bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the thermal decomposition of pyridine in a flow system
Authors: Houser Thomas J. , McCarville Michael E. , Biftu Tesfaye 
Published: January 2005

AbstractThe kinetics of the pyrolysis of pyridine was studied in the temperature range of 875–1050°C, at 1 atm total pressure, in a Vycor stirred‐flow reactor. Initial concentrations ranged from 0.25 to 2 mol % in helium and reaction times from 0.25 to 4 sec. It was found at the lower temperatures that the reaction was mixed first and second order. At the higher temperatures an autocatalytic term, zero order in the substrate and first order in the concentration of pyridine decomposed, was necessary in addition to the other two terms to describe the kinetic data. Most of the product was in the form of a primarily aromatic, nonvolatile tar; the major volatile products were HCN and C2H2. An increase in the surface‐to‐volume ratio of the reactor decreased the rate, indicating a radical chain or sequential reaction with radical consumption on the surface. Experiments with additives showed that C2H2 increased the rate. Using the kinetic and product data, some mechanistic considerations are discussed, and a mechanism is proposed to account for the first‐order term.
Determination of the mechanism of the oxidation of the trichloromethyl radical by the photolysis of chloral in the presence of oxygen
Authors: Ohta Tomohiro , Mizoguchi Isao 
Published: January 2005

AbstractThe photooxidation of chloral was studied by infrared spectroscopy under steady‐state conditions with irradiation of a blackblue fluorescent lamp (300 nm < λ < 400 nm, λmax = 360 nm) at 296 ± 2 K. The products were hydrogen chloride, carbon monoxide, carbon dioxide, and phosgen. The kinetic results reveal that the reaction proceeds via chain reaction of the Cl atom:
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The results lead to the conclusion that mechanism (B) is confirmed to be more likely than mechanism (A), which was favored at one time by Heicklen for the mechanism of the oxidation of trichloromethyl radicals by oxygen molecules:
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The ratio of the initial rates of CO and CO2 formation gave k7/k6 = 4.23M−1, and the lower limit of reaction (5) was found to be 3.7 × 108M−1 sec−1.
A smog chamber and modeling study of the gas phase NOx–air photooxidation of toluene and the cresols
Authors: Atkinson Roger , Carter William P. L. , Darnall Karen R. , Winer Arthur M. , Pitts James N. 
Published: January 2005

AbstractAn experimental and modeling study of irradiated toluene–NOx–air, toluene–benzaldehyde–NOx–air, and cresol–NOx–air mixtures at part‐per‐million concentrations has been carried out. These mixtures were irradiated at 303 ± 1 K in a 5800‐liter Teflon‐lined, evacuable environmental chamber, with temperature, humidity, light intensity, spectral distribution, and the concentrations of O3, NO, NO2, toluene, PAN, formaldehyde, benzaldehyde, o‐cresol, m‐nitrotoluene, and methyl nitrate beingmonitored as a function of time. For the toluene and toluene–benzaldehyde–NOx–air runs a variety of initial reactant concentrations were investigated. Cresol–NOx–air runs were observed to be much less reactive in terms of O3 formation and NO to NO2 conversion rates than toluene–NOx–air runs, with the relative reactivity of the cresol isomers being in the order meta » ortho > para. The addition of benzaldehyde to toluene–NOx–air mixtures decreased the reactivity, in agreement with previous studies. Alternative mechanistic pathways for the NOx photooxidations of aromaticsystems in general are discussed, and the effects of varying these mechanistic alternatives on the model predictions for the toluene and o‐cresol–NOx–air systems are examined. Fits of the calculations to most of the experimental concentration–time profiles could be obtained to within the experimental uncertainty for two of the mechanistic options considered. In both cases it is assumed that (1) O2 adds to the OH–toluene adduct ∼75% of the time forming, after a further addition of O2, a C7 bicyclic peroxy radical, and (2) this C7 bicyclic peroxy radical reacts with NO ∼75% of the time to ultimately form α‐dicarbonyls and conjugated γ‐dicarbonyls (e.g., methylglyoxal + 2‐butene‐1,4‐dial) and ∼25% of the time to form organic nitrates. The major uncertainties in the mechanisms concern (1) the structure of the bicyclicperoxy intermediate, and (2) the γ‐dicarbonyl photooxidation mechanism. Good fits to the o‐cresol concentration–time profiles in the toluene–NOx runs are obtained if it is assumed that o7‐cresol reacts rapidly with NO3 radicals. However, it is observed that the model underpredicts nitrotoluene yields by a factor of ∼10, but this is in any case a minor product. It is concluded that further experimental work will be required toadequately validate the assumptions incorporated in the aromatic photooxidation mechanisms presented here.
FTIR studies of the kinetics and mechanism for the reaction of Cl atom with formylchloride
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P. 
Published: January 2005

AbstractThe rate constant for the reaction Cl + CHClO → HCl + CClO was determined from relative decay rates of CHClO and CH3Cl inthe photolysis of mixtures containing Cl2 (∼1 torr), CH3Cl (∼1 torr), and O2 (∼0.1 torr) in 700 torr N2. In such mixtures CHClO was generated in situ as a principal product prior to complete consumption of O2. The value of k(Cl + CHClO)/k(Cl + CH3Cl) = 1.6 ± 0.2(3σ) combined with the literature value of k(Cl + CH3Cl) = 4.9 × 10−13 cm3/molecule sec gives k(Cl + CHClO) = 7.8 × 10−13 cm3/molecule sec at 298 ± 2 K, in excellent agreement with a previous value of (7.9 ± 1.5) × 10−13 cm3/molecule sec determined by Sanhueza and Heicklen [J. Phys. Chem., 79, 7 (1975)]. Thus this reaction is approximately 100 times slower than the corresponding reactions of aldehydes and alkanes with comparable CH bond energies (≤95 kcal/mol).
H2S‐promoted thermal isomerization of butene‐2 CIS to butene‐1 or butene‐2 trans around 500°C
Authors: Richard C. , Boiveaut A. , Martin R. 
Published: January 2005

AbstractH2S increases the thermal isomerization of butene‐2 cis (Bc) to butene‐1 (B1) and butene‐2 trans (Bt) around 500°C. This effect is interpreted on the basis of a free radical mechanism in which buten‐2‐yl and thiyl free radicals are the main chain carriers. B1 formation is essentially explainedby the metathetical steps:
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whereas the free radical part of Bt formation results from the addition–elimination processes:
equation image
. It is shown that the initiation step of pure Bc thermal reaction is essentially unimolecular:
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and that a new initiation step occurs in the presence of H2S:
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. The rate constant ratio has been evaluated:

and the best values of k1 and k1', consistent with this work and with thermochemical data, are

. From thermochemical data of the literature and an “intrinsic value” of E−3 ⋍ 2 kcal/mol given by Benson, further values of rate constants may be proposed:

equation image
is shown to be E4 ⋍ 3.5 ± 2 kcal/mol, of the same order as the activation energy of the corresponding metathetical step.
Rate coefficients of decomposition of azoethane and azoisopropane
Authors: Ács G. , Péter A. , Huhn P. 
Published: January 2005

AbstractThe thermal decompositions of azoethane and azoisopropane were studied in a large excess of ethylene in the temperature interval of 523–623 K. It was demonstrated that under such conditions, the bulk of the alkyl radicals react with ethylene. Via measurements on the consumption of the azo compound and on the formation of gaseous nitrogen, it was possible to determine the rate coefficients of the initiation reactions:

. The resulting data were as follows: For azoethane,

. For azoisopropane,
Influence of butadiene‐1,3 on ethanal pyrolysis at 495°C
Authors: Richard Claude , Martin René 
Published: January 2005

AbstractAt 495°C and a low extent of reaction, ethanal pyrolysis is slightly inhibited by the addition of small quantities of butadiene‐1,3, whereas it is accelerated by more important quantities. The inhibiting effect is interpreted in terms of a free‐radical chain mechanism in which the main chain carriers of ethanal pyrolysis (CH3.free radicals) reversibly add to butadiene‐1,3 and yield penten‐2‐yl (R.) free radicals. These free radicals either react in a metathetical step:
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or in terminating steps. But butadiene‐1,3 also gives rise to new initiation steps:
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which account for the accelerating effect. Process (i3) seems to be more important than process (i2) in the experimental conditions, but its nature could not be identified. The results are consistent with literature data and the following value of k6:

(4.57T in cal/mol).
Photolysis of azomethane–propane mixtures. Arrhenius parameters for the hydrogen abstraction reactions of methyl with azomethane and with propane
Authors: Durban Philip C. , Marshall Roger M. 
Published: January 2005

AbstractMixtures of up to 14% azomethane in propane have been photolyzed using mainly 366 nm radiation in the ranges of 323–453 K and 25–200 torr. Detailed measurements were made of the yields of nitrogen, methane, and ethane. Other products observed were isobutane, n‐butane, ethene, and propene. A detailed mechanism is proposed and shown to account for the observed variation of product yields with experimental conditions. The quantum yield of the molecular process

is found to be given by the temperature‐independent equation

The values of rate constants obtained are

where the reactions are
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and it is assumed that the rate constant for the reaction
equation image
is given by
Reactivity of amines toward tert‐butoxy radicals: Effect of solvent and amine structure
Authors: Encina M. V. , Díaz S. , Lissi E. 
Published: January 2005

AbstractThe reactivity of amines towards tert‐butoxy radicals depends upon the amine ionization potential and the solvent, indicating that polar structures contribute to the reactivity of these compounds. Nevertheless, the dependence with the amine potential is smaller than the one obtained for the quenching of carbonyl excited states by amines and other factors as the strength of the broken hydrogen bond and steric hindrance are also significant in determining the rate of the process.
Mechanism of the azide–bromine reaction in aqueous medium
Authors: Vivekanandam T. S. , Singh U. Chandra , Ramachandran M. S. 
Published: January 2005

AbstractResults on the oxidation of N by Br2 in neutral and acid media are presented. The rate of the reaction is found to be proportional to [N] and [Br2]. The gaseous product of oxidation is found to be pure nitrogen. The stoichiometry of the reaction is

The reaction shows a positive salt effect. It is found that the addition of Br− stabilizes the complex BrN3, which decomposes into Br− and N2:

The spectroscopic measurements also support the kinetic observation. The equilibrium constant K, the rate constants and the thermodynamic parameters were calculated. It is observed that H+ ion inhibits the reaction. The mechanism is discussed in terms of the kinetic results.
Temperature‐dependent a factor in thermal unimolecular reactions II. Exponential dependence
Authors: Forst Wendell , Turrell Sylvia 
Published: January 2005

AbstractIt is assumed that A∞ in the limiting high‐pressure unimolecular rate constant expression k∞ = A∞ exp(−Ea∞/kT) is given by A∞ = A″∞eBkT. The test case is the decomposition butane → 2 ethyl, where a negative B reproduces the temperature dependence of A∞ about as well as the previously considered power law A∞ = A′∞(kT)n. It is shown that the term eBkT modifies significantly the high‐temperature falloff of the general‐pressure rate constant kuni and its various derivatives, and admits of a fairly simple interpretation in terms of Benson's restricted rotor theory. On physical grounds, the exponential law appears more reasonable than the power law.
From energy profiles to structure–reactivity correlations
Authors: Agmon N. 
Published: January 2005

AbstractModels for the energy profile along the reaction coordinate are utilized to determine the barrier's height and location as a function of ΔG. These form the basis for structure–reactivity correlations and afford a unified formulation for various postulates in the field of physical organic chemistry. Current experimental evidence is examined for the resulting correlations, and some of their applications as an aid to the chemical kineticist are presented.
Kinetics of the oxidation of U (IV) by hydrogen peroxide in sulfuric acid medium
Authors: Bhattacharyya P. K. , Saini R. D. , Ruikar P. B. 
Published: January 2005

AbstractThe kinetics of the reaction
equation image
have been investigated in H2SO4 medium under different conditions. The observed bimolecular rate constant kobs, has been found to depend on [H+]−0.55 and to increase with the initial concentration ratio of the reactants R0 = [H2O2]0/[U (IV)]0 above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R0 = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate‐controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved:
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A kinetic expression has been derived from which a graphical evaluation of (kK4)−1 and k−1 has been made at R0 = 1 as (12.30 ± 0.09) × 10−3 M min, (6.23 ± 2.19) × 10−4 M min; and at R0 = 0.35 as (12.63 ± 2.13) × 10−3 M min, (8.32 ± 6.62) × 10−4 M min, respectively. Indications of some participation of a chain reactionat R0 = 1 have been obtained without affecting thesecond‐order kinetics as observed.
Consistency of theory and experiment in the ethane–methyl radical system
Authors: Skinner Gordon B. , Rogers David , Patel Kalabhai B. 
Published: January 2005

AbstractThe thermal decomposition of ethane has been reinvestigated using the single pulse, reflected shock technique. Reflected shock temperatures were corrected for boundary layer‐induced nonidealities using the thermal decomposition of cyclohexene as a kinetic standard. The rate constant for the reaction
equation image
was calculated from the rate of formation of methane under conditions of very low extent of reaction, over a temperature range of 1000–1241 K. Ethane compositions of 1% and 3% in argon at total reaction pressures of 3 and 9 atm were used, and a small pressure dependence of k1 was observed.An RRKM model is described which gives excellent agreement with this and other recent dissociation and recombination rate constant data in light of a recent revision to the thermochemistry of the methyl radical. In the range of 1000–1300 K an RRKM extrapolated k is given by the expression, log k = 17.2 − 91,000/2.3RT, while at 298 K the calculation gives log k (l/mol sec) = 10.44, where k is calculated from k and the equilibrium constant.
Nonisothermal decomposition of methyl nitrate: Anomalous reaction order and activation energies and their correction
Authors: Gray P. , Griffiths J. F. , Hasegawa K. 
Published: January 2005

AbstractMethyl nitrate decomposition is accompanied by self‐heating. Using very fine thermocouples, direct measurements of excess temperatures have been made to establish the intensity and extent of self‐heating in nonisothermal reaction. The measurements are displayed as contourlines of equal degrees of temperature excess on the pressure–temperature ignition diagram.A twofold kinetic investigation has been made of the overall reaction. One part concentrates on achieving isothermal conditions and full characterization of intermediate products. It uses mass‐spectrometric analyses both to establish stoichiometry throughout decomposition and to validate velocity constant measurements derived from continuous pressure–time records. The best value for E = 151 ± 3 kJ/mol is about 10 kJ/mol less than previously.The other part deliberately invades the nonisothermal region to test the qualitative and quantitative predictions of theory (1) that uncorrected reaction orders and activation energies will exceed their isothermal values, (2) that their relative excess (δn/n, δE/E) will be about the same, and (3) that they will be dependent in a simple and predictable way on the reduced excess central temperature.
Isotope effects in abstraction and exchange reactions H + H′Br
Authors: Hepburn J. W. , Klimek D. , Liu K. , Macdonald R. G. , Mayne H. R. , Northrup F. J. , Polanyi J. C. 
Published: January 2005

AbstractA preliminary report is given of relative reactive cross sections for four abstraction reactions H + H′Br ← HH′ + Br with attacking atom (A) H or D, and atom under attack (B) H or D. The pattern of reactive cross sections, as obtained in a crossed molecular beam experiment at a collision energy ET = 7 kcal/mol, indicates Sr(D,H) ≤ Sr(D,D) > Sr(H,H) > Sr(H,D). The atoms in parentheses are A and B. We describe a three‐dimensional classical trajectory (CT) study on a potential‐energy surface proposed in 1969 by Parr and Kuppermann (PK); the CT results are in fair accord with experiment. It is suggested that (D,H) has the largest cross section because it exhibits the most favorable relative timing of A approach to BC rotation. On the basis of CT it appears that the same sequence of cross sections and the same rationale may be applied to the exchange reactions H + BrH′ ← HBr + H′.
Minor products and initiation rate in the chain pyrolysis of propane
Authors: Juste C. , Scacchi G. , Niclause M. 
Published: January 2005

AbstractWith a continuous jet‐stirred tank reactor operating at small space time (0.05–1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene‐1, 2,3‐dimethyl‐butane, 4‐methylpentene‐1, and 1,5‐hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600–780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are
equation image
The measured rates of formation of the minor products are consistent with the quasi‐identical values estimated by Jezequel and co‐workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A1 ≃ 1016.65 s−1 and E1 ≃ 84.7 kcal/mole) of the chain initiation process
equation image
On the frequency factor in electron transfer reactions and its role in the highly exothermic regime
Authors: Marcus R. A. 
Published: January 2005

AbstractConsideration of current information on the dependence of the electron transfer rate on the radial separation distance and on the reactants′ radial distribution function suggests for adiabatic transfers a frequency factor closer to 1012M−1 s−1 than to 1011M−1 s−1. One effect is to raise the λ values estimated from self‐exchange rate constants, and to extend thereby the range of ΔG°'s in which the “inverted region′” is masked by a diffusion‐controlled reaction rate.
Study of the HNO + HNO and HNO + NO reactions by intracavity laser spectroscopy
Authors: Cheskis S. G. , Nadtochenko V. A. , Sarkisov O. M. 
Published: January 2005

AbstractFlash photolysis of CH3CHO and H2CO in the presence of NO has been investigated by the intracavity laser spectroscopy technique. The decay of HNO formed by the reaction HCO + NO → HNO + CO was studied at NO pressures of 6.8–380 torr. At low NO pressure HNO was found to decay by the reaction HNO + HNO → N2O + H2O. The rate constant of this reaction was determined to be k1 = (1.5 ± 0.8) × 10−15 cm3/s. At high NO pressure the reaction HNO + NO → products was more important, and its rate constant was measured to be k2 = (5 ± 1.5) × 10−19 cm3/s. NO2 was detected as one of the products of this reaction. Alternative mechanisms for this reaction are discussed.
On the photodissociation of nitromethane at 266 nm
Authors: Kwok H. S. , He G. Z. , Sparks R. K. , Lee Y. T. 
Published: January 2005

AbstractIn a crossed laser–molecular beam study of nitromethane it was found that the excitation of nitromethane at 266 nm did not yield dissociation products under collision‐free conditions. When a small cluster of nitromethane was excited at the same frequency, the product was seen only at energies and masses consistent with the rupture of the van der Waals bond by vibrational predissociation of the excited state.
Nonisothermal kinetic analysis of the chemiluminescence from tetramethyl‐1,2‐dioxetane
Authors: Mendenhall G. D. , Tauschek J. C. , Ogle C. A. 
Published: January 2005

AbstractA computerized method is given for the evaluation of Arrhenius parameters which describe the chemiluminescent decomposition of tetramethyl‐1,2‐dioxetane. The parameters were determined in several solvents by linear regression methods and the equation ln ln \documentclass{article}\pagestyle{empty}\begin{document}$ [(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I)/(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I - \sum\nolimits_0^{t + \Delta t} I)] = \ln\, (A_1 \Delta t) - E_1 /RT$\end{document}, where I refers to photons counted by increments of Δt, and E1 and A are the first‐order Arrhenius parameters. The average of E1 and log A1 (s−1) from this method from six runs in CCl4 with initial concentrations of 4.9 × 10−5‐8.45 × 10−4M were 27.21 ± 0.88 kcal/mol (113.7 ± 3.7 kJ/mol) and 13.88 ± 0.50, respectively. Simulated curves of chemiluminescence versus time were obtained with the use of a computer program and an auxiliary plotter.
Pyrolysis of 1‐iodopropane by the variable encounter method
Authors: Wolters F. C. , Chao K.‐J. , Rabinovitch B. S. 
Published: January 2005

AbstractThe pyrolysis of 1‐iodopropane has been studied by the variable encounter method (VEM) at temperatures from 625 to 840 K. Deactivating wall collisions are found to be stronger for this molecule than for the hydrocarbons previously studied in this temperature range. The results of this study are compared with earlier steady‐state work.
Absolute rate constants for the reactions between amino and alkyl radicals at 298 K
Authors: Demissy M. , Lesclaux R. 
Published: January 2005

AbstractThe absolute rate constants for the reactions of NH2 radicals with ethyl, isopropyl, and t‐butyl radicals have been measured at 298 K, using a flash photolysis–laser resonance absorption method. Radicals were generated by flashing ammonia in the presence of an olefin. A new measurement of the NH2 extinction coefficient and oscillator strength at 597.73 nm was performed. The decay curves were simulated by adjusting the rate constants of both the reaction of NH2 with the alkyl radical and the mutual interactions of alkyl radicals. The results are k(NH2 + alkyl) = 2.5 (±0.5), 2.0 (±0.4), and 2.5 (±0.5) × 1010 M−1·s−1 for ethyl, isopropyl, and t‐butyl radicals, respectively. The best simulations were obtained when taking k(alkyl + alkyl) = 1.2, 0.6, and 0.65 × 1010M−1·s−1 for ethyl, isopropyl, and t‐butyl radicals, respectively, in good agreement with literature values.
Rate constants for the gas‐phase reactions of O3 with selected organics at 296 K
Authors: Atkinson Roger , Aschmann Sara M. , Fitz Dennis R. , Winer Arthur M. , Pitts James N. 
Published: January 2005

AbstractRate constants for the gas‐phase reactions of O3 with ethene, propene, 1‐hexene, 1‐heptene, styrene, o‐, m‐, and p‐cresol, o‐ and m‐xylene, benzylchloride, acrylonitrile, and trichloroethene have been determined at 296 ± 2 K. The rate constants ranged from <5 × 10−21 cm3 molecule−1 s−1 for m‐xylene to 2.16 × 10−17 cm3 molecule−1 s−1 for styrene, with those for ethene, propene, and 1‐hexene being in excellent agreement with literature data.