bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the rate coefficients and arrhenius parameters of hydrogen atom transfer reactions. II. Application of the method
Authors: Bérces Tibor , Dombi József
Published: January 2005

The bond‐strength–bond‐length (BSBL) method was used to estimate Arrhenius parameters and rate coefficients for various hydrogen atom transfer reactions of the type A + BC → AB + C. In most cases predicted activation energies agreed within 1.2 kcal/mol with the experimental values (average error = 1.12 and standard deviation = 1.42), and the calculated logAagreed within 0.55 log units with the literature data (average error = 0.47 and standard deviation = 0.57). Predicted activated complex properties were shown to agree very well with potential energy surface properties obtained fromab initioquantum mechanical calculations. Detailed comparison of the BSBL results and the results of bond‐energy–bond‐order (BEBO)‐type calculations are presented.
Atmospheric photodissociation lifetimes for nitromethane, methyl nitrite, and methyl nitrate
Authors: Taylor W. D. , Allston T. D. , Moscato M. J. , Fazekas G. B. , Kozlowski R. , Takacs G. A.
Published: January 2005

Atmospheric photodissociation rate coefficients and photodissociation lifetimes for nitromethane, methyl nitrite, and methyl nitrate were calculated as a function of altitude from their measured visible and near ultraviolet photoabsorption cross sections at 298 K. The lifetime of methyl nitrite is nearly independent of altitude and is approximately 2 min. From 0 to 50 km the lifetime of nitromethane varies from 10 to 0.5 hr, while that of methyl nitrate changes from 5.3 to 0.09 days, respectively.
The thermal unimolecular decomposition of bromocyclobutane
Authors: King Keith D. , Gilbert Robert G.
Published: January 2005

The thermal unimolecular decomposition of bromocyclobutane has been investigated over the temperature range of 791–1224 K using the technique of very low‐pressure pyrolysis (VLPP). HBr elimination is the sole mode of decomposition under the experimental conditions. No evidence could be found for the ring‐cleavage pathway to ethylene and vinyl bromide. Assuming a four‐center transition state and an Arrhenius A factor the same as that for HCl elimination from chlorocyclobutane, RRKM calculations show that the experimental unimolecular rate constants are consistent with the Arrhenius expression

where θ = 2.303RT kcal/mol. The activation energy is higher than that for the open‐chain analog, 2bromobutane. This finding is consistent with the results for the corresponding chloro and iodo compounds.
Kinetics of radiation‐induced abstraction of hydrogen atoms by CCl3 radicals in the liquid phase: 2,3‐dimethylbutane
Authors: Alfassi Zeev B. , Feldman Liviu
Published: January 2005

The kinetics of the gamma‐radiation induced free radical reactions in carbon tetrachloride solutions of 2,3‐dimethylbutane (DMB) were studied in the temperature range 32–118 °C. The kinetics of the following reactions were measured:

and the following rate constants expression was obtained:

. The activation energy and the A factor obtained are in good agreement with the values obtained at the gaseous phase, considering the activation energy for self‐diffusion of CCl4.
Oxidation of formic acid by bromine in aqueous, strongly acid media
Authors: Herbine Peter , Brummer James G. , Field Richard J.
Published: January 2005

Spectrophotometric methods were used to investigate the rate of the reaction of Br2 with HCOOH in aqueous, acidic media. The reaction products are Br− and CO2. The kinetics of this reaction are complicated by both the formation of Br3− as Br− is formed and the dissociation of HCOOH into HCOO− and H+. Previous work on this reaction was carried out at acidities lower than the highest used here and led to the conclusion that only HCOO− reacts with Br2. It is agreed that this is by far the principal reaction. However, at the highest acidity experiments, an added small component of reaction was found, and it is suggested that it results from the direct reaction of Br2 with HCOOH itself. On this assumption, values of the rate constants for both reactions are derived here. The rate constant for the reaction of HCOO− with Br2 agrees with values previously reported, within a factor of 2 on the low side. The reaction involving HCOOH is more than 2000 times slower than the reaction involving HCOO−, but it does contribute to the overall rate as [H+] approaches 1M. These derived rate constants are able to simulate quantitatively the authors' absorbance‐versus‐time data, demonstrating the validity of their data treatment methods, if not mechanistic assignments. Finally, activation parameters were determined for both rate constants. The values obtained are: ΔE‡(HCOOH + Br2) = 13.3 ± 1.1 kcal/mol, ΔS‡ (HCOOH + Br2) = −28 ± 3 cal/deg mol, ΔE‡ (HCOO− + Br2) = 13.1 ± 0.9 kcal/mol, and ΔS‡(HCOO− + Br2) = −12 ± 1 cal/deg mol. That the activation energies of the two reactions turn out to be essentially identical does not support the authors' suggestion that both HCOOH and HCOO− react with Br2.
Mechanism of pyrolysis of C2Cl6
Authors: Weissman Maia , Benson Sidney W.
Published: January 2005

Using published data on the kinetics of pyrolysis of C2Cl6 and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations:
equation image

The steady‐state rate law valid for after about 0.1% reaction is
equation image
and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is
equation image

A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self‐cooling of the gaseous mixture and thus an overall pressure decrease.

From the analysis, the bond dissociation energy DH0(C2Cl5Cl) is found to be 70.3 ± 1 kcal/mol and ΔHf3000(·C2Cl5) = 7.7 ± 1 kcal/mol. The resulting πbond energy in C2Cl4 is 52.5 ± 1 kcal/mol.
Reaction of hydrogen atoms with dimethyldisulfide
Authors: Ekwenchi M. M. , Jodhan A. , Strausz O. P.
Published: January 2005

Hydrogen atoms, generated by the mercury (3P1) sensitization of H2, were allowed to react with dimethyldisulfide in the temperature range of 25–155°C. The only retrievable product is methanethiol, formed in the primary metathetical reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} + {\rm CH}_3 {\rm SSCH}_3 {\rm CH}_3 {\rm SH} + {\rm CH}_3 {\rm S} $\end{document}. The intermediacy of thiyl radicals was clearly demonstrated in experiments carried out in the presence of ethylene where one of the major products detected was ethyl methyl sulfide, formed via CH3S + C2H5 → CH3SC2H5. The major fate of the CH3S radical is recombination and disproportionation, and the yield of methanethiol formed via disproportionation contributes less than 5% to the total thiol yield. The rate coefficient of step 1, from competition with the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} + {\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm C}_{\rm 2} {\rm H}_5 $\end{document}, is k1 = (5.7 ± 1.2) × 1012 exp[(100 ± 100)/RT] cm3/mol sec.
Experimental measurement of the rate of the reaction o(3P) + H2(v = 0) → OH(v = 0) + H at T = 298 K
Authors: Light Glenn C. , Matsumoto James H.
Published: January 2005

Measurement of the rate of the reaction
equation image
is reported. The measurements were made in a flow tube apparatus. The result is based on data for the absolute density of OH(v = 0) obtained from laser‐induced fluorescence measurements in the (0–0) band of the OH(A2Σ+ → X2II) system. The density of oxygen atoms was varied by changing the flow rate of NO which is consumed in the reaction N + NO → O + N2. We find that k1 (298 K) = (5.5 ± 3.0) × 106 cm3/mol sec. This result was obtained with consideration and control of the effect of reaction (2):
equation image
for which vibrationally excited hydrogen is created by energy transfer in the presence of active nitrogen. It was found that the addition of N2 or CO2 effectively suppressed the excitation of H2(v = 1). Measurements of the density of H2(v = 1) were made by VUV absorption in the Lyman band system of H2. All of the reports of low‐temperature measurements and some recent theoretical calculations for k1 are discussed. The present result confirms and extends the growingevidence for significant curvature in the low‐temperature end of a modified Arrhenius plot of k1 (T).
Reaction of carbon monoxide with ozone: Kinetics and chemiluminescence
Authors: Toby Sidney , Ullrich Elizabeth
Published: January 2005

The reaction of carbon monoxide with ozone was studied in the range of 75–160°C in the presence of varying amounts of CO2and, for a few experiments, of O2. At room temperature the reaction was immeasurably slow, but in a flow system it showed chemiluminescence with undamped oscillations. In a static system above 75°C the emission showed damped oscillations when O2was present. In the absence ofadded O2the emission showed a slow decay with a half‐life of 1 hr. The luminescence consisted of partially resolved bands in the range of 325–600 nm, and the source was identified as CO2(1B2) → CO2(1Σg+) +hv. The kinetics were complex, and the observed rate law could be accounted for bya mechanism involving the chain sequence\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm O(}^{\rm 3} P{\rm ) + CO( + M)}\mathop {{\rm rightarrow}}\limits^{\rm 3} {\rm CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) ( + M), CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) + O}_{\rm 3} {\rm }\mathop {{\rm rightarrow}}\limits^{\rm 7} {\rm CO}_{\rm 2} {\rm (}^{\rm 1} \sum\nolimits_{\rm g}^{\rm + } {} {\rm ) + O}_{\rm 2} {\rm + O} $\end{document}. From measurements of ‐d[O3]/dtand relative emission, rate constant ratios were obtained and estimates ofk3were made.
The hydrogen peroxide–iodic acid–manganese (ii)–acetone oscillating system: Further observations
Authors: Cooke David O.
Published: January 2005

The redox potential and iodine concentration behavior of the title reaction and component reactions have been examined. The effect of hydrogen peroxide, potassium iodate, manganese (II) sulfate, sulfuric acid, and acetone concentration on the time period and redox potential behavior is reported. Iodine production and consumption rates for the component reactions are given, and some mechanistic suggestions, involving iodine dioxide as the one electron oxidant, are made.
Azide mechanisms for the production of NCl metastables
Authors: Pritt A. T. , Coombe R. D.
Published: January 2005

The production of both the b1Σ+ and a1Δ states of NCl has been observed from the reaction of HN3 with flowing streams of Cl and F atoms. The results suggest that a two‐step reaction sequence is responsible for the production of excited NCl, as follows:
equation image

The rate contant (all products) for the first step is k(F + HN3) > 1 × 10−11 cm3/molecule sec. Comparison of this value to results obtained in a previous study of the F + HN3 system yields a value k(F + N3) = 2 × 10−12 cm3/molecule sec. The rate constant for the reaction of chlorine atoms with HN3 was determined to be k(Cl + HN3) 1 × 10−12 cm3/molecule sec. The difference between the Cl + HN3 and F + HN3 rates is interpreted in terms of an addition–elimination mechanism.
Reaction of di‐tert‐butylnitroxide radicals
Authors: Lissi E. A. , Rubio M. A. , Araya D. , Zanocco G.
Published: January 2005

Di‐tert‐butylnitroxide (DTBN) is the simplest of the stable nitroxide radicals and is only consumed at temperatures higher than 90°C or in the presence of very reactive substrates. The pyrolysis of DTBN in solution gives, at least at low conversion, 2‐methyl‐2‐nitrosopropane and di‐tert‐butylnitroxide‐tert‐butyl ether. The reaction involves, as the rate‐limiting step, the cleavage of the CN bond. This reaction takes place with an activation energy of 33 kcal/mol. DTBN is stable in the presence of styrene, aldehydes, hydrogen peroxide, α‐methyl‐N‐ethyl nitrone, phenol, and triphenylmethane. On the other hand, it reacts readily with diethylhydroxylamine, ascorbid acid, ethanethiol, and hexanethiol. For the two former compounds the reaction involves a hydrogen transfer as the rate‐determining step, and the reaction proceeds, a low conversion, with simple second‐order kinetics. The reaction with the thiols is complex and shows a clear inductiontime.
Kinetics and mechanism of the addition of trichloromethyl radicals to chloroethylenes. The addition to CIS‐C2Cl2H2, trans‐C2Cl2H2, and C2Cl3H
Authors: Horowitz A. , Baruch G.
Published: January 2005

The addition reactions of CCl3 radicals with cis‐C2Cl2H2, trans‐C2Cl2H2, and C2Cl3H in liquid cyclohexane–CCl4 mixtures were studied between 323 and 448 K. The Arrhenius parameters of these reactions were competitively determined versus H‐atom transfer from cyclohexane and addition to C2Cl4. The present data and the data obtained in previous liquid and gas phase studies show that the reactivities displayed in addition reactions of different radicals with chloroethylenes reflect primarily variations in activation energies rather than in A factors. The activation energies for the addition of CCl3, CF3, and CH3 radicals to chloroethylenes appear, to a large extent, to be determinedby the stability of the adduct radicals. Comparison of the reactivity trends in the addition reactions of chloro‐ and fluoro‐substitutedethylenes indicates that these two electron‐withdrawing substituentshave a converse effect on the reactivity of electrophilic radicals. This behavior is ascribed to the strong mesomeric effect of vinylic chlorosubstituents.
The kinetics of the chlorine isotopic exchange between chloride ion at O,O‐diarylphosphorochloridates or O,O‐diarylphosphorochloridothionates
Authors: ReimschüSsel W. , Mikołajczyk M. , Ślebocka‐tilk H. , Gajl M.
Published: January 2005

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium chloride‐36Cl and O,O‐diarylphosphorochloridates (p‐RC6H4O)2POCl or O,O‐diarylphosphorochloridothionates (p‐RC6H4O)2PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's σ0 constants were obtained. The values of the reaction constants ρ were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron‐donating effect (Δσ0 ∼ 0.80). No correlation has been found for the enthalpy and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the SN2‐P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect–intramolecular interactions revealed in the structure of the compound.
Ion pair catalysis of the autooxidative cleavage of benzoin in emulsion systems
Authors: Franklin Thomas C. , Ogiya Naoyuki
Published: January 2005

A study was made of the autooxidation of benzoin in organic‐aqueous sodium hydroxide emulsions in the presence of several quaternary ammonium salts. The rate of the reaction was found to be accelerated by these salts, probably by ion pair extraction. In pyridine and acetonitrile systems the reaction was almost exclusively the formation of benzoate. Neither benzil nor benzaldehyde were intermediates in the oxidation process. The rate law for the reaction was found to be

which led to the conclusion that the rate‐determining step in the catalyzed pathway was the reaction of oxygen with the ion pair: magnified image
Use of two‐parameter correlations for studying the radical reactivity of aromatic compounds
Authors: Afanas'ev I. B.
Published: January 2005

Two‐parameter equation correlations are reported for radical reactions of aromatic compounds. In these correlations polar and resonance substituent constants identical with the substituent constants of aliphatic compounds were used. The equations correlate the rate constants for H abstraction reactions and for the addition of a variety of free radicals to the ortho‐, meta‐, and para‐substituted aromatic compounds. Besides, they correlate parameters of the spectra for substituted aromatic radicals. The correlations show that the effects of para substituents on the reactions studied are nearly entirely resonance effects, whereas for the meta‐ and ortho‐substituted compounds polar (inductive) effects become essential. Application of the two‐parameter correlations permits also to determine the structure of transition states (σ or π‐complex) in free‐radical reactions.
Rate constants for ozone–alkene reactions under atmospheric conditions
Authors: Adeniji S. A. , Kerr J. A. , Williams M. R.
Published: January 2005

By measuring the rates of decay of ozone in a large excess of reactant, second‐order rate constants have been obtained for the reactions of ozone with ethene, propene, but‐1‐ene, trans‐but‐2‐ene, isobutene, hex‐1‐ene, cyclopentene, cyclohexene, isoprene, vinyl fluoride, 1,1‐difluoroethene, cis‐1,2‐difluoroethene, trans‐1,2‐difluoroethene, trifluoroethene, tetrafluoroethene, and 2,5dihydrofuran. The reactions have been studied in synthetic air at atmospheric pressure and at temperatures of 294 and 260 K. The rate constants and Arrhenius parameters are discussed in relation to existing kinetic data on ozone–alkene reactions.
Kinetics of competitive pathways in the thermal unimolecular decomposition of hex‐1‐yne
Authors: King Keith D.
Published: January 2005

The thermal unimolecular decomposition of hex‐1‐yne has been investigated over the temperature range of 903–1153 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C3C4 fission and molecular retro‐ene decomposition, with the latter being the major pathway under the experimental conditions. 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 at 1100 K given by

and

where θ = 2.303 RT kcal/mol and the A factors were assigned from the results of recent shock‐tube studies of hex‐1‐yne and related alkynes. The results for CC fission are consistent with previous VLPP and shock‐tube determinations of the propargyl resonance energy, and the parameters for the molecular pathway are consistent with systematic trends for the retro–ene decomposition of unsaturated hydrocarbons.
The infrared chemiluminescent reaction of Cl atoms with H2CO
Authors: Fasano D. M. , Nogar N. S.
Published: January 2005

The reaction Cl + H2CO → HCl + HCO has been studied at 295 K. Chlorine atoms were produced via the infrared laser induced dissociation of CCl3F, using a pulsed CO2 TEA laser. Using HCl infrared chemiluminescence as the diagnostic, we find the rate constant to be 7.4 ± 0.7 × 10−11 cm3/molecule sec, in good agreement with several recent studies. An evaluation of TEA laser photolysis as a technique for the generation of chlorine atoms is made, and the relationship of this experiment to recent theories of infrared laser induced chemistry is discussed.
The determination of the arrhenius parameters for the reaction Cl + C2F5I → ICl + C2F5 using a competitive method
Authors: Ahonkhai Samuel I. , Whittle Eric
Published: January 2005

The reactions
equation image

equation image
have been studied competitively over the range of 28–182°C by photolysis of mixtures of Cl2 + C2F5I+ CH4. We obtain

where θ = 2.303RT J/mol. The use of published data on reaction (2) leads to log (k1cm3/mol sec) = (13.96 ± 0.2) − (11,500 ± 2000)/θ.
Very‐low‐pressure pyrolysis of ethylbenzene, isopropylbenzene, and tert‐butylbenzene
Authors: Robaugh David A. , Stein Stephen E.
Published: January 2005

The thermal unimolecular decomposition of ethylbenzene, isopropylbenzene, and tert‐butylbenzene was studied using the very‐low‐pressure pyrolysis (VLPP) technique. Each reactant decomposed by way of β CC bond homolysis, producing methyl radicals and benzyl or benzylic‐type radicals. RRKM calculations show that the observed rate constants, when combined with thermochemical estimates, are consistent with the following high‐pressure rate expressions: \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.3 - (72.7/{\rm \theta)} $\end{document} for ethylbenzene between 1053 and 1234 K, \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.8 - (71.3/{\rm \theta)} $\end{document} for isopropylbenzene between 971 and 1151 K, and \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.9 - (69.1/{\rm \theta)} $\end{document} for tert‐butylbenzene between 929 and 1157 K, where θ (kcal/mol) = 2.303RT. Resulting activation energies combined with heat capacity and heat of formation data led to the following dissociation enthalpies and enthalpies of formation at 298 K: DH° (øCH(CH3)CH3) = 73.8 kcal/mol, ΔHf° (øÇCH(CH3)) = 39.6 kcal/mol, DH° (øC(CH3)2CH3) = 72.9 kcal/mol, and ΔHf° (øÇ(CH3)2) = 32.4 kcal/mol. Derived high‐pressure rate constants are in good accord with results of lower temperature toluene‐ and aniline‐carrier experiments.
Rate constants for the reaction of tert‐butyl radicals with chloroform in solution
Authors: Dütsch H.‐R. , Fischer H.
Published: January 2005

The decay of photochemically generated tert‐butyl radicals in methylcyclopentane solutions containing chloroform is studied by time‐resolved ESR spectroscopy. In the pure solvent it perfectly follows the second‐order rate law for radical self‐termination. Increasing chloroform concentrations cause increasing admixture of a pseudo‐first‐order decay from which the rate constant of the title reaction is obtained. For 273 K ≦ T ≦ 323 K,

where θ = 2.303RT kcal/mol. CIDNP studies of the reaction mechanism and NMR product yields show H and Cl abstractions to occur with the temperature‐independent ratio kH/kCl = 1.4 ± 0.1. The results point to polar effects in the transfer reactions of tert‐butyl. The potential of time‐resolved ESR spectroscopy in studies of first‐ and pseudo‐first‐order reaction rates is discussed.
Kinetics and mechanism of the oxidation of N‐methylformamide and N,N‐dimethylformamide by silver (II) in aqueous perchlorate media and comparison with oxidation by CoIII and MnIII
Authors: Ahmad Firoz , Baswani Vikram S.
Published: January 2005

Detailed measurements on the kinetics and stoichiometry of the oxidation of N‐methylformamide and N,N‐dimethylformamide by aquosilver (II) ions are reported. Four Ag ions are consumed for each amide, and the reaction is first order in [Ag] and first order in [amide]. The reaction is inversely dependent on acidity in the range of 1.5–5.0M HClO4. The oxidation rate is independent of [AgI] and ionic strength. The proposed reaction mechanism and activation parameters are compared with those found for the oxidation of amides by other oxidants such as cobalt(III) and manganese(III).
Steric factors in the kinetically controlled direction of elimination of secondary and tertiary esters in the gas phase. The pyrolysis of 4,4‐dimethylpent‐2‐yl acetate
Authors: Chuchani Gabriel , Dominguez Rosa Maria
Published: January 2005

The pyrolysis kinetics of 4,4‐dimethylpent‐2‐yl acetate, in a static system and in a vessel seasoned with allyl bromide, have been studied in the temperature range of 300–350°C and the pressure range of 48–211 torr. The olefin products were 4,4‐dimethylpent‐1‐ene, cis‐4,4‐dimethylpent‐2‐ene, and trans‐4,4‐dimethylpent‐2‐ene. The rate coefficient for the homogeneous unimolecular elimination of this ester is given by the following Arrhenius equation: log k(sec−1) = (12.87 ± 0.31) − (181.2 ± 3.4)kJ/mol/2.303RT. The direction of elimination of this acetate has been found to proceed to the formation of the corresponding olefin by kinetic control. The present data, together with other pyrolysis work subject to kinetic control, imply that the direction of elimination of bulky alkyl esters is determined by steric hindrance in the eclipsed cis conformation. However, further analyses reveal that if a series of esters are compared, in the case of a gradual increase of alkyl branching when adjacent to a hydrogen atom (alkyl–H interactions), the rate was determined by steric acceleration, owing to the crowding effect at the highly substituted carbon atom. Otherwise if this gradual alkyl increase in size happened to be adjacent to another alkyl substituent (alkyl–alkyl interactions), the rate was affected by steric hindrance of the eclipsed cis conformation.
Study of ionic catalytic systems by the electrodialysis method
Authors: Dyachkovskii F. S. , Grigoryan E. H. , Babkina O. N.
Published: January 2005

A special method of electrodialysis has been developed for investigation of the kinetics and mechanism of polymerization reactions involving ions. The ionic composition of homogeneous systems such as Cp2TiRClAlRCl2, RTiCl3 + AlRCl2, Ti(OR)4 + AlR3, and (RLi)n has been studied. The composition of catalytically active ions has been determined. Using the regularities of “open” systems, the methods of determining the carbocation reactivity under electrodialysis conditions havebeen worked out. The impulse electrodialysis method has been suggested for studying ionic polymerization kinetics and evaluating the rate constants ofion reactions with the monomer and gegenion.
Infrared photochemistry of bis(trifluoromethyl) peroxide
Authors: Francisco J. S. , Findeis M. A. , Steinfeld J. I.
Published: January 2005

Bis(trifluoromethyl) peroxide is readily dissociated by multiple infrared photon excitation at CO2 laser wavelengths. The primary dissociation product is CF3O; approximately 85% of the nascent radicals are further dissociated in the laser field to form CF2O and F. The F atoms then react with the remaining CF3O to produce CF3OF. The formation of CF3OF is strongly inhibited by addition of HI, which reacts preferentially with the F atoms.
Micellar catalyzed enolization of acetone
Authors: Maruthamuthu Meenakshi , Lakshmikanthan N.
Published: January 2005

The acid‐catalyzed enolization of acetone in the presence of bromine is found to be catalyzed by the anionic micelles of sodium dodecyl sulfate. The rate acceleration expected on the basis of lowering of activation energy is largely nullified by the decrease in the entropy of activation, leading to a very small rate enhancement, i.e., kψ/k0 = 1.2 at 30°C. The binding constant for the micelle–substrate complex is determined. The micellar rate enhancement is the same, irrespective of the halogen used, chlorine, bromine, or iodine.
Reactions of the fluorobromocarbene radical studied by laser‐induced fluorescence
Authors: Purdy J. R. , Thrush B. A.
Published: January 2005

CFBr radicals produced by the reaction of atomic oxygen with F2CCFBr were monitored in a discharge flow system by fluorescence excited at 424 nm. The rate coefficients for reactions of the CFBr radicals were measured between 298 and 358 K, and the following values were obtained in units of cm3/molec·s: O2 < 2 × 10−16 at 353 K; NO < 10−14 at 298 K; F2CCFBr < 10−15 at 298 K; Cl2 (1.9 ± 0.6) × 10−12 exp(−762 ± 92/T) Br2 (1.4 ± 0.3) × 10−12 exp(−533 ± 62/T).
Substituent effects on the kinetics of the cerium(IV) oxidation of mandelic acids in sulfate media. Anomalous kinetic behavior of the methoxy derivative
Authors: Calvaruso Giuseppe , Cavasino F. Paolo , Sbriziolo Carmelo
Published: January 2005

The kinetics of the cerium(IV) oxidation of p‐nitro and p‐methoxymandelic acids have been investigated in H2SO4‐MHSO4 (M+ = Li+, Na+, K+) and H2SO4‐MClO4 (M+ = H+, Na+) mixtures at a constant total electrolyte concentration of 2.00 mol/dm3. The oxidation of p+nitromandelic acid proceeds through two [H+]‐independent paths, as was also observed for some substituted mandelic acids studied previously. The kinetic behavior of the p‐methoxy derivative differs from that of the other mandelic acids in that (1) the oxidation occurs via two [H+]‐dependent paths, (2) the reaction rate is anomalously high, (3) the activation enthalpy and entropy of the overall process are markedly lower. It provides strong support to the suggestion that a different mechanism is operative. The substituent effects and the reaction mechanism are discussed.
Addition of hot hydrogen atoms to 1‐butene in the gas phase and dissociation of excited butyl radicals
Authors: Gawłowski Janusz , Niedzielski Jan
Published: January 2005

The reaction of hot hydrogen atoms originating from 253.7‐ and 228.8‐nm photolyses of hydrogen sulfide with 1‐butene was investigated. Of the hydrogen atoms undergoing addition a substantial part undergoes it in a first collision (37 and 48% at 253.7 and 228.8 nm, respectively) yielding highly excited butyl radicals. The ratio of nonterminal to terminal addition is 0.5 and practically does not depend on the energy of the hydrogen atoms over the range of 15–33 kcal/mol. Comparing the results of 229‐ and 254‐nm photolyses of hydrogen sulfide with those of 313‐ and 334‐nm photolyses of hydrogen iodide with the use of the decomposition rate constants of n‐butyl radicals calculated by the RRKM methods, the conclusion is reached that the hydrogen atom from H2S photodissociation has 90–95% of the available energy.
Rate constants for the gas‐phase reactions of O3 with a series of carbonyls at 296 K
Authors: Atkinson Roger , Aschmann Sara M. , Winer Arthur M. , Pitts James N.
Published: January 2005

Rate constants for the gas‐phase reactions of O3 with the carbonyls acrolein, crotonaldehyde, methacrolein, methylvinylketone, 3‐penten‐2‐one, 2‐cyclohexen‐1‐one, acetaldehyde, and methylglyoxal have been determined at 296 ± 2 K. The rate constants ranged from <6 × 10−21 cm3 molecule−1 s−1 for acetaldehyde to 2.13 × 10−17 cm3 molecule−1 s−1 for 3‐penten‐2‐one. The substituent effects of CHO and CH3CO groups on the rate constants are assessed and discussed, as are implications for the atmospheric chemistry of the natural hydrocarbon isoprene.
H + HOONO2 → products: Temperature‐dependent rate constant
Authors: Trevor Paula L. , Barker John R.
Published: January 2005

The absolute reaction rate constant of the title reaction was measured in a stirred‐flow reactor under H‐atom‐rich conditions at seven temperatures from 226 to 315 K. Carbon monoxide was added to convert any OH radicals produced back to H atom by way of the reaction OH + CO → H + CO2. The reaction rate constants were essentially constant between 248 and 315 K: (k ± 2σ) = (2.46 ± 0.35) × 10−14 cm3/s. At temperatures lower than 248 K, the measured rate constant became larger at lower temperatures, possibly due to heterogeneous effects. An hypothesis is advanced that may explain the surprisingly slow rate constant that is virtually independent of temperature, but more experiments are required to determine the dynamical reaction pathway.
INO thermodynamic properties and ultraviolet spectrum
Authors: Forte E. , Hippler H. , Van Den Bergh H.
Published: January 2005

The equilibrium I2(g) + 2NO(g) = 2INO(g) has been studied at room temperature by ultraviolet absorption spectroscopy. The equilibrium constant has been measured as Kp = (2.7 ± 0.3) × 10−6 atm−1 at 298 K. Third‐law calculations lead to ΔH°f,298 (INO) = 120.0 ± 0.3 kJ/mol. The relative absorption spectrum of INO has been measured between 225 and 300 nm. Quantitative measurements gave ϵ(λmax = 238 nm) = (1.79 ± 0.5) × 104 L/mol·cm and ϵ(410 nm) = 234.7 ± 21 L/mol·cm.
Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals
Authors: Bignozzi C. A. , Maldotti A. , Chiorboli C. , Bartocci C. , Carassiti V.
Published: January 2005

The rates of the reactions of hydroxyl radicals (OH) with styrene, α‐methylstyrene, and β‐methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10−11 cm3/molec·s, α‐methylstyrene (5.3 ± 0.6) × 10−11 cm3/molec·s, and β‐methylstyrene (6.0 ± 0.6) × 10−11 cm3/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β‐methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate‐determining OH attack leads to the formation of 1‐hydroxy‐2‐phenyl‐2‐ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.
Kinetics of the sulfodeacylation of 2,4,6,2′,6′‐pentamethylbenzophenone, a process comprising successive first‐order reactions occurring by two alternative routes
Authors: Gore Peter H. , Saad Esmat F. , Waters David N. , Moxon Gerald F.
Published: January 2005

Mesityl 2,6‐xylyl ketone in 89.8% (w/w) sulfuric acid undergoes cleavage to give mesitylenesulfonic acid, xylenesulfonic acid, and carbon dioxide as final products. The reaction has been analyzed in terms of a series of first‐order reactions. Of the two possible reaction paths available it was shown that fission at the mesityl group is responsible for about 98.5% of the overall initial reaction at 25°C.
Kinetics and mechanism of the amine exchange reactions of 2‐aminopyridine derived Schiff‐base ligands and their copper(II) complexes
Authors: Ranganathan Hemalatha , Ramasami T. , Ranganathan C. K. , Ramaswamy D. , Santappa M.
Published: January 2005

The kinetics and product analyses of the amine exchange reactions of two 2‐aminopyridine derived Schiff‐base ligands and their monomeric bischelate and dimeric copper(II) complexes have been studied. The Schiff‐base ligands investigated underwent amine exchange reactions with n‐butyl, cyclohexyl, t‐butyl amines. The coordination of the Schiff‐base ligands to copper(II) rendered the amine exchange reactions slower. With n‐butyl and cyclohexyl amines, parallel first‐ and second‐order terms on their concentrations are observed for the amine exchange reactions of copper(II) bischelates and dimer. The kinetic data favor a mechanism involving a rate‐limiting elimination of 2‐aminopyridine from a diaminoacetal intermediate in preference to a scheme in which a dissociation of the complexes into free ligands and Cu(II) may precede the amine exchange. The steric factors influence the amine exchange reactions of Cu(II) bischelates with the bulkier amines reacting slower as given by the order t‐butylamine (3.3 ± 0.3 × 10−3 dm3/mol·s) < cyclohexylamine (0.2 ± 0.03 dm3/mol·s) < n‐butylamine (2.2 ± 0.2 dm3/mol·s). The bulkiness of the t‐butyl group and the constraints imposed by the changes in the coordination geometry of Cu(II) on amine exchange not only render the reactions of Cu(II) bischelates slower but also make the formation of the mixed adduct ([N‐(5‐methyl)‐2‐pyridyl salicylaldimine][N‐t‐butyl salicylaldimine] Cu(II)) more favored.
Kinetics of the reaction of C2H5O2 with NO at 295 K
Authors: Plumb I. C. , Ryan K. R. , Steven J. R. , Mulcahy M. F. R.
Published: January 2005

The reaction of C2H5O2 with NO in helium carrier gas at 295 K with [He] = 1.6 × 1017 cm−3 has been studied using a gas flow reactor sampled by a mass spectrometer. Because no parent molecular ion or suitable fragment ion produced by C2H5O2 could be detected, the reaction was followed by measuring the formation of NO2. In so doing, account had to be taken of the small amount of HO2 known to be present in the reaction mixture, which also leads to NO2 on reaction with NO. The rate coefficient for the total reaction of C2H5O2 with NO was found to be (8.9 ± 3.0) × 10−12 cm3/s, and the path which produces NO2 was found to account for at least 80% of all C2H5O2.
Kinetics of the thermal reactions of bicyclo[4.2.2]deca‐3,7‐diene and endo‐and exo‐5‐vinylbicyclo[2.2.2]oct‐2‐ene in the gas phase
Authors: Huybrechts G. , Hubin Y. , Narmon M. , Van Mele B.
Published: January 2005

The kinetics of the thermal reactions of bicyclo[4.2.2]deca‐3,7‐diene (BDD) and endo‐ and exo‐5‐vinylbicyclo[2.2.2]oct‐2‐ene (endo‐ and exo‐VBO) have been studied in the gas phase. The temperature range was 459–526 K for BDD, 476–563 K for endo‐VBO, and 513–578 K for exo‐VBO. The initial pressures were varied from 2 to about 40 torr. These compounds isomerize to cis‐1,2,4a,5,8,8a‐hexahydronaphtalene (HHN) and into each other, and decompose to 1,3‐butadiene (BD) + cyclohexa‐1,3‐diene (CHD). The reactions are homogeneous and first order. Their rate constants (in s−1) are given by:
equation image

where the superscripts represent the reagents and the subscripts the products. The heats of formation and the entropies of endo‐VBO, exo‐VBO, and BDD are estimated.
Rate constants for the reaction of ground‐state oxygen atoms with methanol from 297 to 544 K
Authors: Failes R. L. , Singleton D. L. , Paraskevopoulos G. , Irwin R. S.
Published: January 2005

The rate constant for the reaction of ground‐state oxygen atoms with methanol has been determined between 297 and 544 K by a phase‐shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(−2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third‐body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K.
The kinetics and mechanisms of the gas‐phase unimolecular eliminations of halogeno esters. Participation of the carbomethoxy group
Authors: Chuchani Gabriel , Rotinov Alexandra , Dominguez Rosa M.
Published: January 2005

The kinetics of the gas‐phase elimination of several chloroesters were determined in a static system over the temperature range of 410–490°C and the pressure range of 47–236 torr. The reactions in seasoned vessels, and in the presence of a free‐radical inhibitor, are homogeneous, unimolecular, and follow a first‐order law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for methyl 3‐chloropropionate, log k1(s−1) = (13.22 ± 0.07) ‐ (231.5 ± 1.0) kJ/mol/2.303RT; for methyl 4‐chlorobutyrate, log k1(s−1) = (13.31 ± 0.25) ‐ (221.5 ± 3.4) kJ/mol/2.303RT; and for methyl 5‐chlorovalerate, log k1(s−1) = (13.12 ± 0.25) ‐ (221.7 ± 3.2) kJ/mol/2.303RT. Rate enhancements and lactone formation reveal the participation of carbonyl oxygen of the carbomethoxy group. The order COOCH3‐5 > COOCH3‐6 > COOCH3‐4 in assistance is similar to the sequence of group participation in solvolysis reactions. The partial rates for the parallel eliminations to normal dehydrohalogenation products and lactones have been estimated and reported. The present results lead us to consider that an intimate ion‐pair mechanism through participation of the carbomethoxy group may well be operating in some of these reactions.
Kinetics and mechanism of the oxidation of n‐acetyl l‐cysteine by 2,6‐dichloroindophenol in methanol–water medium
Authors: Shrivastava Manjul , Mishra K. K. , Sinha B. P.
Published: January 2005

The principal reactants interact in a molar ratio of 2:1 forming dihydroindophenol and the corresponding disulfide. The order of reaction is unity with respect to each reactant, namely, N‐acetyl L‐cysteine and indophenol. The rate shows an inverse linear relation with hydroxyl ions. It is not influenced by the variation in the initial concentration of indophenol. The rate increases on adding the salts possessing a cholinergic effect and the neutral electrolytes, as well as on increasing the dielectric constant of the medium. The products, namely, N‐acetyl L‐cystine (disulfide) and the leuco dye, do not influence the rate. A low energy and a highly negative entropy of activation (4.11 kcal/mol and ‐60.49 e.u., respectively) suggest the formation of an outer sphere complex as the rate‐determining step.
The reaction of O(3P) with H2O2
Authors: Roscoe John M.
Published: January 2005

The rate constant for the reaction of O(3P) with H2O2 was measured as a function of temperature and the [H2O2]0/[O]0 ratio. The numerical solution of the appropriate rate equations was used to arrive at a mechanism which adequately describes our results and the rather divergent data in the literature. A recommended expression for the temperature dependence of the absolute rate constant is presented from consideration of the available experimental data.
Gas‐phase thermolysis of sulfur compounds. Part IV. n‐propyl allyl sulfide
Authors: Martin Gonzalo , Ropero Marcos
Published: January 2005

The pyrolysis of n‐propyl allyl sulfide has been studied in static and stirred‐flow systems at temperatures between 270 and 400°C. Propene and 2,4,6‐triethyl‐1,3,5‐trithiane were the only reaction products. The order of the reaction was 0.99 ± 0.05 at 377°C. The first‐order rate coefficients followed the Arrhenius equation

The rate coefficients and the product distribution remained unchanged when cyclohexene was used as carrier gas. A molecular mechanism involving a six‐centered cyclic transition state is proposed to explain the present results. This mechanism is further supported by the pyrolysis of 4‐thia‐5‐dideutero‐1‐heptene at 377°C, where only 3‐deuteropropene is formed. The kinetic deuterium isotope effect had a value of 2.6 ± 0.3 at this temperature. The results are compared with those obtained in the pyrolysis of n‐butyl allyl sulfide previously reported.
The kinetics of the gas‐phase reaction between iodine and phenylsilane and the bond dissociation energy D(C6H5SiH2H)
Authors: Barber M. , Doncaster A. M. , Walsh R.
Published: January 2005

The title reaction has been investigated in the temperature range of 490‐573 K. Initial reactant pressures were varied in the range of 0.2‐5.2 torr (I2) and 2‐20 torr (C6H5SiH3). The rate of iodine consumption, monitored spectrophotometrically, was found to obey

both by initial rate and integrated equation fitting procedures. The effect of added initial HI conformed to this expression. The data are consistent with a conventional I‐atom propagated chain reaction, and for the step

the rate constant is given by

From this is derived the bond dissociation energy value C6H5SiH2H = 374 kJ/mol(88 kcal/mol). A comparison with other SiH dissociation energy values indicates that the “silabenzyl” stabilization energy is small, ≈7 kJ/mol.
The thermal decomposition of fluorinated esters. III. Esters without β hydrogen atoms
Authors: Blake P. G. , Shraydeh B. F.
Published: January 2005

The kinetics of the gas‐phase decomposition of methyl trifluoroacetate and 2,2,2‐trifluoroethyl trifluoroacetate, two esters without β hydrogen atoms, have been investigated, and a comparative study was carried out on methyl acetate. All these compounds are thermally much more stable than fluorinated esters with β hydrogens, decomposing at temperatures some 150°C above the latter by a completely different mechanism involving partly heterogeneous radical chains. The marked difference in behavior between the two types of fluorinated ester confirms that none of them decomposes by hydrogen fluoride elimination, but that those with β hydrogen atoms follow the normal ester decomposition route. The fluorinated esters examined here decompose in a manner generally similar to methyl acetate, but the presence of fluorine in the molecule brings about an extreme sensitivity to surface conditions.
Kinetics of the reactions of CH3 with O(3P) and O2 at 295 K
Authors: Plumb I. C. , Ryan K. R.
Published: January 2005

The reactions of CH3 radicals with O(3P) and O2 have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For the reaction between CH3 and O, conditions were such that [O] » [CH3] and the methyl radicals decayed under pseudo‐first‐order conditions giving a rate coefficient of (1.14 ± 0.29) × 10−10 cm3/s. The reaction between CH3 and O2 was studied in separate experiments in which CH3 decayed under pseudo‐first‐order conditions. In this case, the rate coefficient obtained increased with increasing concentration of the helium carrier gas. This was varied over the range of 2.5–25 × 1016 cm−3, resulting in values for the apparent two‐body rate coefficient ranging from 1 × 10−14 to 5.2 × 10−14 cm3/s. No evidence was found for the production of HCHO by a direct two‐body process involving CH3 + O2, and an upper limit of 3 × 10−16 cm3/s was placed on the rate coefficient for this reaction. The experimental results for the apparent two‐body rate coefficient exhibit the curvature one would expect for an association reaction in the fall‐off region. Calculations used to extrapolate these measurements to the low‐pressure limit yield a value for k0 of (3.4 ± 1.1) × 10−31 cm6/s, which is more than a factor of 2 higher than previous estimates.
Kinetics of the isomerization reaction of cholest‐5‐en‐3‐one catalyzed by trichloroacetic acid in aprotic solvents of low dielectric constant
Authors: Salvador Francisco , Gonzalez José Luis , Herræz Miguel A.
Published: January 2005

The isomerization reaction of cholest‐5‐en‐3‐one has been studied in a solution of cyclohexane using trichloroacetic acid as catalyst. At the same time a general reaction scheme is proposed to be valid for all the cases assayed in which the monomer form of the acid is considered as the only effective catalyst. The experimental results agree with these hypotheses and with the calculation of the individual rate constant together with the reaction order with respect to the catalyst. Semiquantitative studies have been carried out with other catalysts and solvents, confirming the validity of the reaction scheme. The thermodynamic activation parameters have also been calculated, and a comparative study was made with the results of the evaluation of the reaction when it takes place in amphiprotic solvents. A reaction mechanism is proposed based on all the kinetic information obtained.
Mechanism of the hydroxyiodination of 2‐butenoic acid
Authors: Furrow Stanley D.
Published: January 2005

Aqueous iodination of trans‐2‐butenoic acid proceeds via hydrolysis of I2 to form HOI and I−, then rapid addition of HOI across the double bond to form the iodohydrin product. In the presence of iodate to keep iodide concentration low, the reaction proceeds at a conveniently measurable rate. The rate for the addition reaction

is −d[C4H6O2]/dt = 5900 [H+][C4H6O2][HOI]M/s at 25.0°C when [IO] = 0.025M and ionic strength = 0.3. The overall rate law in the presence of iodate is

where [H+] and [IO] are total concentrations used to prepare the solution.
Kinetics and mechanism of the thermal decomposition of methyl isocyanate
Authors: Blake P. G. , Ijadi‐Maghsoodi S.
Published: January 2005

The kinetics of gas‐phase decomposition of methyl isocyanate have been investigated in the range of 427–548°C. Two decomposition routes are followed; the predominant one is a radical‐chain process giving CO, H2, and HCN as major products, which has an order of 1.5 and an Arrhenius equation given by log k(L1/2/mol1/2·s) = (13.12 ± 0.06) − (56,450 ± 1670) cal/mol/2.303 RT. The minor route is the bimolecular formation of N,N′‐dimethylcarbodiimide and CO2, which from the low activation parameters Ea = 31.6 kcal, A = 105.30 L1/2/mol1/2·s, and the reaction order of 1.57 appears to be heterogeneous.