bluuebunny/crossref_metadata_2025_split huggingface dataset:
A computational modeling study of the low‐temperature pyrolysis of n‐alkanes; mechanisms of propane, n‐butane, and n‐pentane pyrolyses
Authors: Allara D. L. , Edelson D. 
Published: January 2005

AbstractThe mechanisms of the pyrolyses of the n‐alkanes C3H8, n‐C4H10, and n‐C5H12 at temperatures between 390 and 560°C have been studied by the construction and evaluation of sets of several hundred reactions. Rate parameter values were assigned using literature data and calculated estimates. Time‐dependent numerical solutions were computed for the experimental conditions of several rate and product studies reported in the literature. The comparisons of these a priori computations with experiment show excellent agreement for propane and agreement for butane and pentane within the estimated error limits of the assigned rate parameters. These results demonstrate that the general “state of knowledge” of the mechanism of alkane pyrolysis, namely, the reactions and their rate parameters, is such that reasonable a priori predictions of experimental results can be made. Discussions of the major stepwise processes in the pyrolyses are presented, and the importance of allyl radicals in termination is demonstrated.
Disproportionation‐combination ratios in thermalized cyclic radical systems. Rate of isomerization of pent‐2‐en‐5‐yl radical
Authors: Stein S. E. , Rabinovitch B. S. 
Published: January 2005

AbstractDisproportionation–combination rate ratios have been measured for a number of pairs of thermalized radicals (298°K) generated by thermalization of chemically activated cycloalkyl radicals, their ring‐opened products, and ethyl radicals. These ratios are reported and briefly discussed. The rate of isomerization of the chemically activated pent‐2‐en‐5‐yl radical via H‐atom transfer to the allylic pent‐1‐en‐3‐yl radical is also given.
Kinetics and mechanism of the hydrogenation of cyclohexene
Authors: Hendrikse J. L. , Kaspersma J. H. , Coenen J. W. E. 
Published: January 2005

AbstractThe rate of hydrogenation of cyclohexene, catalyzed by CoH3(PPh3)3, has been measured under various conditions and, based on these data, a mechanism has been postulated. For the individual steps of the mechanism enthalpy and entropy differences have been determined. The interpretation of these parameters gives evidence for a more detailed mechanism, in which solvent molecules play an important part as “stand‐in” for ligands, dissociated from the catalyst species.
Very‐low‐pressure pyrolysis of nitroso‐ and pentafluoronitrosobenzene CNO bond dissociation energies
Authors: Choo Kwang Yul , Golden David M. , Benson Sidney W. 
Published: January 2005

AbstractThe high‐pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very‐low‐pressure pyrolysis (VLPP) technique.Bond dissociation energies of DH0(C6H5NO) = 51.5 ± 1 kcal/mole and DH0 (C6F5NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log kr(M−1·sec−1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δHf0(C6H5NO), δHf0(C6F5NO), and δHf0(C6F5) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH0(C6F5–X), were obtained from the reported values of δHf0(C6F5X) and our estimated δHf0(C6F5) [X = H, CH3, NO, Cl, F, CF3, I, and OH].
Shock initiated ignition in COSO2Ar mixtures
Authors: Lifshitz A. , Frenklach M. , Schechner P. , Carroll H. F. 
Published: January 2005

AbstractThe ignition of COS + O2 mixtures diluted in argon was studied behind reflected shocks in a single‐pulse shock tube over the temperature range of 1100–1700°K. Ignition delay times and the distribution of reaction products before and after ignition were determined experimentally. From a total of 63 tests run at varying initial conditions, the following correlation for the induction times was derived:

where β1 = +0.30, β2 = 1.12, and E = 16.9 kcal/mole. Using a reaction scheme of 14 steps, the following values were obtained by a computer modeling of the induction times: β1 = +0.22, β2 = 1.55, and E = 17.3 kcal/mole. The calculations showed that the reaction COS + S → CO + S2 caused the inhibiting effect of the COS. The reaction COS → O ± CO2 + S has a very strong accelerating effect, whereas the parallel channel COS + O → CO + SO shows the opposite effect. It was also shown that the reaction O + S2 → SO + O is very slow and does not contribute to the overall oxidation reaction. It is suggested that the rate constant given to the four‐center reaction COS + SO → CO2 + S2, that is, 1011 cm3/mole · sec at 300°K is incorrect. This constant is not much higher than 108 cm3/mole · sec at 1300°K.
Kinetics of the pyrolyses of endo‐ and exo‐5‐methylbicyclo (2.2.2) oct‐2‐ene in the gas phase
Authors: Huybrechts G. , Ngoy G. 
Published: January 2005

AbstractThe pyrolyses of endo‐ and exo‐5‐methylbicyclo (2.2.2) oct‐2‐ene (endo‐ and exo‐MBO) have been studied between 608 and 679°K at pressures between 7 and 37 torr. These reactions correspond to parallel first‐order eliminations of propene and ethylene:
equation image
The rate constants (in sec−1) for endo‐MBO are given by

and those for exo‐MBO by

Reaction mechanisms involving diradicals are shown to be compatible with the experimental results. The heats of formation and the entropies of endo and exo‐MBO are estimated.
Very low‐pressure pyrolysis (VLPP) of alkyl cyanides. II. n‐propyl cyanide and isobutyl cyanide. The heat of formation and stabilization energy of the cyanomethyl radical
Authors: King Keith D. , Goddard Richard D. 
Published: January 2005

AbstractThe very low‐pressure pyrolysis (VLPP) technique has been used to study the pyrolysis of n‐propyl cyanide over the temperature range of 1090–1250°K. Decomposition proceeds via two pathways, C2C3 bond fission and C3C4 bond fission, with the former accounting for >90% of the overall decomposition. Application of unimolecular reaction rate theory shows that the experimental unimolecular rate constants for C2C3 fission are consistent with the high‐pressure Arrhenius parameters given by

where θ=2.303RT kcal/mole. The activation energy leads to DH2980[C2H5CH2CN]=76.9±1.7 kcal/mole and ΔH(ĊH2CN, g)=58.5±2.2 kcal/mole. The stabilization energy of the cyanomethyl radical has been found to be 5.1±2.6 kcal/mole, which is the same as the value for the α‐cyanoethyl radical. This result suggests that DH[CH2(CN)H] ∼ 93 kcal/mole, which is considerably higher than previously reported. The value obtained for ΔHƒ0(ĊH2CN) should be usable for prediction of the activation energy for C2C3 fission in primary alkyl cyanides, and this has been confirmed by a study of the VLPP of isobutyl cyanide over the temperature range of 1011–1123°K. The decomposition reactions parallel those for n‐propyl cyanide, and the experimental data for C2C3 fission are compatible with the Arrhenius expression

A significant finding of this work is that HCN elimination from either compound is practically nonexistent under the experimental conditions. Decomposition of the radical, CH3CHCH2CN, generated by C3C4 fission in isobutyl cyanide, yields vinyl cyanide and not the expected product, crotonitrile. This may be explained by a radical isomerization involving either a 1,2‐CN shift or a 1,2‐H shift.
Kinetics of the molybdate catalyzed oxidation of iodide by hydrogen peroxide
Authors: Smith R. H. , Kilford J. 
Published: January 2005

AbstractThe kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped‐flow method. The results are interpreted in terms of the mechanism
equation image
and the implied rate law

where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k4 = (3.3 ± 1) × 102 1./mole · s, K1 = (1.2 ± 0.6) × 104 1./mole, K2 = (1.3 ± 0.7) × 103 1./mole, and K3 = (4 ± 3) × 102 1./mole at 298°K.
The kinetics of the gas‐phase reaction between ozone and alkenes
Authors: Toby Erina S. , Toby Sidney , O'Neal H. Edward 
Published: January 2005

AbstractThe rate law − d[O3]/ dt = k1[A][O3] + k3[A][O3]2/ (k4 + k5[O2]) has been found to obtain for the reaction of ozone with allene and with 1,2‐butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone–ethylene reaction, and we find that as [O3]0 increases, the (O2 formed)/(O3 used) ratio approaches 1.5. Values of k1, k3/k5 for ethylene are compared with those for allene, 1,3‐butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O3 with ethylene, and the thermochemistry of the chain sequence is examined in detail.
Mechanism of isotope exchange reaction between methane and deuterium
Authors: Gardiner W. C. , Herrmann J. M. , Mallard W. G. , Owen J. H. 
Published: January 2005

AbstractThe rate of CH4 disappearance in a shock‐heated CH4:D2:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm−1 He‐Ne laser line over the shockfront temperature range of 1900–2300K. Comparison with CH4 pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH4.Additional simulations for the experimental conditions of previous single‐pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH4.
Radiation‐induced dechlorination of carbon tetrachloride in cyclohexane Solutions. The kinetics of liquid‐phase reactions of trichloromethyl radicals
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A. 
Published: January 2005

AbstractThe kinetics of the gamma‐radiation induced free‐radical chain reaction in solutions of carbon tetrachloride in cyclohexane (RH) has been investigated in the temperature range of 303–383°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated cyclohexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated:

equation image

The following rate expression was obtained:

The error limits are the standard deviation from the least mean square Arrhenius plots. Effects of phase on the kinetics of reactions (3) and (4) are considered.
Gas‐phase ozonolysis of cis‐ and trans‐dichloroethylene
Authors: Blume Cary W. , Hisatsune I. C. , Heicklen Julian 
Published: January 2005

AbstractDichloroethylene (DCE), either cis or trans, was reacted with O3 at 23°C in both N2 and O2 buffered mixtures. Both reactant consumption and product formation were monitored by infrared spectroscopy and, in some cases, O3 consumption was monitored by ultraviolet absorption. For thoroughly dried mixtures, the initial products were only HCClO and O2, but geometrical isomerization also occurred. The stoichiometry of the overall reaction always was

equation image

The HCClO was unstable and disappeared slowly in a first‐order reaction which was, at least in part, heterogeneous. The products were CO and HCl so that the stoichiometric reaction was

equation image
The rate law was complex. The rate was always faster in N2 than in O2. In the N2 buffered reaction, inhibition occurred as the reaction progressed and O2 was produced. From the reactant and product decay curves, the following rate behavior was established:

equation image

where high and low concentrations are relative terms for the initial pressure ranges covered ([DCE]0 = 0.21−78.4 torr, [O3]0 = 0.30−6.76 torr). The rate coefficients k2, k3, and k4 were larger for the trans‐DCE than the cis‐DCE, and for each isomer they were larger in N2 than in O2 buffered reactions.The ozonolysis can be explained in terms of the mechanism

equation image

equation image

where R2 is DCE, RO is HCClO, and RO2 is HCClO2. Rate ceofficients are computed.The isomerization is first order in [O3] and approximately first order in [DCE] for the limited kinetic data we were able to obtain. The isomerization does not appear to be explained by the reverse reactions of reactions (6), (7), and (9). Presumably isomerization occurs through some other route.
Radiation‐induced dechlorination of carbon tetrachloride. II. The kinetics of liquid‐phase reactions of trichloromethyl radicals in n‐hexane solutions
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A. 
Published: January 2005

AbstractThe kinetics of the gamma‐radiation induced free‐radical chain reaction in solutions of carbon tetrachloride in n‐hexane (RH) was investigated in the temperature range of 297.5–373°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated hexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated:

equation image
The following rate expression was obtained:

where θ = 2.303 RT in kcal/mole. The error limits are the standard deviation from the least mean square Arrhenius plots. It is concluded that reaction (4) is diffusion controlled in the liquid phase, and that the activation energies in the gas and liquid phases of reaction (3) are equal.
Molecular beam study of F2+I2
Authors: Coggiola M. J. , Valentini James J. , Lee Y. T. 
Published: January 2005

AbstractCrossed molecular beam techniques have been used to study the endoergic reaction between F2 and I2. Above a threshold energy of 4 kcal/mole the observed products are I2F and F. At higher energies IF is also produced. Angular and velocity distributions indicate that the IF does not result from a four‐center exchange reaction.
Radiolytic decomposition of methanesulfonyl chloride in liquid cyclohexane. A kinetic determination of the bond dissociation energies D(ME‐SO2) and D(c‐C6H11‐SO2)
Authors: Horowitz Abraham 
Published: January 2005

AbstractThe gamma radiation induced decomposition of MeSO2Cl in cyclohexane (RH) was studied between 60 and 150°C. Throughout this temperature range the reaction proceeds by a free radical chain mechanism. Its propagation is described by the following reactions:
equation image

The kinetic analysis of the results of the experiments with added SO2, which were carried out in the temperature range of 80 to 150°C, gives 14.94 ± 0.92 and 11.91 ± 0.82 kcal/mole for D(Me‐SO2) and D(c‐C6H11‐SO2), respectively. These bond dissociation energies are considerably lower than the gas‐phase values, and the possible cause of this difference is discussed. Present results also seem to indicate that D(MeSO2‐H) does not exceed 95 kcal/mole. Competitive experiments with added tetrachloroethylene result in

where θ = 2.303RT in kcal/mole.
Charge transfer reactions in alkane and cycloalkane systems. Estimated ionization potentials
Authors: Lias S. G. , Ausloos P. , Horvath Z. 
Published: January 2005

AbstractRate constants of change transfer reactions kCT, involving C3C9 alkanes and cycloalkanes, have been determined in an ion cyclotron resonance mass spectrometer. The rate constants are significantly lower than the corresponding rate constants for collision when the reaction is less than about 0.5 eV exothermic for linear alkane ions, or less than about 0.2 eV exothermic for cycloalkane ions. In this region of low reaction efficiency, the efficiency of reaction with linear or branched alkanes seems to depend primarily on reaction exothermicity. (The efficiencies of reaction of a given ion with cyclic alkanes also depend on ΔHrn, but are higher than for reactions with other compounds). Although the lowered reaction efficiencies probably result, at least in part, from unfavorable Franck–Condon factors in the energy range near the ionization onset, quantitative correlations between reaction efficiency and estimated relative Franck–Condon factors were not observed. When the enthalpy of reaction is small (less than about −0.15 eV), it is seen that the reverse charge transfer can also occur, and equilibrium is established under the conditions of these experiments. From the observed equilibrium constants, values for the standard free energy change are derived, and assuming that ΔS is small for electron transfer equilibria, values of ΔHrn are estimated. In the case of the equilibria involving cyclohexane ion, these values of ΔHrn lead to estimates of the ionization potentials of methylcyclopentane, 3‐methylpentane, n‐octane, 2,2‐dimethylbutane, and 2,3‐dimethylbutane, which are lower than the ionization potentials of cyclohexane, that is, <9.88 eV, although all these compounds had previously been reported to have ionization potentials above 10.03 eV. That the ionization potentials are indeed lower than 10.03 eV is confirmed by determining the quantum yields of ionization with 10.03‐eV photons.It is pointed out that the conclusions reached here apparently also apply to the charge transfer reactions of alkane ions in the liquid phase.
The gas‐phase kinetics of the reaction of 1,1‐difluoroiodoethane with hydrogen iodide: The C–I bond dissociation energy in 1,1‐difluoroiodoethane
Authors: Pickard J. M. , Rodgers A. S. 
Published: January 2005

AbstractThe kinetics of gas‐phase reaction of CH3CF2I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism:
equation image

A least squares treatment of the data gave

where θ = 2.303 RT kcal/mole. The observed activation energy E1 was combined with E2 = 0 ± 1 kcal/mole to yield

The result, combined with data for several CI bond dissociation energies, leads us to conclude that the C(sp3)I bond is relatively insensitive to F for H substitution and that the C(sp2)–I bond has considerable double‐bond character.
The flash photolysis of azomethane. Minor products from the photolysis of methyl radicals and a rate constant for CH3 + NO
Authors: Pilling M. J. , Robertson James A. , Rogers Graham J. 
Published: January 2005

AbstractThe flash photolysis of azomethane in a quartz reaction vessel produces mainly ethane (>75%) plus smaller quantities of methane, ethylene, and acetylene. The minor products are interpreted quantitatively in terms of methyl radical photolysis at 216 nm to give CH2 and H. This interpretation is substantiated by the dependence of the minor products on flash intensity. The reduction of the ethane yield on adding NO is employed to obtain a rate constant for CH3 + NO as a function of total pressure, based on a value for methyl radical recombination of 4.2 × 10−11 cm3/molec · sec. An RRKM analysis is used to extrapolate the data to give a limiting high‐pressure rate constant for CH3 + NO of (1.2 ± 0.1) × 10−11 cm3/molec · sec at 298°K.
Photochemistry of the SO2, 2‐pentene system at 3660 Å
Authors: Wampler Fred B. 
Published: January 2005

AbstractThe photolysis of SO2 in the presence of cis‐ and trans‐2‐pentene has been investigated at 3660 Å and 22°C. Quantum yield measurements of the SO2 photosensitized conversion of one isomer into the other are consistent with a mechanism in which the only participating excited electronic state of SO2 is the SO2(3B1) state. Quantum yield measurements were made for a variation in PSO2/Pisomer reactant ratios of 4.01–283 and 57.5–351 for the cis and trans isomers, respectively. The data are consistent with a mechanism in which a (SO2‐olefin)3 collision intermediate is the precursor to the photosensitized isomeric products. The intermediate undergoes unimolecular decay to yield the cis and trans isomers with probabilities of 0.26 ± 0.05 and 0.69 ± 0.04, respectively. Estimates of the quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis‐ and trans‐2‐pentene are (0.633 ± 0.125) × 1011 l./mole/sec and (1.00 ± 0.27) × 1011 l./mole/sec, respectively. An experimentally determined photostationary composition, [trans‐2‐pentene]/[cis‐2‐pentene] = 2.3 ± 0.1 was in fair agreement with that of 1.7 ± 0.7 as predicted from kinetic data derived in this study.
The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2
Authors: Barker John R. , Benson Sidney W. , Golden David M. 
Published: January 2005

AbstractThe decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391–432°K:

The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec−1) = (15.7 ± 0.5) ‐ (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M−1· sec−1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined:

When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396–442°K:

A review of literature data produced k7a = 109.8±0.5M−1·sec−1, giving log k12(M−1·sec−1) = (8.5 ± 1.5) ‐ (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.
Some Reactions of OH(v = 1)
Authors: Spencer John E. , Glass G. P. 
Published: January 2005

AbstractReactions of OH(v = 1) with HBr, O, and CO have been studied at 295°K using a fast discharge flow apparatus:
equation image
The reaction O + HBr → OH(v = 1) + Br was used as a source of OH(v = 1), and subsequent chemical reactions of the excited radical were followed using EPR spectroscopy. Rate constants for reactions (2b), (3b), and (6b) were measured as (4.5 ± 1.3) × 10−11, (10.5 ± 5.3) × 10−11, and <5 × 10−12 cm3/molec·sec, respectively. The rate constant for physical deactivation of OH(v = 1) by CO was determined as <4 × 10−13 cm3/molec·sec.
Kinetics and mechanism of oxidation of quinols by tris(1,10‐phenanthroline) iron(III) complexes in aqueous acidic perchlorate media
Authors: Mentasti Edoardo , Pelizzetti Ezio 
Published: January 2005

AbstractThe kinetics of oxidation of several substituted quinols by a series of Tris(1,10‐phenanthroline)iron(III) complexes has been investigated with a stopped‐flow technique at 6.0 and 20.0°C. The reactions were found to be first order on both reactants and independent of acidity. The second‐order specific rate constants were strongly dependent on free energy of reaction. An interpretation of the mechanism in the light of Marcus theory has been developed. The first electron abstraction with semiquinone radical formation has been suggested as the rate‐determining step, and on this basis, intrinsic parameters of the reactions have been derived. A good agreement was found between experimental and computed data.
Thermal dimerization of 1,3‐butadiene: Kinetics of the formation of cis, cis‐cycloocta‐1,5‐diene
Authors: Huybrechts G. , Luyckx L. , Vandenboom Th. , Van Mele B. 
Published: January 2005

AbstractThe thermal reaction of 1,3‐butadiene (BD) has been studied between 464 and 557°K at pressures between 49 and 450 torr. The products are 4‐vinylcyclohexene (VCH) and cis, cis‐cycloocta‐1,5‐diene (COD), and their formations are second order. The rate constant (in 1/mol · sec) for VCH is given by

and that for COD by

The thermal reaction of COD has also been studied. The temperature was varied from 505 to 586°K and the pressure from 15 to 51 torr. The rate constants (in sec−1) for the formations of VCH and BD are given by

A biradical mechanism seems to fit these results. The heat of formation and the entropy of COD are estimated.