bluuebunny/crossref_metadata_2025 huggingface dataset:
The atmospheric chemistry of Oxygenated fuel additives: t‐Butyl alcohol, dimethyl ether, and methylt‐butyl ether
Authors: Japar S. M. , Wallington T. J. , Richert J. F. O. , Ball J. C.
Published: January 2005

The mechanisms for the Cl‐initiated and OH‐initiated atmospheric oxidation of t‐butyl alcohol (TBA), methyl t‐butyl ether (MTBE), and dimethyl ether (DME) have been determined. For TBA the only products observed are equimolar amounts of H2CO and acetone, and its atmospheric oxidation can be represented by (7),
equation image

The mechanism for the atmospheric oxidation of DME is also straight forward, with the only observable product being methyl formate,
equation image

The mechanism for the atmospheric oxidation of MTBE is more complex, with observable products being t‐butyl formate (TBF) and H2CO. Evidence is presented also for the formation of 2‐methoxy‐2‐methyl propanal (MMP), which is highly reactive and presumably oxidized to products. The atmospheric oxidation of MTBE can be represented by (9) and (10),
equation image

equation image

In terms of atmospheric reactivity, DME, TBA, and MTBE all compare favorably with methanol. In terms of rate of reaction in the atmosphere, DME, MTBE, and TBA are 1.4, 0.40, and 0.28 times as reactive as CH3OH towards OH on a per carbon basis. With regard tochemistry, atmospheric oxidation of CH3OH yields highly reactive H2CO as the sole carbon‐containing product. In contrast, only 25% of the carbon in TBA is converted to H2CO, with the balance yielding unreactive acetone. For DME, all the carbon is converted to methyl formate which is unreactive. Finally, for MTBE, 60% is converted to unreactive TBF while the remaining 40% produces highly reactive MMP.

Final assessment of the impact of these materials on the atmospheric reactivity of vehicle emissions requires the determination of their emissions rates under realistic operating conditions.
Thermal decomposition of chlorofluoromethyl peroxynitrates
Authors: Köppenkastrop D. , Zabel F.
Published: January 2005

The thermal decomposition of CCl3O2NO2,CCl2FO2NO2, and CClF2O2NO2 was studied in a temperature‐controlled 420 l reaction chamber using in situ detection of peroxynitrates by long‐path IR absorption. The temperature dependence of the unimolecular dissociation rate constants was determined at total pressures of 10 and 800 mbar in nitrogen as buffer gas, and the pressure dependence was measured at 273 K between 10 and 800 mbar. In Troe's notation, the data are represented by the following values for the limiting low and high pressure rate constants k0/[N2] and k∞ and the fall‐off curvature parameter Fc (in units of cm3 molecule−1 s−1, s−1): CCl3O2NO2,k0/[N2] = 6.3 × 10−3 exp(−85.1 kJ · mol−1/RT), k∞ = 4.8 × 1016 exp(−98.3 kJ · mol−1/RT), Fc = 0.22; CCl2FO2NO2, k0/[N2] = 1.01× 10−2 exp(−90.3 kJ · mol−1/RT), k∞ = 6.6 × 1016 exp(−101.8 kJ · mol−1/RT), Fc = 0.28; and CClF2O2NO2, k0/[N2] = 1.80 × 10−3 exp(−87.3 kJ · mol−1/RT), k∞ = 1.60 × 1016exp(−99.7 kJ · mol−1/RT), Fc = 0.30. From these dissociation rate constants and recently measured rate constants for the reverse reaction (see Caralp, Lesclaux, Rayez, Rayez, and Forst [19]), bond energies (=ΔH) of 100, 103, and 104 kJ/mol were derived for the RO2–NO2 bonds in CCl3O2NO2, CCl2FO2NO2, and CClF2O2NO2, respectively. The kinetic and thermochemical parameters of these decomposition reactions are compared with those of the dissociation of other peroxynitrates. Atmospheric implications of the thermal stability of chlorofluoromethyl peroxynitrates are briefly discussed.
A combined stability‐sensitivity analysis of weak and strong reactions of hydrogen/oxygen mixtures
Authors: Yetter R. A. , Rabitz H. , Hedges R. M.
Published: January 2005

Stability and sensitivity analysis are used to examine the ignition/reaction characteristics of dilute hydrogen‐oxygen mixtures. The analysis confirms the existence of two distinct regions of ignition and fast reaction previously labeled “weak” and “strong” ignition, both of which are located in the explosive pressure‐temperature domain and separated by a region related to the “extended” classical second limit. The stability analysis is based on an eigenanalysis of the Green's function matrix of the governing kinetic equations. The magnitudes of the largest (and system controlling) eigenvalue allow the strengths of the two processes to be quantified, giving a clear definition to the terms “weak” and “strong.” The sensitivities of the largest eigenvalue to the reaction rate constants of the mechanism pinpoint the elementary steps controlling the two ignition processes and the subsequent reaction. The associated eigenvectors yield the direction of change in species concentrations and temperature during the course of reaction. These vectors are found to be nearly constant during the induction period of both “weak” and “strong.” ignition, thus producing constant overall stoichiometric reactions. The subsequent reaction of major reactants associated with “weak” ignition also has a constant overall reaction vector, although, different than that during the induction period. However, the vector describing the reaction of major reactants associated with “strong.” ignition is found never to be constant, but continuously changing beyond the induction period.
Kinetics and mechanisms of chlorine transfer from chloramine to amines in aqueous medium
Authors: Ferriol Michel , Gazet Josette , Adad Marie‐thérèse Saugier‐cohen
Published: January 2005

The kinetics and the equilibrium constant of the chlorine transfer reaction between monochloramine NH2Cl and the amines: C2H5NH2, (CH3)2CHNH2, (CH3)2NH, and (C2H5)2NH are investigated by spectrophotometry in aqueous medium at 25°C, in the pH range from 8 to 13 and for an ionic strength equal to 1.03 ± 0.05M. For a concentration of total ammonia equal to 1M, the observed rate constant is pH independent below 8 and above 12.8 and reaches a maximum located between the pKas of NH4+ and RR'NH2+. From these results and those obtained earlier for NH2Cl and CH3NH2, the reaction is shown to involve an interaction between neutral molecules NH2Cl and RR'NH, subject to general acid catalysis. The ability of an interaction corresponding to a specific catalysis and involving NH3Cl+ and RR'NH rather than NH2Cl and RR'NH2+ is also discussed. The activation parameters are given for each reaction.
Isotopic study of the mechanism of ozone formation
Authors: Larsen N. Wessel , Pedersen T. , Sehested J.
Published: January 2005

The mechanism of ozone formation has been studied using 16O and 18O2. High‐resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end‐on‐addition.
Experimental study on the reactions of vibrationally excited 1,1‐difluorocyclopropane
Authors: Lauterwald H. , Heydtmann H.
Published: January 2005

Vibrationally excited 1,1‐difluorocyclopropane, generated by addition of singlet methylene to 1,1‐difluoroethene, reacts according to four reaction channels by isomerization as well as by elimination of difluoromethylene. Identification of the products leads to a critical view on an early study dealing with this reaction system. The pressure dependence of the reaction is investigated. The apparent rate‐constants of the reaction paths were determined.
Preliminary observations on the high temperature oxidation of ethyl tert‐butyl ether
Authors: Dunphy Mary P. , Simmie John M.
Published: January 2005

The high temperature oxidation of ethyl tert‐butyl ether (ETBE) with oxygen in argon diluent has been studied in reflected shock waves over the temperature range 1160 to 1830 K, with pressures of 3.5 bar and with varying equivalence ratios from 0.3 to 2.4. Measurements of the ignition delay times, characterized by chemiluminescence and pressure rise, show that the rate of oxidation is very similar to that of methyl tert‐butyl ether.
An investigation of temperature and pressure dependence of the reaction of CF2ClO2 radicals with nitrogen dioxide by flash photolysis and time resolved mass spectrometry
Authors: Wu Fuxiang , Carr Robert W.
Published: January 2005

Rate coefficients of the termolecular reaction

were determined over the temperature range of 248–324 K and at pressures from 1 to 10 torr by time resolved mass spectrometry. CF2ClO2 radicals were generated by flash photolysis of CF2ClBr in the presence of oxygen. Their rate of decay was measured by following (CF2O2)+ fragment ions formed in the ion source. With 2 to 40 mtorr of NO2 present the dominant removal pathway is addition to form the peroxynitrate. The third order rate coefficients are wholly within the falloff over the experimental pressure range, and have a negative temperature coefficient. Rate constants for the reverse reaction, the unimolecular dissociation of CF2ClO2NO2, D. Koppenkastrop and F. Zabel, Int. J. Chem. Kinet., 23, 1 (1991) were employed to calculate equilibrium constants, from which a 600 torr value of the combination rate coefficient was obtained at each temperature. From the temperature dependence of the equilibrium constants, the average enthalpy of reaction over the experimental temperature range was found to be 106.1 ± 0.3 kJ/mol. Extrapolation of the combination rate constants to lower and higher pressures, and estimates of low and high pressure limiting rate coefficients, k0 and k∞ were done by nonlinear least squares fit of the experimental data, using the empirical Fc equations developed by Troe.
Shock tube pyrolysis of pyrrole and kinetic modeling
Authors: Mackie John C. , Colket Meredith B. , Nelson Peter F. , Esler Michael
Published: January 2005

The kinetics of pyrolysis of pyrrole dilute in argon have been studied in a single pulse shock tube, using capillary column GC, together with GC/MS and FTIR for product identification, over the temperature range 1200–1700 K, total pressures of 7.5–13.5 atm and nominal mixture compositions of pyrrole of 5000 and 700 ppm (nominal concentrations of 5 × 10−7 and 7 × 10−8 mol cm−3). Time‐resolved measurements of the rate of disappearance of pyrrole behind reflected shock waves have been made by absorption spectroscopy at 230 nm, corresponding to the lowest 1π* ← 1π transition of pyrrole at pressures of 20 atm and mixture compositions between 1000–2000 ppm pyrrole (1.7–3.0 × 10−7 mol cm−3) over the temperature range of 1300 to 1700 K. At the lower end of the studied temperature range, the isomers of pyrrole, allyl cyanide and cis‐ and trans‐crotononitrile, were the principal products, together with hydrogen cyanide and propyne/allene. At elevated temperatures, acetylene, acetonitrile, cyanoacetylene, and hydrogen became important products.

The rate of overall disappearance of pyrrole, as measured by absorption spectrometry, was found to be first order in pyrrole concentration, with a rate constant kdis(pyrrole) = 1014.1±0.7 exp(−74.1 ± 3.0 kcal mol−1/RT) s−1 between 1350–1600 K and at a pressure of 20 atm. First order dependence of pyrrole decomposition and major product formation was also observed in the single pulse experiments over the range of mixture compositions studied.

A 75‐step reaction model is presented and shown to substantially fit the observed temperature profiles of the major product species and the reactant profile. In the model the initiation reaction is postulated to be the reversible formation of pyrrolenine, (2H‐pyrrole). Pyrrolenine can undergo ring scission at the C2N bond forming a biradical which can rearrange to form allyl cyanide and crotononitrile or undergo decomposition to form HCN and C3H4 or acetylene and a precursor of acetonitrile. The model predicts an overall rate of disappearance of pyrrole in agreement with the experimental measurements.
UV absorption spectra and kinetics of the self reaction of CFCl2CH2O2 and CF2ClCH2O2 radicals in the gas phase at 298 K
Authors: Wallington Timothy J. , Nielsen Ole J.
Published: January 2005

The ultraviolet absorption spectra of the peroxy radicals derived from hydrochlorofluorocarbons 141b and 142b, (CFCl2CH2O2 and CF2ClCH2O2, respectively), and the kinetics of their self reactions have been studied in the gas phase at 298 K using a pulse radiolysis technique. Absorption cross sections were quantified over the wavelength range 220–300 nm. Measured absorption cross sections at 250 nm were indistinguishable within the experimental uncertainties (≈10%) and yield;

Errors represent the sum of statistical uncertainty and our estimate of potential systematic errors. Our absorption cross section data were then used to derive the observed self reaction rate constants for reactions (1) and (2), defined as −d[RO2]/dt = 2k[RO2]2 (R = CFCl2CH2 or CF2ClCH2),
equation image
of k1obs = (4.36 ± 0.64) × 10−12 and k2obs = (4.13 ± 0.58) × 10−12 cm3 molecule−1 s−1, quoted errors represent 2σ. These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals.
The reaction of 2,5‐dimethylpyrrole with O2(a1Δg) in the gas phase
Authors: Fiedler E. , Hack W.
Published: January 2005

The chemical reaction of 2,5‐dimethylpyrrole (C6H9N) with O2(1Δg)
equation image
was studied in the gas phase in an isothermal flow reactor at room temperature and low pressures. The C6H9N concentration profiles were studied under pseudo‐first order conditions [C6H9N]∘ ≪ [O2(1Δg)] with mass‐spectrometric detection of C6H9N. O2(1Δg) was produced either in a microwave discharge or in a chemical reaction. The value for the rate constant:

was measured.

The rate constant is compared to the value obtained for the quenching process. The primary product C6H9NO2 was detected by mass spectrometry and the reaction mechanism is proposed. The possibility of using this reaction as a gas phase titration reaction for O2(1Δg) is discussed.
Kinetic model of liquid B2O3 gasification in a hydrocarbon combustion environment: I. Heterogeneous surface reactions
Authors: Brown R. C. , Kolb C. E. , Rabitz H. , Cho S. Y. , Yetter R. A. , Dryer F. L.
Published: January 2005

As part of an ongoing program to model hydrocarbon assisted boron combustion, a kinetic model has been developed to describe gasification of the ubiquitous boron oxide coating that inhibits particulate boron ignition. This model includes homogeneous gas phase oxidation reactions, multi‐component gas phase diffusion, heterogeneous surface reactions, and oxide vaporization. The kinetic processes are treated using a generalized kinetics code, with embeded sensitivity analysis, for the combustion of a one‐dimensional (particle radius), spherical particle.

This article presents the heterogeneous surface reactions used to describe oxide gasification and presents selected model results for a spherical boron oxide droplet which illustrate the dependence of the oxide gasification rates on the ambient temperature and particle diameter.
Shock tube measurements of the reactions of CN with O and O2
Authors: Davidson D. F. , Dean A. J. , Dirosa M. D. , Hanson R. K.
Published: January 2005

The rate coefficients of the reactionsequation imageandequation imagewere determined in a series of shock tube experiments from CN time histories recorded using a narrow‐linewidth cw laser absorption technique. The ring dye laser source generated 388.44 nm radiation corresponding to the CN B2Σ+(v= 0) ←X2Σ+(v= 0) P‐branch bandhead, enabling 0.1 ppm detection sensitivity.

Reaction (1) was measured in shock‐heated gas mixtures of typically 200 ppm N2O and 10 ppm C2N2in argon in the temperature range 3000 to 4500 K and at pressures between 0.45 and 0.90 atm.k1was determined using pseudo‐first order kinetics and was found to be 7.7 × 1013(±20%) [cm3mol−1s−1]. This value is significantly higher than reported by earlier workers. Reaction (2) was measured in two regimes. In the first, nominal gas mixtures of 500 ppm O2and 10 ppm C2N2in argon were shock heated in the temperature range 2700 K to 3800 K and at pressures between 0.62 and 1.05 atm.k2was determined by fitting the measured CN profiles with a detailed mechanism. In the second regime, gas mixtures of 500 ppm O2and 1000 ppm C2N2in argon were shock heated in the temperature range 1550 to 1950 K and at pressures between 1.19 and 1.57 atm. Using pulsed radiation from an ArF excimer laser at 193 nm, a fraction of the C2N2was photolyzed to produce CN. Pseudo‐first order kinetics were used to determinek2. Combining the results from both regimes,k2was found to be 1.0 × 1013(±20%) [cm3mol−1s−1].
A spectroscopic study of the equilibrium NO2 + NO3 + M 2 N2O5 + M and the kinetics of the O3/N2O5/NO3/NO2/ air system
Authors: Hjorth J. , Notholt J. , Restelli G.
Published: January 2005

The equilibrium constant, Keq of the reaction NO2 + NO3 + M 2 N2O5 + M has been determined for a small range of temperatures around room temperature in air at 740 torr by direct spectroscopical measurements of NO2, NO3, and N2O5. At 298 K, Keq was determined as (3.73 ± 0.61) × 10−11 cm3 molecule−1. Averaging this and 11 other independent evaluations of Keq yields Keq = (3.31 ± 0.82) × 10−11 cm3 molecule−1, where the uncertainty is given as one standard deviation. The kinetics of the O3/NO2/N2O5/NO3/ air system was studied in a static chamber at room temperature and 740 torr total pressure. Evidence of a unimolecular decay reaction of NO3, NO3 → NO + O2, was found and its rate coefficient was estimated as (1.6 ± 0.7) × 10−3 s−1 at 295 ± 2 K.
Oxidation by Permanganate in strong alkaline medium. Oxidation of ethane‐1,2‐diol, glycol aldehyde, glycollic acid, and glyoxylic acid
Authors: Szammer J. , Jáky M. , Gerasimov O. V.
Published: January 2005

A study was made on the kinetics and mechanism of the reaction

in aqueous solutions of 0.10 to 2.0 mol dm−3 alkaline concentrations. The substrates (S) applied were ethane‐1,2‐diol (ethylene glycol), glycol aldehyde, glycollic acid, and glyoxylic acid. Glycol aldehyde and glyoxylic acid were present in the form of dihydrate. In each case alkoxy anion is the reactive form and the KB constant of deprotonation can be calculated from the kinetic data. A mechanism based on electron abstraction is suggested. Manganate reacts with these substrates much slower than permanganate.
Study of mechanistic features of tetrahedral‐octahedral interconversion of tetracyanozincate (II) to bis(4‐(2hyphen;Pyridylazo)hyphen;resorcinol)zincate(II) by stopped‐flow technique
Authors: Prasad Surendra , Nigam Prem C. , Phull Madhu
Published: January 2005

The present study examines the kinetics and mechanism of the formation of [Zn(CN)4]2− from ZnR22− (R represents 4‐(2‐Pyridylazo)resorcinol, short named as Par) and vice versa. The reactions have been followed at 494 nm (λmax of [Zn(Par)2]2−, ε = 7.8 × 104 M−1 cm−1) using stopped‐flow spectrophotometer in presence of excess of incoming ligand. The data show that the formation of [Zn(CN)4]2− complex is first order in [ZnR22−] and the order with respect to [CN−] varies from one at higher cyanide concentration to zero at low [CN−]. These observations suggest a slow dissociation of [ZnR2]2− to ZnR and R2− and a cyanide assisted rapid dissociation of [ZnR2]2− to [ZnR(CN)x]x− followed by their rapid conversion to [Zn(CN)4]2−. The reaction of Zn(Par) with cyanide ions also follow first order kinetics at higher as well as lower cyanide concentrations. The reverse reaction exhibits first order dependence each in [Zn(CN)42−] and [Par2−], but an inverse first order dependence in [CN−] at low Par concentrations. However, at higher Par concentration the reaction rate tends to be independent of [Par2−]. On the basis of forward and reverse rate studies, a five step mechanism consistent with these results has been proposed. The activation parameters and the effect of ionic strength have been used in further support to the proposed mechanism. The effect of pH on the rates of forward and reverse reaction has also been investigated.
Kinetics of esterification of palmitic acid with isobutyl alcohol on ion‐exchange resin pellets
Authors: Goto Shigeo , Takeuchi Makoto , Matouq Mohamad H.
Published: January 2005

Cylindrical pellets were made by mixing ion‐exchange resin particles with binding powders and heating to 140°C. To compare catalytic activities of these resin pellets with those of resin particles and sulfuric acid, the esterification of palmitic acid with isobutyl alcohol was carried out in a batch reactor. The rate equation for sulfuric acid could be applied to ion‐exchange resins although the values of parameters were different.
Gas phase thermolysis of aryl t‐butyl amines
Authors: Martin Gonzalo , Ascanio Julian , Rodriguez Jesus
Published: January 2005

N‐t‐butylaniline, N‐t‐butyl‐p‐anisidine, and N‐t‐butyl‐p‐nitroaniline have been pyrolyzed in a stirred‐flow reactor at 510–620°C, 8–15 torr total pressure, and 0.5–1.5 s contact time, using toluene as carrier gas. An order one kinetics was observed for the consumption of the amines. The reactions yielded 95 ± 2% isobutene plus the corresponding anilines as reaction products. The rate coefficients followed the Arrhenius equations
N–t–butylaniline

N‐t‐butyl‐p‐anisidine

N‐t‐butyl‐p‐nitroaniline

The results are consistent with an unimolecular elimination of isobutene involving polar four‐center cyclic transition states. © John Wiley & Sons, Inc.
Pulse radiolysis and fourier transform infrared study of neopentyl peroxy radicals in the gas phase at 297 K
Authors: Wallington Timothy J. , Andino Jean M. , Potts Alan R. , Nielsen Ole J.
Published: January 2005

The ultraviolet absorption spectrum of the neopentyl peroxy radical (CH3)3CCH2O2, and the kinetics and products of its self reaction have been studied in the gas phase at 298 K. Absorption cross sections were quantified over the wavelength range 230–290 nm. The measured cross section at 250 nm was;Errors represent statistical (2σ) together with our estimate of potential systematic errors(15%). The kinetics of the decay of the UV absorption following the generation of the neopentyl peroxy radicals was complicated by the rapid decomposition of the (CH3)3CCH2O radicals formed in channel (4a).equation imageBy measuring the yield oft‐butyl peroxy radicals, the branching ratiok4a/(k4a+k4b) was determined to be 0.39 ± 0.03. The rate constant for the self reaction of neopentyl peroxy radicals wask4= (1.07 ± 0.22) × 10−12cm3molecule−1s−1. Quoted errors represent 2σ. These results are discussed with respect to the available literature data. © John Wiley & Sons, Inc.
Kinetics and mechanism of the thermal gas‐phase reaction between NO2 and trichloroethene at 303–362.2 K
Authors: Czarnowski J.
Published: January 2005

The kinetics of the gas‐phase reaction between NO2 and trichloroethene has been investigated in the temperature range 303–362.2 K. The pressure of NO2 was varied betwen 5.1 and 48.7 torr and that of trichloroethene between 7.3 and 69.5 torr. The reaction was homogeneous. Two products were formed: nitrosyl chloride, ClNO, and glyoxyloxyl chloride, HC[O]C[O]Cl, which was identified by its infrared spectrum and its molecular weight determined by chromatography. The rate of consumption of the reactants was independent of the total pressure and can be represented by a second‐order reaction:

The following mechanism was proposed to explain the experimental results:

equation image

The following expression was obtained for k:

. © John Wiley & Sons, Inc.
The kinetics of the reduction of methyl viologen and 9,10‐anthraquinone‐2‐sulfonate by the benzopinacol anion
Authors: Bigger S. W. , Craig R. A. , Grieser F. , Rouch A. J. , Scheirs J.
Published: January 2005

The reduction of methyl viologen (MV2+) and 9,10‐anthraquinone‐2‐sulfonate (AQS) by the benzopinacol anion in 50% (v/v) propan‐2‐ol/water was investigated spectroscopically. The rate constants for these reactions were found to be 12.9 ± 0.2 and 0.23 ± 0.01 M−1 s−1, respectively. © John Wiley & Sons, Inc.
Rate coefficients for the reaction of OH with HONO between 298 and 373 K
Authors: Burkholder James B. , Mellouki Abdelwahid , Talukdar Ranajit , Ravishankara A. R.
Published: January 2005

Rate coefficients, k1, for the reaction OH + HONO → H2O + NO2, have been measured over the temperature range 298 to 373 K. The OH radicals were produced by 266 nm laser photolysis of O3 in the presence of a large excess of H2O vapor. The temporal profiles of OH were measured under pseudo‐first‐order conditions, in an excess of HONO, using time resolved laser induced fluorescence. The measured rate coefficient exhibits a slight negative temperature dependence, with k1 = (2.8 ± 1.3) × 10−12 exp((260 ± 140)/T) cm3 molecule−1 s−1. The measured values of k1 are compared with previous determinations and the atmospheric implications of our findings are discussed.
An evaluation of the combined application of hammett reaction constant and primary kinetic isotope effects to hydride equivalent transfer reactions
Authors: Srinivasan R.
Published: January 2005

Bunting et al. have suggested that a combined application of Hammett ρ values (or Brønsted exponents) and primary kinetic isotope effects to hydride equivalent transfer reactions involving 1,4‐dihydronicotinamides and organic oxidants is capable of revealing whether this transfer occurs in a single step or follows a two step e− + H° transfer mechanism (J.W. Bunting, V.S.F. Chew, G. Chu, N.P. Fitzgerald, A. Gunasekara, and H.T.P. Oh, Bioorg. Chem., 12, 141 (1984)). We have used this approach with respect to the reduction of flavins by 1‐substituted 1,4‐dihydronicotinamides. Compelling lines of evidence are presented to demonstrate that this reaction follows the single step hydride transfer mechanism. We also present an analysis of the Brønsted exponent and the primary kinetic isotope effect data for the flavin reaction. It is shown that although a simple application of these parameters does indeed favor the two step e− + H° transfer mechanism for flavin reduction, various other empirical data provide conclusive evidence for the single step hydride transfer mechanism. We attribute this discrepancy to the occurrence of nonequilibrium solvation of the transition state. We have considered several mechanistic complexities which could produce seemingly inconsistent Hammett and primary isotope effect values, and have concluded that these complexities must be considered in interpreting the mechanism of a hydride‐equivalent transfer reaction from kinetic parameters. © John Wiley & Sons, Inc.
Shock tube and modeling study of propene pyrolysis
Authors: Hidaka Yoshiaki , Nakamura Takuji , Tanaka Hiroya , Jinno Akinori , Kawano Hiroyuki , Higashihara Tetsuo
Published: January 2005

The thermal decomposition of propene behind reflected shock waves with 1200 < T5 < 1800 K and 1.6 × 10−5 < ρ5 < 2.7 × 10−5 mol/cm3 was studied by IR laser kinetic absorption spectroscopy and gas‐chromatographic analysis of reaction products. The present data together with earlier shock tube data were satisfactorily modeled with a 51‐reaction mechanism. As the initial step of the reaction, three channels, C3H6 = CH3 + C2H3 (1), C3H6 = H + AC3H5 (2), and C3H6 = CH4 + C2H2 (3), were necessary to interpret all the experimental data. © John Wiley & Sons, Inc.
Acid‐catalyzed hydrolysis of triacylglycerols obeys monoexponential kinetics
Authors: Vega‐ríos Aracelly , Villalobos Heidy , Mata‐segreda Julio F.
Published: January 2005

The acid‐catalyzed hydrolyses of triacetyl‐glycerol and of tributyryl‐glycerol take place following a simple monoexponential kinetic scheme. The result can be interpreted as all three ester groups reacting with approximately the same specific rate. This observation reported in 1920 is unusual, because the intrinsic reactivities of primary and secondary esters are different, and because as far as the reaction proceeds, the remaining ester groups have neighboring hydroxyl groups, which undoubtly alter the reactivity of the reaction centers, relative to the situation in the initial reactant structure. The phenomenom can be explained by considering that local solvation effects due to neighboring hydrophylic groups remain unchanged as the transition‐state complex is formed in all three stages of the reaction. © John Wiley & Sons, Inc.
The thermodynamics and kinetics of the proton‐transfer reactions between bromophenol blue and some aromatic amines in aprotic solution
Authors: Sheridan Peter , Ambroziak Amanda , Fryer Ian , Priest Anna
Published: January 2005

The equilibria and the stopped‐flow kinetics of the reaction between the acid bromophenol blue (BPB) and several aromatic amines in toluene to form ion pairs have been investigated. Contrary to expectations, the rate of the proton‐transfer increases with increasing activation enthalpy. This is explained in terms of the entropy of the transition state.

The role of the electronic structure of the amine and of the solvent are discussed. Solvent effects were further investigated by comparing the activation parameters for the reaction between BPB and pyridine in chlorobenzene, toluene, and benzene. The solvent clearly plays a vital role in determining the rate of proton‐transfer via the entropy of activation. The mechanism of the reaction (that proton‐transfer is almost complete in the transition state, and is followed by amine migration and ring opening) is confirmed. © 1993 John Wiley & Sons, Inc.
Discharge‐flow/chemiluminescence and flash‐photolysis/resonance fluorescence studies of the reaction O + SiH4 at room temperature
Authors: Taylor Craig A. , Ding Luying , Marshall Paul
Published: January 2005

DF‐CL studies using NO2 chemiluminescence detection of O yielded a rate constant k1 for O + SiH4 of (2.6 ± 0.5)×10−13 cm3 s−1 at 295 K, where the 95% confidence interval reflects accuracy. FP‐RF studies using flash photolysis of SO2 followed by time‐resolved vuv fluorescence detection of O at 295 K yielded k1 = (3.0 ± 0.5) ×10−13 cm3 s−1. These results are in good accord with most previous measurements and lead to a combined best estimate of k1 = (3.2 ± 0.4) × 10−13 cm3 s−1. The DF‐CL and FP‐RF methods appear to have little unrecognized systematic error. © 1993 John Wiley & Sons, Inc.
Kinetics and mechanisms of substitution of the axial and equatorial ligands in an iron(II) macrocyclic heme model complex
Authors: Tomam Henrique E. , Nunes Fabio S.
Published: January 2005

The complex [Fe(imox) (Nmim)2], where imox is a planar bis(iminooxime) macrocyclic ligand and Nmim=N‐methyl imidazole, undergoes substitution reactions in the presence of 2,2′bipyridine (bipy), leading to a series of intermediate mixed complexes. The forward and reverse rate constants for the substitution of the Nmim ligand by water are k1 = 0.23 s−1 and k−1=62 M−1s−1, respectively. The binding of a bipy to the [Fe(imox) (Nmim) (H2O)]+ complex proceeds according to k2 = 4.7×10−2 M−1 s−1 and k−2 = 3.6 × 10−4 s−1, yielding [Fe(imox) (bipy) (Nmim)]+, which eliminates Nmim according to k3 = 1.6 × 10−4 s−1. Further substitution in the [Fe(imox) (bipy)]+ complex with bipy takes place very slowly leading to the [Fe(imox) (bipy)2]+ and [Fe(bipy)3]2+ complexes. © 1993 John Wiley & Sons, Inc.
High temperature pyrolysis of formaldehyde in shock waves
Authors: Hidaka Yoshiaki , Taniguchi Takashi , Kamesawa Takashi , Masaoka Hiromitsu , Inami Koji , Kawano Hiroyuki
Published: January 2005

Thermal decomposition of formaldehyde diluted with Ar was studied behind reflected shock waves in the temperature range of 1200–2000 K at total pressures between 1.3 and 3.0 atm. The study was carried out for compositions from the concentrated mixture, 4% CH2O, to the highly dilute mixture, 0.01% CH2O by using time‐resolve IR‐laser absorption and IR‐emission, and a single‐pulse technique. From a computer‐simulation study, the mechanism and the rate‐constant expressions that could explain all of our data and previously reported ARAS data were discussed. This data obtained over a wide concentration range from 50 ppm CH2O to 4% CH2O were satisfactorily modeled by a five‐reaction mechanism. © 1993 John Wiley & Sons, Inc.
An evaluation of the kinetic parameters for the reaction of trifluoromethyl radicals with CH3Cl in the gas phase in the temperature range from 416 to 636 K
Authors: Taccone R. A. , Olleta A. , Salinovich O.
Published: January 2005

The hydrogen and chlorine atom abstraction reactions from CH3Cl by CF3 radicals produced by the photolysis of hexafluoroacetone (HFA) and CF3I were studied relative to the recombination of CF3 radicals magnified image

The Arrhenius parameters obtained in the temperature range 416 to 578 K are:

where Θ = 2,303.RT cal mol−1 and k2 is the recombination rate constant for the CF3 radicals.

The factors that influence the transfer processes of chlorine and hydrogen are analyzed in a series of reactions of halomethanes with CF3 and CH3 radicals. © 1993 John Wiley & Sons, Inc.
Autoxidation of NO in aqueous solution
Authors: Awad Hani H. , Stanbury David M.
Published: January 2005

The reaction of NO with O2 has been investigated in aqueous solution. As demonstrated by ion chromatography, the sole product is NO2−. Kinetic studies of the reaction by stopped‐flow methods with absorbance and conductivity detection are in agreement that the rate law is ‐d[O2]/dt=k[NO]2[O2] with k = 2.1 × 106 M−2 s−1 at 25°C. This rate law is unaffected by pH over the range from pH 1 to 13, and it holds with either NO or O2 in excess. By studying the reaction over the temperature range from 10 to 40°C, the following activation parameters were obtained: ΔH≠ = 4.6 ± 2.1 kJ mol−1 and ΔS≠=−96 plusmn; 4 J K−1 mol−1. © 1993 John Wiley & Sons, Inc.
Reaction of energetic hydrogen atoms with 1‐chloropropane
Authors: Gould P. L. , Oldershaw G. A.
Published: January 2005

The reaction of photochemically generated energetic hydrogen atoms with 1‐chloropropane, reaction (1),
equation image
has been examined for translational energies of H* in the range 40 to 110 kJ mol−1. Integral probabilities for reaction (1) have been determined, and the phenomenological threshold energy is 47 ± 10 kJ mol−1. The moderating effect of CO2 on reaction (1) for hydrogen atoms of initial energy 108 kJ mol−1 has also been studied. © 1993 John Wiley & Sons, Inc.
Kinetics of Cl(2P) reactions with CF3CHCl2, CF3CHFCl, and CH3CFCl2
Authors: Warren Rachel F. , Ravishankara A. R.
Published: January 2005

The rate coefficients for the removal of Cl atoms by reaction with three HCFCs, CF3CHCl2 (HCFC‐123), CF3CHFCl (HCFC‐124), and CH3CFCl2 (HCFC 141b), were measured as a function of temperature between 276 and 397 K. CH3CF2Cl (HCFC‐142b) was studied only at 298 K. The Arrhenius expressions obtained are: k1 = (3.94 ± 0.84)× 10−12 exp[−(1740 ± 100)/T] cm3 molecule−1 s−1 for CF3CHCl2 (HCFC 123); k2 = (1.16 ± 0.41) × 10−12 exp[−(1800 ± 150)/T] cm3 molecule−1 s−1 for CF3CHFCl (HCFC 124); and k3 = (1.6 ± 1.1) × 10−12 exp[−(1800 ± 500)/T] cm3 molecule−1 s−1 for CH3CFCl2 (HCFC 141b). In case of HCFC 141b, non‐Arrhenius behavior was observed at temperatures above ca. 350 K and is attributed to the thermal decomposition of CH2CFCl2 product into Cl + CH2CFCl. In case of HCFC‐142b, only an upper limit for the 298 K value of the rate coefficient was obtained. The atmospheric significance of these results are discussed. © 1993 John Wiley & Sons, Inc.
Rate constants for the addition of the 2‐hydroxy‐2‐propyl radical to alkenes in solution
Authors: Héberger K. , Fischer H.
Published: January 2005

Absolute rate constants for the addition of the 2‐hydroxy‐2‐propyl radical to 18 substituted alkenes (CH2 = CXY) were determined at (296 ± 1) K in 2‐propanol by time‐resolved electronspin‐resonance spectroscopy. With alkene substitution the rate constants vary by more than 6 orders of magnitude. For 3,3‐dimethyl‐but‐1‐ene the temperature dependence is given by log k/M−1 · s−1 = 6.4 minus;; 19.1/Θ where Θ = 2.303 RT in kJ/mol−1. As shown by a good correlation with the alkene electron affinities, log k296/M−1 · s−1 = 6.46 + 1.71 · EA/eV (r = 0.930), 2‐hydroxy‐2‐propyl is a very nucleophilic radical, and its addition rates are highly governed by polar effects. © 1993 John Wiley & Sons, Inc.
Modelling of the homogeneously catalyzed and uncatalyzed pyrolysis of neopentane: Thermochemistry of the neopentyl radical
Authors: Mitchell T. J. , Benson S. W.
Published: January 2005

The mechanism for neopentane (NpH) pyrolysis in the absence and presence of additives isobutene, HCl and HBr, in the temperature range 750–800 K, has been reinvestigated with the aid of computer simulation and sensitivity analysis techniques. With best values assigned to all rate constants in the kinetic chain, a basic mechanism comprising 18 reversible reactions involving 19 atomic, radical, and molecular species has been used to simulate pure neopentane pyrolysis data. Predictions of major and minor product yields provided quantitative agreement with experimental data against which the model was tested. The mechanism was supplemented by additional species and reactions in order to simulate experimental neopentane pyrolysis data in the presence of HCl and HBr additives. An apparent discrepancy between a recent direct measurement of k5, the rate constant for thermal decomposition of the neopentyl radical [1], and that reported from studies of neopentane pyrolysis in the presence and absence of HCl [2], has been identified as being due to the use of an incomplete mechanism in the latter determination. Simulations of hydrogen halide catalyzed pyrolyses exhibit a high sensitivity to the thermochemical parameters associated with the neopentyl radical (Np). The influence of uncertainties in ΔH(Np) and S(Np) are evaluated and lead to suggested values ΔH(Np) = 8.7 ± 0.8 kcal mol−1 and S(Np) = 78.8 ± 1.0 cal mol−1 K−1. © 1993 John Wiley & Sons, Inc.
Cryochemistry. Large acceleration of the oxidation of hydroxylamine by iodate in frozen solution
Authors: Vajda Tamás
Published: January 2005

A large rate increase of the oxidation of hydroxylamine by iodate has been shown in frozen aqueous solution as compared to the supercooled one. The experiments were conducted under frozen conditions at −5°, −10°, −15°, and −20°C and in liquid solution at 0°, −5°, and −10°C, as well. At given time intervals the progress of the reaction was traced by the pH decrease of the unbuffered samples. The around 500‐fold enhanced reaction rate of the frozen samples (at −5° and −10°C) points to an important role of the ice itself beside the increased solute concentration in the compartmentalized heterogeneous system. The contribution of ice to this pH‐regulated oxidation is discussed as a consequence of the high mobility and transfer rate of proton on the ice surface. © 1993 John Wiley & Sons, Inc.
Gas‐phase kinetic study of the silylene addition reaction to acetylene and acetylene‐d2 over the temperature range 291–613 K
Authors: Becerra R. , Walsh R.
Published: January 2005

Time‐resolved studies of silylene, SiH2, generated by laser‐flash photolysis of phenylsilane, have been employed to obtain rate constants for its bimolecular reactions with C2H2 and C2D2. The reactions have been studied in the gas‐phase, in the pressure range 1–100 torr (with SF6 bath gas) at five temperatures in the range 291–613 K.

Reaction with C2H2 is pressure dependent, consistent with a third body assisted association reaction. However the lack of a simple fit to RRKM calculated values suggests a more complex process with another reaction channel. Reaction with C2D2 is faster than with C2H2, showing a pressure dependent isotope effect. The data are consistent with a rapid isotopic scrambling mechanism. Further RRKM modeling of a three‐channel decomposition mechanism for the suggested silirene adduct (intermediate) provides a semi‐quantitative fit to the data. Rate constants extracted from the modeling are shown to be consistent with a mechanism leading to formation of both ethynylsilane and vinylsilylene, as previously proposed by O'Neal, Ring et al. from higher temperature studies. An enthalpy surface is shown to be consistent with this mechanism. © 1994 John Wiley & Sons, Inc.
Kinetics and mechanisms of the reactions of OH with some oxygenated compounds of importance in tropospheric chemistry
Authors: Saunders S. M. , Baulch D. L. , Cooke K. M. , Pilling M. J. , Smurthwaite P. I.
Published: January 2005

The kinetics of the reactions magnified image have been studied in a discharge flow system under pseudo‐first‐order conditions. The OH concentration was monitored by laser induced fluorescence and helium was used as the carrier gas. Values of k1 = (8.1 ± 1.7) × 10−13, k2 = (1.31 ± 0.26) × 10−11, k3 = (2.6 ± 0.5) × 10−11, and k4 = (2.5 ± 0.4) × 10−11 cm3 molecule−1 s−1, at 298 K and 1 torr total pressure, were obtained.

To validate the newly constructed system the rate constant for the reaction magnified image was determined in a similar manner. The value of k5 = (6.7 ± 0.9) × 10−12 cm3 molecule−1 s−1 at 298 K and 1 torr total pressure is in very good agreement with other literature values.

The mechanisms for the atmospheric degradation of these compounds have been constructed to allow their incorporation in a photochemical trajectory computer model, to assess their impact on photochemical ozone creation in the troposphere. © 1994 John Wiley & Sons, Inc.
Kinetic studies of the N‐alkylation of secondary amines with 1,2‐dichloroethane
Authors: Yang H. , Thyrion F. C.
Published: January 2005

The reactions of 1,2‐dichloroethane with 2‐(ethylamino)ethanol or diethylamine have been investigated in several solvents from 51 to 80°C. A reaction mechanism has been proposed where 1,2‐dichloroethane reacts with the secondary amines in both bimolecular substitution (SN 2) and elimination (E2) reactions; the substitution product is rapidly converted in an aziridinium ion and undergoes a consecutive reaction with the starting amine to give a tetrasubstituted ethylenediamine. The rate constants as well as the activation energies of these reactions have been determined. © 1994 John Wiley & Sons, Inc.
Kinetic model for hydrocarbon‐assisted particulate boron combustion
Authors: Brown R. C. , Kolb C. E. , Cho S. Y. , Yetter R. A. , Dryer F. L. , Rabitz H.
Published: January 2005

A kinetic model is presented to describe the high temperature (1800 K < T < 3000 K) surface oxidation of particulate boron in a hydrocarbon combustion environment. The model includes a homogeneous gas‐phase B/O/H/C oxidation mechanism consisting of 19 chemical species and 58 forward and reverse elementary reactions, multi‐component gas‐phase diffusion, and a heterogeneous surface oxidation mechanism consisting of ‘elementary’ adsorption and desorption reaction steps. Thermochemical and kinetic parameters for the surface reactions are estimated from available experimental data and/or elementary transition state arguments. The kinetic processes are treated using a generalized kinetics code, with embedded sensitivity analysis, for the combustion of a one‐dimensional (particle radius), spherical particle. Model results are presented for the oxidation of a 200 μm boron particle in a JP‐4/air mixture at ambient temperatures of 1400 K and 2000 K. These results include temperature and gas‐phase species profiles as a function of radial distance and particle burning rates. © 1994 John Wiley & Sons, Inc.
Does the HO2 radical react with H2S, CH3SH, and CH3SCH3?
Authors: Mellouki A. , Ravishankara A. R.
Published: January 2005

The kinetics of the title reactions were investigated in a discharge flow tube by using laser magnetic resonance detection of HO2. The upper limits for the bimolecular rate constants for the reactions of HO2 with H2S (k1), CH3SH (k2), and CH3SCH3 (k3) are <3 × 10−15, <4 × 10−15, and <5 × 10−15 cm3 molecule−1 s−1, respectively, at 298 K. Our upper limit for k1 is three orders of magnitude lower than the previously reported value.

Measurements at higher temperatures also yield similar upper limits. Our results suggest that HO2 is not an important oxidant for these reduced compounds in the atmosphere. © 1994 John Wiley & Sons, Inc.
An analytic hindered rotor model for calculating microcanonical variational unimolecular rate constants from reaction path properties
Authors: Hase William L. , Zhu Ling
Published: January 2005

A model is proposed for performing microcanonical variational transition state theory calculations which incorporates ideas from vibrator and flexible variational transition state models. Vibrational frequencies, moments of inertia, and potential energy for the variational transition state are found by reaction path following as for the vibrator model. However, the transitional modes are treated as hindered rotors using an analytic potential and an analytic density of states, which are fit to barriers for hindered rotation determined from reaction path following. The model proposed here differs from the flexible transition state model in that the density of states for the transitional modes is analytic and transitional modes and external rotational angular momenta are uncoupled. For the H + CH3 ⇌ CH4 system, rate constants calculated with this new model are only 6–23% smaller on average from those of the flexible transition state model for values of total angular momentum which correspond to average rotational temperatures of 0–2000 K. Harmonic frequencies calculated for the transitional modes from the hindered rotor Hamiltonian are in good agreement with the exact values found by a reaction path analysis. © 1994 John Wiley & Sons, Inc.
Modeling the thermal DENOx process in flow reactors. Surface effects and Nitrous Oxide formation
Authors: Glarborg Peter , Dam‐Johansen Kim , Miller James A. , Kee Robert J. , Coltrin Michael E.
Published: January 2005

We have investigated the impact of surface reactions such as NH3 decomposition and radical adsorption on quartz flow reactor data for Thermal DeNOx using a model that accounts for surface chemistry as well as molecular transport. Our calculations support experimental observations that surface effects are not important for experiments carried out in low surface to volume quartz reactors. The reaction mechanism for Thermal DeNOx has been revised in order to reflect recent experimental results. Among the important changes are a smaller chain branching ratio for the NH2 + NO reaction and a shorter NNH lifetime than previously used in modeling. The revised mechanism has been tested against a range of experimental flow reactor data for Thermal DeNOx with reasonable results. The formation of N2O in Thermal DeNOx has been modelled and calculations show good agreement with experimental data. The important reactions in formation and destruction of N2O have been identified. Our calculations indicate that N2O is formed primarily from the reaction between NH and NO, even though the NH2 + NO2 reaction possibly contributes at lower temperatures. At higher temperatures N2O concentrations are limited by thermal dissociation of N2O and by reaction with radicals, primarily OH. © 1994 John Wiley & Sons, Inc.
Kinetic study of the oxidation of ethanol by 3,4‐lutidine chromium(VI) peroxide in dichloromethane solution
Authors: Mousavi Mir Fazlollah , Firouzabadi Habib , Shamsipur Mojtaba
Published: January 2005

The oxidation kinetics of ethanol with 3,4‐lutindine chromium(VI) peroxide (LCP) were investigated by monitoring the absorbance change at 565 nm in dichloromethane solution. The reaction had a first‐order dependence on oxidant and a fractional (one half) dependence on reactant. The stoichiometric ratio between LCP and ethanol was 1 : 2. The activation parameters were determined from temperature dependence of the reaction rate. It was found that the cleavage of the peroxide groups of LCP is primarily responsible for the oxidant of ethanol to acetaldehyde. Based on the kinetic results obtained (including deuterium isotope effect) a plausible mechanism is proposed. © 1994 John Wiley & Sons, Inc.