bluuebunny/crossref_metadata_2025_split huggingface dataset:
The reaction of atomic oxygen O(3P) with isobutane
Authors: Jewell Steven P. , Holbrook Kenneth A. , Oldershaw Geoffrey A. 
Published: January 2005

AbstractThe reaction of O(3P) atoms with isobutane has been studied by using the discharge‐flow system described previously [1]. The rate constant was measured from determinations of the isobutane concentration in the presence of an excess of O atoms and is given by k1 = (7.9 ± 1.4) × 107 dm3/mol·s at 307 K. In order to explain the observed reaction products, the mechanism requires that the principal process be the successive abstraction of H atoms from isobutane and from the t‐butyl radical to give isobutene. A minor part of the reaction between O(3P) and the t‐butyl radical gives the t‐butoxy radical, which decomposes to acetone. The branching ratios are
equation image
.
Very low‐pressure pyrolysis (VLPP) of pentynes. III. Pent‐2‐yne. Heat of formation and resonance stabilization energy of the 3‐methylpropargyl radical
Authors: Nguyen Tam T. , King Keith D. 
Published: January 2005

AbstractThe thermal unimolecular decomposition of pent‐2‐yne has been studied over the temperature range of 988–1234 K using the technique of very low‐pressure pyrolysis (VLPP). The main reaction pathway is C4C5 bond fission producing the resonance‐stabilized 3‐methylpropargyl radical. There is a concurrent process producing molecular hydrogen and penta‐1,2,4‐triene presumably via the intermediate formation of cis‐penta‐1,3‐diene. The 1,4‐hydrogen elimination from cis‐penta‐1,3‐diene is the rate‐determining step in the molecular pathway. This is supported by an independent VLPP study of cis‐ and trans‐penta‐1,3‐diene. RRKM calculations show that the experimental rate constants for CC bond fission are consistent with the following high‐pressure rate expression at 1100 K:

where θ = 2.303RT kcal/mol and the A factor was assigned from the results of shock‐tube studies of related alkynes. The activation energy leads to ΔH[CH3CCĊH2] = 70.3 and DH[CH3CCCH2H] = 87.4 kcal/mol. The resonance stabilization energy of the 3‐methylpropargyl radical is 10.6 ± 2.5 kcal/mol, which is consistent with previous results for this and other propargylic radicals.
Very low‐pressure pyrolysis (VLPP) of penta‐1,3‐dienes. Kinetics of the unimolecular 1,4‐hydrogen elimination from cis‐penta‐1,3‐diene
Authors: Nguyen Tam T. , King Keith D. 
Published: January 2005

AbstractThe thermal unimolecular reactions of cis‐ and trans‐penta‐1,3‐diene (c‐PTD and t‐PTD) have been studied over the temperature range of 1002–1235 K using the technique of very low‐pressure pyrolysis (VLPP). c‐PTD decomposes via 1,4‐hydrogen elimination analogous to that previously reported for cis‐but‐2‐ene. RRKM calculations incorporating a six‐center transition state show that the experimental rate constants are consistent with the following high‐pressure rate expression at 1100 K:

where θ = 2.303RT kcal/mol, and the A factor was assumed to be the same as that for cis‐but‐2‐ene. The activation energy is in excellent agreement with that obtained for cis‐but‐2‐ene. t‐PTD also undergoes decomposition by H2 elimination presumably via the prior rapid isomerization to c‐PTD the results are in exact agreement with those for c‐PTD.
Kinetics and mechanism of the gas‐phase thermal reaction between bis(fluoroxy) difluoromethane CF2(OF)2 and carbon monoxide
Authors: Croce A. E. , Castellano E. 
Published: January 2005

AbstractThe kinetics of the gas‐phase thermal reaction between CF2(OF)2 and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF2O and CO2, giving the following stoichiometry:

The reaction is homogeneous. The rate is strictly second order in CF2(OF)2 and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF2O.The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F2O and CO with an overall rate constant of

From the experimental data obtained on the oxygen‐inhibited reaction, the rate constant for the primary process can be calculated:

The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σ = 6 Å and σCO = 3.74 Å, a value α = 5.3 × 10−3 for the steric factor is obtained.
Mechanism of oxidation of phenylthioacetic acids by potassium peroxodiphosphate
Authors: Srinivasan C. , Pitchumani K. 
Published: January 2005

AbstractThe rates of oxidation of phenylthioacetic acid (PTAA) and several substituted phenylthioacetic acids by potassium peroxodiphosphate (PP) in 50% (v/v) aqueous acetic acid have been studied in detail. The rate of oxidation is expressed as

An analysis of the dependence of the rate on [H+] reveals that H3P2O is the active oxidizing species in the oxidation. The effect of ring substituents on the rate gives a ρ+ value of ‐0.45 ± 0.03 (r = 0.998, s = 0.02 at 40°C), pointing to the development of an electron‐deficient center in the transition state. The results are discussed in terms of a mechanism involving the rate‐determining formation of an intermediate between PP and phenylthioacetic acids, followed by the decomposition of the intermediate. These kinetic results are compared with those obtained in the oxidation of phenylthioacetic acids by peroxodisulfate.
Thiocyanate‐assisted demetallation of α,β,γ,δ‐tetra(p‐sulfophenyl)porphinatoindium(III) in aqueous media
Authors: Reynolds Warren L. , Gall Daniel , Arndt Peter 
Published: January 2005

AbstractThe rate law for the demetallation of the title indium(III)‐porphin complex in aqueous acidic thiocyanate media at 3.00M ionic strength was found to be of the form

where [H4P2−] is the concentration of the diacid product formed, [InP]t is the total concentration of all forms of indium(III)‐porphin complex present, and a and b are constants. The constant a is a pseudo‐third‐order rate constant with the value (0.057 ± 0.005)M−2 s−1 and b has the value 0.704M−2 at 50.5°C. If the mechanism for demetallation involves ringpuckering with the attachment of two H+ ions, then 1/b can be identified with the product K1K2 for the stepwise dissociation of two protons from two ring pyrrolic nitrogen atoms of H2InP−. In the sulfonated tetraphenylporphin used for these studies the ring pyrrolic nitrogen atoms seem to be the most probable sites for protonation. If this identification is correct, the value of 1.42 ± 0.13 found for the product K1K2 shows the enormous effect that the presence of the In3+ center has on the ionization constants of these two protons. That the kinetic studies show saturation effects with respect to proton addition to InP3− may result from the fact that In3+ sits about 0.6 Å above the porphin ring.
Kinetics and mechanism of reaction of p‐methoxystyrene and tetracyanoethylene. I. Evidence for competitive 1,2‐ and 1,4‐cycloadditions
Authors: Uosaki Y. , Nakahara M. , Osugi J. 
Published: January 2005

AbstractTime‐resolved absorption spectra for a reaction mixture of p‐methoxystyrene and tetracyanoethylene (TCNE) are found to have a band maximum at 325 nm which is assigned to the 1,4‐cycloadduct. The reaction in chloroform at 15, 20, and 25°C is followed by the charge‐transfer band at 600 nm. The 1,4‐cycloadduct, besides the so far known 1,2‐cycloadduct and EDA complex, is taken into account to derive the rate equation for the EDA complex that is a linear second‐order differential equation. The rate constants for the elementary steps involved in the reaction are obtained. The 1,4‐cycloaddition has an activation entropy of ‐63 J/K·mol for the cycloreversion and a reaction constant ρ of ‐4.7, both of which indicate the polar transition state. On the other hand, activation entropy of the 1,2‐cycloaddition is 73 J/K·mol more negative than that of the 1,4‐cycloaddition, supporting the zwitterionic mechanism for the 1,2‐cycloaddition.
Kinetics and mechanisms of oxidation of organic compounds by silver(II) species. Part VI: Iminodiacetic acid and N‐methyliminodiacetic acid
Authors: Baiocchi Claudio , Bovio Giuseppe , Mentasti Edoardo 
Published: January 2005

AbstractThe kinetics and mechanism of oxidation of iminodiacetic acid and N‐methyliminodiacetic acid by aquasilver(II) and Ag(II)‐2,2′‐bipyridine complexes has been investigated. The results are discussed with reference to the active reaction pathways, the equilibrium quotient of the title reactions, the protolytic equilibria which involve the oxidizing complex, and the intrinsic self‐exchange rates of the oxidants.
Experimental investigation of chamber‐dependent radical sources
Authors: Carter W. P. L. , Atkinson R. , Winer A. M. , Pitts J. N. 
Published: January 2005

AbstractWhile environmental chamber data have been widely used to generate and validate computer models of the chemistry occurring in polluted atmospheres, the effects of the chambers on the gas‐phase chemistry being studied have been poorly characterized. In order to investigate such chamber effects, a series of NOx—air irradiations, with trace levels of organics present to monitor OH radical concentrations, have been carried out in four different environmental chambers (ranging in volume from ∼100 to 40,000 L) at varying temperatures, humidities, pressures, and reaction conditions. In addition, a number of control experiments have been carried out to validate the technique for measuring OH radical levels in these irradiations. The data show that unknown sources of OH radicals are present in all of the chambers studied. The data are consistent with the presence of two distinct radical sources: (1) the photolysis of initially present HONO, whose importance increases with increasing NO2/NO concentration ratios, but which is a minor contributor to the overall radical flux after 30–60 min of irradiation, and (2) a constant (for these NOx—air irradiations) radical source which dominates beyond approximately the first 60 min of irradiation. The radical input rates, after the first ∽30–60 min of irradiation, are independent of the NO concentration, increase with increasing temperature, humidity, and NO2 concentration, are proportional to light intensity, and are dependent on the chamber employed. Although the exact nature of this radical source is still undetermined, results of experiments reported here allow a number of possible mechanisms to be ruled, out, and these are discussed.
Kinetics and mechanism of the oxidation of halotoluenes by acidic hexacyanoferrate(III)
Authors: Bhattacharjee A. K. , Mahanti M. K. 
Published: January 2005

AbstractThe oxidation of halotoluenes by hexacyanoferrate(III) in aqueous acetic acid containing perchloric acid (0.5M) at 50°C gave the corresponding aldehyde as the major product, and a small amount of polymeric material. The order with respect to each of the reactants—substrate, oxidant, and acid—was found to be unity. Increasing proportions of acetic acid increased the rate of the reaction. The reaction was influenced by changes in temperature, and the activation parameters have been evaluated. The Hammett plot yielded a ρ+ value of −1.8. A kinetic isotope effect kH/kD = 6.0 has been observed. The pathway for the conversion of the halotoluenes to the products has been mechanistically visualized as proceeding through the benzylic radical intermediate, formed in the rate‐determining step of the reaction. The radical undergoes rapid conversion to the products.
F‐to‐HF reactions. IX. Nonthermal complications for the CH4/C3F6/C2F6 moderated nuclear recoil system
Authors: Mathis Chester A. , Root John W. 
Published: January 2005

AbstractResults are reported from moderated nuclear recoil 18F experiments with the CH4/C3F6/C2F6 mixture system. At a 99.5% confidence level measurement precision of ±3.4%, non‐thermal F‐to‐HF reactions are phenomenologically suppressed at C2F6 moderator concentrations in the range of 95.0–99.95 mol‐%. Effectively equilibrium reaction conditions can be established in well‐designed experiments of this type.
Experimental determination of the equilibrium constant of the reaction CH3 + O2 ⇄ CH3O2 during the gas‐phase oxidation of methane
Authors: Khachatryan L. A. , Niazyan O. M. , Mantashyan A. A. , Vedeneev V. I. , Teitel'boim M. A. 
Published: January 2005

AbstractFor the experimental determination of the equilibrium constant of the reaction CH3 + O2 ⇄ CH3O2 (1), the process of methane oxidation has been studied over the temperature range of 706–786 K. The concentration of CH3O2 has been measured by the radical freezing method, and that of CH3 from the rate of accumulation of ethane, assuming that C2H6 is produced by the reaction CH3 + CH3 → C2H6 (2). The equilibrium constant of reaction (1) has been obtained at four temperatures. For the heat of the reaction the value Δ˚H298 = ‐32.2 ± 1.5 kcal/mol is recommended.
Kinetics and thermochemistry of electron attachment to SF6
Authors: Heneghan Shawn P. , Benson Sidney W. 
Published: January 2005

AbstractThermochemical analysis of the electron capture process of SF6 leads to a rate constant for the reverse process \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SF}_6^ - \mathop \to \limits^2 {\rm SF}_6 + e^ -,k_2 = 1.5 \times 10^{13 - 31.4/\theta } {\rm s}^{{\rm - 1}} $\end{document}, where θ = 2.303RT, in kcal/mol. The electron affinity of 32±3 kcal/mol is deduced from the observed bimolecularity of the capture process down to 0.1 torr Ar bath gas and estimated entropies of SF6 and SF. The capture process is discussed from the view point of the formation of a metastable SF electron (SF6·e) Langevin complex which appears to have a lifetime of about 2 × 10−13 s. Curve crossing from the SF6·e complex to vibrationally excited (SF)* appears to have a normal rate and A factor. This is interpreted to indicate near‐resonant coupling between the orbiting electron and the vibronic motions of SF6, together with similarity in structure of SF6 and SF. It is shown that the apparent slowness of thermal electron ejection from SF is a result of an unfavorable equilibrium constant rather than a slow rate.
Thermochemistry and kinetics of the reaction of methyl mercaptan with iodine
Authors: Shum Lilian G. S. , Benson Sidney W. 
Published: January 2005

AbstractThe gas‐phase reaction CH3SH + I2 has been studied spectrophotometrically over the temperature range of 476–604 K. It was found that the reaction undergoes H abstraction by I at ≤575 K, leading to the formation of MeSI and followed by a secondary reaction which leads to the formation of MeSSMe:
equation image
Taking into consideration the effect of reaction (2), the equilibrium constant K1 (554 K) has been evaluated to be 0.025 ± 0.004. This value was combined with the estimated values S (CH3SI, g) = 73.7 ± 1.0 eu and 〈ΔC〉 = 0.87 ± 0.3 eu to obtain ΔH = 4.03 ± 0.73 kcal/mol. This yields ΔH (CH3SI, g) = 7.16 ± 0.73 kcal/mol when combined with known thermochemical values for CH3SH, HI, and I2. A kinetic study was vitiated by the concurrent heterogeneous reaction of MeSH and I2 at lower temperatures and the rather complicated chemistry occurring at elevated temperatures. However, attempts at measuring rate constants at 554 K lead to a lower limit of ΔH (CH3S·, g) ≥ 29.5 ± 2 kcal/mol when an estimated value of A = 1010.8 ± 0.2 L/mol·s for the reactionc
equation image
is used. DH (CH3S–I) is estimated to be 49.3 ± 1.7 kcal/mol. The bond strengths of some divalent sulfurs and the reaction mechanisms are discussed. A crude estimate of DH0(H–CH2SH) = 96 ± 1 kcal has been obtained from the kinetic data.
Rate constants for the gas‐phase reactions of OH radicals with β‐dimethylstyrene and acetone. Mechanism of ββdimethylstyrene NOx – air photooxidation
Authors: Chiorboli C. , Bignozzi C. A. , Maldotti A. , Giardini P. F. , Rossi A. , Carassiti V. 
Published: January 2005

AbstractThe rate constants of gas‐phase reactions of the hydroxyl radical with β‐dimethylstyrene and acetone have been determined by a relative method at 298 K. The values obtained are β‐dimethylstyrene (3.3 ± 0.5) × 10−11 cm3/molecule·s and acetone (6.6 ± 0.9) × 10−13 cm3/molecule·s. A simplified kinetic treatment of the experimental data shows that β‐dimethylstyrene is stoichiometrically converted to benzaldehyde and acetone. In the photooxidation study of benzaldehyde, carbon dioxide was the only detected product. The ratio between carbon dioxide produced and benzaldehyde reacted was ≥1.
The kinetics and mechanism of thermal decomposition of alkyl isocyanates
Authors: Blake P. G. , Ijadi‐Maghsoodi S. 
Published: January 2005

AbstractThe kinetics of the gas‐phase decomposition of ethyl, isopropyl, and t‐butyl isocyanates have been studied in the temperature range of 380–530°C. t‐Butyl isocyanate decomposes almost exclusively by a unimolecular route to isobutene and HNCO, but in EtNCO and i‐PrNCO this route competes with a free‐radical chain which produces CO, CH4, and HCN or CH3CN. In i‐PrNCO, however, the chain process is very rapidly inhibited by the propene formed in the parallel unimolecular route. A minor heterogeneous bimolecular decomposition in each case gives rise to carbon dioxide and a carbodiimide. Mechanisms and trends in the alkyl isocyanates from methyl through t‐butyl are discussed.
Rate constant and products of the reaction CS2 + OH in the presence of O2
Authors: Barnes I. , Becker K. H. , Fink E. H. , Reimer A. , Zabel F. , Niki H. 
Published: January 2005

AbstractThe reaction of OH radicals with CS2 has been investigated by the application of Fourier transform infrared spectroscopy using both photolytic and nonphotolytic competitive techniques in a 420‐L reaction chamber at different pressures over the temperature range of 264–293 K. The measured effective rate constant was found to be dependent on total pressure, temperature, and the mole fraction of O2 present in the system. The products of the reaction were found to be COS and SO2 with one molecule of each being formed for every reacted CS2. A value of (2.7 ± 0.6) × 10−12 cm3/molecule·s was obtained as effective rate constant for the reaction at 293 K in 760 torr of synthetic air.
Direct conversion of synthesis gas to light hydrocarbons on heterogeneous catalysts
Authors: Gadalla Ahmed M. , Chan Ting , Anthony Rayford G. 
Published: January 2005

AbstractSix catalysts consisting of mixtures of catalysts for methanol synthesis and its conversion to hydrocarbons were prepared by mechanical mixing, impregnation, and coprecipitation, followed by extrusion. Phase changes occurring during various stages of preparation and after use were followed by x‐ray diffraction. The catalysts were found to be nontrivial bifunctional catalysts which selectively convert synthesis gas directly to low molecular weight hydrocarbons in the range of C1 to C4. Methanol and dimethylether were detected as intermediates. Olefins were formed, and their further hydrogenation yielded products with high paraffinic content. Carbon dioxide retards the conversion of synthesis gas to hydrocarbons, whereas steam retards the hydrogenation of olefins. On heating the commercial zinc chromite catalyst, dehydration, reduction, and solid‐state reactions occur with the formation of ZnO‐ZnCr2O4 solid solution. Exchanging cations within the zeolite component did not affect the space lattice, but these ions tend to occupy special sites, and during service more order was detected. Copper ions tend to diffuse in ZnO, forming a solid solution, and during service metallic copper was produced.
Kinetics and mechanism of reaction of p‐methoxystyrene and tetracyanoethylene. II. Effect of pressure
Authors: Uosaki Y. , Nakahara M. , Osugi J. 
Published: January 2005

AbstractThe reaction of p‐methoxystyrene and TCNE is studied in 50% CHCl3–50% CCl4 (v/v) at 25°C at high pressures up to 1000 bar by following the disappearance of the absorbance at 600 nm due to the EDA complex. By using the mixed solvent, equations required for the high‐pressure kinetics are simplified. The volume of activation is −42 to −46 cm3/mol for the 1,4‐cycloaddition and −55 cm3/mol for the 1,2‐cycloaddition. The activation volume for the 1,4‐cycloreversion is assumed to be −8 to −12 cm3/mol based on a previous study on a similar system. The rate of the cycloreversion process is affected by solvent polarity. The rate of the 1,2‐cycloaddition is influenced by solvent more significantly than that of the 1,4‐cycloaddition. It is concluded that the transition state is polar in both cycloadditions and that its zwitterionic character is much stronger in the 1,2‐cycloaddition.
Kinetics and equilibria in the system Br + t‐BuO2H ⇆ HBr + t‐BuO2. OH bond dissociation energy in t‐BuO2‐H
Authors: Heneghan Shawn P. , Benson Sidney W. 
Published: January 2005

AbstractThe kinetics and equilibria in the system Br + t‐BuO2H ⇆ HBr + t‐BuO2· have been measured in the range of 300–350 K using the very low pressure reactor (VLPR) technique. Using an estimated entropy change in reaction (1) ΔS1 = 3.0 ± 0.4 cal/mol·K together with the measured ΔG1, we find ΔH1 = 1.9 ± 0.2 kcal/mol and DHº (t‐BuO2‐H) = 89.4 ± 0.2 kcal/mol ΔHf·(tBuO2·) = 20.7 kcal/mol and DHº (t‐Bu‐O2) = 29.1 kcal/mol. The latter values make use of recent values of ΔHf·(t‐Bu) = 8.4 ± 0.5 kcal/mol and the known thermochemistry of the other species. The activation energy E1 is found to be 3.3 ± 0.6 kcal/mol, about 1 kcal lower than the value found for Br attack on H2O2. It suggests a bond 1 kcal stronger in H2O2 than in tBuO2H.
Induced heterogeneity, a novel technique for the study of gas‐phase reactions. 2. Direct study of CC bond scission in ethane
Authors: Kanan Khalid , Purnell Howard , Sepherad Abolgassem 
Published: January 2005

AbstractDeliberate activation of the reaction vessel surface leads to the domination of chain termination in ethane pyrolysis by the reaction

As a result, chains are dramatically reduced in length, methane yields are entirely primary and larger in proportion to other products, and values of k1

can be directly determined from methane yield data without ambiguity. Experiments carried out in the temperature range of 841–913K at initial ethane pressures of 1–20 torr, without and with added nitrogen, yield the infinite pressure Arrhenius equation

It is shown that most previously published data can be combined with those of this study to yield

Fall‐off curves for k1 as a function of pressure are in good agreement with those from other laboratories. From these the relevant data for k−1 can be extracted for use in other kinetic studies.
The reaction of cyclopentyl radicals with carbon tetrachloride
Authors: Matheson Ian , Tedder John , Sidebottom Howard 
Published: January 2005

AbstractThe photolysis of azocyclopentane in the presence of cyclopentane–carbon tetrachloride mixtures has been investigated in the gas phase. Product analysis data have been used to determine the Arrhenius parameters for the reactions

The rate data for chlorine atom abstraction from CCl4 by the cyclopentyl radical were compared with available data for other alkyl radicals in both the gas and the solution phases. The results indicate that the rate constant for chlorine atom abstraction in the gas phase is fairly insensitive to the nature of the attacking alkyl radical and that the activation energy for a secondary radical is about 4 kcal/mol higher than the corresponding reaction in the solution phase.