bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic study of gas‐phase reactions with CF2Cl2 and CFCl3. Analysis using the transition state theory (TST) of the chlorine atom transfer reactions by CF3 and CH3 radicals from halomethanes
Authors: Taccone R. A. , Salinovich O. , Staricco E. H.
Published: January 2005

The following gas‐phase reactions:
equation image
were studied by the competitive method with CF3I as the source of radicals. The kinetic parameters obtained in the temperature range 533–613 K and 503–613 K respectively for chlorine atom transfer reactions are given by:

where θ = 2.303 RT (cal mol−1).

The Arrhenius A values were calculated for seven chlorine atom transfer reactions (CF2Cl2, CFCl3, CCl4 with CF3 radicals; CF3Cl, CF2Cl2, CFCl3 and CCl4 with CH3 radicals) by using the thermochemical kinetic version of the Transition State Theory (TST).
Exchange reactions in selectively excited Br2(B3Π)
Authors: Lum Richard M. , McAfee Kenneth B.
Published: January 2005

Laser‐controlled bimolecular isotopic exchange reactions in bromine leading to alterations in natural isotopic abundance ratios have been directly observed using laser‐modulated molecular beams and mass analysis. Several instances of selective excitation and subsequent rapid isotope exchange are observed within the 7 GHz gain curve of the exciting 514.5 nm line of an argon‐ion laser. These exchange processes are attributed to the direct photochemical participation of excited molecular states in the B3Πou+ system of Br2.
Analysis of flow dynamics in a new, very low pressure reactor. Application to the reaction: Cl + CH4⇌ HCl + CH3
Authors: Dobis Otto , Benson Sidney W.
Published: January 2005

A new, improved variant of the very low pressure reactor (VLPR) system with interchangeable discharge orifices was used for studying the compatibility of the chemical and physical processes occurring simultaneously. It is shown that the ratio of calculated and effective escape rate constants is a complex function of the reactor cell geometry for reactions of non‐spherical symmetry.

The test reaction of atomic chlorine with methane proved to be a pure chemical process free of side reactions and was used to calibrate the system. The measured rate constant is k1 = (0.993 ± 0.013) × 10‐13 cm3/molec‐s at 25°C. A new procedure is outlined for measuring the equilibrium constant by changing the concentrations of all three components resulting in a remarkable accuracy of K1 = 1.406 ± 0.034 for the test reaction at 25°C.
Kinetics of the gas phase reaction of hydroxyl radicals with ethane, benzene, and a series of halogenated benzenes over the temperature range 234–438 K
Authors: Wallington Timothy J. , Neuman Douglas M. , Kurylo Michael J.
Published: January 2005

Absolute rate constants for the gas phase reactions of OH radicals with ethane (k1), benzene (k2), fluorobenzene (k3), chlorobenzene (k4), bromobenzene (k5), iodobenzene (k6), and hexafluorobenzene (k7) have been measured over the temperature range 234–438 K using the flash photolysis resonance fluorescence technique. The rate constants measured at room temperature (296 K), at total pressures of argon diluent between 25 and 50 Torr, were (in units of 10−13 cm3 molecule−1 s−1): k1 = (2.30 ± 0.26), k2 = (12.9 ± 1.4), k3 = (6.31 ± 0.81), k4 = (7.41 ± 0.94), k5 = (9.15 ± 0.97), k6 = (13.2 ± 1.6), and k7 = (1.61 ± 0.24), respectively. The indicated errors are our estimate of 95% confidence limits and include two standard deviations from the least‐squares analysis together with an allowance for any possible systematic errors in the measurements. At elevated temperatures and under pseudo‐first‐order reaction conditions, non‐exponential hydroxyl radical decays were observed for benzene and the monosubstituted halo‐aromatics. For ethane and hexafluorobenzene, exponential decays were observed over the complete temperature range and the data were fit by the Arrhenius expressions: k1 = (8.4 ± 3.1) × 10−12 exp[(−1050 ± 100)/T] and k7 = (1.3 ± 0.3) × 10−12 exp[(−610 ± 80)/T], respectively. The results are compared with previous literature data and the mechanistic implications are discussed.
Kinetic study of the iodine‐catalyzed alcoholysis of Butoxytriethylsilane: n‐butoxy group—s‐butoxy group exchange reaction
Authors: Ito Katsuko , Ibaraki Takeshi
Published: January 2005

In order to appreciate the excellent catalytic effect of iodine on the alcoholyses of alkoxysilanes more precisely, the rates of the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH, were determined at various iodine concentrations.

Both forward and reverse reactions are first order with respect to butoxysilane and to butanol, and pseudo first‐order rate constants were measured at 40°, 30°, and 20°C on reaction mixtures containing both butanols in excess by means of gas‐liquid chromatography. The observed rate constants as a function of iodine concentration gave linear relationships, and from these data the catalytic coefficients of iodine were evaluated:

The enthalpies and the entropies of activation were estimated to be 53.2 kJ mol−1, −103 J K−1 mol−1 (forward, 30°C) and 51.8 kJ mol−1, minus;100 J K−1 mol−1 (reverse, 30°C).
Systematic characterization of transition states for radical decompositions
Authors: Grela M. A. , Colussi A. J.
Published: January 2005

A one‐parameter analytical potential energy function for β‐bonds in free radicals is described, which accounts quantitatively for their observed stretching frequencies and the position and size of the activation barriers for their fission. It is shown that such a function can be used to characterize a priori the corresponding transition states by assuming that the structural and spectroscopic changes taking place along the minimum energy path track the development of pi bonding rather than following a simple exponential dependence on the reaction coordinate. This procedure, tested by comparing predicted A‐factors and isotope effects with experimental data for alkyl radicals and ab‐initio calculations on C2H5, fully encodes the basic features of radical decomposition reactions and provides a simple, realistic, and self‐consistent technique for the estimation of their kinetic parameters.
Kinetics and mechanisms of substitution at paramagnetic metal centers in organometallic complexes
Authors: Trogler William C.
Published: January 2005

The mechanism of ligand substitution in 17‐ and 19‐electron organometallic radicals is discussed. These species substitute ligands by an associative process some 106 to 1010 faster than analogous 18‐electron complexes. When 17‐electron species can be generated by bond homolysis or electron transfer reactions of 18‐electron complexes, they can act as intermediates in radical chain reactions of 18‐electron complexes. A 17–19 electron rule is proposed to explain transformations of organometallic radicals just as the 16–18 electron rule finds use for closed shell organometallic complexes. The origin of this rule is the favorable two‐center three‐electron bond that can form when an odd electron in a sterically accessible metal d‐orbital interacts with an electron pair on an entering nucleophile. Besides simple substitution, these radicals can disproportionate, dimerize, and undergo insertion or atom abstraction reactions.
Kinetics of the reactions of atomic chlorine with methanol and the hydroxymethyl radical with molecular oxygen at 298 K
Authors: Payne W. A. , Brunning J. , Mitchell M. B. , Stief L. J.
Published: January 2005

The rate constants for the reactions Cl + CH3OD → CH2OD + HCl (1) and CH2OH + O2 → HO2 + H2CO (2) have been determined in a discharge flow system near 1 torr pressure with detection of radical and molecular species using collision‐free sampling mass spectrometry. The rate constant k1, determined from the decay of CH3OD in the presence of excess Cl, is (5.1 ± 1.0) × 10−11 cm3 s−1. This is in reasonable agreement with the only previous measurement of k1. The CH2OH radical was produced by reaction (1) and its reaction with O2 was studied by monitoring the decay of the CH2OH radical in the presence of excess O2. The result is k2 = (8.6 ± 2.0) × 10−12 cm3 s−1. Previous estimates of k2 have differed by nearly an order of magnitude, and our value for k2 supports the more recent high values.
Kinetic analysis of a single‐path, and of a dual‐path, sequence of four first‐order reactions. The reactions of dibenzoylmesitylene and acetylbenzoylmesitylene in sulfuric acid
Authors: Farooqi Jameel A. , Gore Peter H. , Waters David N. , Moxon Gerald F.
Published: January 2005

Dibenzoylmesitylene undergoes protiodeacylation in 89.8% (w/w) sulfuric acid at ca. 90°C, with subsequent sulfonation, to give mesitylenedisulfonic acid. The reaction involves a single‐path sequence of four first‐order reactions. The corresponding reaction of acetylbenzoylmesitylene can proceed by two possible routes: it is shown that about 94% of the overall reaction at 75° involves initial protiodeacetylation and about 6% initial protiodebenzoylation. The kinetic analyses provide estimates of concentration ratios as functions of time, and of the buildup and decay of intermediates in the reactions.
Atmospheric reactions of chloroethenes with the OH radical
Authors: Tuazon Ernesto C. , Atkinson Roger , Aschmann Sara M. , Goodman Mark A. , Winer Arthur M.
Published: January 2005

The kinetics and products of the homogeneous gas‐phase reactions of the OH radical with the chloroethenes were investigated at 298 ± 2 K and atmospheric pressure. Using a relative rate technique and ethane as a scavenger for the chlorine atoms produced in these OH radical reactions, rate constants (in units of 10−12 cm3 molecule−1s−1) of 8.11 ± 0.24, 2.38 ± 0.14, and 1.80 ± 0.03 were obtained for 1,1‐dichloroethene, cis‐1, 2‐dichloroethene and trans‐1,2‐dichloroethene, respectively. Under these conditions, the major products observed by long pathlength FT‐IR absorption spectroscopy were HCHO and HC(O)Cl from vinyl chloride; HC(O)Cl from cis‐ and trans‐1,2‐dichloroethene; HCHO and COCl2 from 1,1‐dichloroethene; HC(O)Cl and COCl2 from trichloroethene; and COCl2 from tetrachloroethene. In the absence of a Cl atom scavenger, significant yields of the chloroacetyl chlorides, CHxCl3−xC(O)Cl, were observed from 1,1‐dichloro‐, trichloro‐ and tetrachloroethene, indicating that these products resulted from reactions involving chlorine atoms. The yields of all of these products are reported and the mechanisms of these gas‐phase reactions discussed. In addition, OH radical reaction rate constants were redetermined, in the presence of a Cl atom scavenger, for cis‐ and trans‐1,3‐dichloropropene and 3‐chloro‐2‐chloromethyl‐1‐propene, being (in units of 10−12 cm3 molecule−1 s−1) 8.45 ± 0.41, 14.4 ± 0.8, and 33.5 ± 3.0, respectively.
Kinetics of the chlorination of secondary amines by N‐chlorosuccinimide
Authors: Antelo Juan M. , Arce Florencio , Franco Julia , Lopez Maria C. Garcia , Sanchez Maria , Varela Angel
Published: January 2005

The chlorinations of dimethylamine, diethylamine, methylethanolamine, ethylethanolamine and diethanolamine by N‐chlorosuccinimide have been found to be equilibrium reactions of order one with respect to both N‐chlorosuccinimide and amine in the forward direction and of order one with respect to succinimide and the resulting N‐chloramine in the other. These results are explained by postulating a mechanism in which the rate controlling step consists in direct exchange of positive chlorine between the N‐chlorosuccinimide and the amine.
Transesterification of phenyl salicylate II. Kinetics and mechanism of intramolecular general base‐catalyzed cleavage of phenyl salicylate under the presence of 1,2‐ethanediol and 2‐ethoxyethanol
Authors: Khan M. Niyaz
Published: January 2005

The first‐order rate constants, k1, for 1,2‐ethanediolysis (within the content of 1,2‐ethanediol of 5% to 90%, v/v) and 2‐ethoxyethanolysis (within the 2‐ethoxyethanol content of 5% to 60%, v/v) of phenyl salicylate, PSH, in alkaline aqueous mixed solvents, fit to a relationship: k1 = k[ROH]T/(1 + K[ROH]T) where k and K represent the secondorder rate constant for the reaction of alkanol, ROH, with ionized phenyl salicylate, PS−, and association constant for the dimerization of ROH, respectively, and [ROH]T is the total concentration of ROH. Similar relationship between k1 and [ROH]T has been found for 1,2‐ethanediolysis of PS− studied in mixed solvents containing 1,2‐ethanediol and MeCN. In the alkaline aqueous mixed solvents containing 2‐ethoxyethanol, the k1‐[ROH]T profile reveals the change in the solvent structure of the reaction medium at >60% (v/v) of ROH content. It is proposed that alkanols exist in polymeric form, (ROH)n, and the alkanolysis of PS− involves the pre‐equilibrium formation of monomeric ROH from (ROH)n, followed by an intramolecular general base‐catalyzed nucleophilic attack at carbonyl carbon of ester. A slight negative KCl salt‐ and slight positive n‐Bu4NI salt‐effect are obtained for 1,2‐ethanediolysis while a significant positive n‐Bu4NI salt‐effect is obtained for 2‐ethoxyethanolysis of PS−.
Kinetics of the bromine catalyzed elimination of HCl from 1,1,1‐trichloroethane
Authors: Rodgers A. S. , Jerus Paul
Published: January 2005

The gas phase kinetics of the bromine catalyzed elimination of HCl from 1,1,1‐trichloroethane has been studied over a five fold variation of (CH3CCl3)/(Br2) and from 565 to 634 K. The most important reactions in the mechanism are found to be:

equation image

The preferred analysis of the kinetic data results in log(k1/M−1 s−1) = 11.3 ± 0.3 − (19.9 ± 1.0) × 103/4.575 T. From these results one calculates the C—H bond dissociation energy in CH3CCl3 to be 103.8 ± 2 kcal mol−1, and the heat of formation of 2,2,2‐trichloroethyl to be 17.7 ± 2 kcal mol−1.
Kinetic H/D isotope effects for gas phase hydroxylation of benzene and chlorobenzene between 520–1080 K. Hydroxyl radical versus O(3P) atom attack
Authors: Mulder Peter , Louw Robert
Published: January 2005

Gas phase slow combustion of (chloro)benzene in O2/N2 mixtures, and induced by addends such as tert butylhydroperoxide, cyclohexane, or methanol, leads to (chloro)‐phenol as the only important aromatic product. Using C6H6/C6D6 mixtures, formation of phenol/perdeuterophenol was studied between 520–1080 K. The temperature dependence of this product ratio was found to obey the Arrhenius expression for the intermolecular isotope effect log kH/kD = −0.14 ± 0.03 + (1240 ± 80)/2.303RT (R in cal/mol K). Essentially the same result was obtained for the intramolecular isotope effect, measuring the change in isomer distribution for the chlorophenols formed from p‐deuterio‐chlorobenzene versus those for chlorobenzene.

These results are in accordance with H(D)‐abstraction by ·OH, via a linear transition state, as the first and (relative) rate determining step. Whereas above 1000 K, at reduced pressure, the intramolecular isotope effect continues to prevail, C6H6/C6D6 do not show differences in rate of formation of C6H5OH/C6D5OH. Under these conditions, the only effective reaction of arene to phenol appears to be set in by addition of O(3P).
H2S‐promoted thermal isomerization of cis‐2‐pentene to 1‐pentene and trans‐2‐pentene around 800 K
Authors: Perrin D. , Richard C. , Martin R.
Published: January 2005

H2S accelerates the thermal isomerization of cis‐2‐pentene (P2c) to 1‐pentene (P1) and trans‐2‐pentene (P2t) to around 800 K. This effect is interpreted on the basis of a free radical mechanism in which 2‐pentenyl and thiyl radicals are the main chain carriers. P1 formation is essentially explained by the competing processes:

equation image

equation image

P2t formation is due to addition‐elimination processes:

equation image

the importance of which has been evaluated against process (−4μ):

equation image

The following ratios of rate constants have been measured and are discussed:

(RT in cal mol−1).
The kinetics of photosensitized thymine dimerization
Authors: Kilfoil Valda , Salter Leo
Published: January 2005

Since thymine dimerization is the main photochemical lesion occuring in uv irradiated DNA, an understanding of the mechanism of dimerization is biologically significant. Both photosensitized and direct dimerization are important in DNA, but because photosensitized thymine dimerization has been less thoroughly investigated, this has been the major topic of study in this laboratory. By comparing experimental results with those obtained by computer simulation, attempts have been made to deduce mechanisms for photosensitization by acetone, acetophenone, and benzophenone.

Photolysis of photosensitized solutions was performed using a xenon lamp and quantitative detection of dimer was achieved using h.p.l.c. techniques. A program designed to solve differential rate equations was used for the computer simulation of reaction mechanisms.

Based on the results obtained it has been confirmed that acetone photosensitization over the entire range of thymine concentration considered (10−4 mol dm−3 to 10−2 mol dm−3) proceeds via diffusion controlled triplet transfer from the photosensitizer to thymine, followed by bimolecular collision of ground and excited state thymine monomers. For acetophenone and benzophenone photosensitization this method applied at low thymine concentrations, but at higher concentrations (<10−3 mol dm−3) predicted far lower yields than those observed experimentally. The effect of thymine base stacking was then considered, but it was found that this did not significantly increase the dimer yield. A mechanism involving association of thymine and photosensitizer molecules was therefore proposed. This mechanism was found to give reasonably good agreement between experimental and computed data. On the basis of present data the authors regard this as the most likely mechanism for thymine dimerization and work is in progress to confirm this proposal.
Gas phase oxidation of tetrahydrofuran
Authors: Molera M. J. , Couto A. , Garcia‐Dominguez J. A.
Published: January 2005

The slow gas‐phase oxidation of tetrahydrofuran was studied under static conditions at 220°C. The relative amounts of each product, if extrapolated to zero reaction time, show which are the primary reaction products, and the reaction stoichiometry was thus established. Rate constants for hydroperoxides production and consumption were calculated; these hydroperoxides are responsible for chain branching. Carbon monoxide and carbon dioxide have been shown to be formed in the early stages of the reaction and not simply as end products of oxidative degradation processes. It has been found that at reaction times close to zero one tetrahydrofuran molecule may be attacked in one or several carbon atoms. 65.9% of tetrahydrofuran consumed in the first stages of the reaction forms succinic acid through a mechanism in which one molecule of fuel is attacked by two molecules of oxygen. More than 20% of the tetrahydrofuran molecules are attacked at least by three molecules of oxygen.
Mechanistic and kinetic aspects of the reduction of nitryl chloride in aprotic media
Authors: Boughriet A. , Coumare A. , Fischer J. C. , Wartel M.
Published: January 2005

In order to bring more information on the thermodynamic and kinetic behavior of nitryl chloride in aprotic media, we have surveyed exhaustively the first NO2Cl‐reduction step in sulfolane (at the platinum electrode), taking into account our preliminary results about the electrochemical properties of NO2Cl in aprotic solvents. We have excluded the intervention of the weak ionic dissociation of NO2Cl (NO2Cl ⇆ NO + Cl− [I]) and its slow molecular decomposition as: 2NO2Cl ⇄ Cl2 + 2NO (⇄ N2O4) [II] in this process. We have admitted the occurrence of a rapid chemical reaction which controls kinetically the electrochemical system studied: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm NO} + {\rm NO}_{\rm 2} {\rm Cl}\buildrel {k^*} \over \longrightarrow {\rm NOCl} + {\rm NO}_{\rm 2}^ \cdot {\rm}[{\rm III]} $\end{document}. By analyzing the kinetic currents resulting from the 1 st cathodic wave of NO2Cl at the temperature range 303–323 K, the rate constant, k*, and the activation energy, E*, of reaction [III] have been determined. These results and those previously found in the gas phase are discussed.
Mechanism of oxidations in partially aqueous media: Kinetics of oxidation of thiosemicarbazide and thiosemicarbazone by chloramine‐T and dichloramine‐T in aqueous methanol
Authors: Gowda B. Thimme , Sherigara B. S.
Published: January 2005

Kinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine‐T (CAT) and dichloramine‐T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H+]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H+] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p‐toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis‐Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H+] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.
Gas phase thermolysis of benzyl t‐butyl sulfide, phenyl t‐butyl sulfide, and phenyl t‐butyl ether
Authors: Martin Gonzalo , Martinez Henry , Ascanio Julian
Published: January 2005

The pyrolysis kinetics of the title compounds has been studied in a stirred‐flow reactor over the temperature range 440–530°C and pressures between 5 and 14 torr. Benzyl t‐butyl sulfide and phenyl t‐butyl ether formed isobutene as product in over 98% yield, together with the corresponding benzyl thiol and phenol. The benzyl thiol decomposes to a large extent into hydrogen sulfide and bibenzyl. In the pyrolysis of phenyl t‐butyl sulfide, the hydrocarbon products consisted of 80 ±5% isobutene plus 20% isobutane, while the sulfur containing products were thiophenol and diphenyl disulfide. Order one kinetics was observed for the consumption of the reactants. The first order rate coefficients, based on isobutene production, followed the Arrhenius equations: Benzyl t‐butyl sulfide:

Phenyl t‐butyl sulfide:

Phenyl t‐butyl ether:

For benzyl t‐butyl sulfide and phenyl t‐butyl ether, the results suggest a unimolecular mechanism involving polar four center cyclic transition states. For phenyl t‐butyl sulfide, the t‐butyl‐sulfur single bond fission mechanism is a parallel, less important process than the complex fission one.
A kinetic and mechanistic study of the formation of alkyl nitrates in the photo‐oxidation of n‐heptane studied under atmospheric conditions
Authors: Harris Stephen J. , Kerr J. Alistair
Published: January 2005

The photo‐oxidation of n‐heptane in synthetic air containing methyl nitrite and nitric oxide has been ivestigated in an atmospheric flow reactor. By measuring the total yields of heptyl nitrate products, relative to the depletion of the n‐heptane, the rate constant ratio, k3b/k3a has been determined for the reactions:
equation image
Over the temperature range 253–325 K and at a total pressure of 730 Torr, the following relative Arrhenius equation has been obtained from the present study together with literature data:

These results confirm that the formation of alkyl nitrates from the photo‐oxidation of n‐alkanes arise from a primary reaction between the alkylperoxy radicals and nitric oxide. Furthermore the present experiments show that the lifetime of the intermediate in this type of reaction, presumed to be an alkyl peroxynitrite, ROONO, must be less than a few seconds.
Reactivity of tert‐butoxy radicals towards thiols, alkyl sulfides, and alkyl disulfides
Authors: Encinas M. V. , Lissi E. A. , Majmud C. , Olea A. F.
Published: January 2005

Rate constants for the reactions of tert‐butoxy radicals (generated by the thermal decomposition of di‐tert‐butylperoxyoxalate) with several sulfur containing compounds have been measured at 310 K in benzene. Hexanethiol (k = 6.5 × 107M−1s−1) reacts considerably faster than alkyl sulfides and disulfides. For these compounds the reaction rate constants are slightly dependent on the α‐hydrogen type, changing (when it is expressed per hydrogen atom) only a factor 5 for sulfides and 3 for disulfides when the α‐hydrogen is changed from primary (methyl) to tertiary (isopropyl). The data obtained are compared to those found for the deactivation of the benzophenone triplet. Values of ktert‐butoxy/kbenzophenone range from ca 10−3 (di‐tert‐butyl disulfide) to 7.5 (hexanethiol). The results obtained are rationalized in terms of bond strength, steric hindrance, and charge transfer contributions to the critical configuration energies.
The mechanism in the elimination kinetics of 2‐chloropropionic acid in the gas phase
Authors: Chuchani Gabriel , Rotinov Alexandra
Published: January 2005

The elimination kinetics of 2‐chloropropionic acid have been studied over the temperature range of 320–370.2°C and pressure range of 79–218.5 torr. The reaction in seasoned vessel and in the presence of the free radical suppressor cyclohexene, is homogeneous, unimolecular, and obeys a first‐order rate law. The dehydrochlorination products are acetaldehyde and carbon monoxide. The rate coefficient is expressed by the following Arrhenius equation: log k1(s−1) = (12.53 ± 0.43) – (186.9 ± 5.1) kJ mol−1 (2.303RT)−1. The hydrogen atom of the carboxylic COOH appears to assist readily the leaving chloride ion in the transition state, suggesting an intimate ion pair mechanism operating in this reaction.
Kinetics of UV‐laser induced dehydrochlorination of 1‐chloro‐1,1‐difluoroethane
Authors: Dong Z. F. , Schneider M. , Wolfrum J.
Published: January 2005

The decomposition of 1‐chloro‐1,1‐difluoroethane by a radical chain reaction has been studied in a flow reactor in the temperature range from 503 to 773 K. For the initiation of the chain small amounts of added chlorine were photolyzed with a XeCl laser (λ = 308 nm). The formation of the dehydrochlorination and chlorination products, vinylidene fluoride, and 1,2‐dichloro‐1,1‐difluoroethane respectively, is described by a kinetic model. Arrhenius parameters for the two abstraction reactions

and

were determined by a competition method:

Experimental and modeling results are discussed with respect to former studies on the thermal reaction of 1‐chloro‐1,1‐difluoroethane.
Kinetics and mechanism of formation and decay of 2,2′‐azinobis‐(3‐ethylbenzothiazole‐6‐sulphonate) radical cation in aqueous solution by inorganic peroxides
Authors: Venkatasubramanian Lakshmanan , Maruthamuthu Pichai
Published: January 2005

The kinetics of oxidation of 2,2′‐azinobis‐(3‐ethylbenzothiazole‐6‐sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS.+, on one‐electron abstraction by these peroxides and the further reaction of ABTS.+ with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS.+ at 417 nm. The rate of formation of ABTS.+ was found to obey a total second‐order, first‐order each in [ABTS] and [peroxide], except for H2O2, which reacted through Michaelis‐Menten kinetics. All the peroxides investigated were found to react with ABTS.+; however peroxodisulphate alone oxidized ABTS.+ to the dication (ABTS++), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sulphone as products. The kinetics of decay of the radical cation, ABTS.+, was also found to follow a total second‐order, first‐order each in [ABTS.+] and [peroxide], except peroxodiphosphate the reaction of which obeyed Michaelis‐Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.
Rate constants for hydrogen abstraction reactions of the sulfate radical, SO4−. Alkanes and ethers
Authors: Huie Robert E. , Clifton Carol L.
Published: January 2005

Rate constants have been determined for the reactions of SO4− with a series of alkanes and ethers. The SO4− radical was produced by the laser‐flash photolysis of persulfate, S2O82−. For methane, only an upper limit of 1 × 106 M−1 s−1 could be determined. For ethane, propane, and 2‐methylpropane, rate constants of 0.44, 4.0, and 10.5 × 107 M−1 s−1 were found. For ethyl and n‐propyl ether, rate constants of 1.3 × 108 and 2.2 × 108 M−1 s−1 were found and for 1,4‐dioxane and tetrahydrofuran, rate constants of 7.2 × 107 and 2.8 × 108 were obtained. The reaction of SO4− with allyl alcohol was also studied and found to have a rate constant of 1.4 × 109 M−1 s−1.
Nitroarene products from the gas‐phase reactions of volatile polycyclic aromatic hydrocarbons with the OH radical and N2O5
Authors: Arey Janet , Zielinska Barbara , Atkinson Roger , Aschmann Sara M.
Published: January 2005

The nitroarene products of the gas‐phase reactions of acenaphthylene, acenaphthene, phenanthrene, and anthracene‐d10 with N2O5 and the OH radical (in the presence of NOx) are reported. The calculated atmospheric lifetimes of these polycyclic aromatic hydrocarbons (PAH), as well as those of naphthalene, 1‐ and 2‐methylnaphthalene, biphenyl, fluoranthene, pyrene, and acephenanthrylene, show that reaction with the OH radical is the dominant loss process for these PAH, with the exception of acenaphthylene, acenaphthene, and acephenanthrylene which contain an external cyclopenta‐fused ring. For these latter PAH, reaction with the NO3 radical, and for acenaphthylene and acephenanthrylene reaction with O3, are also expected to be important atmospheric loss processes.

The nitroarenes observed as products of the atmospherically‐important gas‐phase reactions of the PAH in environmental chamber studies are compared with the nitroarenes measured in ambient air samples collected in California. It is concluded that although nitroarenes are formed in low yields (≲5%) from the OH radical‐initiated reactions of the PAH, atmospheric formation of nitroarenes may contribute significantly to ambient nitroarene concentrations.
Decomposition of 1,1,2,2‐tetrafluorocyclopropane. Arrhenius parameters and their influence on the chemical activation results
Authors: Boaglio D. G. , Arbilla G. , Ferrero J. C. , Staricco E. H.
Published: January 2005

The kinetics of the gas‐phase thermal decomposition of 1,1,2,2‐tetrafluorocyclopropane (TFC) to 1,1‐difluoroethylene and CF2 was studied in the temperature range of 507.0‐577.0 K and with a total pressure of 200 to 300 torr of a 1:100 mixture of reactant and C2H4. Also at 557.0 K experiments were made at different total pressures, in the range 2–20 torr with neat TFC and between 20–300 torr with the C2H4/TFC mixture, confirming that the reaction is in the high pressure limit. The reaction is first‐order and the rate constants fit the following Arrhenius relationship:

From this value of the activation energy, the data for the decomposition of chemically activated TFC were revised. The new results yield a minimum energy of the activated molecule of 98 ± 4 kcal/mol and ΔH(TFC) = −155.4 ± 7 kcal/mol, while an analysis of the kinetic data yields ΔH(TFC) = −159 ± 9 kcal/mol.
Rate constants for the reactions of the OH radical with the propyl and butyl nitrates and 1‐nitrobutane at 298 ± 2 k
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate method, rate constants for the gas‐phase reactions of the OH radical with 1‐ and 2‐propyl nitrate, 1‐ and 2‐butyl nitrate and 1‐nitrobutane have been determined in the presence of one atmosphere of air at 298 ± 2 K. Using rate constants for the reactions of the OH radical with propane and cyclohexane of 1.15 × 10−12 and 7.49 × 10−12 cm3 molecule−1 s−1, respectively, following rate constants (in units of 10−12 cm3 molecule−1 s−1) were obtained: 1‐propyl nitrate, 0.62; 2‐propyl nitrate, 0.41; 1‐butyl nitrate, 1.78; 2‐butyl nitrate, 0.93; and 1‐nitrobutane, 1.35. These rate constants are compared and discussed with the literature data.
Micellar effects upon the basic hydrolysis of 2,7‐bis(diethylamino)phenazoxonium chloride
Authors: Cuenca Angela
Published: January 2005

The effect of cationic and anionic surfactants on the reaction of Basic Blue 3 (2,7‐bis(diethylamino)phenazoxonium chloride, 1) with hydroxide ion has been studied. Cetyltrimethylammonium bromide (CTAB), cetyl and tetradecyltrimethylammonium chloride (CTAC and MTAC) enhance the rate of basic hydrolysis whereas sodium dodecyl sulfate (SDS) has an inhibitory effect. The extent of micellar catalysis is reduced by the addition of organic solvents. The results have been analyzed on the basis of the pseudophase ion‐exchange model [1–3].
Determination of the rates of formation of gaseous products from the pyrolysis of octahydro‐1, 3, 5, 7‐tetranitro‐1, 3, 5, 7‐tetrazocine (hmx) by simultaneous thermogravimetric modulated beam mass spectrometry
Authors: Behrens Richard
Published: January 2005

The method for determining the rates of formation of gaseous pyrolysis products during thermal decompositions by simultaneous thermogravimetric modulated beam mass spectrometry is presented. The analysis procedure that handles both molecular and continuum flow from the reaction cell is described. The technique is illustrated with the isothermal decomposition of HMX. The temporal behaviors of the rates of formation of the pyrolysis products, H2O, HCN, CO, CH2O, NO, N2O, methylformamide, C2H6N2O, and octahydro‐1‐nitroso‐3, 5, 7‐trinitro‐1, 3, 5, 7‐tetrazocene, formed during the isothermal decomposition of HMX at 211°C, are presented. The results show that a complex condensed‐phase reaction mechanism controls the decomposition.
The kinetics of successive addition of methyloxirane or ethyloxirane to alkanethiols in the presence of basic catalysts
Authors: Chlebicki Jan , Cichacz Zbigniew
Published: January 2005

Rate constants and activation parameters for the direct addition reaction of methyloxirane or ethyloxirane to alkyl‐2‐hydroxyalkyl sulfides or successive oxypropylene and oxybutylene adducts in the presence of basic catalysts were determined at 373–403 K. This reaction was found to be of the first order with respect to alkyloxirane, sulfide, and catalyst.
Excimer laser‐induced temperature jump‐measurements on the recombination kinetics of the gas‐phase FSO3 + FSO3 ⇔ F2S2O6 equilibrium between 415 and 525 K
Authors: Cobos C. J. , Croce A. E. , Castellano E.
Published: January 2005

The kinetics of the recombination reaction corresponding to the FSO3 + FSO3 ⇔ F2S2O6 equilibrium system has been studied. A time‐resolved absorption spectroscopy technique was employed to monitor the appearance of thermally generated FSO3 radicals at 450 nm following a small temperature jump induced after partial laser photodissociation of F2S2O6 at 193 rim. The recombination rate constants have been determined over the temperature range 415–525 K and a N2 pressure range 10–600 torr. The reaction was found to be in its first order regime. The resulting limiting high pressure rate constants were combined with previous values measured in this laboratory at lower temperatures yielding the expression 𝓀rec, x = (4.5 ± 0.2) × 10−14 (T/300)(1.0 ± 0.1) cm3 molecule−1 s−1 between 293 and 525 K. The temperature coefficient of 𝓀rec, x is smaller than the one derived from steady‐state experiments of the thermal dissociation of F2S2O6 and the equilibrium constant of the system. A recently formulated version of the canonical statistical adiabatic channel model was used to interprete the rate constants.
Homogeneous pyrolysis of acetylacetone at high temperatures in shock waves
Authors: Choudhury T. K. , Lin M. C.
Published: January 2005

The kinetics of the thermal decomposition of acetylacetone has been studied in a shock tube in the temperature range of 1120–1660 K. Detailed analyses of CO and H2O formation data indicate that H2O is formed by a four‐center molecular channel, whereas CO is formed by the rapid dissociation of CH3CO produced by the CC bond dissociation of acetylacetone. The Arrhenius equations for H2O and CH3CO formation channels are 𝓀2 = 1014.24±0.21 exp(−60,800 ± 1,220/RT)sec−1 and 𝓀3 = 1017.05±0.28 exp(−74,600 ± 1,680/RT) sec−1, respectively. The results of the study suggest that the six‐center molecular channel for the production of acetone and ketene is not important under the condition used in this investigation.
Ethylene pyrolysis and oxidation: A kinetic modeling study
Authors: Dagaut Philippe , Boettner Jean‐Claude , Cathonnet Michel
Published: January 2005

Ethylene oxidation and pyrolysis was modeled using a comprehensive kinetic reaction mechanism. This mechanism is an updated version of one developed earlier. It includes the most recent findings concerning the kinetics of the reactions involved in the oxidation of ethylene. The proposed mechanism was tested against ethylene oxidation experimental data (molecular species concentration profiles) obtained in jet stirred reactors (1–10 atm, 880–1253 K), ignition delay times measured in shock tubes (0.2–12 atm, 1058–2200 K) and ethylene pyrolysis data in shock tube (2–6 atm, 1700–2200 K). The general prediction of concentration profiles of minor species formed during ethylene oxidation is improved in the present model by using more accurate kinetic data for several reactions (principally: HO2 + HO2 → H2O2 + O2, C2H4 + OH → C2H3 + H2O, C2H2 + OH → Products, C2H3 → C2H2 + H).
A flash photolysis resonance fluorescence investigation of the reactions of Oxygen O(3P) atoms with aliphatic ethers and diethers in the gas phase
Authors: Liu Renzhang , Dagaut Philippe , Huie Robert E. , Kurylo Michael J.
Published: January 2005

Rate constants for the gas phase reCedex 2, Franceactions of O(3P) atoms with a series of symmetric aliphatic ethers have been determined using the flash photolysis resonance fluorescence technique over the temperature range 240–400 K. The Arrhenius parameters derived from these data are (in units of cm3 molecule −1 s−1):

The error limits are two standard deviations derived from the least‐squares fit. Rate constants for several other ethers were determined only at 298 K. The values obtained were (in units of 10−14 cm3 molecule−1 s−1): tetrahydrofuran (37.5 ± 1.1); 1,4−dioxane 1(6.81 ± 0.46); diethoxymethane (40.4 ± 1.8); ethyl ‐t‐butyl ether (37.0 ± 1.3); and methyl‐t‐amylether (57.3 ± 2.3).
Determination of the absolute concentration of O atoms and OH radicals in laboratory studies
Authors: Canosa‐Mas Carlos E. , Wayne Richard P.
Published: January 2005

The fast reaction of O atoms with NO2 has been used in measurements of absolute concentrations of O atoms. Similarly, the reaction of H with NO2 can be used to generate OH radicals in known concentrations. Relative concentrations of both O atoms and OH radicals have frequently been measured by resonance fluorescence determinations in the ultra‐violet. It will be shown that the stoichiometry of these reactions is strongly dependent on the initial concentration of reactants and on the contact time (in the case of OH on secondary reactions as well), making it impossible to equate directly the loss of NO2 with the loss of O atoms or the production of OH radicals.

In the first part of this work a simple analytical mathematical method for the determination of the concentration of atomic oxygen will be developed. The method is based on the integrated second order kinetic equation, and the effect of the experimental conditions on the results is discussed.

In the second part, the production of OH as a function of contact time and of the initial concentrations of H and NO2 is examined using a five reaction mechanism. By careful choice of the initial concentrations of reactants it is possible to reproduce the experimental results using simplified analytical expressions for the concentration of OH and hence to calculate a calibration factor.

The importance of carrying out the calibration measurements under the same experimental conditions as those employed in kinetic experiments is highlighted.
Kinetics and mechanism of silver(I) catalyzed oxidation of water with bismuth(V) in HClO4HF mixture
Authors: Inani K. M. , Gupta Y. K. , Sharma P. D.
Published: January 2005

The kinetics of the oxidation of water with bismuth(V) in presence of silver(I) has been investigated in a mixture of HClO4 (1.0 mol dm−3) and HF (1.5 mol dm−3). The reaction is second order, viz., first order with respect to bismuth(V) and silver(I), each, and the second order rate constant is (6.6 ± 0.7) × 10−3 dm3 mol−1 s−1. However, rate is independent of hydrogen ion concentration. A comparative analysis of these results with the results obtained for pdp, pds, and Ce(IV), reactions with silver(I) has also been made to correlate the rate constants and the redox‐potentials of the oxidant couples.
Kinetics of Iron‐catalyzed decomposition of hydrogen peroxide in alkaline solution
Authors: Abbot J. , Brown D. G.
Published: January 2005

The decomposition of alkaline hydrogen peroxide solutions at 20°C has been studied in the presence of both supported iron catalysts and in systems with iron initially in solution. Studies with an iron‐alumina supported catalyst showed the decomposition reaction was first order with respect to total peroxide concentration, while studies with alkaline Fe3+ produced more complex behavior. This has been attributed to the presence of at least two distinct catalytically active iron species. The first species is highly active and gives rise to high initial rates of reaction. A decrease in concentration of this species is observed together with an increase in concentration of a second, less active, iron species. The catalytic behavior of this “aged” iron species was found to be very similar to that of the supported iron catalyst.
The formation of the complex pentacyano(3‐pyrazincarboxylate)ferrate(II) in various water‐cosolvent mixtures
Authors: Rodríguez Amalia , Moyá M. Luisa , López Pilar , Muñoz Ernestina
Published: January 2005

This article presents the kinetic of formation of pentacyano(3‐pyrazincarboxylate)ferrate(II) from pyrazincarboxylate and pentacyanoaquoferrate(II) ions in various isodielectric water‐cosolvent mixtures at 298 K. The rate law is in the form d[Fe(CN)5(3‐pzCO2)4−]/dt = 𝓀f[Fe(CN)5H2O−3] [pzCO2−]. Plots of log(𝓀f/dm3 mol−1 s−1) vs. D (where Dm is the bulk dielectric constant of the medium) and log(𝓀f/dm3 mol−1 s−1) vs. the Grunwald‐Winstein parameter are nonlinear for some of the mixtures and to each mixture corresponds a different behavior in respect to the above parameters. The plots of log(𝓀f/dm3 mol−1 s−1) vs. the mol fraction of water are straight lines over the entire composition range studied, except for the water‐methanol mixture. It is evident that the solvation phenomenon plays a dominant role and that the rate of formation is mediated by the dual solvent vectors, the overall basicity and acidity of the solvent mixtures.
Absolute and relative rate constants for the reactions of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols and ethers at 298 K
Authors: Nelson Linda , Rattigan Oliver , Neavyn Ruaidhri , Sidebottom Howard , Treacy Jack , Nielsen Ole John
Published: January 2005

Rate constants for the gas‐phase reactions of hydroxyl radicals and chlorine atoms with aliphatic alcohols and ethers have been determined at 298 ± 2 K and at a total pressure of 1 atmosphere. The OH radical rate data were obtained using both the absolute technique of pulse radiolysis combined with kinetic UV spectroscopy and a conventional photolytic relative rate method. The Cl atom rate constants were measured using only the relative rate method. Values of the rate constants in units of 10−12 cm3 molecule−1 s−1 are:
equation image
The above relative rate constants are based on the values of 𝓀(OH + c‐C6H12) = 7.49 × 10−12 cm3 molecule−1 s−1 and 𝓀(Cl + c‐C6H12) = 311 × 10−12 cm3 molecule−1 s−1. Attempts to corre late the trends in the rate constant data in terms of the bond dissociation energies and inductive effects are discussed.
Effect of solvents and effect of nucleophiles in nucleophilic substitution on benzyl bromide—A kinetic study
Authors: Manikyamba P. , Sundaram E. V.
Published: January 2005

The kinetics of the reaction of benzyl bromide with thiourea was studied in different pure (protic and aprotic) solvents and the rate data was correlated using linear multiple regression analysis. From the regression coefficients which describe the susceptibility of rate to different solvent parameters, information regarding the solvent‐reagent, and the solvent‐intermediate interactions was obtained and solvation models were proposed.

Applicability of the Swain‐Scott free energy relationship was tested using different sulphur nucleophiles in acetonitrile solvent and the nucleophilicity constant of N‐acetylthiourea was computed as 2.74 from the regression line.
A flash photolysis investigation of the gas phase uv absorption spectrum and self‐reaction kinetics of the neopentylperoxy radical
Authors: Dagaut Philippe , Kurylo Michael J.
Published: January 2005

The ultraviolet absorption spectrum of the neopentylperoxy radical, (CH3)3CCH2O2 (or C5H11O2), and the kinetics of its self‐reaction have been studied in the gas phase using a flash photolysis technique. The room temperature absorption cross‐section at 250 nm was determined to be

and was used to normalize the radical absorption spectrum between 210 and 300 nm. Detailed modeling of the self‐reaction system was used to interpret the transient absorption kinetic decay curves over the temperature range 228–380 K, at total pressures between 25 and 100 torr. The results are discussed in relation to previous measurements of alkylperoxy radical spectra and kinetics.