bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of reactions between methoxycarbonyl, methyl, and methoxy radicals formed in flash photolysis of dimethyl oxalate in gas phase
Authors: Hassinen E. , Riepponen P. , Blomqvist K. , Kalliorinne K. , Evseev A. M. , Koskikallio J.
Published: January 2005

Flash photolysis of dimethyl oxalate produced the radicals CH3, CH3O, and COOCH3. Thermally equilibrated methoxycarbonyl radicals did not decompose during radicalradical reactions in the presence of 40‐torr cyclohexane in the temperature range 298–448 K. Cyclohexyl radicals were also generated during the flash photolysis of the reaction mixture. Rate coefficients of radical–radical reactions were calculated from the amounts of stable products determined by gas chromatography: CO, CO2, CH4, C2H4, C2H6, CH2O, CH3OH, CH3OCH3, HCOOCH3, CH3COOCH3, CH3OCOOCH3, CH3C6H11, and CH3OC6H11. Calculations were performed using an iterative computer integration program. Absolute values of rate coefficients were based on the rate coefficient of the reaction between methyl radicals, k1 = 2.7 × 1010 dm3 mol−1 s−1, measured with the same equipment.
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The rate coefficients for reactions (5)–(8) are:
Studies on the composition and kinetics of chromium(III)‐alanine system
Authors: Khan Iqrar A. , Kabir‐Ud‐Din
Published: January 2005

Kinetics of the complex formation of chromium(III) with alanine in aqueous medium has been studied at 45, 50, and 55°C, pH 3.3–4.4, and μ = 1 M (KNO3). Under pseudo first‐order conditions the observed rate constant (kobs) was found to follow the rate equation:

Values of the rate parameters (kan, k, KIP, and K) were calculated. Activation parameters for anation rate constants, ΔH≠(kan) = 25 ± 1 kJ mol−1, ΔH≠(k) = 91 ± 3 kJ mol−1, and ΔS≠(kan) = −244 ± 3 JK−1 mol−1, ΔS≠(k) = −30 ± 10 JK−1 mol−1 are indicative of an (Ia) mechanism for kan and (Id) mechanism for k routes (‥substrate Cr(H2O) is involved in the k route whereas Cr(H2O)5OH2+ is involved in k′ route). Thermodynamic parameters for ion‐pair formation constants are found to be ΔH°(KIP) = 12 ± 1 kJ mol−1, ΔH°(K) = −13 ± 3 kJ mol−1 and ΔS°(KIP) = 47 ± 2 JK−1 mol−1, and ΔS°(K) = 20 ± 9 JK−1 mol−1.
Quenching of O2(1Δg) by aliphatic amines
Authors: Raja Nalini , Arora P. K. , Chatha J. P. S. , Vohra K. G.
Published: January 2005

The quenching rate constants of O2(1Δg) with n‐butylamine, diethylamine, dipropylamine, dibutylamine, and tripropylamine have been determined in a discharge flow system. The rate constants are found to be (1.6 ± 0.2) × 103, (8.5 ± 0.6) × 104, (9.8 ± 0.5) × 104, (2.1 ± 0.1) × 105, and (8.6 ± 0.5) × 105 1 mol−1 s−1, respectively. The rate constants are found to increase in the order, tertiary amine → secondary amine → primary amine. The “inductive effect” of alkyl substitution is also found to increase the rate constant in a given series of amines.
Determination of absolute rate data for the reactions of atomic sodium, Na(32S1/2), with CH3F, CH3Cl, CH3Br, HCl, and HBr as a function of temperature by time‐resolved atomic resonance spectroscopy
Authors: Husain David , Marshall Paul
Published: January 2005

We present a kinetic study of the reactions of ground‐state sodium atoms with the molecules CH3F, CH3Cl, CH3Br, HCl, and HBr at elevated temperatures (537–966 K). Na(32S1/2) was generated by the pulsed irradiation of various sodium halide vapors and monitored by time‐resolved atomic resonance absorption of the unresolved D‐lines at λ = 589 nm [Na(32PJ) ← Na(32S1/2)] in the “single‐shot mode.” The photoelectric signals were amplified without distortion, captured, and digitized in a transient recorder interfaced to a microcomputer for data analysis. Absolute second‐order rate constants were measured at various temperatures in each case, yielding the following Arrhenius parameters (kRX = A exp(–E/RT), errors 1σ):
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which constitute, to the best of our knowledge, the first direct measurements of these quantities. The reaction between Na and HBr demonstrated anomalous behaviour which is discussed in terms of potential surfaces that have been calculated previously for this type of collisional process. The data are compared with analogous results for Na + CF4, CF3Cl, and CF3Br and with single‐temperature measurements on diffusion flames.
Quantum mechanical reactive scattering theory
Authors: Kouri D. J.
Published: January 2005

In this article we briefly discuss a number of promising approaches to the formulation of a general, numerically exact, quantum mechanical theory of fully three‐dimensional reactive atom‐diatom collisions. It is noted that the ability to treat the three‐dimensional H + H2 exchange reactions is pre‐requisite to any demonstration of the success of a general quantum mechanical formalism for reactivescattering. However, it is also noted that the time has come for any such theory to further demonstrate the ability to go beyond this basic, elementary atom‐diatom exchange reaction. It is speculated that there now exist a number of approaches which can potentially provide such a general framework for quantum reactive scattering theory. Finally, a new generalizationof the Faddeev formalism for such systems, which is capable of inclusion ofthree body forces with a completely general form for the potential surface, is presented.
Kinetics and mechanism of the decomposition of N‐bromoalcoholamines in aqueous solution
Authors: Antelo J. M. , Arce F. , Franco J. , Forneas M. J. , Sanchez M. E. , Varela A.
Published: January 2005

The decomposition reactions of N‐bromodiethanolamine, N‐bromoethylethanolamine, and N‐bromomethylethanolamine in aqueous solution have been studied kinetically under various experimental conditions. The results support a proposed reaction mechanism in which the rate controlling step is assumed to be the formation of an imine which is then hydrolyzed to the final decomposition products.
Gas phase thermal isomerization of 4‐acetyl−5‐methyl‐isoxazole
Authors: Perez Jorge Daniel , Wunderlin Daniel A.
Published: January 2005

The gas phase thermal isomerization of 4‐acetyl−5‐methyl‐isoxazole affords 3‐cyano−2,4‐pentanedione as the only product in good agreement with previous proposed isomerization mechanism for isoxazoles. On the other hand, kinetic parameters and MO theoretical calculations do not agree with those previously reported. An alternative reaction mechanism which explains this fact is discussed.
Neighboring group participation in the pyrolysis kinetics of 4‐chloro‐1‐butanol in the gas phase
Authors: Chuchani Gabriel , Martin Ignacio
Published: January 2005

The pyrolysis of 4‐chloro‐1‐butanol has been studied in a static system, seasoned with allyl bromide, and in the presence of the free radical suppressor toluene. The working temperature and pressure ranges were 400–450°C and 43–164 Torr, respectively. The reaction is homogeneous, unimolecular, and follows a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k1(s−1) = (13.34 ± 0.50) − (221.1 ± 6.7) kJ mol−1 (2.303RT)−1. The products tetrahydrofuran, formaldehyde, and propene, arise by the participation of the neighboring OH group in 4‐chloro‐1‐butanol pyrolysis. The reaction is best explained in terms of an intimate ion pair type of mechanism.
Disproportionation‐combination rate constant ratios for haloalkyl radicals: Evidence for heterogeneous disproportionation
Authors: Holmes Bert E. , Rakestraw David J.
Published: January 2005

Disproportionation‐combination rate constant ratios, kd/kc, have been determined for R + RCH2CHCl and for the auto disproportionation‐combination of RCH2CHCl radicals, R = CF3, C2F5, and C3F7. The kd/kc for R = CF3 and to a lesser degree for R = C2F5 and C3F7 were very sensitive to the surface/volume ratio of the reaction vessel suggesting a heterogeneous component for disproportionation.
FTIR study of the DMS/NO2/I2/N2 photolysis system: The reaction of IO radicals with DMS
Authors: Barnes I. , Becker K. H. , Carlier P. , Mouvier G.
Published: January 2005

A steady‐state system involving the photolysis of NO2 in an excess of I2 as a source of IO radicals has been used to study the reaction IO + DMS in 760 Torr N2 at 296 K. IO radicals were found to react rapidly with DMS, one molecule of DMSO being produced for each molecule of DMS consumed. Numerical analysis of the experimental results yielded a rate constant of (3.0 ± 1.5) × 10−11 cm3 s−1 for the reaction IO + DMS → DMSO + I.
A reinvestigation of the rate constants for the reactions of ozone with cyclopentene and cyclohexene under atmospheric conditions
Authors: Bennett Paul J. , Harris Stephen J. , Kerr J. Alistair
Published: January 2005

The rates of decay of ozone in a large excess of the cycloalkene have been re‐measured by an improved experimental procedure, and the following second‐order rate constants (cm3 molecule−1 s−1) have been determined in synthetic air at atmospheric pressure:

The results are discussed in relation to existing literature data on the kinetics of ozonecycloalkene reactions.
The decomposition kinetics of disilane and the heat of formation of silylene
Authors: Martin J. G. , Ring M. A. , O'Neal H. E.
Published: January 2005

The static system decomposition kinetics of disilane (\documentclass{article}\pagestyle{empty}\begin{document}${\rm Si}_{\rm 2} {\rm H}_{\rm 6} \mathop {\longrightarrow}\limits^1 {\rm SiH}_{\rm 2} + {\rm SiH}_{\rm 4}$\end{document}, 538–587 K and 10–500 Torr), are reported. Reaction rate constants are weakly pressure dependent, and best fits of the data are realized with RRKM fall‐off calculations using logA1,∞ = 15.75 and E1,∞ = 52,200 cal. These parameters yield AHf0(SiH2)298 = (63.5 − Eb, c) kcal mol,−1 where Eb, c is the activation energy for the back reaction at 550 K, M = 1 std state. Five other silylene heat‐of‐formation values (ranging from 63.9 – Eb, c to 66.0 ‐ Eb, c kcal mol−1) are deduced from the reported decomposition kinetics of trisilane and methyldisilane, and from the reported absolute and relative rate constants for silylene insertions into H2 and SiH4. Assuming Eb, c = 0, an average value of ΔHf0(SiH2) = 64.3 ± 0.3 kcal mol−1 is obtained. Also, a recalculation of the activation energy for silylene insertion into H2, based in part on the new disilane decomposition Arrhenius parameters, gives (0.6 + Eb, c) kcal mol−1, in good agreement with theoretical calculations.
High‐temperature collisional energy transfer in highly vibrationally excited molecules II: Isotope effects in isopropyl bromide systems
Authors: Brown Trevor C. , King Keith D. , Gilbert Robert G.
Published: January 2005

Values for 〈ΔEdown〉, the average downward energy transferred from the reactant to the bath gas upon collision, have been obtained for highly vibrationally excited undeuterated and per‐deuterated isopropyl bromide with the bath gases Ne, Xe, C2H4, and C2D4, at ca. 870 K. The technique of pressure‐dependent very low‐pressure pyrolysis (VLPP) was used to obtain the data. For C3H7Br, the 〈ΔEdown〉 values (cm−1) are 490 (Ne), 540 (Xe), 820 (C2H4), and 740 (C2D4), and for C3D7Br, 440 (Ne), 570 (Xe), 730 (C2H4), and 810 (C2D4). The uncertainties in these values are ca. ±10%. The 〈ΔEdown〉 values for the inert bath gases Ne and Xe show excellent agreement with the theoretical predictions of the semi‐empirical biased random walk model for monatomic/substrate collisional energy exchange [J. Chem. Phys., 80, 5501 (1984)]. The relative effects of deuteration of the reactant molecule on 〈ΔEdown〉 also compare favorably with the predictions of this theoretical model. Extrapolated high‐pressure rate coefficients (s−1) for the thermal decomposition of reactant are 1013.6±0.3 exp(−200 ± 8 kJ mol−1/RT) for C3H7Br and 1013.9±0.3 exp(−207 ± 8 kJ mol±1/RT) for C3D7Br, which are consistent with previous studies and the expected isotope effect.
Isomerization of n‐hexyl and s‐octyl radicals by 1,5 and 1,4 intramolecular hydrogen atom transfer reactions
Authors: Dóbé S. , Bérces T. , Réti F. , Márta F.
Published: January 2005

n‐Hexyl and s‐octyl radical isomerizations by intramolecular hydrogen atom shift have been studied in the presence of high methyl radical concentration where isomerized alkyl radicals reacted predominantly by combination and disproportionation reactions with methyl radicals.

By assuming the rate coefficient of 1‐hexyl radical recombination to be equal to that of ethyl self‐combination, the rate coefficient of log(k1/s−1) = (9.5 ± 0.3) – (11.6 ± 0.3) kcal mol−1/RT ln 10 has been derived for the 6sp isomerization of n‐hexyl radicals, 1‐hexyl → 2‐hexyl (1).

Investigation of s‐octyl radical isomerization was complicated by fast interconversion between 3‐octyl, 2‐octyl, and 4‐octyl radicals. Use of the methyl trapping technique and systematic variation of methyl radical concentration made possible the determination of log(k2/s−1) = (9.4 ± 0.7) − (11.2 ± 1.0) kcal mol−1/RT ln 10 for the 6ss isomerization of 3‐octyl and the estimation of log(k3/s−1) = 10.5–17 kcal mol−1/RT ln 10 for the 5ss isomerization of 2‐octyl radicals, where 3‐octyl → 2‐octyl (2), and 2‐octyl → 4‐octyl (3).
Pressure and temperature dependence of reactions proceeding via a bound complex. An approach for combustion and atmospheric chemistry modelers. Application to HO + CO → [HOCO] → H + CO2
Authors: Larson C. W. , Stewart P. H. , Golden D. M.
Published: January 2005

Elementary bimolecular processes that involve formation of a chemically activated intermediate species are common. We address the general problem of modeling these processes and describe the necessary and sufficient information that must be specified to assure that a kinetics model will extrapolate the rate constants for those reactions over wide ranges of temperature and pressure. The approach is illustrated for the system centered around the HOCO intermediate. Here, specification of the temperature and pressure dependence of three rate constants, k(T,P) and the temperature dependence of two equilibrium constants, K(T), is necessary and sufficient, viz:

equation image

Rate constants are cast in the form of an analytical expression, suggested by Troe, and appropriate parameters are tabulated.
Kinetics of the reaction of hydroxyl radicals with 2‐(dimethylamino)ethanol from 234–364 K
Authors: Anderson Larry G. , Stephens Robert D.
Published: January 2005

The temperature dependence of the rate of the reaction of OH with 2‐(dimethylamino)‐ethanol, (CH3)2NCH2CH2OH (DMAE) was investigated over the temperature range, 234 to 364 K. The reaction was studied using the flash photolysis‐resonance fluorescence technique. The room temperature rate constant determined for this reaction was (10.3 ± 2.0) × 10−11 cm3 molecule−1 s−1, with essentially no temperature dependence evident within the uncertainty in the experiments. A value of (9.0 ± 2.0) × 10−11 cm3 molecule−1 s−1 is believed to best describe the reaction over the entire temperature range. The room temperature rate constant is about twice the value reported previously for this reaction. The overall reaction of OH with DMAE was apportioned to the reactivity of OH for abstracting individual H‐ atoms from different types of CH bonds and the OH bond within the molecule. This technique predicts the overall rate constant for the OH‐DMAE reaction to within about 15% of the experimental value and makes it possible to estimate the yields of the initial radical products of the OH attack on DMAE. A mechanism is proposed for the subsequent atmospheric reactions that would occur in the photooxidation of DMAE.
Formation of H and D atoms in pyrolysis of 1,3‐butadiene and 1,3 butadiene‐1,1,4,4,‐d4 behind shock waves
Authors: Rao V. S. , Takeda Kunio , Skinner Gordon B.
Published: January 2005

Highly dilute mixtures of 1,3‐butadiene and 1,3‐butadiene‐1,1,4,4‐d4 were pyrolyzed behind reflected and incident shock waves, respectively. Concentrations of H and D atoms were measured by resonance absorption spectroscopy. In the early stages of the reaction, nearly equal amounts of H and D were formed from CD2CHCHCD2, indicating that loss of H from C2 followed by loss of D from C1 is a more important reaction than breaking of the central CC bond. Overall, rate constants for atom‐forming reactions are much slower than rate constants for disappearance of butadiene in earlier experiments, suggesting that most of the butadiene disappears by processes that do not involve H or D atoms or by radicals that produce them rapidly.
The gas phase reactions of hydroxyl radicals with a series of esters over the temperature range 240–440 K
Authors: Wallington Timothy J. , Dagaut Philippe , Liu Renzhang , Kurylo Michael J.
Published: January 2005

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of esters using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 torr. The kinetic data for methyltrifluoroacetate (k1) over the complete temperature range, and for methylacetate (k2), and ethylacetate (k3) over the range 296–440 K were used to derive the Arrhenius expressions;

At 296 K, the measured rate constants (in units of 10−13 cm3 molecule−1 s−1) were: k1 = (0.52 ± 0.08), k2 = (3.41 ± 0.29), and k3 = (15.1 ± 1.4). Room temperature rate constants for the OH reactions with several other aliphatic esters were also measured. These were (in the above units): methylformate, (2.27 ± 0.34); ethylformate, (10.2 ± 1.4); n‐propylformate, (23.8 ± 2.7); n‐butylformate, (31.2 ± 3.3); n‐propylacetate, (34.5 ± 3.4); i‐propylacetate, (37.2 ± 2.9); n‐butylacetate, (41.5 ± 3.0); s‐butylacetate, (56.5 ± 5.9); methylpropionate, (10.3 ± 0.4); ethylpropionate, (21.4 ± 3.0); n‐propylpropionate, (40.2 ± 3.2); methylbutyrate, (30.4 ± 3.3); ethylbutyrate, (49.4 ± 3.8); n‐propylbutyrate, (74.1 ± 3.2), and n‐butylbutyrate, (106 ± 13), error limits represent 2σ from linear least‐squares analyses. The results are discussed in terms of the reaction mechanisms and are compared to previous literature data.
On the ion contamination of atoms produced in a microwave discharge
Authors: Nelson T. O. , Tardy D. C.
Published: January 2005

The present study was undertaken to quantitatively measure the concentration of ions produced by a microwave discharge source commonly used in the production of atomic species. Using a double floating probe to monitor the ion content, the results indicate that the flow of ions was less than 1.8 × 10−6 times the total flow of particles from the discharge cavity. Due to the low ion mole fraction, it is concluded that ion‐molecule reactions are not competitive with previousry reported atom‐molecule reactions.
Rate constants for the gas phase reactions of OH with C5 through C7 aliphatic alcohols and ethers: Predicted and experimental values
Authors: Wallington Timothy J. , Dagaut Philippe , Liu Renzhang , Kurylo Michael J.
Published: January 2005

Absolute rate constants were determined at 298 K for the gas phase reactions of hydroxyl radicals with several C5 through C7 aliphatic alcohols and ethers using the flash photolysis resonance fluorescence technique. The values obtained (in units of 10−12 cm3 molecule−1 s−1) were: 3‐methyl‐2‐butanol, (12.4 ± 0.7); 2‐pentanol, (11.8 ± 0.8); 3‐pentanol, (12.2 ± 0.7); cyclopentanol, (10.7 ± 0.7); 1‐hexanol, (12.4 ± 0.7); 2‐hexanol, (12.1 ± 0.7); 1‐heptanol, (13.6 ± 1.3); methyl‐n‐butylether, (16.4 ± 0.6); ethyl‐n‐butylether, (22.8 ± 0.9); ethyl‐t‐butylether, (8.12 ± 0.32); and methyl‐t‐amylether, (7.91 ± 0.42). These results are discussed in terms of group reactivities in such molecules and are compared with values estimated from an additive structure‐reactivity index.
The formation of hydrogen in ethylene pyrolysis at 900 K
Authors: Jayaweera Indira S. , Pacey Philip D.
Published: January 2005

Ethylene at concentrations of 2.7 × 10−3 to 1.0 × 10−2 mol L−1 has been pyrolyzed at 900 K in a flow system. The products ethane and hydrogen have been analyzed by gas chromatography. The results are consistent with a mechanism in which these products are initially formed as follows:

equation image

Reaction [1] occurs only 1 to 2% as often as the addition reaction,

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The latter reaction is close to equilibrium. Taking the rate constant, k4, and the equilibrium constant, K2, from the literature and making small adjustments for minor processes, k1 is found to be (9 ± 3) × 107 L mol−1 s−1. Here the uncertainty is intended to encompass errors in the present work and in the literature parameters.

A secondary source of hydrogen was also observed. Its dependence on ethylene concentration was consistent with formation from an intermediate with six carbon atoms, such as cyclohexene.
A kinetics study of the reaction of Cl with NO2
Authors: Ravishankara A. R. , Smith G. J. , Davis D. D.
Published: January 2005

The third order rate coefficients for the addition reaction of Cl with NO2, Cl + NO2 + M → ClNO2 (ClONO) + M; k1, were measured to be k1(He) = (7.5 ± 1.1) × 10−31 cm6 molecule−2 s−1 and k1(N2) = (16.6 ± 3.0) × 10−31 cm6 molecule−2 s−1 at 298 K using the flash photolysis‐resonance fluorescence method. The pressure range of the study was 15 to 500 torr He and 19 to 200 torr N2. The temperature dependence of the third order rate coefficients were also measured between 240 and 350 K. The 298 K results are compared with those from previous low pressure studies.
Heterogeneous recombination of O + CO on solid CO2 at 77 K
Authors: Sharpe Steven , Boiani James A. , Sethi Dhanwant S.
Published: January 2005

Heterogeneous recombination of O + CO → CO2 over a solid CO2 surface at 77 K was investigated. A modified discharge flow setup was used to generate low O atom concentrations by the reaction N + NO → N2 + O(3P). The O atom concentrations were measured upstream and downstream of the solid CO2 substrate using resonance fluorescence by monitoring the unresolved 130.3 nm triplet transition 3S1 − 3P2,1,0 at the two fixed points. CO2 formed was determined by measuring the β activity from C14O2 produced from CO containing C14O as a reactant gas. The CO2 formation was found to be first order in CO and independent of O atom concentration over the entire range of 4.3 × 1012 to 1.9 × 1014 cm−3 and 1.2 × 1011 to 5.6 × 1012 cm−3 for CO and O respectively. The first order recombination coefficient, λCO was found to be 1.4 (±.38) × 10−5.
Kinetics of the formation and hydrolysis of the schiff's base of 4‐pyridinecarboxaldehyde with N‐hexylamine in water‐dioxan mixtures
Authors: Llor Juan , Asensio Salvador , Sanchez‐ruiz Jose Manuel
Published: January 2005

We have carried out a kinetic study of the 4‐pyridinecarboxaldehyde plus n‐hexylamine system, at 25°C, in water‐dioxan mixtures (0–60% v/v) and in the pH range pKa + 1.5 > pH > pKa − 1.5, where pKa is the pK value of the conjugate acid of the amine. The results obtained could be interpreted in terms of a rate constant for Schiff's base hydrolysis and a rate constant for the reaction between the nonprotonated n‐hexylamine and the nonhydrated form of 4‐pyridinecarboxaldehyde. Both constants decrease sharply as the dioxan content of the solvent increases, in a manner consistent with Marshall's model [J. Phys. Chem., 74, 346 (1970)]. It is suggested that the transition state of the rate‐limiting step (carbinolamine dehydration) is highly solvated by water molecules and has a high separation of charges.
Heat of formation of Benzophenone Oxide
Authors: Hartstock F. W. , Kanabus‐kaminska J. M. , Griller D.
Published: January 2005

The heat of formation of benzophenone oxide, Ph2CO2, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph2CN2 + O2 → Ph2CO2 + N2 was found to be −48.0 ±0.8 kcal mol−1 and ΔHf(Ph2CN2) was determined by measuring the reaction enthalpy for Ph2CN2 + EtOH → Ph2CHOEt + N2 (−53.6 ±1.0 kcal mol−1). Taking ΔHf(PhCHOEt) = −10.6 kcal mol−1 led to ΔHf(Ph2CN2) = 99.2 ± 1.5 kcal mol−1 and hence to ΔHf(Ph2CO2) = 51.1 ± 2.0 kcal mol−1. The results imply that the self‐reaction of benzophenone oxide i.e., 2Ph2CO2 → 2Ph2CO + O2 is exothermic by −76.0 ±4.0 kcal mol−1.
Kinetic and thermochemical parameters of chlorine atom transfer reactions from CF3Cl, CF3CF2Cl, CF2ClCF2Cl, and CF2ClCFCl2 in gas phase
Authors: Taccone R. A. , Salinovich O. , Staricco E. H.
Published: January 2005

The following reactions:
equation image
were studied over the temperature ranges 533–687 K, 563–663 K, and 503–613 K for the forward reactions respectively and over 683–763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔHr°(1) = −3.95 ± 0.45 kcal mol−1 was calculated and from this value the ΔH∮(C2F5Cl) = −2.66.3 ± 2.5 kcal mol−1 and D(C2F5‐Cl) = 82.0 ± 1.2 kcal mol−1 were obtained. Besides, the ΔHr°(2) was estimated leading to D(CF2ClCF2Cl) = 79.2 ± 5 Kcal mol−1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.
Rate constants for the gas‐phase reactions of the OH radical with a series of aromatic hydrocarbons at 296 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate method, rate constants have been determined at 296 ± 2 K for the gas‐phase reactions of the OH radical with toluene, the xylenes, and the trimethylbenzenes. Using the recommended literature rate constant for the reaction of OH radicals with propene of (2.66 ± 0.40) × 10−11 cm3 molecule−1 s−1, the following rate constants (in units of 10−12 cm3 molecule−1 s−1) were obtained: toluene, 5.48 ± 0.84; o‐xylene, 12.2 ± 1.9; m‐xylene, 23.0 ± 3.5; p‐xylene, 13.0 ± 2.0; 1,2,3‐trimethylbenzene, 32.7 ± 5.3; 1,2,4‐trimethylbenzene, 32.5 ± 5.0; and 1,3,5‐trimethylbenzene, 57.5 ± 9.2. These data are compared with the literature values.
Detailed chemical kinetic modeling of butylbenzene pyrolysis
Authors: Freund H. , Olmstead W. N.
Published: January 2005

A chemical kinetic model was constructed for the pyrolysis of butylbenzene. The mechanism was based on free radical reactions. All relevant reactions were considered, and a final selection of 60 reactions involving 29 molecules and free radicals was made. The rate constants and thermodynamic parameters were taken from the literature or estimated using accepted literature methods such as group additivity. The results from the model were compared to experimental rates and product selectivity for butylbenzene pyrolysis over a temperature range of 778 K to 868 K and to an experimental rate at 923 K. The rates agreed within a factor of two and were usually much closer. The experimental and theoretical yields of the major products, styrene, ethane, toluene, and propylene, agreed within two percentage points. The agreement for seven minor products was not quite as good, with the worst case being an overprediction of the yield of allylbenzene by a factor of 2.6.
Pyrolysis of 1,1,1‐Trichloroethane in the absence and the presence of added HCl and/or CCl4
Authors: Huybrechts G. , Hubin Y. , Van Mele B.
Published: January 2005

The title reaction has been studied in a static quartz reaction vessel between 587 and 658 K at pressures between 40 and 152 torr. The dehydrochlorination is the only significant reaction and is autoaccelerated by the produced HCl. Numerical modelling indicates that the Rice‐Herzfeld mechanism, generally used for describing the pyrolysis of halogenated ethanes, has to be completed in the case of CC13CH3 with additional transfer reactions converting “dead” radicals into chain carriers and vice‐versa. The numerical simulation fits the experimental results, in the absence as well as in the presence of different amounts of added HCl. The dehydrochlorination is also accelerated by the addition of CCl4, which can be explained in terms of additional elementary steps involving · CCl3 radicals.
The UV absorption spectrum of the CCl3 radical and the kinetics of its mutual combination reaction from 253 to 623 K
Authors: Danis F. , Caralp F. , Veyret B. , Loirat H. , Lesclaux R.
Published: January 2005

The UV absorption spectrum and the kinetics of the self combination reaction of the CCl3 radical were studied by flash photolysis in the temperature range 253–623 K. Experiments were performed at the atmospheric pressure, except for a few runs at the highest temperatures, which were performed between 30 and 760 torr. CCl3 radicals were generated by flash photolysis of molecular chlorine in the presence of chloroform. The UV spectrum exhibits a strong unstructured band between 195 and 260 nm with a maximum at 211 ± 2 nm. The absorption cross section, measured relative to σ(HO2), is σ(CCl3) = (1.45 ± 0.35) × 10−17 cm2 molecule−1 at the maximum. This value takes into account the uncertainty in σ(HO2) which was taken equal to (4.9 ± 0.7) × 10−18 cm2 molecule−1. The absolute rate constant for the CCl3 mutual combination was determined by computer simulation of the transient decays. The rate constant, which exhibits a slight negative temperature coefficient, can be expressed as:

The study of the pressure dependence showed that only a slight fall‐off behavior could be observed at the highest temperature (623 K). This result was corroborated by RRKM calculations which showed that the rate constant is at the high pressure limit under most experimental conditions below 600 K.
Lack of kinetic hydrogen isotope effect in acetylene pyrolysis
Authors: Durán R. P. , Amorebieta V. T. , Colussi A. J.
Published: January 2005

Second order rate constants for C2H2 or C2D2 polymerizations into vinylacetylene and higher CnHn products have been measured in a static reactor by dynamic mass spectrometry between 770–980 K. They are nearly identical within experimental error (±50%). It is shown that these results are consistent with the participation of thermally equilibrated vinylidene H2C  C: as a reactive intermediate:
equation image
since this assumption only introduces a modest reverse equilibrium isotope effect (KiH/KiD ca. 0.48 in this range) into overall rate constants. At the same time they seem to discriminate in general against alternative mechanisms in which the required H‐atom transfers take place in rate determining steps. Present evidence, in conjunction with an updated analysis of relevant issues such as experimental and theoretical vs. termochemical estimates of the heat of formation of H2CC:, the nature of the transition states of singlet vinylidene addition reactions and the likelihood of discrete biradical intermediates in C2H2 dimerization, seems to lend further support to the notion that acetylene behaves as a singlet carbene at high temperatures.
The pressure and temperature dependence of methane decomposition
Authors: Stewart P. H. , Smith G. P. , Golden D. M.
Published: January 2005

Single‐channel hindered Gorin model RRKM calculations were performed on reaction (1).
equation image
Good agreement between theory and experiment was obtained for the temperature and pressure dependence of reaction (1). Isotopic data for the reverse association reaction, (−1), reported previously, are consistent with the model. Rate constants were cast in the form of an analytical expression and appropriate parameters were tabulated.
Thermal reaction of CH2O with NO2 in the temperature range of 393–476 K: FTIR product measurement and kinetic modeling
Authors: He Yisheng , Kolby Elizabeth , Shumaker Peter , Lin M. C.
Published: January 2005

The thermal reaction of CH2O with NO2 has been investigated in the temperature range of 393–476 K by means of FTIR product analysis. Kinetic modeling of the measured CH2O, NO, CO, and CO2 concentration time profiles under varying reaction conditions gave rise to the rate constants for the following key reactions:
equation image
and
equation image
The error limits shown represent only the scatter (±1 σ) of the modeled values. In the modeling, the total rate constant for the CHO + NO2 reaction, k2 + k3, was not varied and the value reported by Gutman and co‐workers (ref. [8]) was used for the whole temperature range investigated here. The proposed reaction mechanism, employing these newly established rate constants, can quantitively account for nearly all measured product yields, including the [CO]/([CO] + [CO2]) ratios reported by earlier workers.
Energy transfer from optoacoustic measurements and fourier transform deconvolution
Authors: Braun W. , Price I. , Cadoff B. C. , Peterson N. C.
Published: January 2005

The rate of V → R, T energy relaxation following pulsed ir laser excitation is measured by employing an optoacoustic single pulse method. Under present experimental conditions the operation of convolution applies. The experimental optoacoustic waveform can be viewed as the convolution of the kinetic relaxation waveform with an optoacoustic waveform obtained under very fast energy relaxation conditions. A discrete Fourier transform deconvolution method is applied to optoacoustic measurements on SF6 in argon to obtain the time constant, τ, for energy transfer. The present method gives τP = 182 ± 15 μs torr, in good agreement with other methods. These results were obtained without requiring either a theoretical description of the pressure waveform or an assumed laser irradiation geometry. For convolution to apply, the differential equation describing the pressure pulse must be linear under the conditions of the experiment. The linearity of the system can usually be tested experimentally.
Reaction kinetics of NH in the shock tube pyrolysis of HNCO
Authors: Mertens John D. , Chang Albert Y. , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

The high temperature kinetics of NH in the pyrolysis of isocyanic acid (HNCO) have been studied in reflected shock wave experiments. Time histories of the NH(X3Σ−) radical were measured using a cw, narrow‐linewidth laser absorption diagnostic at 336 nm. The second‐order rate coefficients of the reactions:
equation image
were determined to be:

cm3−mol−1−s−1, where f and F define the lower and upper uncertainty limits, respectively. The data for k1a are somewhat better fit by:
Kinetics and mechanism of tris (p‐bromophenyl) aminium hexachloroantimonate induced decomposition of 9‐diazofluorene
Authors: Ahmad Iftikhar
Published: January 2005

The kinetics and products of the decomposition of 9‐diazofluorene by tris (p‐bromophenyl) aminium hexachloroantimonate in acetonitrile solvent has been investigated. The reaction is first order with respect to the concentration of both 9‐diazofluorene and tris (p‐bromophenyl) aminium hexachloroantimonate. A reaction mechanism has also been proposed.
The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution
Authors: Yun Sock Sung , Choi Ki Young
Published: January 2005

The pressure‐jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are kf = 2.27 × 106 M−1 s−1 and kr = 3.81 × 101 s−1 for the nickel(II) complex and kf = 1.23 × 107 M−1 s−1 and kr = 2.66 × 102 s−1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.
Kinetics of the reactions Br + NO2 + M and I + NO2+ M
Authors: Mellouki A. , Laverdet G. , Jourdain J. L. , Poulet G.
Published: January 2005

The reactions Br + NO2 + M → BrNO2 + M (1) and I + NO2 + M → INO2 + M (2) have been studied at low pressure (0.6‐2.2 torr) at room temperature and with helium as the third body by the discharge‐flow technique with EPR and mass spectrometric analysis of the species. The following third order rate constants were found k1(0) = (3.7 ± 0.7) × 10−31 and k2(0) = (0.95 ± 0.35) × 10−31 (units are cm6 molecule−2 s−1). The secondary reactions X + XNO2 → X2 + NO2 (X = Br, I) have been studied by mass spectrometry and their rate constants have been estimated from product analysis and computer modeling.
Linear free energy relationships for peroxy radical‐phenol reactions. Influence of the para‐substituent, the ortho‐di‐tert‐butyl groups and the peroxy radical
Authors: Héberger Károly , Lopata Antal , Müller József
Published: January 2005

Calculations were carried out on several data sets to study the mechanism of hydrogen abstraction from phenols by peroxy radicals:
equation image

Rate constants, k values, were collected for the reactions of cumyl‐, 1‐phenylethyl‐ and tert‐butyl‐peroxy radicals with ortho‐para‐substituted phenol inhibitors. The rate constants were recalculated for the same temperature. Solvent effects were neglected because the solvents used were similar in nature. The phenol ortho substituents were characterized by an indicator variable ItBu accounting for the presence or absence of di‐tert‐butyl groups. The phenol para substituents were characterized by Charton's σI, σR, and σ substituent constants.

The dependence of log k values on Itbu, σI, σR, σ was investigated using stepwise linear regression analysis. The combined data set of 32 reactions gives:

and

The results suggest that hydrogen abstraction from phenols by peroxy radicals proceeds by an electrophilic mechanism, and that neither the peroxy‐radical nor the ortho‐di‐tert‐butyl groups have considerable effect on the rate of reaction (1).
The pressure‐dependence of fluorescence intensity and photolysis rate of the vapors of carbon bisulfide, nitrogen dioxide, and sulfur dioxide
Authors: Makarov V. I.
Published: January 2005

This article is concerned with the Stern–Volmer dependence on the NO2, SO2, and CS2fluorescence self‐quenching within a wide range of pressure variations of these gases. Besides, the pressure‐dependences of the photolysis rate of these substances have been investigated. The deviations from linearity in the Stern–Volmer dependences and photolysis rate of NO2, SO2, and CS2in the highpressure region have been revealed. These deviations correspond to increasing effective rate constant of the collision quenching ofexcited molecules NO2, SO2, and CS2.

A model to describe the deviations observed has been proposed. The model assumes the formation of excimer particles which may dissociate in a monomolecular way and may be quenched at collisions. The estimates of the lifetimes of excimer particles yield the values of the order of several nanoseconds.
Rate constants for the gas‐phase reactions of the OH radical with the cresols and dimethylphenols at 296 ± 2K
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate technique, rate constants for the gas‐phase reactions of the OH radical with the three cresols and the six dimethylphenols have been determined at 296 ± 2 K and atmospheric pressure. The rate constants for the cresols, which range from 4.3 × 10−11 cm3molecule−1 s−1to 6.8 × 10−11 cm3molecule−1 s−1, are in good agreement with previous literature data. The rate constants for 2,3‐, 2,4‐, 2,5‐, 2,6‐, and 3,4‐dimethylphenol are all in the range (6.6–8.1) × 10−11 cm3 molecule−1 s−1, with the rate constant for 3,5‐dimethylphenol being somewhat higher at 1.13 × 10−10 cm3 molecule−1 s−1. Rate constants estimated from the number, identity, and positions of the substituent groups around the aromatic ring agree to within a factor of approximately 2 with these experimentally determined rate constants.
Kinetics and mechanism of the oxidation of some cyclic and acyclic ketones by dodecatungstocobaltate(III)—A comparative study
Authors: Gupta Mala , Saha Swapan K. , Banerjee Pradyot
Published: January 2005

The kinetics of oxidation of cyclohexanone(chxn), 2‐butanone(but), and 1,3‐dihydroxy‐2‐propanone (dhp) have been investigated in aqueous acidic media. A first‐order dependence in complex is obtained at high acid and low oxidant concentration for these ketones. However, a zero‐order rate prevails at high oxidant and low acid concentration, and this rate has been shown to be the acid catalyzed enolization rate of the ketone. A general rate expression has been derived to explain these behaviors and plausible mechanism has been offered by assuming the enol as the reactive species.
Comments on current aspects of chemical kinetics
Authors: Bauer S. H.
Published: January 2005

An aged kineticist was awakened in 1989 from a 50‐year slumber. After arduous study he sized‐up the present situation, with occasional reflections on the state of knowledge in 1939.
Reactive and non‐reactive counterion surfactants in water and aqueous acetonitrile
Authors: Berndt D. C. , Rossman C. A. , Hach C. L. , Fillar D. J.
Published: January 2005

Rates of hydrolysis of hydroxamic acids with perfluorooctanoic acid as a reactive counterion surfactant and also with sodium sulfonate surfactants plus HCl have been determined in both water and aqueous acetonitrile solvents. The pseudophase ion exchange model satisfactorily explains the micellar effects for both the reactive and non‐reactive counterion surfactants in both solvent systems.
A relative rate study of the reaction of Cl atoms with a series of alkyl nitrates and nitro alkanes in air at 295 ± 2 K
Authors: Wallington T. J. , Hinman M. M. , Andino J. M. , Siegl W. O. , Japar S. M.
Published: January 2005

The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with nitro methane, nitro ethane, nitro propane, nitro butane, nitro pentane, ethyl nitrate, isopropyl nitrate, n‐propyl nitrate, 2‐pentyl nitrate, and 2‐heptyl nitrate. Decay rates of these organic species were measured relative to one or more of the following reference compounds; n‐butane, ethane, chloroethane, and methane. Using rate constants of 2.25 × 10−10 5.7 × 10−11, 8.04 × 10−12, and 1.0 × 10−13 cm3 molecule−1 s−1 for the reaction of Cl atoms with n‐butane, ethane, chloroethane, and methane, respectively, the following rate constants were derived, in units of cm3 molecule−1 s−1: nitro methane, <7 × 10−15; nitro ethane, (2.05 ± 0.14) × 10−13; nitro propane, (1.13 ± 0.05) × 10−11; nitro butane, (5.13 ± 0.68) × 10−11; nitro pentane, (1.40 ± 0.14) × 10−10; ethyl nitrate, (3.70 ± 0.24) × 10−12; n‐propyl nitrate, (2.15 ± 0.13) × 10−11; i‐propyl nitrate, (3.94 ± 0.48) × 10−12; 2‐pentyl nitrate, (1.00 ± 0.06) × 10−10; and 2‐heptyl nitrate, (2.84 ± 0.50) × 10−10. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure (≃740 torr) of synthetic air. The results are discussed with respect to the previous literature data and to the modeling of these compounds in the atmosphere.
Room temperature rate coefficient for the reaction between CH3O2 and NO3
Authors: Crowley J. N. , Burrows J. P. , Moortgat G. K. , Poulet G. , LeBras G.
Published: January 2005

The molecular modulation spectroscopic technique was employed to study the kinetics of NO3 radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO3/CH4/O2 at room temperature. By computer fitting of the NO3 temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10−12 cm3 molecule−1 s−1 was obtained for the reaction between NO3 and CH3O2 at 298 K.
Kinetics of reactions between methyl and acetyl radicals in gas phase produced by flash photolysis of acetic anhydride
Authors: Hassinen Eero , Kalliorinne Kaarlo , Koskikallio Jouko
Published: January 2005

The reaction products of photolysis of acetic anhydride in gas phase at 25°C, where He or CO2 was present as buffer gas, were analyzed by gas chromatography. The extent of photodissociation was 52% ± 5% and the extent of intramolecular hydrogen transfer reaction producing acetic acid and ketene was 48% ± 5%. The rate constants of the hydrogen exchange and radical combination reactions between methyl and acetyl radicals were calculated from the amounts of products. The value of the ratio of the rate constants of hydrogen exchange and radical combination reactions between methyl and acetyl radicals, 𝓀7/𝓀6 = 0.15, indicates that acetyl radical is a relatively poor hydrogen donor. The corresponding ratio of rate constants for the reactions between two acetyl radicals, 𝓀9/𝓀s = 0.42, indicates that acetyl radical is a better hydrogen acceptor than methyl radical.
Ionic atmosphere effects on the energetics of thermal and optical electron‐exchange reactions: Application to ferrocenium‐ferrocene self exchange
Authors: Kuznetsov A. M. , Phelps D. K. , Weaver M. J.
Published: January 2005

A treatment of ionic‐atmosphere effects upon symmetrical electron‐transfer reactions resulting from added electrolyte is outlined. Relationships are derived on the basis of the extended Debye‐Huckel model for the increase in the activation free energy, ΔGia*, associated with reorganization of the ionic atmosphere for homogeneous‐phase reactions involving a pair of spherical reactants with varying internuclear distance R. Similar relationships apply to the energetics of symmetrical optical electron transfer, since the increase in the optical transition energy, ΔE, should equal the corresponding ionic atmosphere reorganization energy, E; under the anticipated linear response conditions, E = 4ΔGia*. The predicted ΔGia* (and hence ΔE) values increase sharply with increasing R, as a consequence of the diminished “sharing” of the ionic cloud surrounding the donor and acceptor sites under these conditions. Outer‐sphere electrochemical reactions, featuring a single “near‐isolated” reactant, are predicted to feature substantially larger ΔGia* values than for homogeneous processes proceeding with the reaction partners in contact. The influence of more specific “ionic atmosphere” effects upon ΔGia*, especially involving reactant‐electrolyte ion pairing, is also discussed. Unlike that of the nonspecific ionic atmosphere, the nuclear reorganization process associated with counterion transport between donor and acceptor sites coupled with electron transfer is nonlinear in nature, so that E ≠ 4ΔGia*. Some recent experimental data for electrolyte effects upon the rate constants for ferrocenium‐ferrocene self exchange and related systems are examined in the light of these considerations.
Influence of the side chain on the stability of Schiff‐bases formed between pyridoxal 5′‐phosphate and amino acids
Authors: Vazquez M. A. , Muñoz F. , Donoso J. , Blanco F. García
Published: January 2005

The stability of some Schiff‐bases formed between PLP and different amino acids has been investigated in a wide range of pH. The kinetic constants of formation of these compounds and their hydrolysis rate constants have been determined. Results show that the α‐position of the carboxyl group of amino acid plays an important role on the mechanism of water attack upon the CNbond. The absence of ionic groups in the surroundings of that bond must be an important factor of stability. Bulky hydrophobic substituents in the amino acid, near the amine part, protect the imine bond against hydrolysis.
Thermal dissociation and recombination of alkyl and haloalkyl peroxynitrates: An SACM modelling study
Authors: Destriau M. , Troe J.
Published: January 2005

Recent experimental results on the thermal decomposition and the reverse recombination of alkyl and haloalkyl peroxynitrates are modelled with an SACM formalism. The molecules RO2NO2 with R = CH3, CF3, CF2Cl, CFCl2, CCl3, and C2H5 are considered. Detailed and simplified reduced falloff expressions are compared. Limiting low (𝓀o) and high pressure (𝓀x) rate constants, such as derived from a fit of these falloff expressions to the experiments, are compared with absolute predictions, based on general knowledge about energy transfer (〈ΔE〉 in 𝓀o) and on a recently proposed simple SACM estimate for 𝓀x. The analysis also allows for a derivation of the bond energies of the mentioned molecules.