and SO2 (0–1300 ppm) at pressures and temperatures ranging from 0.5–10.0 atm and 950–1040 K, respectively. Reaction profile measurements of CO, CO2, O2, NO, NO2, SO2, and temperature were used to further develop and validate a detailed chemical kinetic reaction mechanism in a manner consistent with previous studies of the CO/H2/O2/NOX and CO/H2O/N2O systems. In particular, the experimental data indicate that the spin-forbidden dissociation-recombination reaction between SO2 and O-atoms is in the fall-off regime at pressures above 1 atm. The inclusion of a pressure-dependent rate constant for this reaction, using a high-pressure limit determined from modeling the consumption of SO2 in a N2O/SO2/N2 mixture at 10.0 atm and 1000 K, brings model predictions into much better agreement with experimentally measured CO profiles over the entire pressure range. Kinetic coupling of NOX and SOX chemistry via the radical pool significantly reduces the ability of SO2 to inhibit oxidative processes. Measurements of SO2 indicate fractional conversions of SO2 to SO3 on the order of a few percent, in good agreement with previous measurements at atmospheric pressure. Modeling results suggest that, at low pressures, SO3 formation occurs primarily through SO2 + O(+M) = SO3(+M), but at higher pressures where the fractional conversion of NO to NO2 increases, SO3 formation via SO2 + NO2 = SO3 + NO becomes important. For the conditions explored in this study, the primary consumption pathways for SO3 appear to be SO3 + HO2 = HOSO2 + O2 and SO3 + H = SO2 + OH. Further study of these reactions would increase the confidence with which model predictions of SO3 can be viewed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 317–339, 2000

Kinetics and mechanisms of decomposition reaction of hydrogen peroxide in presence of metal complexes

Abstract: Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H2O2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old [2]. However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent. Although the decomposition of hydrogen peroxide is often employed as a standard reaction to determine the catalytic activity of metal complexes and metal oxides [3,4], it has recently been extensively used in intrinsically clean processes and in end-of-pipe treatment of effluent of chemical industries [5,6]. Furthermore, the adoption of H2O2 as an alternative of current industrial oxidation processes offer environmental advantages, some of which are (1) replacement of stoichiometric metal oxidants, (2) replacement of halogens, (3) replacement or reduction of solvent usage, and (4) avoidance of salt by-products. On the other hand, wasteful decomposition of hydrogen peroxide due to trace transition metals in wash water in the fabric bleach industry, was also recognized [7]. The low intrinsic reactivity of H2O2 is actually an advantage, in that a method can be chosen which selectively activates it to perform a given oxidation. There are three main active oxidants derived from hydrogen peroxide, depending on the nature of the activator; they are (1) inorganic oxidant systems, (2) active oxygen species, and (3) per oxygen intermediates. Two general types of mechanisms have been postulated for the decomposition of hydrogen peroxide in the presence of transition metal complexes. The first is the radical mechanism (outer sphere), which was proposed by Haber and Weiss for the Fe(III)-H2O2 system [8]. The key features of this mechanism were the discrete formation of hydroxyl and hydroperoxy radicals, which can form a redox cycle with the Fe(II)/Fe(III) couple. The second is the peroxide complex mechanism, which was proposed by Kremer and Stein [9]. The significant difference in the peroxide complex mechanism is the two-electron oxidation of Fe(III) to Fe(V) with the resulting breaking of the peroxide oxygen-oxygen bond. It is our intention in this article to briefly summarize the kinetics as well as the mechanisms of the decomposition of hydrogen peroxide, homogeneously and heterogeneously, in the presence of transition metal complexes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 643–666, 2000

Kinetics of OH and Cl reactions with a series of aldehydes

Abstract: The rate constants for the reactions of the OH radicals with a series of aldehydes have been measured in the temperature range 243–372 K, using the pulsed laser photolysis-pulsed laser induced fluorescence method. The obtained data for propanaldehyde, iso-butyraldehyde, tert-butyraldehyde, and n-pentaldehyde were as follows (in cm3 molecule−1 s−1): (a) in the Arrhenius form: (5.3 ± 0.5) × 10−12 exp[(405 ± 30)/T], (7.3 ± 1.9) × 10−12 exp[(390 ± 78)/T], (4.7 ± 0.8) × 10−12 exp[(564 ± 52)/T], and (9.9 ± 1.9) × 10−12 exp[(306 ± 56)/T]; (b) at 298 K: (2.0 ± 0.3) × 10−11, (2.6 ± 0.4) × 10−11, (2.7 ± 0.4) × 10−11, and (2.8 ± 0.2) × 10−11, respectively. In addition, using the relative rate method and alkanes as the reference compounds, the room-temperature rate constants have been measured for the reactions of chlorine atoms with propanaldehyde, iso-butyraldehyde, tert-butyraldehyde, n-pentaldehyde, acrolein, and crotonaldehyde. The obtained values were (in cm3 molecule−1 s−1): (1.4 ± 0.3) × 10−10, (1.7 ± 0.3)10−10, (1.6 ± 0.3) × 10−10, (2.6 ± 0.3) × 10−10, (2.2 ± 0.3) × 10−10, and (2.6 ± 0.3) × 10−10, respectively. The results are presented and discussed in terms of structure-reactivity relationships and atmospheric importance. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 676–685, 2000

Kinetics of hydrogen peroxide decomposition with complexed and “free” iron catalysts

Abstract: The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO2), followed by an irreversible decomposition and using the pseudo-steady-state hypothesis (PSSH). This resulted in a first-order rate at low H2O2 concentrations and a zero order rate at high H2O2 concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO2 complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H2O), EDTA–Fe–(OH), or EDTA–Fe–(OH)2, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H2O2 from pH 2–10 (initial rates = 1 × 10−4 to 1 × 10−7 M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, KML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log KMLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by-product-complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000

Kinetics and mechanism of oxidation of ethylenediamine and related compounds by diperiodatoargentate (III) ion

Abstract: The oxidation of ethylenediamine by diperiodatoargentate (III) ion has been studied by stopped-flow spectrophotometry. Kinetics of this reaction involves two steps. The first step is the complexation of silver (III) with the substrate and is over in about 10 ms. This is followed by a redox reaction in the second step that occurs intramolecularly from the substrate to the silver (III) center. The rate of reduction of silver (III) species by ethylenediamine, ethanolamine, and 1,2-ethanediol were observed to be 1.2 × 104, 1.1 × 102, and 0.14 dm3 mol−1 s−1, respectively, at 20°C. The reaction rate shows an inverse dependence on [IO] and [OH−] in the low concentration range (≤1 × 10-3 mol dm−3). At higher [OH−] (>1 × 10−3 mol dm−3) the rate of reaction starts increasing and attains a limiting value at very high [OH−]. The rate of deamination of ethylenediamine is enhanced by its complexation with silver (III). The involvement of [AgIII(H2IO6) (H2O)2] and [AgIII(H2IO6) (OH)2]2− are suggested as the reactive silver (III) species kinetically in mild basic and basic conditions, respectively. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 286–293, 2000

Rate coefficients for the gas‐phase reaction of OH radicals with selected dihydroxybenzenes and benzoquinones

Abstract: Rate coefficients have been determined for the gas-phase reaction of the hydroxyl (OH) radical with the aromatic dihydroxy compounds 1,2-dihydroxybenzene, 1,2-dihydroxy-3-methylbenzene and 1,2-dihydroxy-4-methylbenzene as well as the two benzoquinone derivatives 1,4-benzoquinone and methyl-1,4-benzoquinone. The measurements were performed in a large-volume photoreactor at (300 ± 5) K in 760 Torr of synthetic air using the relative kinetic technique. The rate coefficients obtained using isoprene, 1,3-butadiene, and E-2-butene as reference hydrocarbons are kOH(1,2-dihydroxybenzene) = (1.04 ± 0.21) × 10−10 cm3 s−1, kOH(1,2-dihydroxy-3-methylbenzene) = (2.05 ± 0.43) × 10−10 cm3 s−1, kOH(1,2-dihydroxy-4-methylbenzene) = (1.56 ± 0.33) × 10−10 cm3 s−1, kOH(1,4-benzoquinone) = (4.6 ± 0.9) × 10−12 cm3 s−1, kOH(methyl-1,4-benzoquinone) = (2.35 ± 0.47) × 10−11 cm3 s−1. This study represents the first determination of OH radical reaction-rate coefficients for these compounds. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 696–702, 2000

Kinetics and products of propargyl (C3H3) radical self‐reactions and propargyl‐methyl cross‐combination reactions

Abstract: Propargyl (HCCCH2) and methyl radicals were produced through the 193-nm excimer laser photolysis of mixtures of C3H3Cl/He and CH3N2CH3/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self-reactions and propargyl-methyl cross-combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C6H6 isomers with 1,5-hexadiyne(CHCCH2CH2CCH, about 60%); 1,2-hexadiene-5yne (CH2CCCH2CCH, about 25%); and a third isomer of C6H6 (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl-methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10−11 cm3 molecule−1 s−1 for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10−10 cm3 molecule−1 s−1 for propargyl-methyl cross-combination reactions. The products of the methyl-propargyl cross-combination reactions were two isomers of C4H6, 1-butyne (about 60%) and 1,2-butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000

Kinetics of the gas-phase reactions of Cl atom with selected C2–C5 unsaturated hydrocarbons at 283 < T < 323 K

Abstract: The reaction of Cl atoms with a series of C2–C5 unsaturated hydrocarbons has been investigated at atmospheric pressure of 760 Torr over the temperature range 283–323 K in air and N2 diluents. The decay of the hydrocarbons was followed using a gas chromatograph with a flame ionization detector (GC-FID), and the kinetic constants were determined using a relative rate technique with n-hexane as a reference compound. The Cl atoms were generated by UV photolysis (λ ≥ 300 nm) of Cl2 molecules. The following absolute rate constants (in units of 10−11 cm3 molecule−1 s−1, with errors representing ±2σ) for the reaction at 295 ± 2 K have been derived from the relative rate constants combined to the value 34.5 × 10−11 cm3 molecule−1 s−1 for the Cl + n-hexane reaction: ethene (9.3 ± 0.6), propyne (22.1 ± 0.3), propene (27.6 ± 0.6), 1-butene (35.2 ± 0.7), and 1-pentene (48.3 ± 0.8). The temperature dependence of the reactions can be expressed as simple Arrhenius expressions (in units of 10−11 cm3 molecule−1 s−1): kethene = (0.39 ± 0.22) × 10−11 exp{(226 ± 42)/T}, kpropyne = (4.1 ± 2.5) × 10−11 exp{(118 ± 45)/T}, kpropene = (1.6 ± 1.8) × 10−11 exp{(203 ± 79)/T}, k1-butene = (1.1 ± 1.3) × 10−11 exp{(245 ± 90)/T}, and k1-pentene = (4.0 ± 2.2) × 10−11 exp{(423 ± 68)/T}. The applicability of our results to tropospheric chemistry is discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 478–484, 2000

Rate constants for the gas-phase reactions of a series of C3?C6 aldehydes with OH and NO3 radicals

Abstract: By using relative rate methods, rate constants for the gas-phase reactions of OH and NO3 radicals with propanal, butanal, pentanal, and hexanal have been measured at 296 ± 2 K and atmospheric pressure of air. By using methyl vinyl ketone as the reference compound, the rate constants obtained for the OH radical reactions (in units of 10−12 cm3 molecule−1 s−1) were propanal, 20.2 ± 1.4; butanal, 24.7 ± 1.5; pentanal, 29.9 ± 1.9; and hexanal, 31.7 ± 1.5. By using methacrolein and 1-butene as the reference compounds, the rate constants obtained for the NO3 radical reactions (in units of 10−15 cm3 molecule−1 s−1) were propanal, 7.1 ± 0.4; butanal, 11.2 ± 1.5; pentanal, 14.1 ± 1.6; and hexanal, 14.9 ± 1.3. The dominant tropospheric loss process for the aldehydes studied here is calculated to be by reaction with the OH radical, with calculated lifetimes of a few hours during daytime. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 79–84, 2000

Oxidation of isoniazid by N-haloarenesulfonamidates in alkaline medium: A kinetic and mechanistic study

Abstract: The kinetics of oxidation of Isoniazid (INH) by sodium N-haloarenesulfonamidates, chloramine-T (CAT), bromamine-T (BAT), chloramine-B (CAB), and bromamine-B (BAB), has been studied in alkaline medium at 303 K. The oxidation reaction follows identical kinetics with a first-order dependence on each [oxidant] and [INH] and an inverse fractional-order on [OH−:]. Addition of the reaction product (p-toluenesulfonamide or benzenesulfonamide) had no significant effect on the reaction rate. Variation of ionic strength and addition of halide ions have no influence on the rate. There is a negative effect of dielectric constant of the solvent. Studies of solvent isotope effects using D2O showed a retardation of rate in the heavier medium. The reaction was studied at different temperatures, and activation parameters have been computed from the Arrhenius and Eyring plots. Isonicotinic acid was identified as the oxidation product by GC-MS. A two-pathway mechanism is pro-posed in which RNHX and the anion RNX− interact with the substrate in the rate-limiting steps. The mechanism proposed and the derived rate laws are consistent with the observed kinetics. The rate of oxidation of INH increases in the order: BAT > BAB > CAT > CAB. This effect is mainly due to electronic factors. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 221–230, 2000

Automatic reduction of detailed mechanisms of combustion of alkanes by chemical lumping

Abstract: This article presents an automatic method for reducing a detailed primary mechanism of combustion of any single alkane. Free radicals having the same molecular formula and the same functional groups are lumped into one single species. The number of free radicals of the primary mechanism is divided by a factor 16 in the case of n-heptane. The kinetic parameters of lumped reactions are computed as weighted means of individual rate constants without any fitting process. The simulations of lumped and detailed mechanisms of combustion of isooctane and n-heptane show a good agreement in a wide temperature range (600–1200 K). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 36–51, 2000

Rate constants for the gas‐phase reactions of chlorine atoms with a series of ketones

Abstract: The pulsed laser photolysis-resonance fluorescence technique has been used to determine the absolute rate coefficient for the Cl atom reaction with a series of ketones, at room temperature (298 ± 2) K and in the pressure range 15–60 Torr. The rate coefficients obtained (in units of cm3 molecule−1 s−1) are: acetone (3.06 ± 0.38) × 10−12, 2-butanone (3.24 ± 0.38) × 10−11, 3-methyl-2-butanone (7.02 ± 0.89) × 10−11, 4-methyl-2-pentanone (9.72 ± 1.2) × 10−11, 5-methyl-2-hexanone (1.06 ± 0.14) × 10−10, chloroacetone (3.50 ± 0.45) × 10−12, 1,1-dichloroacetone (4.16 ± 0.57) × 10−13, and 1,1,3-trichloroacetone (<2.4 × 10−12). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 62–66, 2000

Kinetic study of 2‐propanol and benzyl alcohol oxidation by alkaline hexacyanoferrate(III) catalyzed by a terpyridyl ruthenium complex

Abstract: The complex (Trpy)RuCl3 (Trpy = 2,2′:6′,2″-terpyridine) reacts with alkaline hexacyanoferrate(III) to form a terpyridyl ruthenium(IV)-oxo complex that catalyzes the oxidation of 2-propanol and benzyl alcohol by alkaline hexacyanoferrate(III). The reaction kinetics of this catalytic oxidation have been studied photometrically. The reaction rate shows a first-order dependence on [RU(IV)], a zero-order dependence on [hexacyanoferrate(III)], a fractional order in [substrate], and a fractional inverse order in [HO−]. The kinetic data suggest a reaction mechanism in which the catalytic species and its protonated form oxidize the uncoordinated alcohol in parallel slow steps. Isotope effects, substituent effects, and product studies suggest that both species oxidize alcohol through similar pericyclic processes. The reduced catalytic intermediates react rapidly with hexacyanoferrate(III) and hydroxide to reform the unprotonated catalytic species. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 760–770, 2000

Cavity ring-down study of BrO radicals: Kinetics of the Br + O3 reaction and rate of relaxation of vibrationally excited BrO by collisions with N2 and O2

Abstract: Cavity ring-down (CRD) techniques were used to study the kinetics of the reaction of Br atoms with ozone in 1–205 Torr of either N2 or O2, diluent at 298 K. By monitoring the rate of formation of BrO radicals, a value of k(Br + O3) = (1.2 ± 0.1) × 10−12 cm3 molecule−1 s−1 was established that was independent of the nature and pressure of diluent gas. The rate of relaxation of vibrationally excited BrO radicals by collisions with N2 and O2 was measured; k(BrO(v) + O2 BrO(v − 1) + O2) = (5.7 ± 0.3) × 10−13 and k(BrO(v) + N2 BrO(v − 1) + N2) = (1.5 ± 0.2) × 10−13 cm3 molecule−1 s−1. The increased efficiency of O2 compared with N2 as a relaxing agent for vibrationally excited BrO radicals is ascribed to the formation of a transient BrO–O2 complex. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 125–130, 2000

Rate Constants of CH4 + MCH3 + H + M and CH3OH + MCH3 + OH + M over 1400–2500 K

Abstract: Rate constant k1 of CH4 + MCH3 + H + M was determined from time profiles of IR emission at 3.4 μm obtained for a CH4/Ar mixture heated by incident shock waves at pressures 0.40–0.82 atm and temperatures 1400–2500 K. The emission decrease due to CH4 decay in a very short period at the shockfront was investigated. Computer modeling for the decrease gave the k1 value as: 3.0 × 1016 exp(−81.0 kcal/RT) cm3 mol−1 s−1. The k1 value was almost the same as those reported by all authors except for the report by Klemm et al. The same technique was used for determining the rate constant k2 of CH3OH + MCH3 + OH + M and a new value was proposed as k2 = 4.2 × 1016 exp(−66.8 kcal/RT) cm3 mol−1 s−1. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 1–6, 2000

Experimental and kinetic modeling of the reduction of NO by isobutane in a Jsr at 1 atm

Abstract: A kinetic study of the reduction of nitric oxide (NO) by isobutane in simulated conditions of the reburning zone was carried out in a fused silica jet-stirred reactor operating at 1 atm, at temperatures ranging from 1100 to 1450 K. In this new series of experiments, the initial mole fraction of NO was 1000 ppm, that of isobutane was 2200 ppm, and the equivalence ratio was varied from 0.75 to 2. It was demonstrated that for a given temperature, the reduction of NO is favored when the temperature is increased and a maximum NO reduction occurs slightly above stoichiometric conditions. The present results generally follow those reported in previous studies of the reduction of NO by C1 to C3 hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (979 reversible reactions and 130 species). An overall reasonable agreement between the present data and the modeling was obtained. Furthermore, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethylene, ethane, acetylene, a natural gas blend (methane-ethane 10:1), propene, and HCN. According to this study, the main route to NO reduction by isobutane involves ketenyl radical. The model indicates that the reduction of NO proceeds through the reaction path: iC4H10 C3H6 C2H4 C2H3 C2H2 HCCO; HCCO + NO HCNO + CO and HCN + CO2; HCNO + H HCN NCO NH; NH + NO N2 and NH + H followed by N + NO N2; NH + NO N2O followed by N2O + H N2. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 365–377, 2000

Kinetics and mechanism of the reaction between hypochlorous acid and tetrathionate ion

Abstract: The reaction has been studied spectrophotometrically monitoring the absorbance in the wavelength range. The spectra of the reactants, intermediates, and prod240–400 nm ucts in this system are overlapping; thus special programs [1,2] have been used (and tested) to unravel the kinetics and mechanism of the reaction. The stoichiometry of the reaction in excess hypochlorous acid is Various ex2 2 S O 7HOCl 3H O : 4SO 7Cl 13H . 4 6 2 4 periments are presented to show that—in excess tetrathionate—the reaction produces a light-absorbing intermediate identified as The intermediate slowly hydrolyzes into S O Cl . 2 3 sulfur and sulfate and it yields pentathionate in excess tetrathionate. The rate-determining steps and their rate constants are k1 2 2 1 1 S O HOCl 9: S O Cl S O H ; k 32.4 M s 4 6 2 3 2 4 1 k2 2 1 1 S O Cl HOCl 2H O 9: 2SO 2Cl 5H ; k 7.7 M s 2 3 2 3 2 The further oxidation of and by HOCl to sulfate are fast processes. 2000 John 2 2 S O SO 2 4 3 Wiley & Sons, Inc. Int J Chem Kinet 32: 395–402, 2000

Kinetics of the gas-phase reaction of CF3CF2CH2OH with OH radicals and its atmospheric lifetime

Abstract: CF3CF2CH2OH is a new chlorofluorocarbon (CFC) alternative. However, there are few data about its atmospheric fate. The kinetics of its atmospheric oxidation, the OH radical reaction of CF3CF2CH2OH, has been investigated in a 2-liter Pyrex reactor in the temperature range of 298 ∼ 356 K using gas chromatography (GC)–mass spectrometry (MS) for analysis in this study. The rate coefficient of k1 = (2.27) × 10−12 exp[−(900 ± 70)/T] cm3 molecule−1 s−1 was determined using the relative rate method. The results are in good agreement with the literature values and the prediction of Atkinson's structure–activity relationship (SAR) model. From these results, the atmospheric lifetime of CF3CF2CH2OH in the troposphere was deduced to be 0.34 year, which is 250 and 6 times shorter than those of CFC-113 and hydrochlorofluorocarbons (HCFC-225ca), respectively. Therefore CF3CF2CH2OH has significant potential for the replacement of CFC-113 and HCFC-225ca. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 73–78, 2000

Gas phase rate coefficients and activation energies for the reaction of butanal and 2‐methyl‐propanal with nitrate radicals

Abstract: Rate coefficients have been determined for the reaction of butanal and 2-methyl-propanal with NO3 using relative and absolute methods. The relative measurements were accomplished by using a static reactor with long-path FTIR spectroscopy as the analytical tool. The absolute measurements were made using fast-flow–discharge technique with detection of NO3 by optical absorption. The resulting average coefficients from the relative rate experiments were k = (1.0 ± 0.1) × 10−14 and k = (1.2 ± 0.2) × 10−14 (cm3 molecule−1 s−1) for butanal and 2-methyl-propanal, respectively. The results from the absolute measurements indicated secondary reactions involving NO3 radicals and the primary formed acyl radicals. The prospect of secondary reactions was investigated by means of mathematical modeling. Calculations indicated that the unwanted NO3 radical reactions could be suppressed by introducing molecular oxygen into the flow tube. The rate coefficients from the absolute rate experiments with oxygen added were and k = (1.2 ± 0.1) × 10−14 and = (0.9 ± 0.1) × 10−14 (cm3 molecule−1 s−1) for butanal and 2-methyl-propanal. The temperature dependence of the reactions was studied in the range between 263 and 364 K. Activation energies for the reactions were determined to 12 ± 2 kJ mole−1 and 14 ± 1 kJ mole−1 for butanal and 2-methyl-propanal, respectively. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 294–303, 2000

Gas-phase pyrolytic reactions of N-ethyl, N-isopropyl, and N-t-butyl substituted 2-aminopyrazine and 2-aminopyrimidine

Abstract: The rates of gas-phase elimination of N-ethyl (1), N-isopropyl (2), N-t-butyl (3) substituted 2-aminopyrazine and N-ethyl (4), N-isopropyl (5), and N-t-butyl (6) substituted 2-aminopyrimidine have been measured. The compounds undergo unimolecular first-order pyrolytic reactions. The relative rates of the primary:secondary;tertiary alkyl homologues at 600 K are 1:14.4:38.0 for the pyrazines and 1:20.8:162.5 for the pyrimidines, respectively. The reactivities of these compounds have been compared with those of the alkoxy analogues and with each other. Product analyses, together with the kinetic data, were used to outline a feasible pathway for the elimination reaction of the compounds under study. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 403–407, 2000

Rate constants for the gas‐phase reactions of Cl atoms with a series of ethers

Abstract: The laser photolysis–resonance fluorescence technique has been used to determine the absolute rate coefficient for the Cl atom reaction with a series of ethers, at room temperature (298 ± 2) K and in the pressure range 15–60 Torr. The rate coefficients obtained (in units of cm3 molecule−1 s−1) are dimethyl ether (1.3 ± 0.2) × 10−10, diethyl ether (2.5 ± 0.3) × 10−10, di-n-propyl ether (3.6 ± 0.4) × 10−10, di-n-butyl ether (4.5 ± 0.5) × 10−10, di-isopropyl ether (1.6 ± 0.2) × 10−10, methyl tert-butyl ether (1.4 ± 0.2) × 10−10, and ethyl tert-butyl ether (1.5 ± 0.2) × 10−10. The results are discussed in terms of structure–reactivity relationship. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 105–110, 2000