bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential energy distributions in nonthermal systems: Model calculations and applications to 18F‐for‐F nuclear recoil substitutions in CH3CF3
Authors: Rogers E. B. , Tang Y.‐N. , Rodgers A. S. , Chui C. K.
Published: January 2005

A general method has been developed for the determination of the differential energy distribution in nonthermally activated reacting systems. A series of known distributions and kinetic models has been used to test this method and to determine its efficacy. Application was then made to the kinetic data of energetic CH3CF2 18F formed by the substitution of F by 18F produced by nuclear recoil. The distribution obtained for this activated CH3CF2 18F is seen to be highly energetic with a median energy of 137.6 kcal mol−1 and with 33.1% of the molecules possessing energy in excess of 171 kcal mol−1. The shape of the calculated distribution suggests that there are two mechanisms for the formation of CH3CF2 18F from CH3CF3 and 18F, as well as that 62 kcal mol−1 is a lower limit to the kinetic energy needed by the 18F atom for this substitution to take place.
The pyrolysis of acetylene‐styrene mixtures between 450 and 550°C
Authors: Chanmugathas C. , Heicklen Julian
Published: January 2005

The pyrolysis of acetylene‐styrene mixtures has been studied from 450–550°C in a quartz reaction vessel in the absence and presence of O2 or NO. The rates of disappearance of reactants and formation of adducts are first‐order in each reactant. The major product is polymer, with the adducts accounting for about 2.5% and 6.2% of the styrene removed at 450 and 550°C, respectively. The acetylene‐to‐styrene removal ratio is about 27 independent of temperature. The adducts formed are methyl indene and 1,2‐dihydronaphthalene. These are about half‐suppressed in the presence of O2 or NO. The rate coefficients for reactant removal and adduct formation are:

where the activation energies are in kJ/mol and the uncertainties are one standard deviation. As the reaction proceeds, the methyl indene and 1,2‐dihydronaphthalene decompose, and indene and naphthalene are formed. In addition, an unidentified isomer of naphthalene is produced as an initial minor product, and it also decomposes as the reaction proceeds.
Kinetics of the permanganate oxidation of formic acid in aqueous solution
Authors: Monzó Isidro S. , Palou Juan , Peñalver Joaquín , Valero Rosa
Published: January 2005

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid at 30°C were examined by the spectrophotometric method. The chemical reaction 2MnO + 3HCOOH + 2H+ → 2MnO2 + 3CO2 + 4H2O, appears to proceed via several parallel reactions. The overall rate equation has been obtained by using statistical multilinear regression analysis of the 660 cases studied, and the presence in the rate equation of two new terms in relation to previous studies shows that both permanganate autocatalytic effects and acid media inhibition must be taken into account when the reaction proceeds at constant ionic strength.
Rate constants for hydrogen abstraction by resonance stabilized radicals in high temperature liquids
Authors: Manka M. J. , Brown R. L. , Stein S. E.
Published: January 2005

Benzylic H‐atom abstraction rates by diphenylmethyl radicals from a series of donors were determined in nonpolar liquids at elevated temperatures. Relative rates were converted to absolute rates via available equilibrium constant data for the dimerization of diphenylmethyl radicals. Abstraction by diphenylmethyl from 1, 2, 3, 4‐tetrahydronaphthalene (tetralin) was studied over the temperature range 489–573 K. Its Arrhenius expression is 109.9±0.3 exp{−(10183 ± 373)/T} M−1 s−1. Abstraction from other donors was studied at 548 K. Rate constant values ranged from a low of 3.6 M−1 s−1 for toluene to a high of 3000 M−1 s−1 for 9, 10‐dihydroanthracene. Similar reactions with the fluorenyl radical were also studied. In this case, relative rates were converted to absolute rates with an equilibrium constant for fluorenyl dimerization determined from the observed homolysis rate of the dimer and an assumed recombination rate. In addition, forward and reverse rate measurements yielded the equilibrium constant for hydrogen transfer between fluorenyl and diphenylmethyl. At 548 K, fluorenyl is favored by a factor of 13 over diphenylmethyl.
Kinetics, mechanism, and stereochemistry of Diels‐Alder reactions of carbonyl‐substituted ethenes with cyclohexa‐1,3‐diene in the gas phase
Authors: Van Mele B. , Tybaert C. , Huybrechts G.
Published: January 2005

The kinetics of the Diels–Alder additions of CH2  CHCHO, CH2C(CH3)CHO, and CH2CHC(CH3)O to cyclohexa‐1,3‐diene (CHD) have been studied in the gas phase. The stereochemistry and the mechanism of these reactions are discussed. In contrast with other Diels–Alder additions involving CHD as diene, a biradical mechanism does not fit the experimental results.
Rate constant for the reaction of OH radicals with dimethyl sulfide
Authors: Hsu Yen‐Chung , Chen Dze‐Shu , Lee Yuan‐Pern
Published: January 2005

The rate constants of the gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3) over the temperature range 260–393 K have been studied using the discharge flow‐resonance fluorescence technique. The rate constants were fitted by the Arrhenius equation k = (11.8 ± 2.2) × 10−12 exp[−(236 ± 150)/T] cm3 molecule−1 s−1 with k = (5.5 ± 1.0) × 10−12 cm3 molecule−1 s−1 at 298 K. Our results are in good agreement with the lower range of values reported previously. The observation of a small positive activation energy agrees well with that reported by Hynes et al. The rate constant was not affected by the total pressure variation (0.8–3.0 torr) or by the addition of oxygen (up to 1 torr) in the flow tube.
Pyrolysis of 2‐butyne/vinylacetylene mixtures between 350 and 450°C
Authors: Harper Charles , Heicklen Julian
Published: January 2005

Vinylacetylene and 2‐butyne mixtures were pyrolyzed at 350–450°C in the absence and presence of O2 and NO. The major product of the reaction is a polymer, but o‐xylene is also produced and was studied as the species of interest. The C8H10 formation rate is first‐order in C4H4 and C4H6. The rate coefficient is best fitted by

though it is not inconsistent with

where R is the ideal gas constant in kJ/mol‐K. O‐xylene formation occurs by two processes: a concerted molecular mechanism (⋍67%) and a singlet diradical mechanism (⋍33%).
The gas phase reactions of hydroxyl radicals with a series of aliphatic ethers over the temperature range 240–440 K
Authors: Wallington Timothy J. , Liu Renzhang , Dagaut Philippe , Kurylo Michael J.
Published: January 2005

Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of linear aliphatic ethers using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for dimethylether (k1), diethylether (k2), and dipropylether (k3) were used to derive the Arrhenius expressions

and

At 296 K, the measured rate constants (in units of 10−13 cm3 molecule−1 s−1) were: k1 = (24.9 ± 2.2), k2 = (136 ± 9), and k3 = (180 ± 22). Room temperature rate constants for the OH reactions with several other aliphatic ethers were also measured. These were (in the above units): di‐n‐butylether, (278 ± 36); di‐n‐pentylether, (347 ± 20); ethyleneoxide, (0.95 ± 0.05); propyleneoxide, (4.95 ± 0.52); and tetrahydrofuran, (178 ± 16). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.
Acuchem: A computer program for modeling complex chemical reaction systems
Authors: Braun Walter , Herron John T. , Kahaner David K.
Published: January 2005

Acuchem is a program for solving the system of differential equations describing the temporal behavior of spatially homogeneous, isothermal, multicomponent chemical reaction systems. It is designed to provide modelers, data evaluators, and laboratory scientists with an easy to use program for modeling complex chemical reactions, and for presenting the results in tabular or graphical form. The program is described and some examples of its application given. Acuchem is designed to operate on the IBM Personal Computer family and other compatible microcomputers, and is available in a compiled version on a floppy disk.
Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5‐trioxane between 290 and 600 K
Authors: Zabarnick S. , Fleming J. W. , Lin M. C.
Published: January 2005

Absolute rate constants are measured for the reactions: OH + CH2O, over the temperature range 296–576 K and for OH + 1,3,5‐trioxane over the range 292–597 K. The technique employed is laser photolysis of H2O2 or HNO3 to produce OH, and laser‐induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH2O) = (1.66 ± 0.20) × 10−11 exp[−(170 ± 80)/RT] cm3 s−1 and k(1,3,5‐trioxane) = (1.36 ± 0.20) × 10−11 exp[−(460 ± 100)/RT] cm3 s−1. The transition‐state theory is employed to model the OH + CH2O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH2O) = 1.2 × 10−18 T2.46 exp(970/RT) cm3 s−1. An estimate of 91 ± 2 kcal/mol is obtained for the first CH bond in 1,3,5‐trioxane by using a correlation of CH bond strength with measured activation energies.
The effect of ring size on the gas phase elimination kinetics of cycloalkyl acetates
Authors: Chuchani Gabriel , Martin Ignacio , Rotinov Alexandra , Dominguez Rosa M. , Morris David G. , Shepherd Alistair G.
Published: January 2005

The rates of elimination of seven cycloalkyl acetates containing between 5 and 15 ring carbons have been determined in a static system over a temperature range 280–370°C and a pressure range 35–234 torr. The unimolecular reactions, carried out in the presence of the inhibitor cyclohexene, are homogeneous in seasoned vessels and follow a first‐order rate law. The rate coefficients are exemplified by that found for cyclopentyl acetate:

The sequence of relative rates is analogous to that found in most solution reactions of these compounds. The contribution of ring strain to energy barriers of these compounds is described.
Further experiments on pyrolysis of 2,2‐dimethylpropane behind shock waves
Authors: Rao V. Subba , Skinner Gordon B.
Published: January 2005

Pyrolysis of a dilute mixture of neopentane (2,2‐dimethylpropane) has been studied behind incident shock waves at an average pressure of 0.35 atm; the reaction was followed by absorption spectroscopy for H atoms. In the temperature range 1230–1455 K, the rate constant for dissociation of neopentane to t‐butyl and methyl radicals is 1.1 E 13 exp(−62 kcal/RT) s−1. These data and some of the literature results, between 1000 and 1450 K, can be fitted by an RRKM model of the hindered Gorin type, with five active internal rotors in the complex. To match our data with other literature data down to 800 K, a vibrational model was more satisfactory, but this did not fit very low pressure pyrolysis data in the 1000–1100 K range. Apparently, the VLPP data are too high because of heterogeneous processes or chain reactions.
The kinetics of oxirane reaction with alkanethiols in the presence of basic catalysts
Authors: Chlebicki Jan , Cichacz Zbigniew
Published: January 2005

Rate constants for the reactions of oxirane with alkanethiols in the presence of basic catalyst were studied at the temperature range of 20–50°C. A mechanism of these reactions has been proposed and appropriate kinetic equation has been presented.
Kinetics and mechanisms of the reaction of OH radicals with dimethyl sulfide
Authors: Barnes I. , Bastian V. , Becker K. H.
Published: January 2005

The rate constant of the reaction of OH with DMS has been measured relative to OH + ethene in a 420 l reaction chamber at 760 torr total pressure and 298 ± 3 K in N2 + O2 buffer gas using the 254 nm photolysis of H2O2 as the OH source. In agreement with a recent absolute rate determination of the reaction the measured effective rate constant was found to increase with increasing partial pressure of O2 in the system, for 760 torr air a rate constant of (8.0 ± 0.5) × 10−12 cm3 s−1 was obtained.

Product studies have been performed on the reaction in air using FTIR absorption spectrometry for detection of reactants and products. On a molar basis, SO2 was formed with a yield of 70% and dimethyl sulfone (CH3SO2CH3) with a yield of approximately 20%. These results are considerably different to those obtained in other product studies which were carried out in the presence of NOx. These differences are compared and their relevance for the atmospheric oxidation mechanisms of DMS is discussed.
Ru(III) catalysis in N‐bromoacetamide oxidation of ethylene glycol and glycerol: A kinetic and mechanistic study
Authors: Singh Bharat , Singh Deepika , Singh A. K.
Published: January 2005

Kinetics of oxidation of ethylene glycol and glycerol by acidic solution of N‐bromoacetamide (NBA) in the presence of ruthenium (III) chloride as a homogeneous catalyst and mercuric acetate as scavenger in the temperature range of 30–50°C have been reported. The reactions follow identical kinetics, being zero‐order in substrate and first‐order in Ru(III). First order dependence of the reaction on NBA at its low concentrations tends to zero order in the higher concentration range. Positive effect of [H−] and [Cl−] has been observed. A negative effect of acetamide and ionic strength of the medium is observed while D2O and mercuric acetate show zero effect on the reaction velocity. Various activation parameters have been computed. The main product of the oxidation is corresponding acid. (H2OBr)+ has been postulated as the oxidizing species. A suitable mechanism in conformity with the kinetic data has been proposed.
Kinetics of the reactions of acenaphthene and acenaphthylene and structurally‐related aromatic compounds with OH and NO3 radicals, N2O5 and O3 at 296 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

The kinetics of the atmospherically important gas‐phase reactions of acenaphthene and acenaphthylene with OH and NO3 radicals, O3 and N2O5 have been investigated at 296 ± 2 K. In addition, rate constants have been determined for the reactions of OH and NO3 radicals with tetralin and styrene, and for the reactions of NO3 radicals and/or N2O5 with naphthalene, 1‐ and 2‐methylnaphthalene, 2,3‐dimethylnaphthalene, toluene, toluene‐α,α,α‐d3 and toluene‐d8. The rate constants obtained (in cm3 molecule−1 s−1 units) at 296 ± 2 K were: for the reactions of O3; acenaphthene, <5 × 10−19 and acenaphthylene, ca. 5.5 × 10−16; for the OH radical reactions (determined using a relative rate method); acenaphthene, (1.03 ± 0.13) × 10−10; acenaphthylene, (1.10 ± 0.11) × 10−10; tetralin, (3.43 ± 0.06) × 10−11 and styrene, (5.87 ± 0.15) × 10−11; for the reactions of NO3 (also determined using a relative rate method); acenaphthene, (4.6 ± 2.6) × 10−13; acenaphthylene, (5.4 ± 0.8) × 10−12; tetralin, (8.6 ± 1.3) × 10−15; styrene, (1.51 ± 0.20) × 10−13; toluene, (7.8 ± 1.5) × 10−17; toluene‐α,α,α‐d3, (3.8 ± 0.9) × 10−17 and toluene‐d8, (3.4 ± 1.9) × 10−17. The aromatic compounds which were observed to react with N2O5 and the rate constants derived were (in cm3 molecule−1 s−1 units): acenaphthene, 5.5 × 10−17; naphthalene, 1.1 × 10−17; 1‐methylnaphthalene, 2.3 × 10−17; 2‐methylnaphthalene, 3.6 × 10−17 and 2,3‐dimethylnaphthalene, 5.3 × 10−17. These data for naphthylene and the alkylnaphthalenes are in good agreement with our previous absolute and relative N2O5 reaction rate constants, and show that the NO3 radical reactions with aromatic compounds proceed by overall H‐atom abstraction from substituent‐XH bonds (where X = C or O), or by NO3 radical addition to unsaturated substituent groups while the N2O5 reactions only occur for aromatic compounds containing two or more fused six‐membered aromatic rings.
Kinetics and mechanism of autocatalytic oxidation of formaldehyde by nitric acid
Authors: Horváth Monika , Lengyel István , Bazsa György
Published: January 2005

The kinetics of the reaction between nitric acid and formaldehyde have been studied by spectrophotometry. The reaction is autocatalytic. A two‐step mechanism is proposed, which accounts for this behavior and describes the effect of reactant concentrations on the characteristics of the kinetic curves: the length of the induction period, ti, the maximum rate, rmax of nitrous acid production and the final product concentration, cf.
Decomposition of methylamino and aminomethyl radicals. The heats of formation of methyleneimine (CH2NH) and hydrazyl (N2H3) radical
Authors: Grela M. A. , Colussi A. J.
Published: January 2005

A kinetic analysis of the thermal decomposition of methylamino and aminomethyl radicals into methyleneimine, reactions (1) and (2):

equation image

leads to ΔH(CH2NH) = 25.0 ± 3 kcal/mol in excellent agreement with ion cyclotron resonance spectroscopy measurements and to a pi bond energy of Eπ = 55.0 kcal/mol in CH2NH which is comparable but smaller than to the corresponding value in CH2CH2 (63.7 kcal/mol). Assuming that Eπ(CH2NH) = 0.5 [Eπ(CH2CH2) + Eπ(NHNH)] then requires that Eπ(NHNH) = 46.8 kcal/mol in diimine and BDE(N2H3‐H) = 87.5 kcal/mol i.e. about 11.5 kcal/mol larger than current data for hydrazine but otherwise consistent with additional evidence.

The entropy and heat capacity of methyleneimine, calculated from recent infrared and microwave spectroscopic data using the rigid rotor harmonic oscillator approximation, are also reported.
Measurement of diffusion coefficients for diffusion‐controlled reactions
Authors: Ayscough Peter B. , Bartle Keith D. , Clifford Anthony A. , Mills Derek
Published: January 2005

The Taylor dispersion technique has been used to measure the diffusion coefficients of nine compounds in dilute solution in isopropanol at 300 K. These compounds correspond, by the difference of a single hydrogen atom, to nine free radicals, for which the rate constants for bimolecular (termination) reactions have been previously measured under the same conditions by e.s.r. Comparison of the two sets of results show the termination reactions to be essentially diffusion‐controlled, and, assuming no activation‐energy effect, interaction parameters for the termination reactions are calculated and discussed.
A kinetic study of the decomposition of HNO3 and its reaction with NO
Authors: Svensson Roger , Ljungström Evert
Published: January 2005

The rate of reaction between NO and HNO3 and the rate of thermal decomposition of HNO3 have been measured by FTIR spectroscopy. The measurements were made in a teflon lined batch reactor having a surface to volume ratio of 14 m−1. During the experiments, with initial HNO3 concentrations between 2 and 12 ppm and NO concentrations between 2 and 30 ppm, a reactant stoichiometry of unity and a first order NO and HNO3 dependence were confirmed. The observed rate constant for the reaction

at 22°C and atmospheric pressure was determined to 1.1 (±0.3) 10−5 ppm−1 min−1. At atmospheric pressure, HNO3 decomposes into NO2 and other products with a first order HNO3 dependence and with a rate constant of 2.0 (±0.2) 10−3 min−1. The apparent activation energy for the decomposition is 13 (±4) kJ mol−1.
Pulse radiolysis study of formation of poly(4‐vinylbiphenyl) anions in 2‐methyltetrahydrofuran solution at 100–120 K
Authors: Kato Noriyuki , Miyazaki Tetsuo , Fueki Kenji , Saito Atsushi
Published: January 2005

The reactions of poly(4‐vinylbiphenyl) (denoted as PVB) polymers and biphenyl molecules with solvated electrons in the 2‐methyltetrahydrofuran (MTHF) solvent have been studied at 100–120 K by electron‐pulse radiolysis. The formation of PVB polymer anions as well as biphenyl anions was observed by the electron‐pulse irradiation of the MTHF‐PVB(or biphenyl) solution. The anions are formed by two processes; a rapid formation during the pulse irradiation (<20 ns) and a slow formation after the pulse irradiation. The slow formation is due to a diffusion‐controlled reaction between solutes, such as PVB and biphenyl, and solvated electrons. It was found that the reaction efficiency, expressed in monomer unit, of PVB polymers is 1/27 of that of biphenyl molecules. The reaction radius for the electron capture reaction of PVB polymers is estimated as 200–370 A, which is much larger than the gyration radius (107 A) of polymer coils in MTHF solution.
Kinetic measurements on the system: 2NO2 = N2O4 at (224 ± 2) K using time‐resolved infrared laser absorption
Authors: Brunning John , Frost Michael J. , Smith Ian W. M.
Published: January 2005

Direct kinetic measurements have been made on the reaction: 2NO2 = N2O4. Equilibrium mixtures of NO2 and N2O4 at (224 ± 2) K were perturbed by flash photolysis of a fraction of the N2O4. The rate of relaxation back to equilibrium was monitored by observing the transmittance of the 14P(11) line from a cw CO laser selected to coincide with the v9 band of N2O4. Measurements were made in the presence of 350–750 torr of He, N2, or CF4. Within this limited pressure range, the kinetics were consistent with third‐order behavior with the following rate constants (cm3 molecule−1 s−1): k0 = (2.4 ± 0.5) × 10−34 [He]; (1.0 ± 0.1) × 10−33 [N2]; (1.8 ± 0.3) × 10−33 [CF4].
The kinetics of successive addition of oxirane to alkanethiols in the presence of basic catalysts
Authors: Chlebicki Jan , Cichacz Zbigniew
Published: January 2005

Rate constants and activation parameters of direct reaction of oxirane with certain alkyl‐2‐hydroxyethyl sulfides and/or successive oxyethylene adducts in the presence of basic catalyst were studied at temperatures 323–353 K. The reactions were found to be of the first order with respect to oxirane, sulfide, and catalyst concentrations. The kinetics are consistent with a termolecular mechanism.
Kinetics and mechanisms of the permanganate oxidation of L‐valine in neutral aqueous solutions
Authors: Pérez‐benito Joaquin F. , Rodriguez Rosa M. , De Andrés Jaime , Brillas Enrique , Garrido José A.
Published: January 2005

The permanganate oxidation of L‐valine has been studied by visible spectrophotometry in neutral aqueous solutions. Under these conditions, both the zwitterionic and anionic forms of the amino acid are oxidized, the reaction being autocatalyzed by soluble colloidal manganese dioxide. Kinetic data for both the uncatalyzed and autocatalytic reaction pathways have been obtained, and reaction sequences consistent with the experimental findings are proposed.
Reaction rate analysis of complex kinetic systems
Authors: Turányi T. , Bérces T. , Vajda S.
Published: January 2005

Using the elementary sensitivity densities, a reaction rate sensitivity gradient is obtained which is the derivative of the rate of species concentration change with respect to the rate coefficient. The dimensionless (log‐normalized) form of the reaction rate sensitivity gradient is the ratio of the rate of concentration change of species i due to elementary reaction j and the net rate of concentration change of species i. This result provides a mathematical basis for the use of various forms of reaction rate analyses in the study of complex reaction mechanisms. The kinetic information inherent in the relative reaction rate matrix is extracted by principal component analysis. The method is used to analyze the mechanism of high‐temperature formaldehyde oxidation and high‐temperature propane pyrolysis. Ranking of the elementary reactions allowed us to reduce significantly the original mechanisms and a detailed study of the results revealed the reaction structures and the major reaction paths of the species.
Canonical statistical adiabatic channel model calculations of the H + CH3 → CH4 recombination reaction on an ab initio potential energy surface. The role of the transitional modes
Authors: Cobos C. J.
Published: January 2005

The canonical formalism of the statistical adiabatic channel model is used to calculate limiting high pressure rate constants for the H + CH3 → CH4 recombination reaction on a recently reported analytic potential energy surface based on ab initio calculations. An effective adiabatic channel potential which incorporates the Gϕϕ matrix element of the twofold degenerate H3CH transitional bending mode, quartic anharmonicity, and state selected mode coupling effects is implemented. The rate constants calculated over the temperature range 200–1000 K are in very good agreement with recent canonical variational transition state theory calculations performed on the same surface. The comparison with experimental results is also discussed.
Kinetics of gas‐phase thermal elimination of (α‐phenylethyl) and (β‐phenylethyl)‐pyrazole
Authors: Perez Jorge Daniel , Phagouape Leonardo Miguel
Published: January 2005

Flash Vaccum Pyrolysis of (α‐phenylethyl) and (β‐phenylethyl)‐pyrazole were studied. Pyrazole and Styrene were found as only products of both reactions. The kinetic parameters obtained reinforce the results previously found about the poor influence of the substitutents on the α and β carbons of the ethyl group in the FVP of N‐alkyl pyrazoles and (β‐haloethyl) pyrazoles.
Kinetics of oxidation of some ortho, meta, and para substituted S‐phenylmercaptoacetic Acids by N‐Chloro‐3‐Methyl‐2,6‐Diphenyl piperidin‐4‐one in buffered ethanol‐water
Authors: Ganapathy K. , Kabilan S.
Published: January 2005

The kinetics of oxidation of a number of ortho, meta, and para substituted S‐phenylmercaptoacetic acids by N‐Chloro‐3‐Metyl‐2,6‐Diphenylpiperidin‐4‐one (NCP) has been studied in buffered ethanol‐water (75:25 v/v) of pH 5.46. The reaction is of first order each in [oxidant] and [substrate]. The rate constant decreases with increase in pH from 5.22 to 5.70. The reaction is accelerated by electron releasing and retarded by electron withdrawing substitutents. The ρ value obtained for this reaction is −1.88 at 10°C with a good correlation coefficient of 0.99 showing an electron deficient transition state. The effect of ortho substitutents also is discussed in detail.
CH bond dissociation energies, isolated stretching frequencies, and radical stabilization energy
Authors: McKean D. C.
Published: January 2005

An earlier correlation between isolated CH stretching frequencies, v, and experimental CH bond dissociation energies, in hydrocarbons, fluorocarbons, and CHO compounds, is updated. A stabilization energy, E, which reflects only the properties of the radical, is defined by the deviation of a point from the above correlation. E values for a variety of radicals are listed and discussed. In HCN and HCO compounds E is low or negligible, due to the low v found in these compounds. The conventional definition of ES then represents a serious misnomer, which distracts attention from the probable source of discrepancies between experimental and ab initio values of DH°(CH), namely, the parent molecules. Stereo electronic effects concerned with the breaking of CH bonds are predicted in a variety of situations.

Some experimental determinations of DH°(CH), viz., in C2H4, HCOOH, CH3CHO, CH3NH2, are considered to be probably in error.

Schemes for partitioning energies of atomization into ‘standard’ or ‘intrinsic’ bond energies are criticized.
Rate constants for the reactions of Br atoms with a series of alkanes, alkenes, and alkynes in the presence of O2
Authors: Barnes I. , Bastian V. , Becker K. H. , Overath R. , Tong Zhu
Published: January 2005

Rate constants of Br atom reactions have been determined using a relative kinetic method in a 20 l reaction chamber at total pressures between 25 and 760 torr in N2 + O2 diluent over the temperature range 293–355 K. The measured rate constants for the reactions with alkynes and alkenes showed dependence upon temperature, total pressure, and the concentration of O2 present in the reaction system.

Values of (6.8 ± 1.4) × 10−15, (3.6 ± 0.7) × 10−14, (1.5 ± 0.3) × 10−12, (1.6 ± 0.3) × 10−13, (2.7 ± 0.5) × 10−12, (3.4 ± 0.7) × 10−12, and (7.5 ± 1.5) × 10−12 (units: cm3 s−1) have been obtained as rate constants for the reactions of Br with 2,2,4‐trimethylpentane, acetylene, propyne, ethene, propene, 1‐butene, and trans‐2‐butene, respectively, in 760 torr of synthetic air at 298 K with respect to acetaldehyde as reference, k = 3.6 × 10−12 cm3 s−1.

Formyl bromide and glyoxal were observed as primary products in the reaction of Br with acetylene in air which further react to form CO, HBr, HOBr, and H2O2. Bromoacetaldehyde was observed as an primary product in the reaction of Br with ethene. Other observed products included CO, CO2, HBr, HOBr, BrCHO, bromoethanol, and probably bromoacetic acid.
Rate constants for hydrogen abstraction reactions of the sulfate radical, SO4−. Alcohols
Authors: Clifton Carol L. , Huie Robert E.
Published: January 2005

Rate constants have been determined for the reactions of SO4− with a series of alcohols, including hydrated formaldehyde. The SO4− radical was produced by the laser‐flash photolysis of persulfate, S2O82−. Rate constants for the reactions of SO4− with alcohols range from 1.0 × 107 for methanol to 3.4 × 108 M−1 s−1 for 1‐octanol. Rate constants for the reactions of SO4− with deuterated methanol and ethanol are lower by about a factor of 2.5. For methanol, ethanol, and 2‐propanol, the temperature dependence of the rate constant was determined over the range 10–45°C.
Thermal decomposition of propane in shock waves
Authors: Hidaka Yoshiaki , Oki Takashi , Kawano Hiroyuki
Published: January 2005

The thermal decomposition of propane was studied behind reflected shock waves over the temperature range 1100–1450 K and the pressure range 1.5–2.6 atm, by both monitoring the time variations of absorption at 3.39 μm and analyzing the concentrations of the reacted gas mixtures. The rate constants of the elementary reactions were discussed from the results. The rate constant expressions, k1 = 1.1 × 1016 exp (−84 kcal/RT) s−1 and k4 = 9.3 × 1013 exp(−8 kcal/RT) cm3 mol−1 s−1, of reactions C3H8 → CH3 + C2H5 and C3H8 + H → n‐C3H7 + H2 were evaluated, respectively.
Kinetic study of the iodine monobromide‐or iodine monochloride‐catalyzed alcoholysis of butoxytriethylsilane: n‐butoxy group — s‐butoxy group exchange reaction
Authors: Ito Katsuko , Ibaraki Takeshi
Published: January 2005

The catalytic activity of iodine monobromide and iodine monochloride were investigated in the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH. Pseudo first‐order rate constants were measured by gas chromatography, at 10°, 20°, 30°, and 40°C for iodine monobromide and at 10°, 20°, and 30°C for iodine monochloride, on reaction mixtures containing both butanols in excess.
The catalytic coefficients of both catalysts were evaluated from the observed rate constants as follows:

The activation paramaters were estimated from these data, and were compared with the values for iodine catalysis. These results are consistent with the mechanism previously proposed.
Formation of ring‐retaining products from the OH radical‐initiated reactions of benzene and toluene
Authors: Atkinson Roger , Aschmann Sara M. , Arey Janet , Carter William P. L.
Published: January 2005

The aromatic ring‐retaining products formed from the gas–phase reactions of the OH radical with benzene and toluene, in the presence of NOx, have been identified and their formation yields determined. These products, and their formation yields, are as follows: from benzene – phenol, 0.236 ± 0.044; nitrobenzene, {(0.0336 ± 0.0078) + (3.07 ± 0.92) × 10−16[NO2]}; from toluene – benzaldehyde, 0.0645 ± 0.0080; benzyl nitrate, 0.0084 ± 0.0017; o−cresol, 0.204 ± 0.027; m− + p−cresol, 0.048 ± 0.009; m‐nitrotoluene, {(0.0135 ± 0.0029) + (1.90 ± 0.25) × 10−16[NO2]}, where the NO2 concentration is in molecule cm−3 units. The formation yields of o‐ and p‐nitrotoluene from toluene were ca. 0.07 and 0.35 that of m‐nitrotoluene, respectively. The observations that the nitro‐aromatic yields do not extrapolate to zero as the NO2 concentration approaches zero are not consistent with current chemical mechanisms for these OH radical‐initiated reactions, and suggest that under the experimental conditions employed in this study the hydroxycyclohexadienyl radicals formed from OH radical addition to the aromatic ring react with NO2 rather than with O2. However, these data concerning the nitroaromatic yields are consistent with our previous conclusions that many of the nitrated polycyclic aromatic hydrocarbons present in ambient air are formed, at least in part, in the atmosphere from OH radical reactions.
Radical sensitization of acetylene pyrolysis
Authors: Durán R. P. , Amorebieta V. T. , Colussi A. J.
Published: January 2005

The kinetics of acetylene polymerization initiated by neopentane (Np) or acetone (Ac) decompositions has been investigated in a static reactor dynamically coupled to a modulated beam mass spectrometer between 850–950 K. Overall rates follow the expression: R = −d[C2H2]/dt = ks[X]1/2[C2H2] + ku[C2H2]2 (I), where X represents Np or Ac and ks, ku the rate constants of the sensitized and unsensitized reactions, respectively. The rate law of the sensitized reaction clearly suggests a chain polymerization mechanism with ks = kp(ki/kt)1/2 (i, t, and p stand for initiation, termination, and propagation, respectively). Remarkably, the derived values of kp are nearly independent of the sensitizer, although Ac acts as a source of methyl radicals whereas Np also produces hydrogen atoms, and fall in the expected range for the addition of vinylic radicals to acetylene. It is shown that a chain transfer process involving the fast [1,5] intramolecular hydrogen atom shift in 4‐methyl‐buta‐1,3‐dien‐1‐yl radicals (CH3CH  CHCH ĊH) followed by further addition to C2H2 and aromatization, transforms methyl radicals into hydrogen atoms and is able to account for the presence of toluene among the products of the sensitized reactions. Based on current thermochemical data for the but‐1‐en‐3‐yn‐2‐yl radical (CH2ĊCCH) and present rates of propagation it is argued that if the unsensitized polymerization of acetylene also proceeded by a vinyl radical chain, then even the most favorable self‐initiation reaction: 2C2H2 = C4H3 + H (a), would be far too slow. Finally, present results also show that acetone at impurity levels (⩽ 0.1%) can not provide fast enough spurious initiation rates in chain mechanisms for the “unsensitized” acetylene pyrolysis at pressures above 10 torr.
Selectivity–reactivity correlations for thermal Diels–Alder reactions of cyclohexa‐1,3‐diene with substituted Ethenes in the gas phase
Authors: Van Mele B. , Huybrechts G.
Published: January 2005

Selectivity–reactivity correlations are shown to support a biradical pathway for the gas phase thermal Diels–Alder reactions of cyclohexa‐1,3‐diene with substituted ethenes except for those involving a carbonyl group.
Kinetics of the reaction of OH radicals with a series of ethers under simulated atmospheric conditions at 295 K
Authors: Wallington Timothy J. , Andino Jean M. , Skewes Loretta M. , Siegl Walter O. , Japar Steven M.
Published: January 2005

Ethers are being increasingly used as motor fuel additives to increase the octane number and to reduce CO emissions. Since their reaction with hydroxyl radicals (OH) is a major loss process for these oxygenated species in the atmoshpere, we have conducted a relative rate study of the kinetics of the reactions of OH radicals with a series of ethers and report the results of these measurements here. Experiments were performed under simulated atmospheric conditions; atmospheric pressure (≃ 740 torr) in synthetic air at 295 K. Using rate constants of 2.53 × 10−12, and 1.35 × 10−11 cm3 molecule−1 s−1 for the reaction of OH radicals with n‐butane and diethyl ether, the following rate constants were derived, in units of 10−11 cm3 molecule−1 s−1: dimethylether, (0.232 ± 0.023); di‐n‐propylether, (1.97 ± 0.08); di‐n‐butylether, (2.74 ± 0.32); di‐n‐pentylether, (3.09 ± 0.26); methyl‐t‐butylether, (0.324 ± 0.008); methyl‐n‐butylether, (1.29 ± 0.03); ethyl‐n‐butylether, (2.27 ± 0.09); and ethyl‐t‐butylether, (0.883 ± 0.026). Quoted errors represent 2σ from the least squares analysis and do not include any systematic errors associated with uncertainties in the reference rate constants used to place our relative measurements on an absolute basis. The implications of these results for the atmospheric chemistry of ethers are discussed.
FTIR study of the reaction of ethyl radicals with O2 and Cl2 in air at 295 K
Authors: Wallington Timothy J. , Andino Jean M. , Kaiser E. W. , Japar Steven M.
Published: January 2005

Using Fourier transform infrared spectroscopy, the ethene yield from the reaction of C2H5 radicals with O2 has been determined to be 1.50 ± 0.09%, 0.85 ± 0.11%, and <0.1% at total pressures of 25, 50, and 700 torr, respectively. Additionally, the rate constant of the reaction of C2H5 radicals with molecular chlorine was measured relative to that with molecular oxygen.
equation image
A ratio k6/k7 = 1.99 ± 0.14 was measured at 700 torr total pressure which, together with the literature value of k7 = 4.4 × 10−12 cm3 molecule−1s−1, yields k6 = (8.8 ± 0.6) × 10−12 cm3 molecule−1s−1. Quoted errors represent 2σ. These results are discussed with respect to previous kinetic and mechanistic studies of C2H5 radicals.
The mechanism of the elimination kinetics of 2‐bromo‐2‐butene in the gas phase
Authors: Chuchani Gabriel , Dominguez Rosa M.
Published: January 2005

The kinetics of the gas phase elimination of 2‐bromo‐2‐butene were determined in a static system over the temperature range of 340–380°C and pressure range of 37–134 torr. The reaction in seasoned vessels, even in the presence of a free radical inhibitor, is catalyzed by hydrogen bromide. Under maximum catalysis of HBr, the kinetics were found to be of order 1.0. The reaction, when maximally catalyzed with HBr, appears to undergo a molecular elimination of HBr which follows first‐order kinetics. The products are 1,2‐butadiene and hydrogen bromide. The rate coefficients. under maximum catalysis, are given by the Arrhenius equation log 𝓀1(s−1) = (13.57 ± 0.56) − (200.4 ± 6.8) kJ mol−1 (2.303RT)−1. The catalyzed pyrolysis of 2‐bromo‐2‐butene appears to proceed through a six‐membered cyclic transition‐state type of mechanism.
Kinetic study of the bromine‐catalyzed alcoholysis of butoxytriethylsilane: n‐Butoxy group–s‐butoxy group exchange reaction
Authors: Ito Katsuko , Ibaraki Takeshi
Published: January 2005

In order to compare the catalytic activity of bromine with those of iodine and iodine monohalides, kinetic studies on the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH, were undertaken. Pseudo first‐order rate constants were determined at 0°, 10°, 15°, 20°, and 30°C by means of gas chromatography on the reaction mixtures containing both butanols in excess. From the observed rate constants, the catalytic coefficients of bromine were evaluated as follows:

The enthalpies and entropies of activation were estimated to be (42.0 – 42.2) kJ/mol, −(103 – 104) J/K (forward reaction), and (40.4 − 40.7) kJ/mol, − (101 − 102) J/K (reverse reactions). These data suggest that bromine is much more active than iodine and iodine monohalides, and its high activity was interpreted on the basis of the structure of the reaction intermediate.
Kinetics of the reactions of Cl(2PJ) and Br(2P3/2) with O3
Authors: Nicovich J. M. , Kreutter K. D. , Wine P. H.
Published: January 2005

A laser flash photolysis‐resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reactions Cl(2PJ) + O3 → ClO + O2 and Br(2P3/2) + O3 → BrO + O2 as a function of temperature. The temperature dependence observed for the Cl(2PJ) + O3 reaction is nonArrhenius, but can be adequately described by the following two Arrhenius expressions (units are cm3 molecule−1 s−1, errors are 2σ and represent precision only): 𝓀1(T) = (1.19 ± 0.21) × 10−11 exp [(−33 ± 37)/T] for T = 189–269K and 𝓀1(T) = (2.49 ± 0.38) × 10−11 exp[(−233 ± 46)/T] for T = 269–385 K. At temperatures below 230 K, the rate coefficients determined in this study are faster than any reported previously. Incorporation of our values for 𝓀1(T) into stratospheric models would increase calculated ClO levels and decrease calculated HCl levels; hence the calculated efficiency of ClOx catalyzed ozone destruction would increase. The temperature dependence observed for the (2P3/2) + O3 reaction is adequately described by the following Arrhenius expression (units are cm3 molecule−1 s−1, errors are 2σ and represent precision only): 𝓀2(T) = (1.50 ± 0.16) × 10−1 exp[(−775 ± 30)/T] for T = 195–392 K. While not in quantitative agreement with Arrhenius parameters reported in most previous studies, our results almost exactly reproduce the average of all earlier studies and, therefore, will not affect the choice of 𝓀2(T) for use in modeling stratospheric BrOx chemistry.
Rate constants for Hydrogen abstraction reactions of NO3 in aqueous solution
Authors: Shastri L. V. , Huie Robert E.
Published: January 2005

Rate constants have been measured by pulse radiolysis for the reactions of the NO3 radical with five cyclic ethers and a series of alcohols. Rate constants ranged from 3.5 × 104 M×1 s×1 for deuterated methanol to 1.1 × 107 M−1 s−1 for tetrahydrofuran. The rate constants for the reactions of NO3 with the alcohols 1‐propanol to 1‐heptanol were found to be linearly dependent on the number of CH3 groups with a group reactivity of 6.4 × 105 M−1 s−1.
High temperature reaction rate coefficients derived from N‐atom ARAS measurements and excimer photolysis of NO
Authors: Davidson D. F. , Hanson R. K.
Published: January 2005

Mixtures of NO and NO/H2 in Ar were shock‐heated and photolyzed with an ArF excimer laser. Measurements in these experiments of N‐atom profiles using atomic resonance absorption spectrophotometry (ARAS) permitted the determination of two rate coefficients. The rate coefficient for the reaction
equation image
was found to be 4.29 × 1013 exp(−787/T) cm3 mol−1 sec−1 (±20% at 1400 K to ±10% at 3500 K). This is the first direct high temperature measurement of this rate coefficient in the exothermic direction. The rate coefficient for the reaction
equation image
was found to be 1.60 × 1014 exp(−12650/T) (±35% from 1950 to 2850 K). To our knowledge, this is the first direct measurement of this rate coefficient.

A study of the N‐atom ARAS absorption behavior revealed a noticeable pressure dependence, as well as a weak temperature dependence, in the Beer‐Lambert law absorption coefficient. Proper consideration of these effects is important when the N‐atom ARAS diagnostic is used for absolute concentration measurements.
Kinetics and nitro‐products of the gas‐phase OH and NO3 radical‐initiated reactions of naphthalene‐d8, Fluoranthene‐d10, and pyrene
Authors: Atkinson Roger , Arey Janet , Zielinska Barbara , Aschmann Sara M.
Published: January 2005

The kinetics and nitroarene product yields of the gas‐phase reactions of naphthalene‐d8, fluoranthene‐d10, and pyrene with OH radicals in the presence of NOx and in N2O5NO3NO2air mixtures have been investigated at 296 ± 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene‐d8 was shown to react in N2O5NO3NO2air mixtures a factor of 1.22 ± 0.10 times faster than did naphthalene, with the 1‐ and 2‐nitronaphthalene‐d7 product yields being similar to those of 1‐ and 2‐nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2‐, 7‐, and 8‐nitrofluoranthene‐d9 and 2‐ and 4‐nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical‐initiated reactions. Effective rate constants for the reactions of fluoranthene‐d10 and pyrene with N2O5 in N2O5;NO3NO2air mixtures of ca. 1.8 × 10−17 cm3 molecule−1 s−1 and ca. 5.6 × 10−17 cm3 molecule−1 s−1, respectively, were derived. Formation yields of 2‐nitrofluoranthene‐d9 and 4‐nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2‐Nitropyrene was also observed to be formed in these N2O5NO3NO2 reactions, but was found to be a function of the NO2 concentration and, therefore, would be a negligible product under ambient NO2 concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations.
Kinetic study of the reaction OH + HI by laser photolysis‐resonance fluorescence
Authors: Leod H. Mac , Balestra C. , Jourdain J. L. , Laverdet G. , Bras G. Le
Published: January 2005

The gas phase reaction of OH radicals with hydrogen iodide (HI) has been studied using a Laser Photolysis‐Resonance Fluorescence (LP‐RF) apparatus, recently developed in our group. The measured rate constant at 298 K was (2.7 ± 0.2) × 10−11 cm3 molecule−1 s−1. This rate constant is compared with the ones of the reactions OH + HCl and OH + HBr. The role of the reaction OH + HI in marine tropospheric chemistry is discussed.

In addition, the LP‐RF apparatus was tested and validated by measuring the following rate constants (in cm3 molecule−1 s−1 units): 𝓀(OH + HNO3) = (1.31 ± 0.06) × 10−13 at p = 27 and 50 Torr of argon and 𝓀(OH + C3H8) = (1.22 ± 0.08) × 10−12. These rate constants are in very good agreement with the literature data.
On the mechanism of C2F5I photolysis in the presence of trifluoroacetic acid
Authors: Lane S. I. , Oexler E. V. , Staricco E. H.
Published: January 2005

The photolysis of C2F5I with CF3COOH in the temperature range 473–533 K was studied in the gas phase.

Evidence is presented that supports a complex mechanism for the formation of C2F5H through the H‐atom abstraction reaction from CF3COOH by C2F5 radicals as well as the participation of I(2P½).
Chemical effects of radical vibrational energy content on the abstraction reaction: CF3 + Br2 → CF3Br + Br
Authors: Young Mark A. , Pimentel George C.
Published: January 2005

We have studied the effect of vibrational mode activation in the CF3 radical on the bromine abstraction reaction; CF3 + Br2 → CF3Br + Br. Excess vibrational energy resides in the symmetric modes of the radical after 248 nm photolysis of the parent molecule, CF3I. Our data indicate that the hot radicals react no faster than thermalized CF3, and may actually have a lower cross‐section for reaction. Dynamical factors that result in poor coupling of the vibrational energy to the reaction coordinate, as well as other similar considerations, could be responsible for the experimental observations. In addition, we have made an independent determination of the rate for the bromine abstraction reaction of (1.08 ± .13) × 1012 s−1 cm3 mol−1.
Formation of ring‐retaining products from the OH radical‐initated reactions of o‐, m‐, and p‐xylene
Authors: Atkinson Roger , Aschmann Sara M. , Arey Janet
Published: January 2005

The ring‐retaining products formed from the OH radical‐initiated reactions of o‐, m‐, and p‐xylene in the presence of NOx have been identified and their formation yields determined. Experiments were carried out at 298 ± 2 K and in the presence of 740 torr total pressure of air. The products observed, and their yields, were: from o‐xylene, o‐tolualdehyde, 0.0453; 2‐methylbenzyl nitrate, (0.0135 + 5.5 × 10−17 [NO2]); 2,3‐dimethylphenol, 0.097; 3,4‐dimethyl‐phenol, 0.064; 3‐nitro‐o‐xylene, 0.0059; 4‐nitro‐o‐xylene, (0.0111 + 9.9 × 10−17 [NO2]); from m‐xylene, m‐tolualdehyde, 0.0331; 3‐methylbenzyl nitrate, 0.0061; 2,4‐dimethylphenol, 0.099; 2,6‐dimethylphenol, 0.111; 4‐nitro‐m‐xylene, 0.0018; 5‐nitro‐m‐xylene, (0.0032 + 1.6 × 10−17 [NO2]); from p‐xylene, p‐tolualdehyde, 0.0701; 4‐methylbenzyl nitrate, 0.0082; 2,5‐dimethylphenol, 0.188, 2‐nitro‐p‐xylene, (0.0120 + 2.8 × 10−17 [NO2]), where the NO2 concentration is in molecule cm−3 units. The nitro‐xylene data are consistent with our recent product study of the corresponding reactions of benzene and toluene and indicate that under the experimental conditions employed the dimethylhydroxycyclohexadienyl radicals reacted with NO2 and not with O2. When combined with literature ring‐cleavage product yields, these data show that ca. 55–80% of the reaction pathways are accounted for.
Propagating reaction front in ‘frozen’ phase
Authors: Szirovicza Lajos , Nagypál István , Bárdi István
Published: January 2005

It is reported and explained that the front‐like reaction sustains, and its velocity is enhanced in frozen phase in the chlorite‐thiosulphate system.