bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Using 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

Since 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

During 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

A 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

Demetallation 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

The 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

Flash 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

Data 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

The 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

The 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

The 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

The 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

The 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

The 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

Studies 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.
Studies on the effect of the cation nature on the kinetics of the isotopic exchange reaction between chloride ion and O,O‐diphenylphosphorochloridothionate in acetonitrile
Authors: Reimschüssel W. , Tilk S. , Mikołajczyk M. , Ślebocka‐tilk H.
Published: January 2005

Rate constants and activation parameters for the isotopic exchange reactions between (PhO)2PSCl and M36Cl (M = Me4N+, Et4N+, n‐Bu4N+, Et3HN+, EtH3N+, Li+) in acetonitrile were measured in order to find the effect of the cation nature onthe kinetics of the reaction. The rate constants measured for a range of concentrations of Et3HN36Cl, EtH3N36Cl, and Li36Cl were analyzed using the Acree equation. The equivalent conductance of LiCl in acetonitrile was determined. The nature of the cation has no effect on the mechanism of the reaction. The cation changes only the experimental rate constant proportionally to the dissociation degree of the salt. Smaller values of the rate constant and smaller activation parameters ΔH‡ and ΔS‡ for the reaction with Li36Cl indicate the existenceof the intermolecular interaction between lithium ions and O,O‐diphenylphosphorochloridothionate.
The thermal decomposition of fluorinated esters
Authors: Blake P. G. , Shraydeh B. F.
Published: January 2005

The kinetics of thermal decomposition of ethyl, isopropyl, and t‐butyl trifluoroacetates have been studied in the gas phase. In each case initial decomposition follows the normal ester route to give an olefin and trifluoroacetic acid, and elimination of hydrogen fluoride does not occur. However, trifluoroacetic acid is thermally unstable at ethyl and isopropyl ester decomposition temperatures, and further products result, including those from the difluorocarbene produced by decomposing trifluoroacetic acid. Placing a CF3 group at an ester's γ carbon increases the polarity of its transition state and decreases its thermal stability. The activation energies of the ethyl and isopropyl esters are lowered by 3.8 and 4.7 kcal/mol compared to the corresponding acetates, and the primary decomposition kinetics, which are homogeneous and of the first order, are expressed by
equation image
α‐Methylation enhances the reactivity of the trifluoroacetates, and the t‐butyl ester, the transition state for which is sufficiently polar for heterogeneous decomposition to occur, shows signs of thermal instability at room temperature. The equilibrium
equation image
was also investigated and gave ΔH° = +13,580 cal/mol and ΔS° = +31.07 gibbs/mol in the forward direction. The results obtained extend and support the known structure–rate correlations in the gas‐phase elimination of esters.
Cl‐atom transfer from CFCl3 to the c‐C6H11 radical. An indirect estimation of the CFCl2Cl bond dissociation energy
Authors: Baruch G. , Rajbenbach L. A. , Horowitz A.
Published: January 2005

The Cl‐transfer reaction between CFCl3 and c‐C6H11 radicals (R) was studied in liquid cyclohexane (RH). The Arrhenius parameters for Cl abstraction were determined in the RH‐CFCl3 system versus the termination reaction between cyclohexyl radicals and competitively versus addition to C2Cl4 in the RH‐CFCl3‐C2Cl4 system. The two sets of results are in very good agreement and give the following Arrhenius expression for the reaction R + CFCL3 → RCl + CFCl2 (2):

where θ = 2.303RT in kcal/mol. Comparison with Cl‐transfer data of other chloromethanes and chloroethanes shows that an increase in the CCl bond dissociation energy is the main cause of the reduced reactivity of CFCl3. Based on a previously developed correlation, D(CFCl2  Cl) is estimated to be equal to 74.4 kcal/mol.
The kinetics of radiation induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclanes
Authors: Alfassi Zeev B. , Feldman Liviu
Published: January 2005

The kinetics of gamma‐radiation induced free radicals reactions in carbon tetrachloride solutions of cyclohexane, cyclooctane and cyclododecane were studied in the range of 27–190°C. The activation energies found were in the order cC6H12 > cC12H24 > cC8H16, which was explained as due to their ring strain which has the same order. The following log k1 was obtained using the known Arrhenius parameters for CCl3 radical recombination:
equation image
The correlation of rate coefficients for H‐atom abstraction by HO radicals with CH bond dissociation enthalpies
Authors: Heicklen Julian
Published: January 2005

For H‐atom abstraction reactions by HO radicals it has been shown that
equation image
If Di is taken as the CH bond dissociation enthalpy at 298 K, then a = 0.323 and D0is obtained from the empirical formula

where D0 is in kcal/mol and T is in K. Thisrelationship is valid for T between 200 and 400 K. Finally empiricalrelationships are given to help estimate Di.
The thermal decomposition of 4‐methyl‐3,6‐dihydro‐2H‐pyran
Authors: Frey Henry M. , Watts Hugo P.
Published: January 2005

The thermal decomposition of the title compound has been studied in the gas phase in the temperature range of 584–634 K. The decomposition was found to be a first‐order homogeneous process yielding 2‐methylbuta‐1,3‐diene and formaldehyde. The rate constants obtained at 11 temperatures within the quoted range fitted the Arrhenius equation

The decomposition is probably unimolecular and concerted.
Evidence for chamber‐dependent radical sources: Impact on kinetic computer models for air pollution
Authors: Carter W. P. L. , Atkinson R. , Winer A. M. , Pitts J. N.
Published: January 2005

A series of NOx–air irradiations, with trace amounts of propane and propene present to monitor OH radical concentrations, have been carried out in a 5800‐L evacuable environmental chamber to investigate radical levels and sources during such irradiations. The data obtained show conclusively that unknown radical sources are present, and that photolysis of initial nitrous acid can be, at best, only a minor source of radicals after ∼30–60 min of irradiation.
Thermal reactions of ethane‐d6–acetylene and D2–acetylene mixtures behind shock waves
Authors: Rogers David , Skinner Gordon B.
Published: January 2005

A study of the thermal decomposition of an acetylene–ethane‐d6 mixture indicates that the rate constant for hydrogen abstraction from acetylene by methyl is more than 20 times less than for abstraction from ethane. Isotopic exchange is initiated by a rapid reaction between product D atoms and C2H2. A series of experiments involving the reactions of a D2–acetylene mixture indicated that a molecular exchange process was also occurring, and it was shown that d[C2HD]/dt = k[D2]0.7[C2H2]0.3, effective activation energy = 15.8 kcal/mol. This mechanism made an insignificant contribution to isotope exchange in C2H2–C2D6 mixtures.
Kinetics of the bimolecular initiation process in the thermal reactions of ethylene
Authors: Ayranci G. , Back M. H.
Published: January 2005

The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 750 K have been measured in the presence and absence of the additive butene‐1. It has been shown that this ratio of rates is related to the ratio of rate constants for the two initiation processes:
equation image
The ratio k′1/k1 has been measured over the temperature range of 700–773 K and may be expressed as (R = 1.987 cal/mol deg) log k′1k1(mol/L) = 2.8 − 4400/2.3RT. Assuming a value for k′1 of log k′1 (s−1) = 16 − 71,500/2.3RT, the value of k1 may be expressed as log k1(L/mol) = 13.2 − 67,000/2.3RT. The values for the frequency factor and activation energy for reaction (1) are discussed in relation to the heat of formation of the vinyl radical, and it is concluded that reaction (1) is the main initiation process in the thermal decomposition of ethylene under the present conditions.
The dynamics of formation of vibrationally excited HF in reactions of O (21D2) atoms with partially fluorinated alkanes
Authors: Burks T. L. , Lin M. C.
Published: January 2005

The nascent vibrational energy distributions of the HF† formed in the reactions of a series of partially fluorinated alkanes (RFH; RF = CH2F, CHF2, CF3, C2F5, C3F7, and C7F15) with electronically excited oxygen atoms O(21D2) have been determined by measuring the appearance times of stimulated emissions from various vibration–rotation transitions in a grating‐tuned optical cavity. The vibrational energy contents of the HF formed in these reactions were found to be considerably greater than statistically expected. These reactions are believed to occur via vibrationally excited short‐lived α;‐fluorinated alcohols (RFOH†), formed by insertion of the O(21D2) atoms into CH bonds. The observation of nonstatistical energy partitioning in the above reactions is in clear contrast to the result obtained from the O(21D2) + CF3CH3 reaction that produces the β‐fluorinated alcohol CF3CH2OH, from which the HF product carries a near statistical vibrational energy distribution. A mechanism for HF† formation in these very exothermic reactions is presented.
Kinetic studies of the reaction of C2H5 with O2 at 295 K
Authors: Plumb I. C. , Ryan K. R.
Published: January 2005

The reaction between C2H5 and O2 at 295 K has been studied with a flow reactor sampled by a mass spectrometer. With helium as the carrier gas the rate coefficient was found to increase from (1.2 ± 0.3) × 10−12 to (3.6 ± 0.9) × 10−12 cm3/s as [He] was increased from 2 × 1016 to 3.4 × 1017 cm−3. The importance of
equation image
has been determined from a knowledge of the initial C2H5 concentration together with a measurement of the C2H4 produced in reaction (5). F, the fraction of the C2H5 radicals removed by path (5), was found to decrease from 0.15 to 0.06 as [He] increased from 2 × 1016 to 3.4 × 1017 cm−3. The rate coefficient for reaction (5) was found to be independent of [He] and to have a value of (2.1 ± 0.5) × 10−13 cm3/s. The variation in F reflects the fact that k1b increases as [He] increases. These observations are taken as evidence for a direct mechanism for C2H4 production and a collision‐stabilized route for C2H5O2 formation. Calculations indicate that the high‐pressure limit for reaction (1b) is ∼4.4 × 10−12 cm3/s and that in the polluted troposphere the branching ratio for reactions (1b) and (5) will be ∼l20.
On the kinetics of the transition metal catalyzed decomposition of secondary hydroperoxides
Authors: Hajdu I. P. , Nemes I. , Sümegi L. , Vidóczy T. , Gál D.
Published: January 2005

A general mechanism was proposed for the title reactions which describes the kinetics of hydroperoxide decomposition as well as product accumulation throughout the whole reaction period in an analytical form. The following catalytic steps were included: magnified image where the deactivation takes place as a result of radical–catalyst interaction inside the cage. The resulting equations give satisfactory description of the literature data in the case of various catalysts and hydroperoxides.
The kinetics of propylene oxide reaction with certain alkylamino alcohols in the presence of basic catalysts
Authors: Ślipko Kazimiera , Chlebicki Jan
Published: January 2005

Rate constants for direct reactions of propylene oxide with certain aminoisopropanols in the presence of basic catalysts were studied at a temperature of 363–383 K. This reaction was found to be of the first order in propylene oxide, amino alcohol and catalyst. The observed kinetics are consistent with a termolecular mechanism.
The acetyl radicals CH3CO· and CD3CO· studied by flash photolysis and kinetic spectroscopy
Authors: Adachi Hiroyuki , Basco N. , James D. G. L.
Published: January 2005

Ultraviolet absorption spectra have been characterized for the acetyl‐h3 and acetyl‐d3 radicals, which were generated by the flash photolysis of the corresponding acetones. The spectra are broad and intense, with values of the extinction coefficient at the respective maxima estimated as: ϵCH3CO(215) = (1.0 ± 0.1) × 104 L/mol·cm and ϵCD3CO(207.5) = (1.0 ± 0.05) × 104 L/mol·cm. Rate constants for the reactions of mutual interaction
equation image
were estimated as: k = 3.5 × 1010 L/mol·s and k = 3.4 × 1010 L/mol·s. Rate constants for the reactions of cross interaction
equation image
were estimated as: k = 8.6 × 1010 L/mol·s and k = 5.2 × 1010 L/mol·s. The related values of the cross interaction ratios k/(kk)1/2 = 2.6 and k/(kk)1/2 = 1.6 do not differ significantly from the statistical value of 2. The participation of the radical displacement reactions
equation image
was estimated in terms of the fractions k/k = 0.38 and k/k = 0.47.

Corroborative spectra were obtained from the flash photolysis of methyl ethyl ketone and biacetyl, and the relative rates of the competing primary processes were estimated from the relative peak heights of the acetyl and methyl radicals in each system.
Chain reactions in stirred‐flow reactors–a tool for exploring initiation and termination steps independently
Authors: Benson Sidney W. , Weissman Maia
Published: January 2005

It is shown that chain reactions may be studied in stirred‐flow reactors under conditions in which the escape of radicals from the reactor competes significantly with the chemical termination reaction. The appropriate rate law permits the independent evaluation of the rate constants of the initiation and termination steps. Such information is of special interest in the study of surface effects on chain reactions.
Kinetics and mechanism of the addition of 1,3‐butadiene to cyclohexa‐1,3‐diene in the gas phase
Authors: Huybrechts G. , Hubin Y. , Narmon M. , Van Mele B.
Published: January 2005

The thermal reactions of 1,3‐butadiene (BD) with cyclohexa‐1,3‐diene (CHD) have been studied in a static system between 437 and 526 K. The pressures of BD and CHD were varied from 61 to 397 torr and from 50 to 93 torr, respectively. The percentages of consumed BD and CHD were always kept lower than 14%. The reactions—in the order of importance—are
magnified image
All the reactions are homogeneous and of the first order with respect to the reagents. Their rate constants (in L/mol·s) are given by

A thermochemical analysis of a biradical mechanism is in agreement with these results.
Heterogeneous reactions of sulfur dioxide with carbonaceous particles
Authors: Baldwin Alan C.
Published: January 2005

The rate of adsorption of SO2 on a prototype carbonaceous surface was measured at low pressure in a flow reactor. The measured rate indicates a maximum atmospheric loss of SO2 by heterogeneous reaction of 1%/h for a particle density of 100 μg/m3. The capacity of carbon particles to adsorb SO2 is limited at ∼1 mg SO2 g−1 C. NO2 has no effect on the rate of SO2 adsorption or the saturation behavior.
The thermal decomposition of fluorinated esters. II. The effect of γ‐substitution
Authors: Blake P. G. , Shraydeh B. F.
Published: January 2005

The gas‐phase kinetics of thermal decomposition of ethyl difluoroacetate, pentafluoropropionate, and hepatfluorobutyrate have been studied. The normal ester decomposition route to ethylene plus carboxylic acid is taken in each case, but the fluorinated acids decompose rapidly at the temperatures used. The primary decompositions are homogeneous and unimolecular, and the three Arrhenius equations are

The postulate of a slightly electron‐rich γ carbon in six‐center ester transition states is supported by the higher rates and lowered activation energies observed when increasingly electron‐withdrawing fluorinated groups are linked to this center. The stabilization is reflected in a ρ constant of +0.30. The results are compared with previous work on α substitution in fluorinated esters.
Effects of buffer gases on the infrared multiphoton dissociation of C2H4DCl: A chemical clock to explore highly excited molecules
Authors: Papagiannakopoulos P. J. , Kosnik Ken , Benson S. W.
Published: January 2005

Observations are reported of the effect of the buffer gases He, Ne, and CF4, in the pressure range of 0–30 torr, on the branching ratio [HCl]/[DCl] of the unimolecular decomposition magnified image

The ratio R = kH/kD has been measured in high‐pressure thermal decomposition (670–1100 K) and was shown to give a unique measure of the internal energy of the decomposing molecules and hence, with RRKM theory and pressure fall‐off data, a time scale for their decomposition.

Applying the thermal data to the photolysis leads to the conclusion that excitation and decomposition are produced by the laser spike (high intensity, 70 ns FWHM) and also at a slower rate by the larger, less intense tail (1.6 μs). Added buffer gases quench the latter, leaving the former which, from measurements of R, is shown to correspond to excitations of 115 ± 15 kcal/mol and lifetimes of ∼30 ps. No bond breaking is seen despite the high energies, in accord with theoretical expectations. The results require an enhanced rate of photon absorption by the highly excited molecules, which are about hundredfold greater than that observed for 300 K molecules. Data are also reported for C2H2F2 and the secondary multiphoton photolysis of the ethylenes produced. Effects of beam geometry and wavelength are explored.
Temperature and third‐body dependence of the rate constant for the reaction O + O2+ M → O3+ M
Authors: Lin C. L. , Leu M. T.
Published: January 2005

The flash photolysis resonance fluorescence technique was used to measure the rate constants of the reaction O + O2+ M → O3+ M (M = N2, O2, Ar, and He) as a function of temperature. The results for the rate constants are given byequation imageThe activation energies with N2, O2, and Ar as third bodies are equal within the experimental error, (−1370 → 340 cal/mol), and the relative third‐body efficiencies at 298 K for N2, O2, Ar, and He are 1.00, 0.99, 0.69, and 0.60, respectively.
Laser‐induced chemical kinetics: Absolute rate constants for the reactions Ċ2F2 + Br2 → C2F5Br + Ḃr and n‐Ċ3F7 + Br2 → n‐C3F7Br + Ḃr
Authors: Rossi M. J. , Barker J. R. , Golden D. M.
Published: January 2005

Absolute rate constants at room temperature for the metathesis reaction have been measured under VLPP conditions: k1 = (2.0 ± 0.5) × 108M−1·s−1, k2 = (3.0 ± 0.7) × 108M−1·s−1. The radicals were generated through collisionless infrared‐multiphoton decomposition of the corresponding iodides by irradiation from a high‐power CO2‐TEA laser. The reaction of Ċ2F5 and Ċ3F7 with \documentclass{article}\pagestyle{empty}\begin{document}$$\mathop {\rm N}\limits^{\rm .} {\rm O}_{\rm 2} $$\end{document} are briefly discussed in relation to the reaction of Ċ3 with \documentclass{article}\pagestyle{empty}\begin{document}$$\mathop {\rm N}\limits^{\rm .} {\rm O}_{\rm 2} $$\end{document}, which had been measured previously.
F‐to‐HF reactions. VIII. Nonthermal complications for the CHF3/C3F6/C2F6 moderated nuclear recoil system
Authors: Mathis Chester A. , Gurvis Rafael , Knickelbein Mark , Knierim Kathleen D. , Mo Siu‐Hong , Root John W.
Published: January 2005

Results are reported from moderated nuclear recoil 18F experiments with the 273 K CHF3/C3F6/C2F6 system. Although the measurement sensitivity is only about ±12%, there is no evidence to support the occurrence of nonthermal F‐to‐HF reactions at 95 mol % C2F6 moderator concentration.
Chemiluminescence simulation method for the evaluation of the termination rate constant for 2‐cyanopropyl peroxy and α‐phenyl‐ethyl peroxy radicals
Authors: Lampert R. , Phillips D. , Vidoczy T. , Lukacs J. , Vasvari G. , Gal D.
Published: January 2005

An iterative method has been devised for the simulation of chemiluminescence data during the oxidative decomposition of αα′ azobisisobutyronitrile in the presence of ethylbenzene. From this simulation the cross termination rate constant of the two types of peroxy radicals present has been estimated.
Kinetics of the gas‐phase reactions of OH radicals with alkyl nitrates at 299 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L. , Winer Arthur M.
Published: January 2005

Relative rate constants for the gas‐phase reactions of OH radicals with a series of alkyl nitrates have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3/molec·s, the rate constants obtained are (× 1012 cm3/molec·s): 2‐propyl nitrate, 0.18 ± 0.05; 1‐butyl nitrate, 1.42 ± 0.11; 2‐butyl nitrate, 0.69 ± 0.10; 2‐pentyl nitrate, 1.87 ± 0.12; 3‐pentyl nitrate, 1.13 ± 0.20; 2‐hexyl nitrate, 3.19 ± 0.16; 3‐hexyl nitrate, 2.72 ± 0.22; 3‐heptyl nitrate, 3.72 ± 0.43; and 3‐octyl nitrate, 3.91 ± 0.80. These rate constants, which are the first reported for the alkyl nitrates, are significantly lower than those for the parent alkanes, and a formula, based on the numbers of the various types of CH bonds in the alkyl nitrates, is derived for rate constant estimation purposes.
Pyridiniumchlorochromate oxidations: Studies on the kinetics and substituent effect in the oxidation of aniline in nonaqueous systems
Authors: Panigrahi G. P. , Mahapatro D. D.
Published: January 2005

Pyridiniumchlorochromate (PCC) oxidizes aniline and substituted anilines except nitro anilines smoothly in chlorobenzene–nitrobenzene mixtures in the presence of dichloroacetic acid. The reaction has unit dependence on each of the aniline, PCC, and dichloroacetic acid concentrations. Electron‐releasing substituents accelerate the reaction, whereas electronwithdrawing groups retard the reaction, and the rate data obey Hammett's relationship. The reaction constant ρ is ‐3.75. Azobenzene and p‐benzoquinone have been obtained as products. The observed experimental data have been rationalized in terms of the formation of an intermediate complex involving PCC–amine undergoing a rapid decomposition to products.
Reaction of hot H atoms with CDCl3
Authors: Gould Philip L. , Oldershaw Geoffrey A.
Published: January 2005

Energetic hydrogen atoms generated by photolysis of HBr or HI react with CDCl3 by abstracting either a deuterium atom (1) or a chlorine atom (2):
equation image
The integral probability of reaction (2) has been measured for several defined initial translational energies of H*, and the phenomenological threshold energy is 31 ± 14 kJ/mol. For initial translational energies in the range of 66–121 kJ/mol, the ratio of the integral probabilities of Cl abstraction and of D abstraction, when normalized to equal numbers of Cl and D atoms, is 2.4 ± 0.3. The interpretation of the integral reaction probabilities in terms of the excitation functions of reactions (1) and (2) is discussed. Measurements of the moderating effect of CO2 on reactions (1) and (2) show that CDCl3 is slightly more effective than CO2 as a moderator of H atoms in the energy range of 90–30 kJ/mol.
Mechanism of oxidation of diphenyl sulfide by peroxyanions
Authors: Srinivasan C. , Kuthalingam P. , Arumugam N.
Published: January 2005

Reactions of diphenyl sulfide with the two oxidants peroxydisulfate and peroxydiphosphate are described. With each oxidant, the reaction is first order in the oxidant and zero order in the substrate. The rate of the reaction is also independent of the effect of the substituent. Hydrogen ion catalyzes the reactions. The lack of inhibition of the reaction rate by added acrylamide rules out the possibility of a radical reaction initiated by the homolysis of the peroxyanions. From the effect of [H+] on the oxidation rates, the active species involved in the reactions have been determined. The redox reaction is essentially proceeding via hydrolysis of the protonated peroxy anions in a rate‐determining step, followed by a fast step involving the oxidation of diphenyl sulfide to diphenyl sulfoxide. This has been confirmed by estimating the hydrolyzed products in each case and also by the product analyses.
Anomalous kinetic hydrogen isotope effect in the oxidation of formate by bromine: Tunneling via an intermediate
Authors: Brusa M. A. , Colussi A. J.
Published: January 2005

Rates of oxidation of XCOO− (X = H, D) by Br2 in acid aqueous media were measured between 274 and 332 K. The derived Arrhenius parameters for both reactions

where θ = 4.575T × 10−3 kcal/mol, with (kH/kD)298K = 2.85, reveal a primary isotope effect, but the difference (ED ‐ EH) = 3.29 kcal/mol and the ratio AD/AH = 91 fall beyond the limits imposed by semiclassical transition‐state theory, suggesting tunneling or a multiple‐stage mechanism. However, it can be shown that either tunneling in a single step or a three‐step, internal return mechanism can be ruled out as alternative models, since both require unreasonable kinetic parameters to fit the data. The simplest scheme accounting for the present observations involves tunneling in the decomposition of a charge transfer complex in equilibrium with the reactants.
Reactions of isopropylperoxy radicals with NO and NO2
Authors: Adachi Hiroyuki , Basco Norman
Published: January 2005

The rate constants for the reactions magnified image have been measured directly by flash photolysis and kinetic spectroscopy. At room temperature, k3 = (3.4 ± 0.1) × 109 L/mol·s, independent of pressure in the range of 55–400 torr, and k6 = (2.1 ± 0.2) × 109 L/mol·s.
Free‐energy correlation for catalysis of outer sphere electron‐transfer reactions by noncoordinated pyridine derivatives
Authors: Fanchiang Yueh‐Tai
Published: January 2005

Recent experimental data concerning the rate constants and their free energy of the outer sphere electron‐transfer reactions, as catalyzed by noncoordinated pyridine derivatives in aqueous solution, are examined for possible correlation. For the electron transfer reactions between V or Eu and the bipyridyl derivatives, such as N,N'‐dimethyl‐4,4′‐bipyridyl (paraquat) or diquat, the data are correlated quite well by the Marcus equation. The electron exchange rate constant, 5 × 107M−1·s−1, for an organic radical ion and its parent molecule obtained from semiquinones or their related compounds can be applied to these pyridine derivatives. However, in some cases such as electron transfer from paraquat or diquat cation radical to Co(en), positive departures from the Marcus model are observed. These positive departures are interpreted in terms of interaction between the molecular orbitals of electron donors and electron acceptors in the transition state.
The use of transition‐state theory to extrapolate rate coefficients for reactions of oh with alkanes
Authors: Cohen N.
Published: January 2005

A method is described for extrapolating existing experimental data on the reactions of OH radicals with alkanes to higher temperatures using conventional transition‐state theory. Expressions are developed for the estimation of the structural properties of the activated complex necessary for calculating ΔS± and ΔH±. The vibrational frequencies and internal rotations of the activated complex are given by those of the reacting alkane or the analogous alcohol and a set of additional internal modes that is the same for all OH + alkane reactions considered. Differences between primary, secondary, and tertiary hydrogen attack are discussed, and the validity of representing the activated complexes of all OH + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Calculations are presented for the reaction of OH with CH4, C2H6, C3H8, n‐C4H10, i‐C4H10, c‐C4H8, c‐C5H10, c‐C6H12, (CH3)2CHCH(CH3)2, (CH3)3CCH(CH3)2, (CH3)4C, and (CH3)3CC(CH3)3, and the results are compared with experiments.
Mechanism of acetylene–chlorine mixture explosion initiated by small additions of oxygen
Authors: Revsin A. F.
Published: January 2005

An improved radical‐chain scheme of acetylene–chlorine mixture explosion initiated by small additions of oxygen is proposed. It includes among others the three‐body formation of chemically activated state (2) and describes the inhibiting effect of oxygen below the explosion limit.
Kinetics of oxidation of some meta‐ and para‐substituted phenyl methyl sulfoxides by chloramine‐T in buffered ethanol–water
Authors: Ganapathy K. , Jayagandhi P.
Published: January 2005

The kinetics of oxidation of methyl phenyl sulfoxide by chloramine‐T (CAT) has been studied in buffered ethanol–water (1:1 v/v) of pH 7.0. The reaction was found to follow no simple‐order kinetics. A possible mechanism is suggested involving three rate‐controlling steps: (1) the reaction between RNHCl (R = CH3C6H4SO2) and the sulfoxide, (2) the disproportionation of RNHCl, and (3) the reaction between RNCl2 and the sulfoxide. A mixed‐order rate law is derived as rate/[C][SO] = k1 + Kdk2[C]/[SA]. The rate law is found to be obeyed for the meta‐ and para‐substituted phenyl methyl sulfoxides also. The ρ value is obtained using Hammett's σ constants. The ρ values obtained for the attack of both RNHCl and RNCl2 with the sulfoxides are almost the same, showing that both are converting the sulfoxide to the same intermediate. A chlorinium ion transfer is suggested.
A novel kinetic and mechanistic study of the oxidation of pinacol by acid bromate—homogeneous catalysis of maganous ions
Authors: Reddy Ch. Sanjeeva , Sundaram E. V.
Published: January 2005

A detailed kinetic study of the Mn(II)‐catalyzed and ‐uncatalyzed oxidation of pinacol by bromate has been carried out in aqueous acetic acid media containing Hg(II) ions. The uncatalyzed reaction exhibits 1.5 order that is, 0.5 order in [pinacol] and 1.0 in [bromate]. A decrease in k1 by increasing [bromate] has been accounted for due to the formation of Br2O5, which is inactive toward reduction. Mn(II)‐catalyzed oxidation follows first order in [oxidant], 0.5 order in [manganous ion], and variable order with respect to [pinacol]. At lower [pinacol] (0.005–0.025M) the order is 0.5, but at higher concentration (0.03–0.15M) it becomes negative (−1.0). These observations can be accounted for qualitatively by the formation of 1:1 and 1:2 Mn(II)–pinacol complexes of which only 1:1 is active toward bromate oxidation. At higher [pinacol] the ratio of 1:2 and 1:1 complexes reached 98.2. All reactions were accelerated with acidity, and the rate constant follows the h0 function. Participation of H2O in the rate‐limiting step and a free‐radical mechanism were proposed for the manganous‐ion‐catalyzed reaction, whereas for the uncatalyzed reaction this was not true. The effects of NaClO4, Na4P2O7, and the dielectric constant of the media are also in accordance with the proposed mechanism.