bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Reactions of OH(v = 1)
Authors: Spencer John E. , Glass G. P.
Published: January 2005

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

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

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

and that for COD by

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

A biradical mechanism seems to fit these results. The heat of formation and the entropy of COD are estimated.
Free radical decomposition of bromoacetonitrile in liquid cyclohexane
Authors: Gonen Y. , Rajbenbach L. A. , Horowitz A.
Published: January 2005

The 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

A 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

Using 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

The 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

The 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

The 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

A 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

The 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

The 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

The 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

The 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

The 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

Electron 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

The 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.
Calculation of the average energy and the energy distribution function of chemically activated species
Authors: McCluskey Richard J. , Carr Robert W.
Published: January 2005

Equations for the average energy of chemically activated species are developed, and uncertainties in the various energy quantities involved are discussed. Various approaches to the energy distribution function of chemically activated species are discussed. Trial calculations on methylcyclobutane are presented.
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

The 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

A 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

The 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

The 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

Atomic 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

The 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

4‐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

The 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

The 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.
The gas‐phase pyrolysis of alkyl nitrites. VII. Primary and secondary nitrites in the presence of nitric oxide
Authors: Batt L. , Islam T. S. A. , Scott H.
Published: January 2005

Although our pyrolytic studies of five alkyl nitrites (RONO) have shown that it is possible to determine precise, acceptable values for k1:
equation image
we have been uncertain about the mechanism for the first order production of nitroxyl from primary and secondary nitrites. Nitroxyl could arise either from the direct elimination process (5) or from the disproportionation of the alkoxyl radical concerned and nitric oxide:
equation image
Thus kexp = k5 or k1k6/[k2 + k6]. If the route is reaction (6), Eexp should be identical to E1, since the ratio k6/k2 is temperature independent. We preferred the elimination process because Eexp < E1 and Aexp was in agreement with transition‐state calculations for such elimination processes. This study was concerned with the pyrolyses of ethyl and i‐propyl nitrites in the presence of nitric oxide. The results show that nitroxyl is produced via the disproportionation of the alkoxyl radical and nitric oxide, as originally suggested by Levy. This is supported by the wealth of particularly photochemical data in the literature. Our and other previous spuriously low Arrhenius parameters are attributed to heterogeneous effects.
EPR kinetic study of the reactions of CF3Br with H atoms and OH radicals
Authors: Le Bras G. , Combourieu J.
Published: January 2005

Reactions of CF3Br with H atoms and OH radicals have been studied at room temperature at 1–2 torr pressures in a discharge flow reactor coupled to an EPR spectrometer. The rate constant of the reaction H + CF3Br → CF3 + HBr (1) was found to be k1 = (3.27 ± 0.34) × 10−14 cm3/molec·sec. For the reaction of OH with CF3Br (8) an upper limit of 1 × 10−15 cm3/molec·sec was determined for k8. When H atoms were in excess compared to NO2, used to produce OH radicals, a noticeable reactivity of OH was observed as a result of the reaction OH + HBr → H2O + Br, HBr being produced from reaction (1).
Competitive unimolecular reactions at low pressures. The pyrolysis of cyclobutyl chloride
Authors: King Keith D. , Gaynor Brendan J. , Gilbert Robert G.
Published: January 2005

The thermal decomposition of cyclobutyl chloride has been investigated over the temperature range of 892–1150 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via two competitive unimolecular channels, one to yield ethylene and vinyl chloride and the other to yield 1,3‐butadiene and hydrogen chloride, with the latter being the major reaction under the experimental conditions. With the usual assumption that gas‐wall collisions are «strong,» RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters given by log k1(sec−1) = (14.8 ± 0.3) − (61.1 ± 1.0)/Θ for vinyl chloride formation and log k2(sec−1) = (13.6 ± 0.3) − (55.7 ± 1.0)/Θ for 1,3‐butadiene formation, where Θ = 2.303 RT kcal/mol. The A factors were assigned from previous high‐pressure low‐temperature data of other workers assuming a four‐center transition state for 1,2‐HCl elimination and a chlorine‐bridged biradical transition state for vinyl chloride formation. The activation energies are in good agreement with the high‐pressure results which were obtained with a conventional static system. The difference in critical energies is 4.6 kcal/mol.
Pressure saturation of SO2(3B1 0,0,0) lifetimes
Authors: Wampler Fred B. , Oldenborg Richard C. , Rice Walter W.
Published: January 2005

Lifetime data have been obtained for the decay of SO2(3B1 0,0,0) at 25°C over the pressure range of 1–762 torr. The 3B1 state was populated by direct absorption to eliminate any possible complications in interpretation due to the participation of excited‐singlet manifolds. At pressures greater than about 10 torr, the measured lifetimes are longer than predicted from low‐pressure Stern–Volmer parameters. This deviation can be interpreted in terms of Freed's theory on collisionally induced intersystem crossing and provides unequivocal evidence to support earlier speculations that the lengthening of the lifetimes at high pressures is due to saturation in depopulation of the 3B1 state.
Kinetics of oxidation of some amino acids by KMNO4 in a moderately concentrated H2SO4 medium in the presence and absence of Ag+
Authors: Surender Rao V. , Sethuram B. , Navaneeth Rao T.
Published: January 2005

The kinetics of oxidation of glycine, alanine, phenylalanine, serine threonine, aspartic, and glutamic acid by acid permanganate were investigated to elucidate the mechanism of the reactions. The rate law was found to be

The reactions were found to be acid catalyzed, and the kinetic data indicate the participation of the water molecules in the rate‐determining step as a proton‐abstracting agent from the substrate, as per Bunnett's hypothesis. As Ag+ was found to catalyze these reactions, the oxidation of glycine and glutamic acid was studied, and the rate law was found to be

A probable mechanism consistent with the observed results is discussed.
Evidence for production of the hydroxycarbonyl radical in the decomposition of formic acid on platinum
Authors: Tevault D. E. , Lin M. C. , Umstead M. E. , Smardzewski R. R.
Published: January 2005

Formic acid molecules highly diluted in argon were passed through a clean platinum screen at 420–730 K and condensed onto an 8‐K CsI window. The well‐known decomposition products, CO2, CO, and H2O, were observed in the infrared spectra of the resulting matrices. In addition, new absorptions which are attributed to the OCOH free radical were also observed. Experiments with partially deuterated formic acids confirmed that the carbon‐hydrogen bond of the formic acid was lost in the formation of the new intermediate species. The activation energy for CO2 production, Ea = 3.5 ± 0.2 kcal/mol, was determined by monitoring its appearance rate at several different catalyst temperatures.
The reactions of methyl radicals with chloromethanes
Authors: Macken Kenneth V. , Sidebottom Howard W.
Published: January 2005

The reaction of methyl radicals with CCl4 and CCl3Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di‐tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH3CCl3, formed via the combination of methyl and trichloromethyl radicals.

From these investigations Arrhenius parameters for the reactions
equation image
have been determined:

Pyrolysis of dtBP in the presence of relatively high‐pressure mixtures of CCl4 and CCl3Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C2Cl6, and the HCl precursor CH3CCl3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high‐pressure mixtures of CCl3Br and a chloromethane. Arrhenius parameters were obtained for the reactions
equation image
and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.
Very‐low‐pressure pyrolysis (VLPP) of group IV (A) tetramethyls: Neopentane and tetramethyltin
Authors: Baldwin Alan C. , Lewis Karan E. , Golden David M.
Published: January 2005

The decomposition of neopentane was studied using the very‐low‐pressure pyrolysis (VLPP) technique at temperatures from 1000 to 1260 K. The derived Arrhenius parameters

are consistent with δHf0(t‐butyl) = 8.4 kcal/mol. Using the above A factor, data on the decomposition of tetramethyltin yield DH0(Sn(CH3)3 ‐ CH3) = 69 ± 2 kcal/mol.
Effect of substituents in the gas‐phase elimination kinetics of β‐substituted ethyl acetates
Authors: Chuchani Gabriel , Martin Ignacio , Avila Irama
Published: January 2005

The kinetics of gas‐phase elimination of 3‐methyl‐1‐butyl acetate and 3,3‐dimethyl‐1‐butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360–420°C and the pressure range of 63–250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first‐order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation

3‐methyl‐1‐butyl acetate:

3,3‐dimethyl‐1‐butyl acetate:

The points in a plot of log (k/k0) of β‐alkyl and several β‐substituted ethyl acetates against Es values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.
Bimolecular self‐reactions of 2‐arylindandione‐ 1,3‐yl radicals studied by flash photolysis
Authors: Khudyakov I. V. , Yasmenko A. I. , Kuzmin V. A.
Published: January 2005

Kinetic and thermodynamic data for reaction (1) of certain C‐centered aromatic radicals (referred to in this paper by the numbers I to X) in chlorobenzene:
equation image
have been obtained. The k1 values of radicals varied between (1.1 ± 0.2) × 106M−1·sec−1 (radical VIII) and (3.6 ± 0.7) × 109M−1 sec−1 (radical VI) at 20°C. An investigation of the relationship between the recombination rates of radicals I–VIII and X and the solvent viscosity (mixture of toluene and dibutylphthalate, 0.6 < η < 18.4 cP) has shown that the recombination reactions involving radicals I–IV are limited by diffusion in solvents having a viscosity η> 10 cP and are activation reactions in solvents having a viscosity η < 10 cP. The recombination of radicals VIII and IX is an activation reaction, while that of radicals V–VII is diffusion‐controlled in the entire viscosity range. The recombination of radical X is limited, in the viscosity range of 18.4 to 2 cP, by intrusion into the first coordination sphere of the partner, the effect of viscosity on the radical X recombination rate in the specified range being the same as its effect on diffusion‐controlled reactions. The possible reasons of the discrepancies between the experimental fast recombination rate constants and the theoretical values calculated by the Debye–Smoluchowski theory are discussed. The equilibrium constant depends strongly on the nature of the substituent in the phenyl fragment: the substituents which increase unpaired electron delocalization in the radical intensify the dissociation of the respective dimer. Long‐wave absorption bands have been recorded for radicals I–X and their extinction coefficients obtained. Dimers I–V are thermo‐ and photochromic compounds.
Rate constants for the termination of benzyl radicals in solution
Authors: Lehni M. , Schuh H. , Fischer H.
Published: January 2005

The rate constant for the bimolecular combination of benzyl radicals in cyclohexane and toluene is determined as a function of temperature. Further, it is studied in cyclohexane–toluene mixtures of different compositions. In the entire range covered, 9.8 × 108 ⩽ 2kt ⩽ 9.0 × 109M−1·sec−1, the data are very well described by the Smoluchowski equation for a diffusion‐controlled reaction to ground‐state products using a spin statistical factor of 1/4, a temperature‐ and solvent‐independent reaction distance, and the known diffusion coefficient of toluene.
Absolute rate constants for the reaction of bromine atoms with ozone from 234 to 360 K
Authors: Michael J. V. , Payne W. A.
Published: January 2005

The rate constant for the reaction of Br + O3 → BrO + O2 has been measured at four temperatures from 234 to 360 K by the technique of discharge flow coupled with resonance‐fluorescence detection of bromine atoms. The measured rate constants obey the Arrhenius expression k = (9.45 ± 2.48) × 10−12 exp(‐659 ± 64/T) cm3/molec·sec (one standard deviation). The results are compared with two previous studies, one of which utilized the flash‐photolysis–resonance‐fluorescence technique and the other utilized the discharge‐flow–mass‐spectrometric technique. The result is also discussed from a theoretical point of view.
Kinetics and mechanism of palladium (II) chloride catalyzed oxidation of allyl alcohol by potassium hexacyanoferrate (III)
Authors: Ahmad Iftikhar , Muhammad ashraf C.
Published: January 2005

A kinetic study of the oxidation of allyl alcohol by potassium hexacyanoferrate (III) in the presence of palladium (II) chloride is reported. The reaction was observed by measuring the disappearance of the potassium hexacyanoferrate (III) spectrophotometrically. The reaction is first order with respect to allyl alcohol and palladium (II) chloride, inverse second order with respect to [Cl−], and zero order with respect to potassium hexacyanoferrate (III). The rate is found to increase linearly with hydroxyl ion concentration.
The reaction of CH3O2 with SO2
Authors: Sanhueza Eugenio , Simonaitis R. , Heicklen Julian
Published: January 2005

Mixtures of Cl2, CH4, and O2 were flash photolyzed at room temperature and pressures of ∽60–760 Torr to produce CH3O2. The CH3O2 radicals decay by the second‐order process
equation image
with k6 = (3.7 ± 0.3) × 10−13 cm3/sec in good agreement with other studies. This value ignores any removal by secondary radicals produced as a result of reaction (6), and therefore the true value might be as much as 30% lower. The value is independent of total pressure or the presence of H2O vapor. With SO2 also present, the CH3O2 decay becomes pseudo first order at sufficiently high SO2 pressure which indicates the reaction
equation image
The value of (8.2 ± 0.5) × 10−15 cm3/sec at about 1 atm total pressure (mostly CH4) was found for CH3O2 removal by SO2, in good agreement with another recent measurement. This value can be equated with k1, unless the products rapidly remove another CH3O2 radical, in which case k1 would be a factor of 2 smaller.
Kinetic flash spectroscopic study of the CH3O2CH3O2 and CH3O2SO2 reactions
Authors: Kan Charles S. , McQuigg Robert D. , Whitbeck Michael R. , Calvert Jack G.
Published: January 2005

Methylperoxy radicals were generated by the flash photolysis of azomethane–oxygen mixtures. The observed broadband spectrum of the CH3O2 radical is similar, but not identical to those reported previously. The CH3O2 decay followed second‐order kinetics at high CH3O2 concentrations with k4' = (2.5 ± 0.3) × 108 liter/mol·sec (23 ± 2°C); 2CH3O2 → products (4). Because of the potential loss of CH3O2 through the reactions with HO2 and CH3O radicals subsequently formed in this system, simulations suggest that the true k4 is in the range: 2.5 × 108 ≥ k4 ≥ 2.3 × 108 liter/mol·sec. Deviations from linearity of the plot of the reciprocal of the CH3O2 absorbance versus time were seen at long times and were attributed to the reaction (5) with an apparent rate constant k5' ⋍ (1.6 ± 0.4) × 105 liter/mol·sec; CH3O2 + Me2N2 → product (5). The CH3O2–SO2 reaction, CH3O2 + SO2 → products (16), was studied by observing CH3O2 decay in flashed mixtures of Me2N2, O2, and SO2. The results gave the apparent second‐order rate constant k16' ⋍ (6.4 ± 1.4) × 106 liter/mol·sec. It appears likely that each occurrence of reaction (5) and (16) is followed by the loss of an additional CH3O2 radical and that k5 ⋍ k5'/2 and k16 ⋍ k16'/2. Our findings suggest that a significant fraction of the SO2 oxidation in a sunlight‐irradiated NOx−RH‐polluted atmosphere, may occur by reaction with CH3O2 as well as from the HO and HO2 reactions.
Kinetics of the thermal decomposition of bis‐pentafluorosulfur trioxide(SF5O3SF5) in the presence of carbon monoxide
Authors: Czarnowski J. , Schumacher H. J.
Published: January 2005

The thermal decomposition of SF5O3SF5 in the presence of CO has been investigated between ‐9.8°C and + 9.9°C. Besides traces of S2F10, equimolecular amounts of SF5O2SF5 and CO2 are formed.

The reaction is homogeneous. Its rate is proportional to the pressure of the trioxide and in dependent of the total pressure, the pressure of inert gases and of carbon monoxide:

where k = k1∞ = 1016.32±0.40 exp(−25,300 ± 500 cal)/RT sec−1. Consequently,

In the presence of oxygen a sensitized CO2 formation is observed. A mechanism is given which explains the experimental results.
Pyrolytic production of Se (3P) from carbon diselenide. II. Rate of CSe2decay
Authors: Belford R. L. , Marquart J. R. , Fraenkel H. A. , Cross A. J. , Lenhardt T. M. , Wei G. J.
Published: January 2005

Pyrolytic decay of carbon diselenide was monitored by ultraviolet absorption spectroscopy in reflected shock waves in the temperature range of 1600–2600°K. The temperature dependence of the absorption coefficient of CSe2at 2308 Å was determined and was used to provide kinetic information along with a deconvolution procedure which accounted for and removed systematic distortions of the fast time‐resolved absorbance profile. For temperatures of 1600–2600°K and argon densities of 1.5–7.0 × 10−5mol/cm3dilute (1.0–9.0 × 10−9mol/cm3) CSe2pyrolyzed with measured first‐order decay rates in the range of log10k1(sec−1) = 3.0−5.7; at midrange (2100°K and 4.3 × 10−5mol/cm3in Ar)k1≈ 3 × 104sec−1. The decay probably occurs via a unimolecular low‐pressure process, first order in both CSe2and Ar, for whichk2± 109cm3/mol·sec at 2100°K. The deconvoluted data yield Arrhenius activation energies of 53.2 kcal/mol under second‐order treatment, but the activation energy is less reliable than the general magnitude of the rate constant. A comparison of CSe2with other molecules which are isoelectronic in their valence shells (CO2, CS2, OCS, and N2O) is made.
Kinetics of the thermal dimerization and isomerization of cis, trans‐1,5‐cyclooctadiene in the gas phase and of related reactions. A simple algorithm to determine the rate constants of competing first‐ and second‐order reactions
Authors: Leitich J.
Published: January 2005

In the gas phase, cis,trans‐1,5‐cyclooctadiene (\documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 1\limits_\sim} $\end{document}) undergoes a unimolecular rearrangement to cis,cis‐1,5‐cyclooctadiene (\documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 2\limits_\sim} $\end{document}) and bimolecular formation of dimers \documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 3\limits_\sim}-{\mathop 5\limits_\sim} $\end{document} $\end{document}. The Arrhenius parameters are EA = 135.7 ± 4.4 kJ mole−1 and log(A/sec−1) = 12.9 ± 0.6 for the first reaction and EA = 66.1 ± 6.0 kJ mole−1 and log[A/(liter mole−1 sec−1)] = 5.5 ± 0.8 for the second reaction. Using thermochemical kinetics, the first reaction is shown to proceed via a rate determining Cope rearrangement of \documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 1\limits_\sim} $\end{document} to cis1,2‐divinylcyclobutane (\documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 6\limits_\sim} $\end{document}), EA = 136.2 ‐ 4.4 kJ mole−1 and log(A/sec−1) = 13.0 ± 0.6. The corresponding back reaction, \documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 6\limits_\sim}{\rightarrow}{\mathop 1\limits_\sim} $\end{document}, which was investigated separately, shows EA = 110.2 ± 1.2 kJ mole−1 and log(A/sec−1) = 10.9 ± 0.2. The heat of formation of \documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 6\limits_\sim} $\end{document} is determined to 188 ± 5.5 kJ mole−1. The mechanism of formation of dimers \documentclass{article}\pagestyle{empty}\begin{document}$ {\mathop 3\limits_\sim}-{\mathop 5\limits_\sim} $\end{document} is discussed. To allow the formal analysis of the kinetic problem, a simple algorithm to obtain the rate constants of competing first‐ and second‐order reactions was developed.
The vacuum UV photolysis of various C4 and C5 olefins: The energy content of the α‐ and β‐methallyl fragments
Authors: Collin Guy J. , Deslauriers Hélène
Published: January 2005

In recent publications from this laboratory, we have shown that the fragmentation of photoexcited olefinic molecules in the vacuum UV region leads mainly to the cleavage of a C—C bond located in the ß position relative to the double bond. The allyl fragment bears away part of the excess energy of the photon. At low pressure, this excited radical is capable of undergoing further decomposition. From the pressure effect, we were able to measure the first order rate constant for this secondary fragmentation. In this paper we shall use RRKM calculations in order to get a better idea on how the energy is distributed among the primary fragments. In cases where α‐ and β;‐methallyl radicals were involved, the results show that an important part of the excess energy is located in the methallyl fragment in the 7.1 and 7.6 eV photolysis of 3‐methyl‐1‐butene, 2‐methyl‐1‐butene, and cis‐2‐pentene.
A dual‐path sequence of first‐order reactions the protiodeacylation of acetylpropionylmesitylene
Authors: Gore Peter H. , Nassar Ahmed M. G. , Waters David N. , Moxon Gerry F.
Published: January 2005

An example of a sequence of competing first‐order reactions, leading to a common product, has been found for the sulfodeacylation of acetylpropionylmesitylene. The basic reaction scheme is Scheme l
equation image
and a kinetic analysis of the component rate constants allows an estimate to be made of the concentrations of the reactant and products as a function of time. In the present system the total concentration of the intermediates B, C, and D never exceeds 0.26% at 25°C, and therefore the kinetics, which were followed spectrophotometrically, were essentially of the conversion of substrate A to the final product E.

The kinetics of protiodeacylation have been measured, over a range of temperatures, of propionyl‐, dipropionyl‐, and acetylpropionylmesitylenes in 89.8% (w/w) sulfuric acid.