bluuebunny/crossref_metadata_2025_split huggingface dataset:
Free radical decomposition of bromoacetonitrile in liquid cyclohexane
Authors: Gonen Y. , Rajbenbach L. A. , Horowitz A. 
Published: January 2005

AbstractThe kinetics of the gamma radiation induced free radical chain decomposition of BrCH2CN in liquid cyclohexane (RH) was investigated over the temperature range of 60–170°C. In addition competitive experiments in the presence of CCl4 were carried out between 80 and 180°C. For the reactions
equation image
the following Arrhenius expressions were derived:

where θ = 2.303RT in kcal/mol.The effect of CN substitution on the activation energies of reactions (2) and (3) was evaluated based on the present and previously published results. The CN group effect on halogen atom abstraction [reaction (2)] is discussed in terms of inductive and enthalpic factors.The differences E3 − E(CH3 + RH) and E(CCl2CN + RH) − E(CCl3 + RH), which yield a value of about 5.5 kcal/mol, are considered to reflect the cyano stabilization effect at the radical center confirming D(CH2(CN)–H) ∼ 93 kcal/mol.
Influences of ClH and BrH on the pyrolyses of neopentane and ethane at small extents of reaction
Authors: Muller J. , Baronnet F. , Scacchi G. , Dzierzynski M. , Niclause M. 
Published: January 2005

AbstractA symbolic mechanism “μH, YH” has been proposed to account for the homogeneous chain pyrolysis of an organic compound μH in the presence of a hydrogenated additive YH at small extents of reaction. An analysis of this mechanism leads to two limiting cases: the thermal decomposition of neopentane corresponds to the first one (A), that of ethane to the second one (B). Previous experimental work has shown that this mechanism seems to account for a number of experimental observations, especially the inhibition of alkane pyrolyses by alkenes.Experimental investigations were extended by examining the influences oftwo hydrogen halides (ClH and BrH) upon the pyrolyses of neopentane (at 480°C) and ethane (around 540°C). The experiments have been performed in a conventional static Pyrex apparatus and reaction products have been analyzed by gas‐liquid chromatography.The study shows that ClH and BrH accelerate the pyrolysis of neopentane (into i‐C4H8 + CH4). The experimental results are interpreted by reaction schemes which appear as examples of the mechanism “μH, YH” in the first limiting case (A). The proposed schemes enable one to understand why the accelerating influence of ClH is lower or higher than that of BrH, depending on the concentration of the additive. An evaluation of the rate constant of the elementary steps neo‐C5H11 · → i‐C4H8 + CH3 · is discussed.In the case of ethane pyrolysis, BrH inhibits the formation of the majorproducts (C2H4 + H2) and, even more, that of n‐butane traces. The experimental results are interpreted by a reaction scheme which appears as an example of the mechanism “μH, YH” in the second limiting case (B). On the contrary, ClH has no noticeable influence on the reaction kinetics. This result inessentially due to the fact that the bond dissociation energy of ClH(⋍103 kcal/mol) is higher than that of C2H5—H (⋍98 kcal/mol), whereas that of Br—H (⋍88 kcal/mol) is lower.
The oxidation of methyl radicals at room temperature
Authors: Parkes D. A. 
Published: January 2005

AbstractUsing the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature:
equation image
k1 is in the fall‐off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second‐orderlimit of (1.2 ± 0.6) × 10−12 cm3/molec · sec, together with third‐order rate constants of (3.1 ± 0.8) × 10−31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10−30 with neopentane;
equation image
we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10−13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10−13 cm3/molec · sec;
equation image
k3 = (6.0 ± 1.0) × 10−11 cm3/molec · sec.
The cycloaddition of ethylene to butene‐2. I. Stereochemistry of the reaction
Authors: Scacchi G. , Richard C. , Back M. H. 
Published: January 2005

AbstractThe rate of the thermal cycloaddition of ethylene to cis and trans butene‐2 has been measured at 693°K and at pressures of about 12 atmospheres. The ratio of trans‐ to cis‐1,2‐dimethylcyclobutane from the reaction of trans‐butene‐2 with ethylene was 5.1, obtained from the initial rates of formation of the products. Similarly, the ratio of cis‐ to trans‐1,2‐dimethyl‐cyclobutane from the reaction of cis‐butene‐2 with ethylene was 2.8. The results show that the cycloaddition reactions are the reverse of the decomposition reactions of the dimethyl‐cyclobutanes and may be interpreted in terms of a biradical intermediate. Several ratios of rate constants have been measured as well as the rate constants for the reaction of the olefins to form the intermediate biradical.
The cycloaddition of ethylene to butene‐2. II. Energy relations
Authors: Scacchi G. , Back M. H. 
Published: January 2005

AbstractThe rate of the thermal cycloaddition of ethylene to cis‐and trans‐butene‐2 has been measured at 663, 678, 693, and 703°K, and the energy relations between the reactants, intermediates, and products have been determined. The intermediate biradicals formed from the cis reactants and from the trans reactants were shown to be separated by a small but measurable enthalpy difference. This result further supports the conclusion of Part I that the intermediates are distinct species which retain some of the original configuration of the reactant. The significance of the results in relation to the mechanism of “forbidden” reactions is discussed.
Oxygen evolution as a critical test of mechanism in the ferric‐ion catalyzed decomposition of hydrogen peroxide
Authors: Walling Cheves , Cleary Michael 
Published: January 2005

AbstractThe stoichiometry of O2 evolution in the Fe3 catalyzed decomposition of H2O2 in dilute HClO4 at high [Fe3+]/[H2O2] ratios is 2H2O2 → 2H2O + O2 with no deficiency indicating accumulation of an intermediate complex. This and the observed kinetics are shown to be consistent with a “redox chain” but not a “complex” mechanism for the reaction.
Reaction between nitrous acid and hydrogen peroxide in perchloric acid medium
Authors: Bhattacharyya P. K. , Veeraraghavan R. 
Published: January 2005

AbstractA kinetic investigation on the reaction
equation image
has been carried out in HClO4 medium under different conditions. A spectrophotometric method of estimation of nitrous acid at various time intervals has been employed. The results are interpreted on the basis ofthe following mechanism:
equation image
The absolute rate constant value of 39.7 M−1 plusmn; s−1 for k4 and the equilibrium constant Keq = 116M−1 for reaction (2) have been evaluated. The activation energy of the overall reaction has also been determined as Ea = 13.2 kcal/mol.
Thermal gas‐phase decomposition of chloroethylenes. II. Vinyl chloride
Authors: Zabel F. 
Published: January 2005

AbstractThe thermal gas‐phase decomposition of vinyl chloride has been studied behind shock waves over the temperature range of 1350‐1900°K and the density range of 7 × 10−7‐1.5 × 10−3 mol/cm3 (at 1600°K) in mixtures of C2H3Cl highly diluted with argon. The ultraviolet absorption of C2H3C was recorded at 230 nm as a function of time. The decomposition proceeds via molecular elimination of HCl. The unimolecular dissociation rate is pressure dependent at all but the highest pressures applied. Application of modified HKRR theory results in the rate expression

for the limiting high pressure rate constant, and in a collision efficiency of

derived from the limiting low‐pressure rate constant.
The kinetics and equilibrium of the gas‐phase reaction CH3CF2Br + I2 = CH3CF2I + IBr the C‐Br bond dissociation energy in 1,1‐difluorobromoethane
Authors: Pickard J. M. , Rodgers A. S. 
Published: January 2005

AbstractThe kinetics and equilibrium of the gas‐phase reaction of CH3CF2Br with I2 were studied spectrophotometrically from 581 to 662°K and 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 log k1 (M−1 · sec−1) = (11.0 ± 0.3) ‐ (27.7 ± 0.8)/θ where θ = 2.303 RT kcal/mol. The error represents one standard deviation. The equilibrium data were subjected to a “third‐law” analysis using entropies and heat capacities estimated from group additivity to derive ΔHr° (623°K) = 10.3 ± 0.2 kcal/mol and ΔHrr (298°K) = 10.2 ± 0.2 kcal/mol. The enthalpy change at 298°K was combined with relevant bond dissociation energies to yield DH°(CH3CF2 ‐ Br) = 68.6 ± 1 kcal/mol which is in excellent agreement with the kinetic data assuming that E2 = 0 ± 1 kcal/mol, namely; DH°(CH3CF2 ‐ Br) = 68.6 ± 1.3 kcal/mol. These data also lead to ΔHf°(CH3CF2Br, g, 298°K) = ‐119.7 ± 1.5 kcal/mol.
Demetallation of α, β, γ, δ‐tetra(p‐sulfophenyl)porphineiron(III) in sulfuric acid‐ethanol‐water media
Authors: Reynolds Warren L. , Schufman Jay , Chan Fanny , Brasted Robert C. 
Published: January 2005

AbstractThe rate of demetallation of α, β, γ,δ‐tetra(p‐sulfophenyl)porphineiron (III), Fe(TPPS)3‐, was determined in sulfuric acid‐ethanol‐water media for 8.5‐10.65M sulfuric acid at different temperatures. The overall reaction was the conversion of the complex Fe(TPPS)3‐ into the diacid species H4TPPS2‐ without other spectrophotometrically important species being formed to an appreciable extent, as shown by three isosbestic points at 418, 462, and 563 nm. The rate was first order in the Fe(TPPS)3‐ concentration. The pseudo‐first‐order rate constants k were exponentially dependent on the sulfuric acid concentration, and log k was linearly dependent on the Hammett acidity function –H0. The average ΔH‡ and ΔS‡ values for five reaction media were 18.4 ± 1.4 kcal/mol and 19 ± 3 cal/°K · mol, respectively. The linear relationship between log k and (‐H0) and the approximately constant values of ΔH‡ ΔS‡ over the acid range investigated indicated that the same mechanism of demetallation was operative over this acid range. Because of the dependence of the pseudo‐first‐order rate constants on the acidity of the medium, the mechanism probably involves the addition of protons to pyrrole N atoms to assist in the breaking of iron (III)‐nitrogen bonds.
The thermal decomposition of diimide in the gas phase: Kinetics and stoichiometry
Authors: Willis C. , Back R. A. , Purdon J. G. 
Published: January 2005

AbstractThe kinetics and stoiehiometry of the decomposition of N2H2 and N2D2 have been studied as a function of sample size, pressure, and temperature. The reaction follows a single first order kinetic expression over most of its time course. It is suggested that the rate‐determining step in the mechanism is a first‐order homogeneous gas‐phase isomerization of trans‐diimide with rate constants:k = 1.8 exp (‐4.2 kcal/mol/RT) sec−1 and k = 1 exp (‐4.4 kcal/mol/RT) sec−1. The detailed mechanism of this isomerization, however, is not evident. At temperatures above room temperature, self‐heating has been observed which leads to an initial fast decay. At room temperature the reaction exhibits autocatalysis with the rate increasing as the reaction proceeds. This has been attributed to enhancement by a surface decay process involving adsorbed hydrazine.The only significant products from the decomposition of N2H2 are N2, H2, and N2H4, and the results are interpreted in terms of two parallel reactions:magnified image The decomposition of N2D2 occurs almost completely by the single reaction giving N2 + N2D4. No azide formation has been detected from either N2D2, or N2D2, and limits have been put on the yield of ammonia. Extinction coefficients at 365 nm of 3.9 ± 0.2 for N2H2 and 3.3 ± 0.1 for N2D2 have been measured.Both the rate of decay and the stoichiometry of products show pressure dependence below 150 torr, and this is suggested to be due to direct decomposition of cis‐N2H2 on the surface.
BrNO—thermodynamic properties, the ultraviolet/vis spectrum, and the kinetics of its formation
Authors: Houel N. , Bergh H. Van Den 
Published: January 2005

AbstractThe equilibrium
equation image
has been studied between 275°and 363°K. Third‐law calculations lead to ΔH°298(1) = ‐11.50 ±0.17 kcal/mol, from which

Absorption bands of BrNO in the ultraviolet with e (γmax = 215 nm) = 1.84±0.17 × 104 1/mol·cm, and in the red with e (γmax = 708 nm) = 7.7±1.9 1/mol·cm at 298°K have been investigated.The rate of formation of BrNO has also been measured between 275°and 363°K.
The Dependence on H2O and on NH3 of the Kinetics of the self‐reaction of HO2 in the gas‐phase formation of HO2·H2O and HO2·NH3 complexes
Authors: Hamilton Edwin J. , Lii Ruey‐Rong 
Published: January 2005

AbstractElectron pulse radiolysis at ⋍298°K of 2 atm H2 containing 5 torr O2 produces HO2 free radical whose disappearance by reaction (1), HO2 + HO2 →H2O2 + O2, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO2 absorption cross section, the values k1 = 2.5×10−12 cm3/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO2) ⋍13 are obtained. In the presence of small amounts of added H2O or NH3, the observed second‐order decay rate of the HO2 signal is found to increase by up to a factor of ⋍2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO2 + H2O ⇋ HO2·H2O (4a) and HO2 + NH3⇋ HO2·NH3 (4b), which are more reactive than uncomplexed HO2 toward a second uncomplexed HO2 radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10−20≲K4a≲6.3 × 10−19 cm3/molec at 295°K and K4b = 3.4 × 10−18 cm3/molec at 298°K. Several deuterium isotope effects are also reported, including kH/kD = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.
Flash photolysis study of the NO‐catalyzed recombination of bromine atoms
Authors: Hippler H. , Luu S. H. , Teitelbaum H. , Troe J. 
Published: January 2005

AbstractThe recombination of bromine atoms at room temperature has been studied by flash photolysis in the range of 1–100 atm of the inert diluent He, leading to a value for the third‐order rate constant of (1.5 ± 0.2) × 1015 cm6/mol2.sec. In the presence of NO the recombination is considerably accelerated. The falloff curve of the recombination Br + NO (+He) → BrNO (+He) was also measured resulting in a value for the limiting low‐pressure rate constant of (3.4 ± 1.3) × 1015 cm6/mol2.sec. In experiments with excess NO, rate constants of (2.2 ± 1) × 1014 cm3/mol·sec for the reaction Br + BrNO → Br2 + NO, and (6.1 ± 0.4) × 109 cm6/mol2.sec for the reaction Br2 + 2NO → 2BrNO were obtained.
Kinetic study of a retro Diels–Alder reaction in a single‐pulse shock tube: Decyclization of 1‐methylcyclohex‐1‐ene
Authors: Simmie John M. 
Published: January 2005

AbstractThe kinetics of the gas‐phase decomposition of 1‐methylcyclohex‐1‐ene has been studied over the temperature range of 1000°–1180° K in a single‐pulse shock tube using a comparative‐rate technique. The retro Diels‐Alder reaction to ethylene and isoprene accounts for the bulk of the products with a rate constant given by
Diffusion of hydrogen atoms in spherical vessels
Authors: Lynch K. P. , Michael J. V. 
Published: January 2005

AbstractA previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction at the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first‐order decay constants of H at room temperature in various pressures (10‐1500 torr) of six heat bath gases. The atomic concentration is monitored by Lyman‐α absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to ∼400 torr and depend only on one parameter,γ, the recombi‐nation coefficient. This should be contrasted with the earlier work where slight variation in γ was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.
Further study of cyclopropane structural isomerization behind reflected shock waves
Authors: Lewis David K. , Giesler Stephen E. , Brown Michael S. 
Published: January 2005

AbstractThe homogeneous thermal isomerization of cyclopropane to propene was studied in the presence of large excesses (99.6%–99.8%) of argon or helium diluent. Reaction temperatures ranged from 1038°−1208°K, and total gas pressures were varied from 533 to 5097 torr. The comparative‐rate single‐pulse shock‐tube method was used, with the well characterized decomposition of cyclohexene serving as the internal standard reaction. Comparison of the measured rate constants for cyclopropane isomerization with k∞ values extrapolated from “preferred˝” lower‐temperature rate constants suggests that collision efficiencies for helium and argon relative to cyclopropane, under the present conditions, are βc ≈ 0.04 and 0.05, respectively. Although the uncertainties are rather large, these results do not support the suggestion that rapidly declining βc values are largely responsible for the anomalously low rate constants for this reaction at T≥1130°K previously reported by other workers.
Reactions of (CO2)2+ and (CO)2+ association ions
Authors: Sieck L. Wayne 
Published: January 2005

AbstractThe reactons of (CO2)2+ and (CO)2+ with various additives have been investigated using the NBS high‐pressure photoionization mass spectrometer at total pressures of 0.4–1.0 torr of either CO2 or CO. The additives include CH4, CD4, C2H2, O2, H2O, 15,14N2O, and CO in both CO2 and 13CO2. Second‐ and third‐order rate coefficients based on an ambipolar diffusion model are reported for 25 separate reaction pairs at 295°K, as well as sequential cationic reaction mechanisms. An approximate value of 225 ± 3 kcal/mol (941 ± 13 kJ/mol) was derived for ΔHf (CO)2+ based on the kinetics observed in various CO‐additive mixtures. Some projections regarding the utility of the data under other conditions are also included.
Kinetics of fluorine atom reactions using resonance absorption spectrometry in the far vacuum ultraviolet reactions F + HCl, CH4, CHCl3 CHCl2F, and CHClF2
Authors: Clyne Michael A. A. , Nip Wing S. 
Published: January 2005

AbstractAtomic resonance absorption spectrometry with a nonreversed fluorine resonance lamp (∼95 nm) has been used to study the kinetics of elementary reactions of ground state F2PJ atoms in a discharge‐flow system. The following rate constants (in cm3/molec·sec)All rate constants are given with 1.5 σ.
were determined at 298° K:
equation image
The reaction F 2PJ + HCl(1) was found to give J‐excited Cl 2P1/2 atoms with a product branching ratio [Cl 2P1/2]/[Cl 2P3/2] = 0.10.
Reactions of NO2+ and solvated NO2+ ions with aromatic compounds and alkanes
Authors: Ausloos P. , Lias S. G. 
Published: January 2005

AbstractThe rate constants and modes of reaction of NO2+ and C2H5ONO2NO2+ with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and substitution reactions (NO2+ + M → MO+ + NO; C2H5ONO2NO2+ + M → MNO2+ + C2H5ONO2) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C2H5ONO2NO2+ ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO2+ and C2H5ONO2. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C2H5ONO2NO2+ ions, on the energetics of the competing charge transfer process. Both NO2+ and C2H5ONO2NO2+ undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k (collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO2+.
Thermal stability of intermediate sized acetylenic compounds and the heats of formation of propargyl radicals
Authors: Tsang Wing 
Published: January 2005

Abstract4‐Methylhexyne‐1, 5‐methylhexyne‐1, hexyne‐1, and 6‐methylheptyne‐2 have been decomposed in comparative‐rate single‐pulse shock‐tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are

In combination with previous results, rate expressions for propargyl CC bond cleavage are related to that for the alkanes by the expression

These results yield a propargyl resonance energy of D(nC3H7‐H) – D(C3H3‐H) = 36 ± 2 kJ, in excellent agreement with a previous shock‐tube study. They also lead to D(CH3C≡CCH2‐H) – D(C3H3‐H) = 0.6 ± 3 kJ, D(sC4H9‐H) – D(iC3H7‐H) = 0 ± 3 kJ, D(iC4H9‐H) – D(nC3H7‐H) = 2 ± 3 kJ, and D(nC3H7‐H) – D(iC3H7‐H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.
The photolysis of 2‐fluorocyclohexanone in the 313‐nm region. The elimination of hydrogen fluoride from vibrationally excited fluorocyclopentane
Authors: Pritchard Glyn O. , Gute John P. 
Published: January 2005

AbstractThe gas‐phase photolysis of 2‐fluorocyclohexanone at 313 nm and 120°C is reported. The primary dissociative step appears to be magnified image The 1‐fluoropentanediyl species can disproportionate to form the 1‐ and 5‐fluoro‐1‐pentenes, or cyclize to form vibrationally excited fluorocyclopentane. The latter molecule either undergoes collisional stabilization or decomposes unimolecularly to give cyclopentene and HF. The half‐quenching pressure for the latter reaction was 2 torr. The disproportionation‐to‐combination ratic for the diradical was found to be 1.2. Some brief preliminary experiments on the liquid‐phase photolysis of 2‐chlorocyclohexanone and 2‐fluorocyclohexanone are also described.
Decay kinetics of aryloxy and semiquinone radicals in the presence of copper ions
Authors: Khudyakov I. V. , Kuzmin V. A. , Emanuel N. M. 
Published: January 2005

AbstractThe decay kinetics of aryloxy and semiquinone radicals in the presence of copper ions in aqueous solutions has been studied by means of the flash photolysis technique. The radicals are involved in electron transfer reactions and those leading to the formation of intermediate complexes with copper ions. The complexes of p‐benzosemiquinone anion radicals and 2‐hydroxyphenoxy radicals with cupric ions decay in bimolecular self‐reactions at a much slower rate than the original radicals. The increased stability of the complexes compared with the initial radicals is attributed to partial delocalization of the unpaired electron over the electron shell of copper and to steric hindrances in the self‐reactions of complexes.