bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the gas‐phase decomposition rate constants of heptyl‐1 and heptyl‐2 hydroperoxides C7H15OOH
Authors: Sahetchian K. A. , Heiss A. , Rigny R. , Ben‐aïm R. I. 
Published: January 2005

AbstractThe gas‐phase decomposition of n‐heptyl‐1 and n‐heptyl‐2 hydroperoxides C7H15OOH, which split into two radicals C7H15O and OH, has been investigated in the temperature range of 250–360°C. The decomposition has been carried out in a hydrogen–oxygen mixture (the hydroperoxide represents about 50 ppm) so as to avoid secondary reactions between the formed radicals and the reactants. Although the H2–O2 mixture is not spontaneously reactive in our conditions, it operates the transformation, through a fast and well‐known process, of the OH radicals into HO2 radicals and then into H2O2. However, C7H15O radicals are also transformed into HO2 radicals and then into H2O2, but through an unknown process. To avoid heterogeneous reactions, vessel and probe are coated by B2O3 and then treated by the slow combustion of hydrogen at 510°C and 250 torr before the experiments are performed. As the reaction scheme is very simple, due to the use of the H2–O2 mixture, the determination of the evolutions of the HO2 concentration (followed by electronic paramagnetic resonance) lead to the determination of the gas‐phase decomposition rate constant of hydroperoxides. For the n‐heptyl‐1 hydroperoxide the rate constant is

and for the n‐heptyl‐2 hydroperoxide it is

.
Pyrolysis studies of main group metal‐alkyl bond dissociation energies: VLPP of GeMe4, SbEt3, PbEt4, and PEt3
Authors: Smith Gregory P. , Patrick Roger 
Published: January 2005

AbstractThe bond dissociation energies of tetramethyl germane, triethyl stibine, tetraethyl lead, and triethylphosphine were determined using the technique of very‐low‐pressure pyrolysis. Arguments are presented for log A ≥ 17.0. The respective dissociation energies ΔH298 are 83, 57, 54, and 68 (±2) kcal/mol. A consistent set of methyl bond energies to main group metals is determined from these and previous results, and is examined for trends. Bond energies for various radicals to tin are also derived.
The pyrolysis kinetics of ethyl esters in the gas phase. The alkyl substituent effect at the acyl carbon
Authors: Chuchani Gabriel , Martin Ignacio 
Published: January 2005

AbstractThe gas‐phase elimination of ethyl 3‐methylbutanoate and ethyl 3,3‐dimethylbutanoate has been studied, in a static system, over the temperature range of 360–420°C and in the pressure range of 71–286 torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3‐methylbutanoate, logk1(s−1) = (12.70 ± 0.36) – (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3‐dimethylbutanoate, logk1(s−1) = (13.04 ± 0.08) – (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.
Rate of formation of toluene from ethylbenzene
Authors: Davis Hubert G. 
Published: January 2005

AbstractThe rate of formation of toluene from ethylbenzene was studied at atmospheric pressure in the temperature range of 600–725°C in conventional flow equipment. Residence times were 0.55–1.7 s, and initial partial pressures of ethylbenzene (H2O diluent) were 0.05–0.17 atm. The rate of appearance of toluene measures [1] the rate of the reaction C6H5C2H5 → C6H5CH + CH, with log k = 15.70 – 74.49 ± 3.2/θ. From the activation energy, E0 for the decomposition is estimated to be 72.2 ± 3.2 kcal/mol. The results are compatible with those of Esteban et al. [2], for which regression analysis gives log k1 = 14.79 – 70.76/θ. A composite, log k = 15.10 – 72.0/θ, fits both sets of data and is experimentally indistinguishable from Robaugh and Steina's [3] recent estimate by the VLPP technique or other estimates in the literature [4–6]. In light of the high overall conversion of ethylbenzene studied (2–80%), the industrial‐type flow equipment, and the widely differing methods of characterization and analysis, the excellent agreement with the results of [2,3,5] is worthy of note. The data are compatible with current estimates of the heat of formation of benzyl radicals [6,7].
The thermal decomposition of n‐hexane
Authors: Ebert K. H. , Ederer H. J. , Isbarn G. 
Published: January 2005

AbstractThe kinetics of the pyrolysis of n‐hexane was studied in a conventional static reactor over a temperature range of 650–840 K. The overall reaction is essentially first order with the kinetic parameters A = 1013.92 s−1 and EA = 260.3 kJ/mol. The distributions of the main products were analyzed by gas chromatography. A reaction model involving 240 elementary reactions was developed to describe the experimental rate data. The agreement of the model with experimental data was surprisingly good over a wide range of temperatures and pressures and up to medium extents of conversion. Methods for sensitivity studies based upon the quasi‐stationary‐state assumption (QSSA) were developed, and for a number of more detailed effects, such as self‐inhibition, explanations could be given. It was also shown that the hexyl isomerization reactions influence strongly the product distribution. The outstanding capability of kinetic modeling with computer simulations in handling complex kinetic systems is demonstrated.
Kinetics of the gas‐phase reaction CH3F + I2 ⇆ CH2FI + HI: The CH bond dissociation energy in methyl and methylene fluorides
Authors: Pickard J. M. , Rodgers A. S. 
Published: January 2005

AbstractThe kinetics of the gas‐phase reaction of CH3F with I2 have been studied spectrophotometrically from 629 to 710 K, and were determined to be consistent with the following mechanism:
equation image
A least‐squares analysis of the kinetic data taken in the initial stages of reaction resulted in

where θ = 4.575T/1000 kcal/mol. The errors represent one standard deviation. The experimental activation energy E4 = 30.8 ± 0.2 kcal/mol was combined with the assumption E3 = 1 ± 1 kcal/mol and estimated heat capacities to obtain

The enthalpy change at 298 K was combined with selected thermochemical data to derive

The kinetic studies of ĊHF2 and CH2F2 have been reevaluated to yield

These results are combined with literature data to yield the CH, CF, and CCl bond dissociation energies in their respective fluoromethanes, and the effect of α‐fluorine substitution is discussed.
An FTIR study of the mechanism for the reaction HO + CH3SCH3
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P. 
Published: January 2005

AbstractProduct studies were made using the Fourier transform infrared method in the uv (300–400‐nm) photolysis of mixtures containing CH3SCH3, C2H5ONO, and NO in ppm concentrations in 700 torr of O2–N2 diluent. Methyl thionitrite, CH3SNO, arising from the reaction CH3S + NO, was detected as an intermediate product. In addition, the yields of the major sulfur‐containing products SO2 and CH3SO3H coincided with those of the oxidation of the CH3S radicals generated directly by the photodissociation of CH3SNO. The formation of CH3S in the HO‐initiated oxidation of CH3SCH3 in the presence of NO suggests a reaction scheme involving the H‐abstraction reaction HO + CH3SCH3 → CH3SCH2 + H2O as the primary step.
Sensitivity analysis and parameter estimation in dynamic modeling of chemical kinetics
Authors: Miller David , Frenklach Michael 
Published: January 2005

AbstractA new approach to the dynamic modeling of chemical kinetics is presented. The technique is based on systematic planning of computer experiments, which allows an empirical model for the computed responses to be developed in the space of parameters. The empirical equations which are obtained provide complete information on the sensitivities with respect to various rate constants, disclosing their interrelationships. Utilization of these equations instead of numerical integration of the differential equations associated with the chemical reactions makes parameter estimation a trivial task. As a consequence the adequacy of the mechanism can be tested. The technique is applied to the thermal decomposition of propane.
Effects of diffusion on the self‐termination kinetics of isopropylol radicals in solution
Authors: Lehni M. , Fischer H. 
Published: January 2005

AbstractRate constants for the bimolecular self‐reaction of isopropylol radicals [(CH3)2ĊOH] in various solvents are determined as functions of temperature by kinetic electron spin resonance. For hydrocarbon solvents they are well described by theoretical equations for reactions controlled by translational diffusion if diffusion coefficients of 2‐propanol, a constant reaction distance, and a spin statistical factor of 1/4 are applied. Deviations from 2kt ∼ D at high diffusion constants agree with trends expected from recent theoretical models. For hydrogen‐bonding solvents large negative deviations are observed. They are attributed to steric constraints and slower rotational diffusion of radical–solvent aggregates. The disproportionation‐to‐combination ratio of isopropylol increases with solvent viscosity. As previously for tert‐butyl, this is explained by anisotropic reorientation during encounters. Further, rate data are given for the decarbonylation of the 2‐hydroxy‐2‐methylpropanoyl radical and for several hydrogen abstraction reactions of isopropylol.
High‐temperature determination of the rate coefficient for the reaction H2 + CN → H + HCN
Authors: Szekely Attila , Hanson Ronald K. , Bowman Craig T. 
Published: January 2005

AbstractThe rate coefficient of the reaction

has been determined in the temperature range of 2700–3500 K using a shock tube technique. C2N2H2Ar mixtures were heated behind incident shock waves and the early‐time CN history was monitored using broad‐band absorption spectroscopy. The rate coefficient providing the best fit to the data was

in good agreement with extrapolations of previously published low‐temperature results.
Kinetics and mechanism of the reactions of the superoxide ion in solutions. I. Absorption spectra and interaction with solvents and cations
Authors: Afanas′ev I. B. , Kuprianova N. S. , Polozova N. I. 
Published: January 2005

AbstractAbsorption spectra of the superoxide ion have been studied in dimethylformamide (DMF) and acetonitrile (AN). It was found that the superoxide ion existed in equilibrium with an ion pair in AN (Keq = 20M−1, Bu4N+ is the cation) and as “free” (solvated) ion in DMF. The addition of DMF caused the destruction of an ion pair in AN. The addition of the proton donors HX (water or ethanol) to the \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} solutions in DMF and AN caused the formation of new ion pairs (Bu4N+\documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document})2HX. The equilibrium constants of these ion pairs were determined in DMF and AN.
Method for the measurement of diffusion coefficients of labile gas‐phase species: The diffusion coefficient of O(3P) in He at 294 K
Authors: Plumb I. C. , Ryan K. R. , Barton N. G. 
Published: January 2005

AbstractThe dispersion of a pulse of O(3P) atoms in flowing helium has been analyzed by a modification of Taylor's method in order to determine the diffusion coefficient. Atoms of O(3P) were produced in a flowing stream of helium by a pulsed microwave discharge of molecular oxygen. After traversing a known length of the flow tube, the arrival time distribution of the O(3P) atoms was obtained using a mass spectrometer. The value obtained for D0 at 294 K, where D0 = D[He], is (2.40 ± 0.06) × 1019 cm−1 ·s−1, which corresponds to a diffusion coefficient of (731 ± 18) cm2/s at 1 torr. In addition to D0, analysis of the arrival time distributions gives an estimate of the mean flow velocity for O atoms in helium. There was no significant difference between the value of the velocity found this way and that obtained from the mean bulk gas flow measurement. Thus for this system there is no evidence for a chromatographic effect for O(3P) atoms on the walls of the flow tube.
Kinetic study of the reactions of the hydroxyl radical with ethane and propane
Authors: Tully F. P. , Ravishankara A. R. , Carr K. 
Published: January 2005

AbstractAbsolute rate coefficients for the reactions of the hydroxyl radical with ethane (k1, 297–300 K) and propane (k2, 297–690 K) were measured using the flash photolysis–resonance fluorescence technique. The rate coefficient data were fit by the following temperature‐dependent expressions, in units of cm3/molecule·s: k1(T) = 1.43 × 10−14T1.05 exp (−911/T) and k2(T) = 1.59 × 10−15T1.40 exp (‐428/T). Semiquantitative separation of OH‐propane reactivity into primary and secondary H‐atom abstraction channels was obtained.
Kinetics and the mechanism of the thermal reaction between trifluoromethylhypofluorite and hexafluoropropene
Authors: dos Santos Afonso M. , Schumacher H. J. 
Published: January 2005

AbstractThe kinetics of the thermal reaction between CF3OF and C3F6 have been investigated between 20 and 75°C. It is a homogeneous chain reaction of moderate length where the main product is a mixture of the two isomers 1‐C3F7OCF3 (68%) and 2‐C3F7OCF3 (32%). Equimolecular amounts of CF3OOF3 and C6F14 are formed in much smaller quantities. Inert gases and the reaction products have no influence on the reaction, whereas only small amounts of oxygen change the course of reaction and larger amounts produce explosions.The rate of reaction can be represented by eq. (I):
equation image
The following mechanism explains the experimental results:
equation image
Reaction (5) can be replaced by reactions (5a) and (5b), without changing the result:
equation image
Reaction (4) is possibly a two‐step reaction:
equation image

For ∣CF3 = ∣C3F6∣, ν20°C = 36.8, ν50°C = 24.0, and ν70°C = 14.2.
The kinetics of pyrolysis of barrelene[1]: A concerted process on the C8H8 energy surface
Authors: Martin H.‐D. , Urbanek T. , Braun R. , Walsh R. 
Published: January 2005

AbstractThe static vessel pyrolysis of bicyclo[2.2.2]octa‐2,5,7‐triene (barrelene) has been studied between 483 and 523 K. The products were acetylene and benzene (in equal quantities) with no other detectable C8H8 isomer (down to less than 1% of total). The time dependence fitted first‐order kinetics, and the data are consistent with a homogeneous unimolecular reaction close to, if not at, its high‐pressure limit at 0.25 torr. The rate constant was fitted to the Arrhenius equation

These Arrhenius parameters are shown to imply a concerted single‐step process. Alternative mechanisms are discussed and a comparison is made with the retro‐Diels—Alder reactions of other bicyclo[2.2.2]octa‐olefin systems.
Pyrolysis of vinylacetylene between 300 and 450°C
Authors: Lundgard Richard , Heicklen Julian 
Published: January 2005

AbstractVinylacetylene was pyrolyzed at 300–450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half‐suppressed by the addition of the free‐radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(−79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free‐radical processes in a second‐order process with an overall k ≃ 3 × 108 exp(−122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (−118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(−77 kJ/mol RT), 1.7 × 105 exp(−89 kJ/mol RT), and 3.1 × 109 exp(− 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free‐radical process and by isomerization of COT.
Kinetic study of Ru(VI)‐catalyzed oxidation of cyclic alcohols by hexacyanoferrate(III) in aqueous alkaline medium
Authors: Behari K. , Narayan H. , Shukla R. S. , Gupta K. C. 
Published: January 2005

AbstractThe kinetics of the oxidation of cyclopentanol, cyclohexanol, 2methylcyclohexanol, and cycloheptanol by hexacyanoferrate(III) ions in mild alkaline medium has been studied in the presence of traces of ruthenium(VI) ≈ 10−7Mat constant ionic strength (0.26M). The results suggest that the oxidation of the studied cyclic alcohols proceeds via the formation of a complex between Ru(VI) and the substrate which slowly decomposes, giving the reduced form of ruthenium which was reoxidized to Ru(VI) in a fast step by alkaline hexacyanoferrate(III) ions. The product study shows the production of the corresponding ketone.
Reaction of hot H atoms with CD3Br
Authors: Oldershaw Geoffrey A. , Smith Alan 
Published: January 2005

AbstractEnergetic H atoms produced by photolysis of gaseous HI react with CD3Br by D abstraction (1) and Br abstraction (2) and possibly also by the substitution reactions (4) and (5).
equation image
Yields of HD and CD3H have been determined for several defined initial translational energies of H*. The phenomenological threshold energy of reaction (1) is 53 ± 5 kJ/mol. Over the range of initial energies of 76–109 kJ mol the integral probability of reaction (1) increases substantially, but the sum of the integral probabilities of reactions (2) and (5) shows little change. The ratio of the sum of the integral yields of reactions (2) and (5) to the integral yield of reaction (1), when normalized to equal numbers of Br and D atoms, is 69 ± 33 at an initial energy of 76 kJ/mol and 31 ± 6 at 109 kJ/mol.
Further relaxation kinetic investigations of iron(III) chelation. Data for diglycolic, tartaric, and citric acids
Authors: Cavasino F. Paolo , Di Dio Emanuele , Sbriziolo Carmelo 
Published: January 2005

AbstractThe kinetics of the reactions of iron(III) with diglycolic, tartaric, and citric acids have been studied in aqueous acid solutions by the temperature‐jump method at 25.0°C and at ionic strengths 1.0 (for tartaric and citric acids) and 0.50 mol/dm3 (for diglycolic acid). The experimental data indicate that iron(III) monochelate formation occurs by the same reaction mechanism for all three ligands examined and that only pathways involving the FeOH2+ ion contribute to the chelation process. The reacting species for citric acid is the undissociated ligand. For tartaric and diglycolic acids both the neutral ligands and the corresponding monoanions react significantly under the experimental conditions used. Kinetic evidence for the contribution of intermediate steps to the limiting rate in the overall chelate‐formation process has been obtained and discussed.
Photodecomposition reaction of ethyl bromide at 147 nm
Authors: Jung Kyung‐Hoon , Yoo Hee Soo , Hahn Jong Hoon 
Published: January 2005

AbstractA vacuum ultraviolet photolysis of C2H5Br at 147 nm was studied over a pressure range of 0.5–50 torr at 298 K. The effects of additives He and NO were also investigated.The principal reaction products were found to be C2H4 and C2H6, with lesser yields of CH4 and C2H2. With increasing pressure the product quantum yields Φi of C2H4, CH4, and CH2H6 remained constant, while that of C2H2 decreased from 0.03 to almost 0. The effect of He as an additive was found to be extremely small on the quantum yields of the major products. Addition of NO completely suppresses the formation of CH4, C2H2, and C2H6, and reduces partially the production of C2H4. The primary processes appear to involve two electronically excited states. One state mainly yields C2H4 by molecular elimination of HBr and is thought to be due to a Rydberg transition. The other state decomposes to C2H5 and Br radicals by CBr bond fission. These two competitive reaction modes contribute to the photodecomposition in proportions of 50% and 50%. The extinction coefficient for C2H5Br at 147 nm and at 298 K has been determined as ϵ = (1/PL) In(Io/It) = 712 ± 7 atm−1 · cm−1.
The addition of methyl radicals to hexafluoroacetone
Authors: Batt L. , Mowat S. I. 
Published: January 2005

AbstractThe reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place: magnified image where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide:
equation image
such that k6a is given by:

where θ = 2.303RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps:
equation image
Product analysis shows that k17/kk = 2.0 ± 0.2 such that k17 = 1010.4±0.5M−1 · s−1. The rate constant k5 is given by:

It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins.
Kinetic study of chemically activated chlorocyclopropane
Authors: Eichler K. , Heydtmann H. 
Published: January 2005

AbstractChlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3‐chloropropene, cis‐ and trans‐1‐chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.
Yields of singlet nitrenes from halogen atom—azide molecule reactions
Authors: Pritt A. T. , Patel D. , Coombe R. D. 
Published: January 2005

AbstractChemiluminescence from the a1Δ and b1Σ+ excited electronic states of nitrogen halide diatomics is observed when HN3 is allowed to react with mixtures of halogen atoms in a discharge‐flow apparatus. Excited NF (a1Δ) is produced by the F + HN3 reaction, and NCl (a1Δ, b1Σ+) and NBr (a1Δ, b1Σ+) are produced by the F, Cl, + HN3 and F, Br + HN3 reactions, respectively. In the low‐density limit, the yield of NF(a1Δ) was found to be near unity. The yields of the b1Σ+ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N3 radicals in the flow, support a hypothetical mechanism in which N3 acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.