bluuebunny/crossref_metadata_2025_split huggingface dataset:
Disproportionation‐to‐combination ratios for cyclohexyl‐h11 and ‐d11 radicals in the gas phase as determined by the radiolysis of water vapor–cyclohexane mixtures
Authors: Fujisaki Noboru , Gäumann Tino 
Published: January 2005

AbstractIn the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70–200°C), total pressures (50–2400 torr), and total doses (0.15–2.0 Mrad). The disproportionation–combination ratio k/k for c‐C6H11 radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c‐C6D12, the ratio k/k for c‐C6D11 radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C6H11 and C6D11 radicals leads to (k)/(k)/(k/k) = 1.47 ± 0.02. The corresponding values for the reactions of c‐C6H11 with c‐C6D11 were also determined.
Bimolecular self‐reactions of phenyl‐substituted phenoxyl radicals studied by flash photolysis
Authors: Khudyakov I. V. , Levin P. P. , Kuzmin V. A. , De Jonge C. R. H. I. 
Published: January 2005

AbstractRate, equilibrium, and thermodynamic data for reaction (1) of 2,6‐diphenyl‐4R‐phenoxyl radicals, where R==OCH3 (I), Ph (II), OC2H5 (III), O‐n‐C18H37 (IV), and 2,6‐dicyclohexyl‐4‐phenylphenoxyl radical (V),
equation image
in various solvents are obtained. The k1 values of radicals I to V are within (5.5 ± 1.0) × 107‐(1.4 ± 0.3) × 109M−1·sec−1 in propanol. The solvent effect on k1 for radicals I and II was studied. The dimerization of radical I is diffusion‐controlled in all solvent studies. The dimerization of radical II is viscosity‐dependent but not diffusion‐controlled. Plots of k1 against ET have a V shape. Specific solvent–solute interactions are seeming to be responsible for numerical k1 values of radicals I and II. The solvent effect is more pronounced for “slow” dimerization of radicals II than for “fast” dimerization of radicals I. The minimum k1 values correspond to pyridine and chloroform. The reaction (1) rate strongly depends upon the composition of a chloroform (S)–cosolvent binary mixture. Besides reaction (1) the following reactions proceed in binary mixture:
equation image

(radical I, S‐CCL4 mixture)

(radical II, S‐C6H14 mixture)

(radical II, S‐CCL4 mixture)In all cases k16 ≪ k15. Factors influencing dimerization rates in strongly nonideal mixtures CH3OH‐CCL4 and CH3OH‐CHCl3 are discussed.
Anionic σ‐complexes from sulfite ion attack on n‐methyl‐N‐β‐hydroxyethyl picramide and its spiro complex. Search for geometric isomerism in 1:2 complexes. An instructive example of complex kinetics
Authors: Bernasconi Claude F. , Wang Hsien‐Chang 
Published: January 2005

AbstractN‐Methyl‐N‐β‐hydroxyethyl picramide (PH) forms a 1:1 (PHS2−) and a 1:2 (PHS) anionic σ‐complex with sulfite ion. In alkaline solution PH is present mainly in the form of its spiro Meisenheimer complex (M−) which also adds sulfite ion to form a complex MS3−. Rate and equilibrium constants for the various reactions which interrelate the five species PH, PHS2−, PHS, M−, and MS3− (scheme I) were determined. PHS and MS3− can, in principle, exist in the form of two geometric isomers. Despite a careful search by nuclear magnetic resonance and kinetic techniques, no experimental manifestation of this isomerism could be found. Various limiting situations are discussed under which the absence of experimental evidence does or does not exclude the presence of two isomers. Our preferred but unproven interpretation is that in the case of PHS one isomer (trans?) is thermodynamically strongly favored over the other, whereas in the case of MS3− both isomers are of similar thermodynamic stability and have also similar rates. This latter feature would make the isomerism kinetically undetectable. Several other features of scheme I make it an instructive example in complex chemical kinetics.
Study of the reactions of oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro‐1,3‐dithietane
Authors: Slagle Irene R. , Gutman David 
Published: January 2005

AbstractThe reactions of ground‐state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro‐1,3‐dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast‐flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants are𝔨(O + C2CS) =(3.09 ± 0.54) × 10−11 exp(+115 ± 106 cal/mol/RT),𝔨(O + F2CS) = (1.22 ± 0.19) × 10−11 exp(‐747 ± 95 cal/mol/RT), and𝔨(O + F4C2S2) = (2.36 ± 0.52) × 10−11 exp(‐1700 ± 128 cal/mol/RT) cm3/molec˙sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy‐rich adduct which then decomposes by C‐S bond cleavage.
Kinetic study of some elementary reactions of sulfur compounds including reactions of S and SO with OH radicals
Authors: Jourdain J. L. , Bras G. Le , Combourieu J. 
Published: January 2005

AbstractThe reactions of S + OH → SO + H (1) and SO + OH → SO2 + H (2) were studied in a discharge flow reactor coupled to an EPR spectrometer. The rate constants obtained under the pseudo‐first‐order conditions with an excess of S or SO were found to be k1 = (6.6 ± 1.4) × 10−11 and k2 = (8.4 ± 1.5) × 10−11 at room temperature. Units are cm3/molec·sec. Besides no reactivity was observed between S and CO2 at 298 K and between CIO and SO2 up to 711 K.
Kinetics of iodination of hydrogen sulfide by iodine and the heat of formation of the SH radical
Authors: Hwang R. J. , Benson S. W. 
Published: January 2005

AbstractThe kinetics of the gas‐phase thermal iodination of hydrogen sulfide by I2 to yield HSI and HI has been investigated in the temperature range 555–595 K. The reaction was found to proceed through an I atom and radical chain mechanism. Analysis of the kinetic data yields log k (l/mol·sec) = (11.1 ± 0.18) – (20.5 ± 0.44)/θ, where θ = 2.303 RT, in kcal/mol. Combining this result with the assumption E−1 = 1 ± 1 kcal/mol and known values for the heat of formation of H2S, I2, and HI, ΔHf,2980(SH) = 33.6 ± 1.1 kcal/mol is obtained. Then one can calculate the dissociation energy of the HSH bond as 90.5 ± 1.1 kcal/mol with the well‐known values for ΔHf,2980 of H and H2S.
Photosensitized decomposition of hydrocarbons by infrared‐laser‐induced energy transfers
Authors: Pazendeh H. , Marsal C. , Lempereur F. , de Maleissye J. Tardieu 
Published: January 2005

AbstractUsing the technique of CO2 laser photosensitized decomposition, ethane and propane decomposition was investigated in relation to energy transfer from an SF6 photosensitizer to the hydrocarbon. The end products appearing in the course of irradiation are similar to those formed during classical thermal pyrolysis. The energy transfer from SF6 to the hydrocarbon is closely related to hydrocarbon decomposition. A similar overall kinetic behavior for the two alcanes allows the use of a general diffusional kinetic treatment, provided pressure, intensity, and duration of irradiation are well defined.
The detailed mechanism of the Dushman reaction explored by computer
Authors: Liebhafsky Herman A. , Roe Glenn M. 
Published: January 2005

AbstractSince 1926 investigations of the Dushman reaction have relied mainly upon “constant‐rate” measurements, usually by instrumental methods. Since about that time, the confusion surrounding this venerable reaction has been growing. In part, the confusion arises because the reaction involves reactive intermediate species that have not been studied directly—and may never be. Alternative detailed mechanisms have been assumed with little restraint. One of these, which is built around H2I2O3, has been explored by computer with promising results. The mechanism seems capable of reducing the confusion now attending the Dushman reaction and others related to it.
A model for explosions during carbon monoxide oxidation
Authors: Pilling M. J. , Noyes R. M. 
Published: January 2005

AbstractDuring the oxidation of carbon monoxide containing a trace of water, ten well‐known atomic and molecular species can be identified as of potential significance. All conceivable reactions of these species in their ground electronic states were considered, and rate constants for all those that are of potential importance are either known or can be estimated with considerable confidence. For compositions and temperatures of experimental interest an isothermal system goes to a single steady state that is stable to perturbation and will neither explode nor oscillate. These steady‐state computations also predict that as the temperature is raised above about 1000 K most of the water is converted to H, OH, and HO2 radicals. Under such conditions, exothermic reactions would be so rapid that strong thermal gradients would develop in any real system of plausible dimensions. A simple model based on these calculations predicts explosion limits consistent with those observed experimentally. Simultaneous behavior in time and in space must be calculated in detail before it is clear whether or not this model based on ground electronic states can model the oscillations that are sometimes observed in this system.
The kinetics of the interaction of peroxy radicals. II. Primary and secondary alkyl peroxy
Authors: Nangia Prakash S. , Benson Sidney W. 
Published: January 2005

AbstractA chain mechanism is proposed to account for the very rapid termination reactions observed between alkyl peroxy radicals containing α‐C—H bonds which are from 104 to 106 faster than the termination of tertiary alkyl peroxy radicals. The new mechanism is
equation image
with termination by
equation image
. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\overline {{\rm CHOO}} $\end{document} is the zwitterion originally postulated by Criegee to account for the chemistry of O3‐olefin addition. Heats of formation are estimated for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {{\rm CH}_2 {\rm OO,}} {\rm }\overline {{\rm RCHOO}} $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ ({\rm C}\overline {{\rm H}_3 )_2 {\rm COO}} $\end{document} and it is shown that all steps in the mechanism are exothermic. The second step can account for (1Δ)O2 which has been observed. k1 is estimated to be 109–2/θ liter/M sec where θ = 2.303RT in kcal/mole. The second and third steps constitute a chain termination process where chain length is estimated at from 2 to 10. This mechanism for the first time accounts for minor products such as acid and ROOH found in termination reactions. Trioxide (step 3) is shown to be important below 30°C or in very short time observations (<10 s at 30°C). Solvent effects are also shown to be compatible with the new mechanism.
Demetallation of α,β,γ,δ‐tetrakis(p‐sulfophenyl) porphiniron(III) in mineral acid–alcohol–water media
Authors: Reynolds Warren L. , Kooda Kevin , Florine Brent , Johnson Nancy , Thielman Kenneth 
Published: January 2005

AbstractDemetallation rates of α,β,γ,δ‐tetrakis(p‐sulfophenyl)porphiniron(III) in hydrochloric acid–ethanol–water, perchloric acid–ethanol–water, and sulfuric acid–alcohol–water media were determined. For a given acidity value H0 the order of the rates for the three acids was HCl > H2SO4 > HClO4. This is also the order for complex formation between acid anion and iron(III). Consequently ligands as well as protons are involved in the breaking of bonds between the metal and the porphyrin leading to the formation of the activated complex. The log k values for HCl and HClO4 media were not linearly related to the Hammett acidity function as they were for sulfuric acid–ethanol–water media. The average ΔH‡ and ΔS‡values for the HCl media were 18.4 ± 1.4 kcal/mol and 19 ± 3 cal K mol, respectively, in very close agreement with those for H2SO4 media despite the difference in H 0 dependence. For H2SO4–alcohol–water media the order of the rates was butanol > propanol > ethanol with little difference between isomeric alcohols.
Thermal decomposition of 2,2‐propane‐d2. CH3CDCH3 radical isomerization
Authors: Szirovicza L. , Sziláagyi I. 
Published: January 2005

AbstractThe decomposition of CH3CD2CH3 was studied from 713 to 853 K at pressures of 98–466 torr. The values of k1/k2 = 2.08 ± 0.05 and k3/k4 = 2.04 ± 0.66 were found independent of temperature by measuring the ratios of CH4/CH3D and CH3CHD2/CH3CD3, respectively, for the following reactions:
equation image
. Isomerization of CH3CDCH3 was detected by measuring CHDCH2 formed from the isomerized radical. The expression of k21/k22 was found to be
equation image
where k21 and k22 are the rate constants of
equation image
. The results and conclusions are discussed and compared with previous works.
Effect of solvent viscosity on the kinetics of reversible dimerization of phenoxy radicals
Authors: Levin P. P. , Khudyakov I. V. , Kuzmin V. A. 
Published: January 2005

AbstractFlash photolysis technique has been used to obtain the rate and thermodynamic parameters of the reversible dimerization reactions of a range of ten phenoxy radicals (I–X) in a toluene–dibutylphthalate mixture (0.6 cP ≤η≤18.4 cP):

The main reason for the difference in the k1 values are the different steric hindrances in radicals. It has been found that the values of k1 for 2,6‐diphenyl‐4‐methoxy‐ (I), 2‐phenyl‐(III), and 2‐methoxyphenoxy (IV) radicals are 3–5 times smaller than the respective diffusion constants calculated according to the Debye formula with regard to the spin‐statistical factor:

The resultant ΔH1≠values for these radicals in toluene and dibutylphthalate are close to the activation energies of the viscous flow of the solvents B. Linear relationships with a slope equal to unity are observed between log k1 and log(T/η). The recombination of radicals I, III, and IV is limited by translational diffusion. The k1 values for 2,6‐diphenyl‐ (VII), 2,6‐di‐tert‐butyl‐ (IX), and 2,6‐di‐tert‐butyl‐4‐methylphenoxy (X) radicals are 10–60 times smaller than kdiff and Δ H≠ B. In the case of radical X in toluene ΔH1≠ 0. The recombination of these three radicals includes an intermediate step of complex formation:

For 4‐phenyl‐ (II), 2,6‐ dimethoxy‐ (V), 2,4‐diphenyl‐ (VI), and radicals VII, IX, and X the linear relationships between log k1 and log (T/η) have a slope of from 0.5 ± 0.05 to 0.8 ± 0.05. The k1‐1 versus η relationships for these radicals are not straight lines. The recombination of these six radicals is limited by translational and rotational diffusion. With the aid of theoretical models, the k1 versus η relationships have been used to derive the steric factor f in radical recombination and the angle θ between the axis and the solid angle generatrix. The solid angle defines the reaction spot on the radical‐sphere surface. The recombination of the 2,6‐diphenyl‐4‐diphenylmethylphenoxy radical (VIII) takes place in the region intermediate between the diffusion and the kinetic ones, and the relationship between log k1 and log (T/η) for this radical has a plateau portion. The log k‐1 versus log (T/η) relationships have precisely the same form as the corresponding k1 relationships, which is quite in line with the theory of diffusion‐controlled reversible recombination reactions.
Liquid‐phase oxidation of isobutane—a reanalysis of the data
Authors: Nangia Prakash S. , Benson Sidney W. 
Published: January 2005

AbstractData on the liquid‐phase oxidation of isobutane at 50 and 100°C have been reexamined, using a modified mechanism to take into account the termination by isobutylperoxy radicals. Algebraic expressions are derived from steady‐state methods. Using Arrhenius parameters fitted by transition‐state A factors and activation energies derived from observed “best” rate constants, new sets of parameters are derived for the rate constants for propagation by tBuO2 + tBuH → t‐BuO2H + tBu⋅:

where θ = 2.303RT in kcal/mol. This, together with new values for the termination parameters and rates of i‐butyl production by k4B, is shown to give good agreement with the published data. An important reaction:

is shown to quench the possible contributions to termination of adventitious radicals such as CH3O⋅2.
The rate constant for combination of a CCl3 radical with cyclohexyl or n‐hexyl radicals. An evidence for the value of the rate constant for a Cl atom transfer
Authors: Alfassi Zeev B. 
Published: January 2005

AbstractThe variation of the radiolytic yield of hexachloroethane in the system alkane + carbon tetrachloride can be used to measure the rate constant for the combination of a CCl3 radical with an alkyl radical. The treatment of the data for hexane and cyclohexane shows that the rate for a Cl atom transfer must be lower than the high values of Katz et al. and Tuan et al.
Kinetics of oxidation of organic compounds by silver(II) in aqueous perchloric acid solution. IV. Aliphatic alcohols
Authors: Baiocchi Claudio , Mentasti Edoardo 
Published: January 2005

AbstractThe kinetics and mechanism of the silver(II) oxidation of methanol, ethanol, 1‐propanol, 1‐methyl‐ ethanol, 1‐butanol, 2‐methyl‐1‐propanol, 2‐butanol, 2‐methyl‐2‐propanol, D4‐methanol, and D6‐methanol have been investigated at 8.0 and 20.0°C in aqueous perchloric acid media (1.00 ≤ [HClO4] ≤ 4.00M; μ = 4.0M). The kinetics were monitored by following the disappearance of Ag(II) with a spectrophotometric stopped‐flow technique. The reactions are first order in each reactant and involve both Ag2+ and AgOH+ species. No kinetic or spectroscopic evidence for complex formation between reactants was obtained. The results are discussed with reference to electron density on the OH or αC‐H substrate sites and to the isotopic hydrogen/deuterium rate quotients found for methanol and ethanol.
Gas phase thermolysis of sulfur compounds. II. Ditertiary butyl sulfide
Authors: Martin Gonzalo , Barroeta Nestor 
Published: January 2005

AbstractThe pyrolysis of di‐tert‐butyl sulfide has been investigated in static and stirred‐flow systems at subambient pressures. The rate of consumption of the sulfide was measured in some experiments, and the rate of pressure increase was followed in others. The results suggest that the reaction is essentially homogeneous in a seasoned reactor and proceeds through a free radical mechanism. In the initial stages, the decomposition rate follows first‐order kinetics, and the rate coefficient in the absence of an inhibitor is given by

between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately

between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately.
Direct determination of the rate constant of the reaction NO + HO2 → NO2 + OH with the LMR
Authors: Hack W. , Preuss A. W. , Temps F. , Wagner H. Gg. , Hoyermann K. 
Published: January 2005

AbstractThe rate of the reaction
equation image
was determined in an isothermal discharge flow reactor with a combined ESR–LMR detection under pseudo‐first‐order conditions in HO2. The rate constant was identical in experiments with two different HO2 sources: F + H2O2 and H + O2 + M. The absolute rate constant at T = 293 K was measured as

In the range 2 ≤ p mbar ≤ 17 no pressure dependence for k1 was found.
Kinetics of oxidation of benzyl alcohol by sodium N‐chloro‐p‐toluenesulfonamide
Authors: Uma K. V. , Mayanna S. M. 
Published: January 2005

AbstractThe kinetics of oxidation of benzyl alcohol and substituted benzyl alcohols by sodium N‐chloro‐p‐toluenesulfonamide (chloramine‐T, CAT) in HClO4 (0.1–1 mol/dm3) containing Cl− ions, over the temperature range of 30–50°C have been studied. The reaction is of first order each with respect to alcohol and oxidant. The fractional order dependence of the rate on the concentrations of H+ and Cl− suggests a complex formation between RNCl− and HCl. In higher acidic chloride solution the rate of reaction is proportional to the concentrations of both H+ and Cl7hyphen;. The observed solvent isotope effect (k/k) is 1.43 at 30°C. The reaction constant (p = −1.66) and thermodynamic parameters are evaluated. Rate expressions and probable mechanisms for the observed kinetics have been suggested.
Studies of the photochemical reactions of sulfur dioxide with pentane in the presence of nitrogen oxide
Authors: Makarov V. I. , Skubnevskaya G. I. , Bazhin N. M. 
Published: January 2005

AbstractThe spectrum of the intermediate product ascribed to nitrosopentane has been detected in the photolysis of the SO2–pentane (RH)–NO mixture. This result has been interpreted in terms of the radical mechanism by assuming the H‐atom abstraction from RH by the excited SO2 molecules to be the primary act. The contribution of the singlet and triplet SO2 states to the product formation rate and the ratio of the singlet‐to‐triplet rate constants have been evaluated. At NO pressures above 5 torr, the product formation rate significantly deviates from the Stern–Volmer dependence.
Very low‐pressure pyrolysis (VLPP) of pentynes. II. 4‐methylpent‐2‐yne and 4,4‐dimethylpent‐2‐yne. Heats of formation and resonance stabilization energies of methyl‐substituted propargyl radicals
Authors: King Keith D. , Nguyen Tam T. 
Published: January 2005

AbstractStudies of the unimolecular decomposition of 4‐methylpent‐2‐yne (M2P) and 4,4‐dimethylpent‐2‐yne (DM2P) have been carried out over the temperature range of 903–1246 K using the technique of very‐low pressure pyrolysis (VLPP). The primary reaction for both compounds is fission of the CC bond adjacent to the acetylenic group producing the resonance‐stabilized methyl‐substituted propargyl radicals, CH3CĊH(CH3) from M2P and CH3CCĊ(CH3)2 from DM2P. RRKM calculations were performed in conjunction with both vibrational and hindered rotational models for the transition state. Employing the usual assumption of unit efficiency for gas‐wall collisions, the results show that only the rotational model with a temperature‐dependent hindrance parameter gives a proper fit to the VLPP data over the entire experimental temperature range. The high‐pressure Arrhenius parameters at 1100 K are given by the rate expressions log k2 (sec−1) = (16.2 ± 0.3) − (74.4 ± 1.5)/θ for M2P and log k3 (sec−1) = (16.4 ± 0.3) − (71.4 ± 1.5)/θ for DM2P where θ = 2.303RT kcal/mol. The A factors were assigned from the results of recent shock‐tube studies of related alkynes. Inclusion of a decrease in gas‐wall collision efficiency with temperature would lower both activation energies by ∼1 kcal/mol. The critical energies together with the assumption of zero activation energy for recombination of the product radicals at 0 K lead to DH0[CH3CCCH(CH3)CH3] = 76.7 ± 1.5, ΔHf0[CH3CCCH(CH3)] = 65.2 ± 2.3, DH0[CH3CCCH(CH3)H] = 87.3 ± 2.7, DH0[CH3CCC(CH3)2CH3] = 72.5 ± 1.5, ΔH[CH3CCĊ(CH3)2] = 53.0 ± 2.3, and DH0[CH3CCC(CH3)2H] = 82.3 ± 2.7, where all quantities are in kcal/mol at 300 K. The resonance stabilization energies of the 1,3‐dimethylpropargyl and 1,1,3‐trimethylpropargyl radicals are 7.7 ± 2.9 and 9.7 ± 2.9 kcal/mol at 300 K. Comparison with results obtained previously for other propargylic radicals indicates that methyl substituents on both the radical center and the terminal carbon atom have little effect on the propargyl resonance energy.