bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser pyrolysis studies of OH reaction rates with several butenes at 1200 K
Authors: Smith Gregory P. 
Published: January 2005

AbstractUsing 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

AbstractThe 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

AbstractWe 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

AbstractThe 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

AbstractEthyl 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractFlash 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractReactions 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

Abstract3‐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

AbstractUncertainty 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

AbstractThe 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

AbstractRate 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

AbstractThe 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

AbstractHydrogen 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.