bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared laser‐induced decomposition of 2,2‐dimethyloxetane
Authors: Holbrook K. A. , Shaw C. J. , Oldershaw G. A. , Dyer P. E.
Published: January 2005

The unimolecular decomposition of 2,2 dimethyloxetance to give either isobutence and formaldehyde or ethene and acetone induced by a pulsed CO2 laser has been investigated. Absorption characteristics and fractional decomposition have been studied as a function of laser fluence, irradiation frequency, reactant pressure, and added inert bath gas. Both absorption cross section and fractional decomposition are approximately independent of pressure of 2,2‐dimethyloxetane below 50 times; 10−3 torr and increase with pressure at higher pressures of 2,2‐dimethyloxetane. At pressures sufficiently low that collisions are negligible during the laser pulse, added inert gases reduce the amount of decomposition. Calculations of the fractional decomposition have been carried out based on RRKM theory and assuming either a Boltzmann or a Poisson intermolecular energy distribution. Master equation calculations of both absorption and decomposition for 10R20 irradiation have also been performed. Agreement between observed and calculated results for 10R20 irradiation could be obtained only by assuming that most, but not all, of the molecules in the irradiated volume absorb the laser radiation. Differences between the absorptions of the 10R20 and 9P20 lines and in the resulting extents of decomposition indicate that the fraction of irradiated molecules which absorbs 9P20 radiation is smaller than the fraction which absorbs 10R20 radiation.
The kinetics and the mechanism of the thermal gas‐phase reaction between bis(trifluoromethyl)trioxide, CF3O3CF3 and 1,1‐dichlorodifluoroethylene, CF2CCI2
Authors: Czarnowski J.
Published: January 2005

The thermal addition of CF3O3CF3(T) to CF2CCl2(E) has been investigated between 49.6 and 69.5°C. The initial pressure of CF3O3CF3 was varied between 7 and 240 torr and that of CF2CCl2 between 4 and 600 torr. Four products of formula CF3O(E)j OOCF3, where j = 1 → 4 are formed. The sum of the products Σ CF3O(E)jOOCF3 is equal to the amount of trioxide decomposed.

The reaction is homogeneous. Its rate is not affected by the total pressure and the presence of inert gas. It is a free radical telomerization with four basic steps: thermal decomposition of CF3O3CF3 into CF3O. and CF3O2., chain initiation by addition of CF3O. to olefin incorporated in, and telomeric radicals termination.

The consumption of alkene is well represented by the equation:

where (d[E]/d[T]) =

is the mean chain length of telomerization.

varies from 1.45 at 1.5 torr of E to 3.3 at 400 torr of E. Above this pressure E has no influence on

.

The estimated value of the constant for the addition of telomeric radicals to alkene is:
On the errors of Arrhenius parameters and estimated rate constant values
Authors: Héberger Károly , Kemény Sándor , Vidóczy Tamás
Published: January 2005

A detailed statistical study is presented, based on simulated experimental data, on the estimation of activation parameters using the Arrhenius equation: k = A exp(B/T). The close correlation of the two parameters is shown, which requires the computation of the covariance matrix for the representation of uncertainties. This matrix facilitates the correct estimation of the confidence interval for interpolated (or extrapolated) values of rate coefficients. It is proposed that the full correlation matrix should be published in any article dealing with the determination of Arrhenius parameters.

The importance of correct weighting is emphasized. Nonlinear fitting to the Arrhenius equation can be carried out without weighting only in case the (absolute) error of rate coefficient is independent of the temperature. Simulated experiments show that noncorrect weighting shifts the average values of fitted parameters and increases the variance of the parameters as well.

With respect to the modified Arrhenius equation: k = A · Tn exp(B/T), statistical analysis shows that the physically meaningful estimation of all three parameters is impossible. Nonlinear fitting of three parameters is suggested for interpolation (and extrapolation) of rate coefficients, whereas in case of activation parameter estimation, the fixing of “n” on the basis of theoretical considerations is advised followed by the estimation of the remaining two parameters.
Laser pyrolysis studies of OH reaction rates with several butenes at 1200 K
Authors: Smith Gregory P.
Published: January 2005

Using a laser pyrolysis/laser fluorescence method, we have measured the rate constants for OH reacting with 1‐butene, t‐2‐butene, isobutene, and 2,3‐dimethyl‐2‐butene near 1200 K. The butene rate constants are large, ranging from 2.0–3.7 × 10−11 cm−3 s−1, and increase with the number of allylic hydrogens. Transition‐state theory considerations indicate these allylic hydrogens are easily abstracted, in contrast to prior observations on propene.
Structure–reactivity relationships and the rate–determining step in the reactions of methyl salicylate with primary amines
Authors: Khan M. Niyaz
Published: January 2005

The aqueous cleavage of methyl salicylate has been studied in the buffer solutions of various primary mono‐ and di‐amines as well as secondary amines at 30°C. Both ionized (MS−) and nonionized (MSH) methyl salicylate are reactive toward primary mono‐ and di‐amines. The second‐order rate constants for the reactions of MS− with primary mono‐ and di‐amines of pKa > 9.4 exhibit Bronsted plot of slope (βnuc) of 0.82. This high value of βnuc is attributed to an intramolecular proton transfer in a thermodynamically unfavorable direction in the rate‐determining step in a stepwise process for the formation of monoanionic tetrahedral intermediate. However, a concerted process for the formation of a monoanionic tetrahedral intermediate in the reactions of MS− with amine nucleophiles wherein expulsion of leaving group is a rate‐determining step is not completely ruled out. The α‐effect nitrogen nucleophiles hydroxylamine and hydrazine reveal, respectively, ca. 104‐ and 103‐fold higher reactivity compared to other amine nucleophiles of comparable basicity. The value of βnuc of 1.03 obtained for the reactions of primary monoamines with MSH is ascribed to the expulsion of leaving group as the rate‐determining step. The significantly lower value of βnuc of 0.60 obtained in the reactions of MSH with both monoprotonated and unprotonated diamines is explained in terms of possible occurrence of intramolecular general acid‐base catalysis. Intramolecular general base catalysis is responsible for the enhanced nucleophilic reactivity of primary amines toward MS−. Dimethylamine, piperidine, morpholine, and piperazine have no detectable nucleophilic reactivity toward MS−.
Approximation techniques in complex reaction kinetics
Authors: Summers Danny , Scott John M. W. , Ralph Scott K.
Published: January 2005

We examine the kinetic model D. The differential equations describing this reaction scheme are cast in a nondimensional form and analyzed in four basic approximation regimes: a ‘pseudo‐first order’ approximation valid for small values of the ratio of the initial concentrations of the reactants; an asymptotic solution valid for large values of k3; the standard steady state (Bodenstein) approximation; and an approximation to a second order system without intermediate. Interconnecting relationships between the various approximations derived are examined, and the approximations are compared to numerical solutions to the full equations. The results are assessed from the standpoint of the experimental kineticist, and it is suggested that the reaction studied, and consequently many other more complex reactions, may under certain circumstances be subject to non‐unique interpretation.
Kinetics and mechanism of transesterification of phenyl salicylate
Authors: Khan M. Niyaz
Published: January 2005

The first‐order rate constants, k1, obtained for methanolysis and ethanolysis of phenyl salicylate (PSH) in aqueous mixed solvents, fit to a relationship: k1 = A1 · [ROH]T/(1 + A2[ROH]T) where A1 and A2 are the unknown parameters and [ROH]T is the total concentration of alkanol. It is proposed that the alkanolysis of PSH involves the preequilibrium formation of monomeric ROH from polymeric (ROH)n, followed by an intramolecular general base‐catalysed nucleophilic attack by monomeric ROH on the carbonyl carbon of the ester. In the mixed solvents containing alkanol and MeCN, the k1 – [ROH]T profiles obtained in the presence of K+ ions are different from those obtained in the presence of Na+ ions which could be attributed to the cation‐induced changes in the alkanol structure. Negative KCl salt effect has been observed on methanolysis of PSH, while it is essentially unaffected by the presence of tetraalkylammonium iodide salts (R4NI). The rates of ethanolysis of PSH have been found to increase with increase in [R4NI] and this increase becomes more pronounced with increasing hydrophobic surface area of R4NI. The rate constants for methanolysis of PSH in aqueous mixed solvents containing 80% MeOH (v/v) are independent of [ŌH] within the [ŌH] range of 0.01 to 0.15 M. The rate of methanolysis could not be detected within ca. 47 h in mixed solvents containing 96% HeOH (3.8% MeCN and 0.2% H2O), 80% MeOH (19.8% MeCN and 0.2% H2O), and 0.022 M HCl. It is concluded that for efficient transesterification, PSH should exist in ionized form. The reaction of PSH with MeOH is ca. 400 times faster than that with t‐BuOH which could be ascribed to the most likely steric effect. The values of ΔH* and ΔS* obtained for methanolysis and ethanolysis are essentially independent of [ROH] within the ROH content of 20% to 96% for MeOH and 50% to 96% for EtOH. The effect of organic co‐solvent on rate of hydrolysis of PSH could be explained in terms of organic co‐solvent‐induced water polarization.
The mechanisms of the homogeneus, unimolecular elimination kinetics of ethyl 4‐chlorobutyrate and 4‐chlorobutyric acid in the gas phase
Authors: Chuchani Gabriel , Rotinov Alexandra
Published: January 2005

Ethyl 4‐chlorobutyrate, which is reexamined, pyrolyzes at 350–410°C to ethylene, butyrolactone, and HCl. Under the reaction conditions, the primary product 4‐chlorobutyric acid is responsible for the formation of γ‐butyrolactone and HCl. In seasoned vessels, and in the presence of a free‐radical inhibitor, the ester elimination is homogeneous, unimolecular, and follows a first‐order rate law. For initial pressures from 69–147 Torr, the rate is given by the following Arrhenius expression: log k1(s−1) = (12.21 ± 0.26) − (197.6 ± 3.3) kJ mol−1 (2.303RT)−1. The rates and product formation differ from the previous work on the chloroester pyrolysis.

4‐Chlorobutyric acid, an intermediate product of the above substrate, was also pyrolyzed at 279–330°C with initial pressure within the range of 78–187 Torr. This reaction, which yields γ‐butyrolactone and HCl, is also homogeneous, unimolecular, and obeys a first‐order rate law. The rate coefficient, is given by the following Arrhenius equation: log k1(s−1) = (12.28 ± 0.41) − (172.0 ± 4.6) kJ mol−1 (2.303RT)−1. The pyrolysis of ethyl chlorobutyrate proceeds by the normal mechanism of ester elimination. However, the intermediate 4‐chlorobutyric acid was found to yield butyrolactone through anchimeric assistance of the COOH group and by an intimate ion pair‐type of mechanism. Additional evidence of cyclic product and neighboring group participation is described and presented.
Pyrolysis of acetylene behind reflected shock waves
Authors: Wu C. H. , Singh H. J. , Kern R. D.
Published: January 2005

The thermal decomposition of acetylene has been studied in the temperature and pressure regimes of 1900–2500 K and 0.3–0.55 atm using a shock tube coupled to a time‐of‐flight mass spectrometer. A series of mixtures varying from 1.0–6.2% C2H2 diluted in a Ne‐Ar mixture yielded a carbon atom density range of 0.24–2.0 × 1017 atoms cm−3 in the reflected shock zone. Concentration profiles for C2H2, C4H2, and C6H2 were constructed during typical observation times of 750 μs. C8H2 and trace amounts of C4H3 were found in relatively low concentrations at the high‐temperature end of this study. A mechanism for acetylene pyrolysis is proposed, which successfully models this work and the results obtained by several other groups employing a variety of analytical techniques. Two values of the heat of formation for C2H(134 ± 2 and 127 ± 1 kcal/mol) were employed in the modeling process; superior fits to the data were attained using the latter value. The initial step of acetylene decomposition involves competition between two channels. In mixtures (<200 ppm) where the acetylene concentrations are less than 2.18 × 10−9 mol cm−3, the decay is predominantly first order with respect to C2H2; in mixtures >200 ppm, the dominant initial step is second order. The rate constant for the second‐order reaction is described by the equation

Benzene concentrations predicted by the model are below the TOF detectability limit. C4H3 was observed in the 6.2% C2H2 mixture in accordance with the proposed mechanism.
Gas phase thermolysis of cyanomethyl t‐butyl sulfide and cyanomethyl t‐butyl ether
Authors: Martin Gonzalo , Martinez Henry
Published: January 2005

The pyrolyses of cyanomethyl t‐butyl sulfide and its oxygen homologue have been studied in a stirred‐flow system over the temperature range 490–540°C and pressures between 5 and 14 Torr. In both cases, isobutene is formed as product in over 97% yield. Hydrogen sulfide is obtained in about half the amount of isobutene in the pyrolysis of the sulfide. Hydrogen cyanide is formed in the pyrolysis of the ether. The first‐order rate coefficients for the consumption of the reactants followed the Arrhenius equations Cyanomethyl t‐butyl sulfide:

Cyanomethyl t‐butyl ether:

A molecular mechanism involving polar four‐centered cyclic transition states is proposed for both reactions, with the CN group stabilizing the partial negative charge developed at the S and O atoms.
Rate constant for the reaction Br + O3 → BrO + O2 from 248 to 418 K: Kinetics and mechanism
Authors: Toohey Darin W. , Brune Wm. H. , Anderson J. G.
Published: January 2005

The rate constant for the Br + O3 → BrO + O2 reaction was measured by the discharge flow technique, employing resonance fluorescence detection of Br. Over the temperature range 248 to 418 K, in 1 to 3 torr of He, decays of Br in excess O3 yield the value k1 = (3.28 ± 0.40) × 10−11 e[−944±30]/T cm3 molecule−1 s−1. Cited uncertainties are at the 95% confidence level and include an estimate of the systematic errors. The rate constants for the reactions of O3 with Br, Cl, F, OH, O, and N correlate with the electron affinities of the radicals suggesting that the reactions proceed through early transition states dominated by transfer of electron density from the highest occupied molecular orbital of ozone to the singly occupied radical MO. The implications of this new measurement of k1 for stratospheric chemistry are discussed.
Multistep reaction analysis. A numerical approach based on relaxation theory
Authors: Bacaloglu Radu , Bunton Clifford A. , Ortega Francisco
Published: January 2005

A general numerical method and program for simulation of the kinetics of multistep reactions is described, with details for collation of data, construction of a mechanistic model, and simulation of reciprocal relaxation times and calculation of individual rate constants. The working scheme of the program includes an initial approximate simulation by adjustment of the rate constants followed by their optimization with a Powell minimization subroutine. The procedure is applied to aromatic nucleophilic addition.
Kinetics of the gas‐phase thermal elimination of (β‐chloro ethyl)‐pyrazole
Authors: Perez Jorge Daniel , Phagouape Leonardo Miguel
Published: January 2005

Flash vacuum pyrolysis of (β‐chloro ethyl)‐pyrazole was studied. Pyrazole elimination and vinyl chloride formation were found. Competitive reactions with (β‐chloro ethyl)‐pyrazole were carried out using N‐ethyl‐3,5‐dimethyl pyrazole as internal standard to obtain the kinetic parameters (Ea). Δ(ΔH) for this reaction was calculated.
The gas phase reactions of hydroxyl radicals with a series of carboxylic acids over the temperature range 240–440 K
Authors: Dagaut Philippe , Wallington Timothy J. , Liu Renzhang , Kurylo Michael J.
Published: January 2005

The temperature dependencies of the rate constants for the gas phase reactions of OH radicals with a series of carboxylic acids were measured in a flash photolysis resonance fluorescence apparatus over the temperature range 240–440 K. The data at total pressures (using Ar diluent gas) between 25–50 torr for acetic acid (k1), propionic acid (k2), and i‐butyric acid (k3) were used to derive the Arrhenius expressions

and

At 298 K, the measured rate constants (in units of 10−12 cm3 molecule−1 s−1) were: k1 = (0.74 ± 0.06), k2 = (1.22 ± 0.12), and k3 = (2.00 ± 0.20). In addition a rate constant of (0.37 ± 0.04), in the above units, was determined for the reaction of OH with formic acid. The error limits cited above are 2σ from the linear least squares analyses. These results are discussed in terms of the mechanisms for these reactions and are compared to literature data.
Oxidation of thallium(I) by hexacyanoferrate(III) in aqueous acetic acid
Authors: Gokavi G. S. , Raju J. R.
Published: January 2005

The hexacyanoferrate(III)‐thallium(I) reaction in aqueous acetic acid containing large concentrations of hydrochloric acid is considerably accelerated both by hydrogen and chloride ions as well as increasing acetic acid in the medium. The experimental results obey the rate law (1) where β1 to β6

are the cumulative stability constants of the species TlCl, TlCl, TlCl, HFe(CN), H2Fe(CN) and H3Fe(CN)6 respectively and ka and kb are the rate constants associated with the mono‐ and di‐protonated oxidant species. The main active species are H2Fe(CN) and TlCl.
Isomerization of unsaturated radicals. V. Unimolecular isomerization of hot α,α‐ and α,β‐dimethallyl radicals
Authors: Deslauriers Hélêne , Collin Guy J.
Published: January 2005

The 147 nm photolysis of 3,3 dimethylbut‐1‐ene leads mainly to the formation of very hot (≅375 kJ/mol) α,α‐dimethallyl radicals. On the other hand, that of 3‐methyl‐cis‐and trans‐pentene‐2, as well as that of 2,3‐dimethylbut‐1‐ene is a source of very hot α,β‐dimethallyl radicals. These allylic radicals are coolled down using pressure and are allowed to combine with available methyl radicals. From the formation of various C6H12 products, it is concluded that the very hot α,α‐ radical isomerizes towards the α,β‐structure at low pressures and vice versa. The equilibrium constant of the following process has been evaluated to be 1.72 ± 0.30.
Relative rate measurements of some reactions of hydroxyl radicals with alkanes studied under atmospheric conditions
Authors: Harris Stephen J. , Kerr J. Alistair
Published: January 2005

A flow system has been developed to study relative rate coefficients of hydroxyl radicals reacting with alkanes under conditions relating to tropospheric chemistry. Relative Arrhenius parameters have been measured over the temperature range 243–328 K for pairs of alkanes from a list consisting of n‐butane, 2‐methylpropane, n‐pentane, n‐hexane, 2,2‐ and 2,3‐dimethylbutane, 2,3,3‐trimethylbutane, and 2,3,4‐trimethylpentane.

The results have been incorporated into a Structure‐Activity Relation for hydroxylalkane reactions which leads to the following group rate coefficients for a temperature range of 240–500 K.
A shock tube study of the reaction of the hydroxyl radical with H2, CH4, c‐C5H10, and i‐C4H10
Authors: Bott J. F. , Cohen N.
Published: January 2005

Reactions of the hydroxyl radical, OH, with several reactants have been studied near 1200 K in shock tube experiments in which UV absorption was used to monitor the OH concentration. The values of the rate coefficients were found to be 2.7 × 1012, 2.6 × 1012, 2.8 × 1013, and 1.26 × 1013 cm3/mol‐s for the reactions of OH with hydrogen, methane, cyclopentane, and isobutane, respectively. These measured values are compared with previous experimental results and transition‐state theory calculations.
Formation of 3‐Methylfuran from the gas‐phase reaction of OH radicals with isoprene and the rate constant for its reaction with the OH radical
Authors: Atkinson Roger , Aschmann Sara M. , Tuazon Ernesto C. , Arey Janet , Zielinska Barbara
Published: January 2005

3‐Methylfuran has been identified as a product of the gas‐phase reaction of the OH radical with isoprene, and under simulated atmospheric conditions a formation yield of 0.044 ± 0.006 was determined. In an analogous manner, the OH radical reaction with 1,3‐butadiene formed furan with a yield of 0.039 ± 0.011. Using a relative rate method, a rate constant for the reaction of the OH radical with 3‐methylfuran of 9.35 × 10−11 cm3 molecule−1 s−1 (with an estimated overall uncertainty of ±20%) at 296 ± 2 K was also determined. These data show that 3‐methylfuran is a reactive compound which will be present in the troposphere at concentrations ⩽5% of those of its isoprene precursor.
Determination of initial reaction rates using wilkinson's relation
Authors: Ernst William R.
Published: January 2005

Uncertainty sometimes exists in determining initial reaction rates from experimental data. A method, originally proposed by Wilkinson [9] for estimating orders and rate constants for simple batch nth order reactions, has been generalized to complex kinetic systems. This method yields very accurate initial rates for all systems and extends the conversion range of experimental investigation of initial rates well beyond the “zero‐order” region. Accurate initial rates are required in analytical methods used for screening alternate reaction mechanisms.
Effect of Micelles on kinetics and mechanism of the oxidation of Serine by acid Permanganate
Authors: Hussain M. Yousuf , Ahmad Firoz
Published: January 2005

The oxidation of serine (HORCO2H) by acid permanganate was investigated both in the absence and presence of sodium dodecyl sulfate (SDS). It has been observed that the presence of surfactant enhanced the reaction rate. The reaction is first order with respect to [Serine] and [MnO4−]. The reaction is retarded by the hydrogen ion in the absence of SDS but catalyzed in the presence of SDS. The overall rate expression for the reduction of Mn(VII) may be written as

In the presence of SDS of the rate law is

The reaction appears to involve a parallel consecutive reaction mechanism in which Mn(IV) appears as the reaction intermediate. 𝓀′4f signifies the rate constant for the reaction path leading to the formation of Mn(IV) from Mn(VII) as reaction intermediate, whereas 𝓀′2f signifies the rate constant for the reaction path leading to the reduction of Mn(VII) to Mn(II) without prior formation of Mn(IV). A mechanism satisfying the various kinetic parameters has been proposed.
Rate constants for the reactions of OH radicals and Cl atoms with diethyl sulfide, Di‐n‐propyl sulfide, and Di‐n‐butyl sulfide
Authors: Nielsen Ole J. , Sidebottom Howard W. , Nelson Linda , Rattigan Oliver , Treacy Jack J. , O'Farrell Denis J.
Published: January 2005

Rate constants for the reactions of OH radicals and Cl atoms with diethyl sulfide (DES), di‐n‐propyl sulfide (DPS), and di‐n‐butyl sulfide (DBS) have been determined at 295 ± 3 K and a total pressure of 1 atm. Hydroxyl radical rate data was obtained using the absolute technique of pulse radiolysis combined with kinetic spectroscopy. The chlorine atom rate constants were measured using a conventional photolytic relative rate method. The rate constant for the reaction of Cl atoms with dimethyl sulfide (DMS) was also determined. The following rate constants were obtained:
Determination of initial rates for a general class of chemical reactions: A methodology
Authors: Piscitelle Louis J.
Published: January 2005

The initial rate of any general nth order (n not necessarily integer) chemical reaction can be accurately and easily computed from the slope of a chord joining two points on the progress curve. Expressions for calculating the intermediate concentration corresponding to this initial rate are provided. Examples of the technique applied to second‐ and third‐order reactions as well as an example of a reaction with fractional order (n = 0.6) are given.
Smog chamber study of H2O2 formation in etheneNOx and propeneNOx mixtures
Authors: Meagher James F. , Olszyna Kenneth J. , Simonaitis Romualdas
Published: January 2005

Hydrogen peroxide formation in the photooxidation of CONOx, etheneNOx, and propeneNOx mixtures has been determined in the TVA 31 cubic meter smog chamber under the following conditions: [NOx] ca. 22–46 ppb; ethene = 0.22–1.1 ppm, [propene] = 0.12–0.97 ppm; [H2O] ca. 8 × 10−3 ppm. Ethene, propene, NO, NOx, PAN, HCHO, and CH3CHO were also monitored. Computer modeling was performed using the gas phase ethene and propene mechanism of the Regional Acid Deposition Model. There is good agreement between the model predicted and observed H2O2 concentrations. However, to successfully model all the propeneNOx experimental results, organic nitrate formation from the reaction of peroxy radicals with NO must be included in the mechanism.
Travelling wave in the chlorite‐thiourea reaction
Authors: Simoyi Reuben H. , Masere Jonathan , Muzimbaranda Charles , Manyonda Morningstar , Dube Sithembile
Published: January 2005

The oxidation of thiourea by chlorite within the pH range of 2 to 5.5 has been found to produce a single wave of chlorine dioxide in unstirred solutions. The wave has been studied in narrow tubes of varying diameters and in petri dishes. The wave appears after an induction period that depends on the acid concentration, the [ClO2−]/[CS(NH2)2] ratio, the temperature, and the diameter of the tube. The wave starts from the surface in a tube and from the edges in a petri dish. The rate of wave movement is proportional to the ratio and the acid concentration. Barium chloride and starch were used as indicators. The wave could be initiated electrochemically and by addition of a drop of solution containing chlorine dioxide. The chlorine dioxide is produced by the oxidation of chlorite by hypochlorous acid.
A kinetic study of the permanganate oxidation of triethylamine. Catalysis by soluble colloids
Authors: Perez‐Benito Joaquin F. , Arias Conchita
Published: January 2005

The kinetics of the reaction between permanganate ion and triethylamine in aqueous phosphate buffers (pH 6–8) has been studied. The reaction is autocatalytic, a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface having been identified as the autocatalyst. The reaction is also catalyzed by gum arabic. Mechanisms in agreement with the kinetic data are proposed for the reaction pathways taking place in the bulk solution (for both triethylamine and triethylammonium ion as reductants) and on both the gum arabic and manganese dioxide colloidal particles.
An extended mechanism for chemical activation systems
Authors: Olzmann M. , Gebhardt J. , Scherzer K.
Published: January 2005

The classical mechanism of chemically activated unimolecular reactions is extended to interpret experimental results in systems olefin/hydrogen atoms. In the case of a large excess of the latter, one has to take into consideration a second chemical activation of the primarily formed radicals by their recombination with H‐atoms to yield chemically activated alkane molecules. The radicals as well as the alkane molecules may decompose, and a method based on the coupling of two steady‐state master equations is developed to evaluate the contribution of either of the two reaction paths to the ratio decomposition to stabilization. The treatment proposed is demonstrated for the example cis but‐2‐ene/excess of thermal hydrogen atoms in the presence of molecular hydrogen as a bath gas at 298 K. It turns out that the step via activated butane is not negligible under these conditions.
A shock tube study of the reactions of the hydroxyl radical with several combustion species
Authors: Bott J. F. , Cohen N.
Published: January 2005

Reactions of the hydroxyl radical, OH, with several organic species of interest in combustion chemistry have been studied near 1200 K and 1 atm in shock tube experiments in which UV absorption was used to monitor the OH concentration. Rate coefficients were measured for the reactions of OH with 2,3‐dimethylbutane, isooctane, neooctane, ethylene, propylene, acetylene, formaldehyde, methanol, and ethanol. The values were found to be (in units of 1012 cm3/mol‐s): 21, 22, 18, 2.6, 9.6, 0.28, 12, 5.2, and 5.3. These measured values are compared with previous experimental results and, where appropriate, transition‐state theory calculations.
The thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN)
Authors: Roberts James M. , Bertman Steven B.
Published: January 2005

The rate coefficients of thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN) were measured over the temperature range 302–323 K. The resulting Arrhenius expressions were k = 1017.4±0.4 exp(−28.5 ± 0.5/RT) for PAN, and k = 1016.2±0.7 exp(−26.8 ± 1.0/RT) for MPAN, where the activation energy is in Kcal/mol. These results are in good agreement with previous studies of PAN and other PAN‐type compounds, and imply that energies of RC(O)OONO2 bonds are relatively independent of the nature of R.
A theoretical analysis of the reaction between hydrogen atoms and isocyanic acid
Authors: Miller James A. , Melius Carl F.
Published: January 2005

Using BAC‐MP4 potential‐surface parameters, supplemented by an MP2 normal‐mode analysis at one transition state, and statistical theoretical methods, we have computed thermal rate coefficients for the reactions,

equation image

and

equation image
Over the entire temperature range considered, 300 K < T < 3300 K, reaction (2) is the dominant product channel. The theoretical predictions are in excellent agreement with the experimental results available for k2 and k−1, the rate coefficient for the reverse of reaction (1). Modified Arrhenius expressions are given for k1, k−1, and k2. In addition, we identify and discuss a weakness in utilizing a Hartree‐Fock normal‐mode analysis in the prediction of k2. The present result for k2 is much smaller than that used in the initial modeling of the RAPRENOx process. The implications of this are discussed.
Aromatic nucleophilic substitution reactions of 2‐chloro‐quinoxaline with anilines in ethanol
Authors: Patel R. D.
Published: January 2005

The reactions of 2‐chloroquinoxaline with anilines in ethanol are found to follow second order kinetics, first order in each reactant. The activation parameters determined, from the rate data at five different temperatures are found to be typical of bimolecular aromatic nucleophilic substitutions (SN2Ar). The rate data are also correlated in terms of Hammett as well as Bronsted relationships.
Kinetics of the thermal unimolecular decomposition of hex‐1‐ene‐3‐yne. Heat of formation and resonance stabilization energy of the 3‐ethenylpropargyl radical
Authors: Staker Warren S. , King Keith D. , Nguyen Tam T.
Published: January 2005

The thermal unimolecular decomposition of hex‐1‐ene‐3‐yne (HEY) has been investigated over the temperature range 949–1230 K using the technique of very low‐pressure pyrolysis (VLPP). One reaction pathway is the expected C5C6 bond fission to form the resonance‐stabilized 3‐ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa‐1,3‐diene. RRKM calculations yield the extrapolated high‐pressure rate parameters at 1100 K given by the expressions 1016.0±0.3 exp(−300.4 ± 12.6 kJ mol−1/RT) s−1 for bond fission and 1013.2+0.4 exp(−247.7 ± 8.4 kJ mol−1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔH [H2CCHCCĊH2] = 391.9, DH [H2CCHCCCH2H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol−1 for the 3‐ethenylpropargyl radical, based on a value of 420.2 kJ mol−1 for the primary CH bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol−1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH2CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.
Thermal decomposition of vinylacetylene in shock waves
Authors: Hidaka Yoshiaki , Masaoka Hiromitsu , Oshita Hidekazu , Nakamura Takuji , Tanaka Koji , Kawano Hiroyuki
Published: January 2005

The thermal decomposition of vinylacetylene (C4H4) was studied behind reflected shock waves using both a single‐pulse method (reaction time between 0.8 and 3.3 ms) and a time‐resolved UV‐absorption method (230 nm). The studies were done over the temperature range of 1170–1690 K at the total pressure range of 1.3–2.3 atm. The mechanism was used to interpret both the early and late stages of vinylacetylene decomposition at the high temperatures. It was confirmed that C4H4 dissociation proceeded through the following three channels.

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The rate constant expression of reaction (1) was determined as k1 = 6.3 × 1013 exp(−87.1 kcal/RT) s−1. The rate constants of the succeeding reactions (chain reaction, C4H4 + H → i‐C4H3 + H2 and C4H4 + H → C2H2 + C2H3 and decomposition reactions of free radicals, i‐C4H3 + M → C4H2 + H + M) were confirmed or estimated. © John Wiley & Sons, Inc.
Disproportionation kinetics of N  Cl‐n‐propylamine and N  Cl‐isopropylamine
Authors: Antelo Juan M. , Arce Florencio , Parajo Mercedes , Rodriguez Pilar , Varela Angel
Published: January 2005

The kinetics of the disproportionation of N  Cl‐n‐propylamine and N – Cl‐isopropylamine to the corresponding N, N‐dichloramines were found to be a second order with respect to the N‐chloramine. The influence of amine concentration, pH, buffers, ionic strength, and temperature were also studied. The observed influence of pH supports a reaction mechanism which allowed estimation of the protonation constants of the chloramines studied. The influence of buffers, which was studied for both the above chloramines and N  Cl‐3‐aminopropanol, reflects general acid catalysis, for which a mechanism is proposed. Bronsted's equation was fitted to the catalytic constants obtained therefrom so as to estimate the values of the parameter α for these three N‐chloramines. © John Wiley & Sons, Inc.
Kinetics and mechanism of oxidation of some aliphatic esters by sodium N‐bromo‐p‐toluenesulfonamide
Authors: Rangappa K. S. , Mythily C. K. , Mahadevappa D. S. , Gowda N. M. Made
Published: January 2005

The kinetics of oxidation of methyl, ethyl, n‐propyl, isopropyl, and n‐butyl acetates to acetic acid and the corresponding aldehyde by the title oxidant in aqueous HCl medium at 40°C has been studied. The reaction shows first‐order with respect to [oxidant] and fractional orders in [H+] and [ester]. An isokinetic relationship was observed with β = 374 K indicating enthalpy as the rate controlling factor. Attempts have been made to arrive at a linear free energy relationship through the Taft treatment. Electron releasing groups in the ester moiety increase the rate with ρ* = −9.88. A two‐pathway mechanism, consistent with the observed kinetic data, has been proposed. © 1993 John Wiley & Sons, Inc.
Two‐film effects on the kinetics of hydrogen isotope exchange between CHCl3 and D2O in two liquid phase system
Authors: Iwasaki Matae , Sakka Tetsuo , Ohashi Shigeyuki , Miyake Yoshikazu , Matsushita Hiroshi
Published: January 2005

A model based on the two film approximation is proposed for the description of the kinetics of the hydrogen isotope exchange between CHCl3 and D2O. In this model, details of mass transfer in interfacial region between the two liquid phases are considered and the kinetics of the exchange reaction is quantitatively described without an adjusting parameter. This model is successful in explaining the experimental results obtained with high alkali concentrations, which has not been sufficiently explained in our previous article [M. Iwasaki et al., J. Phys. Chem., 93, 5139 (1989)]. © 1993 John Wiley & Sons, Inc.
Electron‐transfer kinetics and activation barriers for the reductions of nitrosonium and nitronium ions in aprotic solvents
Authors: Boughriet A. , Wartel M.
Published: January 2005

Using the cyclic voltammetry (CV), the electron‐transfer kinetics for the reductions of NO+ and NO2+ cations have been studied at the Pt electrode in nitromethane, sulfolane, and propylene carbonate. The heterogeneous rate constants have been determined by two independent procedures from the transfer coefficient α, the diffusion coefficient D, from a detailed examination of the CV‐peak separations, and from an inspection of the values of the cathodic peak potentials at different scan rates. The results have been compared to those reported in the literature, and discussed. In the classical model, outer‐sphere electron‐transfer reactions are considered subject to an activation energy arising from solvent reorganization and bond reorganization processes. The solvent and molecular reorganizational barriers for these electroreductions have been assessed in aprotic media. The Marcus‐Hush theory has been applied to the self‐exchange reactions of the NO2+/NO2 and NO+/NO couples in an attempt to predict the rate of electron transfer. The findings indicate some improvement between theory and experiment. However, it should be noted that the experimental values of ks found for the NO2+ reduction in the solvents used are still too high in comparison with those determined theoretically. In view of the fairly strong coordination of the solvent molecule(s) as ligand(s) to NO2+ and NO+ cations, we believe that such discrepancies should stem, to some extent, from the involvement of an inner‐sphere pathway by generation of an activated complex on the surface of the Pt electrode. © 1993 John Wiley & Sons, Inc.
CF3BrH2 reaction in shock waves
Authors: Hidaka Yoshiaki , Nakamura Takuji , Kawano Hiroyuki , Koike Tohru
Published: January 2005

CF3BrH2 mixtures highly diluted with Ar were studied by using a time‐resolved IR‐emission of HBr and a gas‐chromatography for reaction products. The temperature range covered was 1000–1600 K and the total pressure behind the reflected shock waves used was 1.2–2.6 atm. CF3H, C2F6, and C2F4 were produced and the yields of these products were determined as a function of temperature. The main product under our experimental conditions was CF3H. The mechanism and the rate constants of CF3BrH2 reaction at high temperatures were discussed. The experimental data was satisfactorily modeled using a 14‐reaction mechanism. Reaction (5) played an important role in the formation of CF3H together with reaction (4).
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The rate constant expression k5 = 2.2 × 1013 exp(−12 kcal/RT) cm3 mol−1 s−1 gave the best agreement between the calculated and observed results. © 1993 John Wiley & Sons, Inc.
CO2 laser‐induced decomposition of propan‐2‐ol, butan‐2‐ol, pentan‐2‐ol, pentan‐3‐ol, and hexan‐2‐ol
Authors: Bishop M. , Holbrook K. A. , Oldershaw G. A. , Dyer P. E.
Published: January 2005

The pulsed CO2 laser‐induced decompositions of propan‐2‐ol, butan‐2‐ol, pentan‐2‐ol, pentan‐3‐ol, and hexan‐2‐ol in the gas phase have been investigated. Like ethanol which we examined previously [1] the absorption cross section of propan‐2‐ol for pulsed 9R14 radiation increases with pressure at low pressures, an effect attributed to rotational hole‐filling. In contrast the absorption cross section of butan‐2‐ol (10R24) has only a small pressure dependence and those of pentan‐2‐ol (9R26), pentan‐3‐ol (10R14), and hexan‐2‐ol (9P20) show little or no variation with pressure in the range 0.1–5.0 torr.

Decomposition products have been investigated at low pressure where the excitation of the alkanols was essentially collision free. The observed products for all the alkanols can be rationalized on the basis of primary dehydration and CC fission channels, with minor contributions from other molecular eliminations. © 1994 John Wiley & Sons, Inc.
Photochemistry of formic acid monomer at 222 nm
Authors: Irwin Robert S. , Singleton Donald L. , Paraskevopoulos George , McLaren Robert
Published: January 2005

The yields of CO2 and CO formed from the gas‐phase photolysis at 222 nm of very low pressures of formic acid where the monomer predominates have been determined using FTIR spectroscopy. The observed ratio of CO2/CO approaches unity as the formic acid pressure approaches zero. Previous studies have shown that the quantum yield for HCOOH + hv → OH + HCO (or H + CO) is 0.70 at 298 K. The present experimental results indicate that the ratio of the quantum yields of the possible molecular photolysis channels forming H2 + CO2 (ϕ1b) and H2O + CO (ϕ1c) is ca. 1. Including this result in an analysis of previously reported quantum yields of CO and CO2 determined at higher pressures of formic acid, where both monomer and dimer contribute significantly to the products, indicates that ϕ1b = ϕ1c = 0. © 1994 John Wiley & Sons, Inc.
The CSP method for simplifying kinetics
Authors: Lam S. H. , Goussis D. A.
Published: January 2005

The Computational Singular Perturbation (CSP) method of simplified kinetics modeling is presented with emphasis on its comparative merits versus conventional methodologies. A new “refinement” procedure for the basis vectors spanning the fast reaction subspace is presented. A simple example is first worked through using the conventional partial‐equilibrium and quasi‐steady approximations, and is then treated in some detail using CSP. © 1994 John Wiley & Sons, Inc.
Kinetics of the reactions of Cl atoms with CH3Br and CH2Br2
Authors: Gierczak Tomasz , Goldfarb Leah , Sueper Donna , Ravishankara A. R.
Published: January 2005

The rate coefficients for the reactions of Cl atoms with CH3Br, (k1) and CH2Br2, (k2) were measured as functions of temperature by generating Cl atoms via 308 nm laser photolysis of Cl2 and measuring their temporal profiles via resonance fluorescence detection. The measured rate coefficients were: k1 = (1.55 ± 0.18) × 10−11 exp{(−1070 ± 50)/T} and k2 = (6.37 ± 0.55) × 10−12 exp{(−810 ± 50)/T} cm3 molecule−1 s−1. The possible interference of the reaction of CH2Br product with Cl2 in the measurement of k1 was assessed from the temporal profiles of Cl at high concentrations of Cl2 at 298 K. The rate coefficient at 298 K for the CH2Br + Cl2 reaction was derived to be (5.36 ± 0.56) × 10−13 cm3 molecule−1 s−1. Based on the values of k1 and k2, it is deduced that global atmospheric lifetimes for CH3Br and CH2Br2 are unlikely to be affected by loss via reaction with Cl atoms. In the marine boundary layer, the loss via reaction (1) may be significant if the Cl concentrations are high. If found to be true, the contribution from oceans to the overall CH3Br budget may be less than what is currently assumed. © 1994 John Wiley & Sons, Inc.
Investigation of the correlation between the energy of the highest occupied molecular orbital (HOMO) and the logarithm of the OH rate constant of hydrofluorocarbons and hydrofluoroethers
Authors: Bartolotti L. J. , Edney E. O.
Published: January 2005

A regression based model was developed to determine whether highest occupied molecular orbital (HOMO) energies, calculated using Kohn‐Sham orbital density functional theory (DFT), could be used to estimate the OH rate constants of hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs), proposed substitutes for stratospheric O3 depleting chlorofluorocarbons. The goodness of fit of the DFT model was compared with a second regression model, derived using recently reported HOMO energies obtained from Hartree Fock theory (HFT). Both models were employed to predict OH rate constants for a number of HFCs and HFEs whose OH rate constants have not been measured, thus providing data on the types of chemical structures that may increase the OH reactivity of the substitute and hence decrease its contribution to global warming. The estimated percent standard errors in the OH rate constant HFT and DFT regression models were 72% and 78%, respectively. The goodness of fits were such that the models can differentiate between two rate constants only when their ratio exceeds about a factor of four. Model results suggest that (1) only a limited number of HFEs will have OH rate constants that are more than an order of magnitude greater than the value for their corresponding HFCs and (2) the strategy of introducing an ether linkage into an HFC to dramatically enhance its reactivity will be most effective for the least fluorinated HFCs. © 1994 John Wiley & Sons, Inc.

This article is a US Government work and, as such, is in the public domain in the United States of America.
Kinetics of the reactions of OH with alkanes
Authors: Talukdar R. K. , Mellouki A. , Gierczak T. , Barone S. , Chiang S‐Y. , Ravishankara A. R.
Published: January 2005

The rate coefficients for the reactions of OH with ethane (k1), propane (k2), n‐butane (k3), iso‐butane (k4), and n‐pentane (k5) have been measured over the temperature range 212–380 K using the pulsed photolysis‐laser induced fluorescence (PP‐LIF) technique. The 298 K values are (2.43±0.20) × 10−13, (1.11 ± 0.08) × 10−12, (2.46 ± 0.15) × 10−12, (2.06 ± 0.14) × 10−12, and (4.10 ± 0.26) × 10−12 cm3 molecule−1 s−1 for k1, k2, k3, k4, and k5, respectively. The temperature dependence of k1 and k2 can be expressed in the Arrhenius form: k1 = (1.03 ± 0.07) × 10−11 exp[−(1110 ± 40)/T] and k2 = (1.01 ± 0.08) × 10−11 exp[−(660 ± 50)/T]. The Arrhenius plots for k3 – k5 were clearly curved and they were fit to three parameter expressions: k3 = (2.04 ± 0.05) × 10−17 T2 exp[(85 ± 10)/T] k4 = (9.32 ± 0.26) × 10−18 T2 exp[(275 ± 20)/T]; and k5 = (3.13 ± 0.25) × 10−17 T2 exp[(115 ± 30)/T]. The units of all rate constants are cm3 molecule−1 s−1 and the quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The present measurements are in excellent agreement with previous studies and the best values for atmospheric calculations are recommended. © 1994 John Wiley & Sons, Inc.