bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and mechanisms of the reaction of acetylene with cyclohexa‐1,3‐diene and the decomposition of bicyclo[2.2.2]‐octa‐2,5‐diene in the gas phase
Authors: Huybrechts G. , Leemans W. , Van Mele B.
Published: January 2005

The reaction of acetylene (A) with cyclohexa‐1,3‐diene (CHD) has been studied between 450 and 592 K. The pressures of A ranged from 25 to 112 torr and those of CHD from 8 to 62 torr. The reaction yields only ethene (E) and benzene (B) instead of bicyclo[2.2.2]octa‐2,5‐diene (BOD), the product that is expected for a 1,4,1′,2′ addition of the Diels–Alder type. It is first order with respect to each reagent. The rate constant (in L/mol·s) is given by

The thermal decomposition of BOD has also been studied. In the ranges of 354–435 K and 0.5–6 torr, the reaction is first order and results in the formation of equal amounts of B and E as the reaction of A with CHD does. Its rate constant (in s−1) is given by

The following consecutive reactions are proposed for the reaction between A and CHD: magnified image where BOD is the primary product that is too unstable to be detected. This implies that the rate constant k is equal to ka. The reaction mechanisms and the strain energy in BOD are discussed.
Determination of the gas‐phase decomposition rate constants of heptyl‐1 and heptyl‐2 hydroperoxides C7H15OOH
Authors: Sahetchian K. A. , Heiss A. , Rigny R. , Ben‐aïm R. I.
Published: January 2005

The gas‐phase decomposition of n‐heptyl‐1 and n‐heptyl‐2 hydroperoxides C7H15OOH, which split into two radicals C7H15O and OH, has been investigated in the temperature range of 250–360°C. The decomposition has been carried out in a hydrogen–oxygen mixture (the hydroperoxide represents about 50 ppm) so as to avoid secondary reactions between the formed radicals and the reactants. Although the H2–O2 mixture is not spontaneously reactive in our conditions, it operates the transformation, through a fast and well‐known process, of the OH radicals into HO2 radicals and then into H2O2. However, C7H15O radicals are also transformed into HO2 radicals and then into H2O2, but through an unknown process. To avoid heterogeneous reactions, vessel and probe are coated by B2O3 and then treated by the slow combustion of hydrogen at 510°C and 250 torr before the experiments are performed. As the reaction scheme is very simple, due to the use of the H2–O2 mixture, the determination of the evolutions of the HO2 concentration (followed by electronic paramagnetic resonance) lead to the determination of the gas‐phase decomposition rate constant of hydroperoxides. For the n‐heptyl‐1 hydroperoxide the rate constant is

and for the n‐heptyl‐2 hydroperoxide it is

.
Pyrolysis studies of main group metal‐alkyl bond dissociation energies: VLPP of GeMe4, SbEt3, PbEt4, and PEt3
Authors: Smith Gregory P. , Patrick Roger
Published: January 2005

The bond dissociation energies of tetramethyl germane, triethyl stibine, tetraethyl lead, and triethylphosphine were determined using the technique of very‐low‐pressure pyrolysis. Arguments are presented for log A ≥ 17.0. The respective dissociation energies ΔH298 are 83, 57, 54, and 68 (±2) kcal/mol. A consistent set of methyl bond energies to main group metals is determined from these and previous results, and is examined for trends. Bond energies for various radicals to tin are also derived.
The pyrolysis kinetics of ethyl esters in the gas phase. The alkyl substituent effect at the acyl carbon
Authors: Chuchani Gabriel , Martin Ignacio
Published: January 2005

The gas‐phase elimination of ethyl 3‐methylbutanoate and ethyl 3,3‐dimethylbutanoate has been studied, in a static system, over the temperature range of 360–420°C and in the pressure range of 71–286 torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3‐methylbutanoate, logk1(s−1) = (12.70 ± 0.36) – (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3‐dimethylbutanoate, logk1(s−1) = (13.04 ± 0.08) – (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.
Rate of formation of toluene from ethylbenzene
Authors: Davis Hubert G.
Published: January 2005

The rate of formation of toluene from ethylbenzene was studied at atmospheric pressure in the temperature range of 600–725°C in conventional flow equipment. Residence times were 0.55–1.7 s, and initial partial pressures of ethylbenzene (H2O diluent) were 0.05–0.17 atm. The rate of appearance of toluene measures [1] the rate of the reaction C6H5C2H5 → C6H5CH + CH, with log k = 15.70 – 74.49 ± 3.2/θ. From the activation energy, E0 for the decomposition is estimated to be 72.2 ± 3.2 kcal/mol. The results are compatible with those of Esteban et al. [2], for which regression analysis gives log k1 = 14.79 – 70.76/θ. A composite, log k = 15.10 – 72.0/θ, fits both sets of data and is experimentally indistinguishable from Robaugh and Steina's [3] recent estimate by the VLPP technique or other estimates in the literature [4–6]. In light of the high overall conversion of ethylbenzene studied (2–80%), the industrial‐type flow equipment, and the widely differing methods of characterization and analysis, the excellent agreement with the results of [2,3,5] is worthy of note. The data are compatible with current estimates of the heat of formation of benzyl radicals [6,7].
The thermal decomposition of n‐hexane
Authors: Ebert K. H. , Ederer H. J. , Isbarn G.
Published: January 2005

The kinetics of the pyrolysis of n‐hexane was studied in a conventional static reactor over a temperature range of 650–840 K. The overall reaction is essentially first order with the kinetic parameters A = 1013.92 s−1 and EA = 260.3 kJ/mol. The distributions of the main products were analyzed by gas chromatography. A reaction model involving 240 elementary reactions was developed to describe the experimental rate data. The agreement of the model with experimental data was surprisingly good over a wide range of temperatures and pressures and up to medium extents of conversion. Methods for sensitivity studies based upon the quasi‐stationary‐state assumption (QSSA) were developed, and for a number of more detailed effects, such as self‐inhibition, explanations could be given. It was also shown that the hexyl isomerization reactions influence strongly the product distribution. The outstanding capability of kinetic modeling with computer simulations in handling complex kinetic systems is demonstrated.
Kinetics of the gas‐phase reaction CH3F + I2 ⇆ CH2FI + HI: The CH bond dissociation energy in methyl and methylene fluorides
Authors: Pickard J. M. , Rodgers A. S.
Published: January 2005

The kinetics of the gas‐phase reaction of CH3F with I2 have been studied spectrophotometrically from 629 to 710 K, and were determined to be consistent with the following mechanism:
equation image
A least‐squares analysis of the kinetic data taken in the initial stages of reaction resulted in

where θ = 4.575T/1000 kcal/mol. The errors represent one standard deviation. The experimental activation energy E4 = 30.8 ± 0.2 kcal/mol was combined with the assumption E3 = 1 ± 1 kcal/mol and estimated heat capacities to obtain

The enthalpy change at 298 K was combined with selected thermochemical data to derive

The kinetic studies of ĊHF2 and CH2F2 have been reevaluated to yield

These results are combined with literature data to yield the CH, CF, and CCl bond dissociation energies in their respective fluoromethanes, and the effect of α‐fluorine substitution is discussed.
An FTIR study of the mechanism for the reaction HO + CH3SCH3
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P.
Published: January 2005

Product studies were made using the Fourier transform infrared method in the uv (300–400‐nm) photolysis of mixtures containing CH3SCH3, C2H5ONO, and NO in ppm concentrations in 700 torr of O2–N2 diluent. Methyl thionitrite, CH3SNO, arising from the reaction CH3S + NO, was detected as an intermediate product. In addition, the yields of the major sulfur‐containing products SO2 and CH3SO3H coincided with those of the oxidation of the CH3S radicals generated directly by the photodissociation of CH3SNO. The formation of CH3S in the HO‐initiated oxidation of CH3SCH3 in the presence of NO suggests a reaction scheme involving the H‐abstraction reaction HO + CH3SCH3 → CH3SCH2 + H2O as the primary step.
Sensitivity analysis and parameter estimation in dynamic modeling of chemical kinetics
Authors: Miller David , Frenklach Michael
Published: January 2005

A new approach to the dynamic modeling of chemical kinetics is presented. The technique is based on systematic planning of computer experiments, which allows an empirical model for the computed responses to be developed in the space of parameters. The empirical equations which are obtained provide complete information on the sensitivities with respect to various rate constants, disclosing their interrelationships. Utilization of these equations instead of numerical integration of the differential equations associated with the chemical reactions makes parameter estimation a trivial task. As a consequence the adequacy of the mechanism can be tested. The technique is applied to the thermal decomposition of propane.
Effects of diffusion on the self‐termination kinetics of isopropylol radicals in solution
Authors: Lehni M. , Fischer H.
Published: January 2005

Rate constants for the bimolecular self‐reaction of isopropylol radicals [(CH3)2ĊOH] in various solvents are determined as functions of temperature by kinetic electron spin resonance. For hydrocarbon solvents they are well described by theoretical equations for reactions controlled by translational diffusion if diffusion coefficients of 2‐propanol, a constant reaction distance, and a spin statistical factor of 1/4 are applied. Deviations from 2kt ∼ D at high diffusion constants agree with trends expected from recent theoretical models. For hydrogen‐bonding solvents large negative deviations are observed. They are attributed to steric constraints and slower rotational diffusion of radical–solvent aggregates. The disproportionation‐to‐combination ratio of isopropylol increases with solvent viscosity. As previously for tert‐butyl, this is explained by anisotropic reorientation during encounters. Further, rate data are given for the decarbonylation of the 2‐hydroxy‐2‐methylpropanoyl radical and for several hydrogen abstraction reactions of isopropylol.
High‐temperature determination of the rate coefficient for the reaction H2 + CN → H + HCN
Authors: Szekely Attila , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

The rate coefficient of the reaction

has been determined in the temperature range of 2700–3500 K using a shock tube technique. C2N2H2Ar mixtures were heated behind incident shock waves and the early‐time CN history was monitored using broad‐band absorption spectroscopy. The rate coefficient providing the best fit to the data was

in good agreement with extrapolations of previously published low‐temperature results.
Kinetics and mechanism of the reactions of the superoxide ion in solutions. I. Absorption spectra and interaction with solvents and cations
Authors: Afanas′ev I. B. , Kuprianova N. S. , Polozova N. I.
Published: January 2005

Absorption spectra of the superoxide ion have been studied in dimethylformamide (DMF) and acetonitrile (AN). It was found that the superoxide ion existed in equilibrium with an ion pair in AN (Keq = 20M−1, Bu4N+ is the cation) and as “free” (solvated) ion in DMF. The addition of DMF caused the destruction of an ion pair in AN. The addition of the proton donors HX (water or ethanol) to the \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} solutions in DMF and AN caused the formation of new ion pairs (Bu4N+\documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document})2HX. The equilibrium constants of these ion pairs were determined in DMF and AN.
Method for the measurement of diffusion coefficients of labile gas‐phase species: The diffusion coefficient of O(3P) in He at 294 K
Authors: Plumb I. C. , Ryan K. R. , Barton N. G.
Published: January 2005

The dispersion of a pulse of O(3P) atoms in flowing helium has been analyzed by a modification of Taylor's method in order to determine the diffusion coefficient. Atoms of O(3P) were produced in a flowing stream of helium by a pulsed microwave discharge of molecular oxygen. After traversing a known length of the flow tube, the arrival time distribution of the O(3P) atoms was obtained using a mass spectrometer. The value obtained for D0 at 294 K, where D0 = D[He], is (2.40 ± 0.06) × 1019 cm−1 ·s−1, which corresponds to a diffusion coefficient of (731 ± 18) cm2/s at 1 torr. In addition to D0, analysis of the arrival time distributions gives an estimate of the mean flow velocity for O atoms in helium. There was no significant difference between the value of the velocity found this way and that obtained from the mean bulk gas flow measurement. Thus for this system there is no evidence for a chromatographic effect for O(3P) atoms on the walls of the flow tube.
Kinetic study of the reactions of the hydroxyl radical with ethane and propane
Authors: Tully F. P. , Ravishankara A. R. , Carr K.
Published: January 2005

Absolute rate coefficients for the reactions of the hydroxyl radical with ethane (k1, 297–300 K) and propane (k2, 297–690 K) were measured using the flash photolysis–resonance fluorescence technique. The rate coefficient data were fit by the following temperature‐dependent expressions, in units of cm3/molecule·s: k1(T) = 1.43 × 10−14T1.05 exp (−911/T) and k2(T) = 1.59 × 10−15T1.40 exp (‐428/T). Semiquantitative separation of OH‐propane reactivity into primary and secondary H‐atom abstraction channels was obtained.
Kinetics and the mechanism of the thermal reaction between trifluoromethylhypofluorite and hexafluoropropene
Authors: dos Santos Afonso M. , Schumacher H. J.
Published: January 2005

The kinetics of the thermal reaction between CF3OF and C3F6 have been investigated between 20 and 75°C. It is a homogeneous chain reaction of moderate length where the main product is a mixture of the two isomers 1‐C3F7OCF3 (68%) and 2‐C3F7OCF3 (32%). Equimolecular amounts of CF3OOF3 and C6F14 are formed in much smaller quantities. Inert gases and the reaction products have no influence on the reaction, whereas only small amounts of oxygen change the course of reaction and larger amounts produce explosions.

The rate of reaction can be represented by eq. (I):
equation image
The following mechanism explains the experimental results:
equation image
Reaction (5) can be replaced by reactions (5a) and (5b), without changing the result:
equation image
Reaction (4) is possibly a two‐step reaction:
equation image

For ∣CF3 = ∣C3F6∣, ν20°C = 36.8, ν50°C = 24.0, and ν70°C = 14.2.
The kinetics of pyrolysis of barrelene[1]: A concerted process on the C8H8 energy surface
Authors: Martin H.‐D. , Urbanek T. , Braun R. , Walsh R.
Published: January 2005

The static vessel pyrolysis of bicyclo[2.2.2]octa‐2,5,7‐triene (barrelene) has been studied between 483 and 523 K. The products were acetylene and benzene (in equal quantities) with no other detectable C8H8 isomer (down to less than 1% of total). The time dependence fitted first‐order kinetics, and the data are consistent with a homogeneous unimolecular reaction close to, if not at, its high‐pressure limit at 0.25 torr. The rate constant was fitted to the Arrhenius equation

These Arrhenius parameters are shown to imply a concerted single‐step process. Alternative mechanisms are discussed and a comparison is made with the retro‐Diels—Alder reactions of other bicyclo[2.2.2]octa‐olefin systems.
Pyrolysis of vinylacetylene between 300 and 450°C
Authors: Lundgard Richard , Heicklen Julian
Published: January 2005

Vinylacetylene was pyrolyzed at 300–450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.

The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half‐suppressed by the addition of the free‐radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(−79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5dihydropentalene (DHP).

The C8H8 compounds are formed by both molecular and free‐radical processes in a second‐order process with an overall k ≃ 3 × 108 exp(−122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (−118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(−77 kJ/mol RT), 1.7 × 105 exp(−89 kJ/mol RT), and 3.1 × 109 exp(− 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free‐radical process and by isomerization of COT.
Kinetic study of Ru(VI)‐catalyzed oxidation of cyclic alcohols by hexacyanoferrate(III) in aqueous alkaline medium
Authors: Behari K. , Narayan H. , Shukla R. S. , Gupta K. C.
Published: January 2005

The kinetics of the oxidation of cyclopentanol, cyclohexanol, 2methylcyclohexanol, and cycloheptanol by hexacyanoferrate(III) ions in mild alkaline medium has been studied in the presence of traces of ruthenium(VI) ≈ 10−7Mat constant ionic strength (0.26M). The results suggest that the oxidation of the studied cyclic alcohols proceeds via the formation of a complex between Ru(VI) and the substrate which slowly decomposes, giving the reduced form of ruthenium which was reoxidized to Ru(VI) in a fast step by alkaline hexacyanoferrate(III) ions. The product study shows the production of the corresponding ketone.
Reaction of hot H atoms with CD3Br
Authors: Oldershaw Geoffrey A. , Smith Alan
Published: January 2005

Energetic H atoms produced by photolysis of gaseous HI react with CD3Br by D abstraction (1) and Br abstraction (2) and possibly also by the substitution reactions (4) and (5).
equation image
Yields of HD and CD3H have been determined for several defined initial translational energies of H*. The phenomenological threshold energy of reaction (1) is 53 ± 5 kJ/mol. Over the range of initial energies of 76–109 kJ mol the integral probability of reaction (1) increases substantially, but the sum of the integral probabilities of reactions (2) and (5) shows little change. The ratio of the sum of the integral yields of reactions (2) and (5) to the integral yield of reaction (1), when normalized to equal numbers of Br and D atoms, is 69 ± 33 at an initial energy of 76 kJ/mol and 31 ± 6 at 109 kJ/mol.
Further relaxation kinetic investigations of iron(III) chelation. Data for diglycolic, tartaric, and citric acids
Authors: Cavasino F. Paolo , Di Dio Emanuele , Sbriziolo Carmelo
Published: January 2005

The kinetics of the reactions of iron(III) with diglycolic, tartaric, and citric acids have been studied in aqueous acid solutions by the temperature‐jump method at 25.0°C and at ionic strengths 1.0 (for tartaric and citric acids) and 0.50 mol/dm3 (for diglycolic acid). The experimental data indicate that iron(III) monochelate formation occurs by the same reaction mechanism for all three ligands examined and that only pathways involving the FeOH2+ ion contribute to the chelation process. The reacting species for citric acid is the undissociated ligand. For tartaric and diglycolic acids both the neutral ligands and the corresponding monoanions react significantly under the experimental conditions used. Kinetic evidence for the contribution of intermediate steps to the limiting rate in the overall chelate‐formation process has been obtained and discussed.
Photodecomposition reaction of ethyl bromide at 147 nm
Authors: Jung Kyung‐Hoon , Yoo Hee Soo , Hahn Jong Hoon
Published: January 2005

A vacuum ultraviolet photolysis of C2H5Br at 147 nm was studied over a pressure range of 0.5–50 torr at 298 K. The effects of additives He and NO were also investigated.

The principal reaction products were found to be C2H4 and C2H6, with lesser yields of CH4 and C2H2. With increasing pressure the product quantum yields Φi of C2H4, CH4, and CH2H6 remained constant, while that of C2H2 decreased from 0.03 to almost 0. The effect of He as an additive was found to be extremely small on the quantum yields of the major products. Addition of NO completely suppresses the formation of CH4, C2H2, and C2H6, and reduces partially the production of C2H4. The primary processes appear to involve two electronically excited states. One state mainly yields C2H4 by molecular elimination of HBr and is thought to be due to a Rydberg transition. The other state decomposes to C2H5 and Br radicals by CBr bond fission. These two competitive reaction modes contribute to the photodecomposition in proportions of 50% and 50%. The extinction coefficient for C2H5Br at 147 nm and at 298 K has been determined as ϵ = (1/PL) In(Io/It) = 712 ± 7 atm−1 · cm−1.
The addition of methyl radicals to hexafluoroacetone
Authors: Batt L. , Mowat S. I.
Published: January 2005

The reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place: magnified image where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide:
equation image
such that k6a is given by:

where θ = 2.303RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps:
equation image
Product analysis shows that k17/kk = 2.0 ± 0.2 such that k17 = 1010.4±0.5M−1 · s−1. The rate constant k5 is given by:

It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins.
Kinetic study of chemically activated chlorocyclopropane
Authors: Eichler K. , Heydtmann H.
Published: January 2005

Chlorocyclopropane has been produced by addition of CH2(1A1) and CH2(3B1) to chloroethene. CH2 was generated by the photolysis of ketene at 313 and 366 nm. Chlorocyclopropane was formed in a chemically activated state, had an energy content between 378 and 427 kJ/mol, and reacted in three parallel channels to 3‐chloropropene, cis‐ and trans‐1‐chloropropene. As secondary reactions elimination of HCl from the chemically activated primary products occurred to form allene and propyne. The apparent rate constants for the isomerization and elimination reactions are reported. The results of RRKM calculations including distribution functions for the activated chlorocyclopropane and a stepladder model for the deactivation support the proposed reaction scheme.
Yields of singlet nitrenes from halogen atom—azide molecule reactions
Authors: Pritt A. T. , Patel D. , Coombe R. D.
Published: January 2005

Chemiluminescence from the a1Δ and b1Σ+ excited electronic states of nitrogen halide diatomics is observed when HN3 is allowed to react with mixtures of halogen atoms in a discharge‐flow apparatus. Excited NF (a1Δ) is produced by the F + HN3 reaction, and NCl (a1Δ, b1Σ+) and NBr (a1Δ, b1Σ+) are produced by the F, Cl, + HN3 and F, Br + HN3 reactions, respectively. In the low‐density limit, the yield of NF(a1Δ) was found to be near unity. The yields of the b1Σ+ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N3 radicals in the flow, support a hypothetical mechanism in which N3 acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.
Rates and equilibria in the reaction system Br + i‐C4H10 ⇌ HBr + t‐C4H9. The heat of formation of the t‐butyl radical
Authors: Islam Tajmeri S. A. , Benson Sidney W.
Published: January 2005

The very low pressure reactor (VLPR) technique has been used to measure the bimolecular rate constant of the title reaction at 300 K. The rate constant is given by log k1 (1/mol s) = (11.6 ± 0.4) − (5.9 ± 0.6)/θ the equilibrium constant has also been measured at the same temperature and is given by K1 = (5.6 ± 1) × 10−3 and hence log k−1 (1/mol s) = 9.5 ± 0.1. The results show that the reaction Br + tC4H9 → HBr + iC4H8 is unimportant under the present experimental conditions. Assigning the entropy of t‐butyl radical to be 74 ± 2 eu which is in the possible range, the value of K1 gives ΔH (t‐butyl) = 9.1 ± 0.6 kcal/mol−1. This yields for the bond dissociation, DH° (t‐butyl‐H) = 93.4 ± 0.6 kcal/mol. Both of these values are found to be in good agreement with recent VLPP studies.
Basic hydrolysis of glyceryl nitrate esters. III. Trinitroglycerin
Authors: Capellos C. , Fisco W. J. , Ribaudo C. , Hogan V. D. , Campisi J. , Murphy F. X. , Castorina T. C. , Rosenblatt D. H.
Published: January 2005

Kinetics of the basic hydrolysis of glyceryl trinitrate (TNG) were investigated in CO2‐free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. TNG hydrolyzed via second‐order reaction at 25°C, 18°C, and 10°C. The activation energy of the hydrolysis reaction of TNG was calculated from the kinetic data and found to be equal to 27.53 kcal/mol. The major products of the hydrolysis of TNG in solution of calcium hydroxide were calcium nitrate and calcium nitrite, accounting for approximately 50% of the degradation products. The minor identified products such as calcium oxalate and nitrate esters amounted to approximatey 6% of the products. The remaining 30% of the isolated products was a mixture of calcium formate, a nitrate ester, and unidentified volatiles, polymerlike substances, and other organic residue.
Self‐ and cross‐termination rate constants for the isopropylol radical and its anion in aqueous solution
Authors: Wu Lung‐Min , Fischer H.
Published: January 2005

Rate constants for the self‐ and cross‐termination of the isopropylol radical [(CH3)2ĊOH] and its anion [(CH3)2ĊO−] in aqueous solution are determined by kinetic electron spin resonance. Whereas the self‐termination of the neutral radical occurs close to the diffusion‐controlled limit, the cross‐ and self‐terminations involving the anion are slower and reflect effects of charge repulsion and steric constraints by solvation.
Origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate—application of the 18O isotope effect in 31P NMR
Authors: Risley John M. , Van Etten Robert L.
Published: January 2005

Potassium persulfate oxidizes triphenylphosphine to triphenylphosphine oxide in 60% aqueous acetonitrile. It has been suggested that the oxygen of the product, triphenylphosphine oxide, might originate from solvent water, following nucleophilic attack on an intermediate phosphonium ion. We have investigated the origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate in 60% aqueous acetonitrile containing 20% [18O]water. The product was analyzed by using the 18O isotope effect in 31P NMR spectroscopy. The magnitude of the 18O isotope‐induced shift was determined by synthesizing triphenylphosphine [18O]oxide and was found to be 0.038 ppm upfield. The product of the oxidation reaction in 20% [18O]water displayed no 18O isotope effect. The origin of the oxygen in the oxidation reaction is the persulfate ion, consistent with an alternative mechanism involving nucleophilic attack by water at the sulfur atom of a phosphonium peroxysulfate intermediate.
Rate constants for concurring radical reactions in solution obtained by kinetic electron spin resonance
Authors: Münger K. , Fischer H.
Published: January 2005

It is shown how kinetic electron spin resonance spectroscopy with intermittent radical generation can be used to obtain rate constants of various simultaneous reactions in systems containing more than one kind of transient radicals. The technique is applied to reactions of tert‐butyl [(CH3)3Ċ] and isopropylol [(CH3)2ĊOH] radicals generated by photolysis of di‐tert‐butyl ketone and acetone in 2‐propanol/acetone mixtures. It yields the rates of generation of the two radicals, the rate constants for their self‐ and crossterminations and for the reaction of tert‐butyl with 2‐propanol. The extent of diffusion control of the termination constants is discussed.
Reactions of ozone with olefins: Ethylene, allene, 1,3‐butadiene, and trans‐ 1,3‐pentadiene
Authors: Bahta Abraha , Simonaitis R. , Heicklen Julian
Published: January 2005

The reactions of O3 with ethylene, allene, 1,3‐butadiene, and trans‐1,3‐pentadiene have been studied in the presence of excess O2 over the temperature range 232 to 298 K. The initial O3 pressure was varied from 4–18 mtorr, and the olefin pressure was varied from 0.1 to 4.5 torr (ethylene), 2.8 to 39.6 torr (allene), 52.7 to 600 mtorr (1,3‐butadiene) or 26.2 to 106 mtorr (trans‐1,3‐pentadiene). The O3 decay was monitored by ultraviolet absorption. The reactions are first order in both O3 and olefin, and the rate coefficients are independent of the O2 pressure. For the O3‐ethylene system, various diluent gases (O2, N2, air) were used and the rate coefficients were found to be independent of the nature of the diluent gas. The various rate coefficients fit the Arrhenius expressions (k in cm3 s−1):

where the reported uncertainties are one standard deviation and R is in cal/mol K.
The photolysis of 3,4‐dimethylcyclopentanone
Authors: Becerra Rosa , Frey H. Monty
Published: January 2005

The photolysis of trans‐3,4‐dimethylcyclopentanone has been studied in the gas phase, principally at 313 nm. However, a few experiments have also been performed using laser sources at 308 and 325 nm. Additionally, experiments were also carried out using the cis isomer. The major products produced by all three wavelengths and in the temperature range 100 to 150°C were propene, 1,2‐dimethylcyclobutane, carbon monoxide, and 3,4‐dimethylpent‐4‐en‐al. The formation of the cyclobutane was stereospecific and the effects of temperature, pressure, and wavelength on the relative product yields could be rationalized in terms of a mechanism involving the formation of a vibrationally excited triplet state which could yield both hydrocarbons and the aldehyde and a nonexcited triplet yielding only the aldehyde. Some high intensity experiments with an exciplex laser at 308 nm gave results which could be due to the occurrence of some two photon absorption by the cyclopentanone or absorption by an excited intermediate. The results are compared with those previously reported for other substituted cyclopentanones.
High temperature molecular beam source reactor
Authors: Rotzoll G.
Published: January 2005

Small low residence time flow tube reactors made of alumina and used as molecular beam sources are described. In these reactors, gas mixtures are rapidly heated and brought to reaction. The composition of the gas leaving the reactor is analyzed by molecular beam mass spectroscopy. For quantitative simulation of the reacting gas flow, the theory of one‐dimensional compressible flow with friction, heat transfer, and chemical reaction is brought into a form suitable for practical computation. The system has been applied to study the thermal decompositions of O3 and N2O. The experimental results on both reactions can be well modeled by homogeneous reaction mechanisms with accepted rate constants. Heterogeneous reaction steps are shown to be unimportant.
Solvent effect on reversible self‐termination reactions of aromatic free radicals
Authors: Khudyakov I. V. , Kuzmin V. A. , Yasmenko A. I. , Smit W. , Salve J. , De Jonge C. R. H. I.
Published: January 2005

Rates and thermodynamic data have been obtained for the reversible self‐termination reaction:

Involving aromatic 2‐(4′dimethylaminophenyl)indandione‐1,3‐yl (I), 2‐(4′diphenylaminophenyl)indandione‐1,3‐yl (II), and 2,6 di‐tert‐butyl‐4‐(β‐phthalylvinyl)‐phenoxyl (III) radicals in different solvents. The type of solvent does not tangibly affect the 2k1 of Radical(I), obviously due to a compensation effect. The log(2k1) versus solvent parameter ET(30) curves for the recombination of radicals (II) and (III) have been found to be V shaped, the minimum corresponding to chloroform. The intensive solvation of Radical (II) by chloroform converts the initially diffusion‐controlled recombination of the radical into an activated reaction. The log (2k−1) of the dimer of Radical (I) has been found to be a linear function of the Kirkwood parameter (ε ‐ 1)/(2ε + 1), the dissociation rate increasing with the dielectic constant of the solvent. The investigation revealed an isokinetic relationship for the decay of the dimer of Radical (I), an isokinetic temperature β = 408 K and isoequilibrium relationship for the reversible recombination of Radical (I) with β° = 651 K. For Radical (I) dimer decay In(2k−1) = const + 0.8 In K, where K is the equilibrium constant of this reversible reaction. The transition state of Radical (I) dimer dissociation reaction looks more like a pair of radicals than the initial dimer. The role of specific solvation in radical self‐termination reactions is discussed.
Very low pressure pyrolysis of phenyl acetate
Authors: Ghibaudi E. , Colussi A. J.
Published: January 2005

The kinetics of the unimolecular decomposition of phenyl acetate into phenol and ketene, reaction (1):

has been studied under very low‐pressure conditions between 950 and 1120 K. In this range alternative processes such as the Fries rearrangement to o‐hydroxyacetophenone or bond fission into phenoxyl and acetyl radicals are not observed. Based on present and previous evidence a novel four‐center transition state is proposed for reaction (1) which corresponds to the high‐pressure Arrhenius expression log (k1, s−1) = 12.8 – 56.2/θ, θ = 4.575 × 10−3T kcal/mol.
Kinetics of the gas phase reaction of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Using a relative rate technique, rate constants have been determined for the gas phase reactions of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure of air. Using a rate constant of 1.97 × 10−10 cm3 molecule−1 s−1 for the reaction of Cl atoms with n‐butane, the following rate constants (in units of 10−11 cm3 molecule−1 s−1) were obtained: ethane, 6.38 ± 0.18; propane, 13.4 ± 0.5; isobutane, 13.7 ± 0.2; n‐pentane, 25.2 ± 1.2; isopentane, 20.3 ± 0.8; neopentane, 11.0 ± 0.3; n‐hexane, 30.3 ± 0.6; cyclohexane, 31.1 ± 1.4; 2,3‐dimethylbutane, 20.7 ± 0.6; n‐heptane, 34.1 ± 1.2; acetylene, 6.28 ± 0.18; ethene, 10.6 ± 0.3; propene, 24.4 ± 0.8; benzene, 1.5 ± 0.9; and toluene, 5.89 ± 0.36. These data are compared and discussed with the available literature values.
Absolute rate constants for radical rearrangements in liquids obtained by muon spin rotation. Substituent effects on ring fission and cyclization reactions
Authors: Burkhard Peter , Roduner Emil , Fischer Hanns
Published: January 2005

By addition of the light hydrogen isotope muonium (Mu = μ+e−) the 1‐ethyl‐hexen‐1‐yl radicals CH2 = CHCH2CH2CH2CHCH2Mu, CH2 = CHOCH2CH2CHCH2Mu, and CH2 = CHCH2CH2OCHCH2Mu are generated in liquids. Their Fourier transform muon spin rotation spectra show linewidths increasing with increasing temperature which are attributed to the ring closure reactions. Analysis yields the absolute rate constants and their Arrhenius parameters. Together with previously reported results on analogous cyclization and on related ring fission reactions they are discussed in terms of steric and electronic effects on the reaction pathways and compared with predictions of semiempirical calculations.
Kinetics of some reactions of vinyl and isopropyl radicals in the gas phase
Authors: Szirovicza Lajos
Published: January 2005

Vinyl and isopropyl radicals were generated by the pyrolysis of azoisopropane in the presence of acrolein at 473–563 K. Reaction products were analyzed by gas chromatography. Rate constant ratios k2/k1 = 0.02 ± 0.01 and k4/k3 = 0.01 ± 0.005 are suggested for the following reactions:
equation image
The rate constant ratio of reactions (7) and (c) obeys the Arrhenius equation

equation image
The Arrhenius equation was derived for (k8 + k9).
The high temperature pyrolysis of 1,3‐butadiene: heat of formation and rate of dissociation of vinyl radical
Authors: Kiefer J. H. , Wei H. C. , Kern R. D. , Wu C. H.
Published: January 2005

The high temperature pyrolysi of 1,3‐butadiene has been investigated in the shock tube with two time‐resolved diagnostic techniques: laser schlieren measurements of density gradient with 1, 2, 4, and 5% C4H6 in Ar or Kr, 0.26 < P2 < 0.66 atm, over 1550–2200 K, and time‐of‐flight mass spectra for 3% C4H6–Ne, P5 ∼ 0.4 atm, 1400–2000 K. When combined with a recent single‐pulse shock tube product analysis covering 1050–2050 K, these measurements permit a complete modeling of major species in C4H6 pyrolysis. Extrapolated density gradients and product analyses show initiation is dominated by C4H6 → 2C2H3., significant falloff and Arrhenius curvature being seen in the derived rates. A restricted rotor, Gorin model RRKM fit to these rates with reasonable parameters generates

The derived barrier, ΔH = 99 ± 4 kcal/mol, translates to ΔH,298 = 63.4 ± 2 kcal/mol for the heat of formation of vinyl radical. A mechanism for the formation of all products detected in the above experiments is given, together with a successful but semiquantitative kinetic model for major products. The measurements require the rate of vinyl radical dissociation, C2H3 + M → C2H2 + H + M, to be extremely low, k < 109 cm3/mol s for 1600 K, so that the dominant chain carrier in C4H6 pyrolysis is vinyl radical.
Intramolecular conversions. V. Rational rate constants for reversible unimolecular reactions
Authors: Bauer S. H.
Published: January 2005

The available RRKM programs which cover the full pressure range (high → low‐pressure limits) were written for nonreversible reactions. For reversible reactions the correct shapes of the fall‐off curves can be estimated by applying a correction factor to the RRKM bimolecular rate constant, which depends on a ratio of state densities at the potential maximum. It is proposed that the analysis of such systems in terms of relaxation kinetics provides a more rational treatment, free of the ambiguities associated with specifying a “transition state.”
An FTIR study of the Cl‐atom‐initiated reaction of glyoxal
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P.
Published: January 2005

The kinetics and mechanism of Cl‐atom‐initiated reactions of CHOCHO were studied using the FTIR detection method to monitor the photolysis of Cl2–CHOCHO mixtures in 700 torr of N2–O2 diluent at 298 ± 2 K. The observed product distribution in the [O2] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHOCHO → HCl + CHOCO with a rate constant of [3.8 ± 0.3(σ)] × 10−11 cm3 molecule−1 s−1; (2) the primary product CHOCO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10−7 s; (3) alternatively, the CHOCO reacts with O2 leading to the formation of CO, CO2, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO2 radical, formed in the secondary reaction CHO + O2 → HO2 + CO, reacts with the CHOCHO with a rate constant ca. 5 × 10−16 cm3 molecule−1 s−1 to form HCOOH and a new transient product resembling that detected previously in the HO2 reaction with HCHO.
Kinetics of the oxidation of cyclohexene by thallium(III) acetate
Authors: Loucks Leon F. , Liu Michael T. H. , Durant Danny K.
Published: January 2005

The kinetics of the reaction by which thallium(III) acetate oxidizes cyclohexene in glacial acetic acid medium, has been studied by UV spectrophotometric observation at 30°C. The consumption of thallium(III) acetate follows a second‐order rate law exhibiting first‐order dependence on each of thallium(III) acetate and cyclohexene; however, the first‐order dependence on cyclohexene disappears at high cyclohexene concentrations as pseudo‐first‐order conditions prevail above 0.2 M cyclohexene. A steady‐state model of the following form is proposed:
equation image
where Tl, Cy, and Com are units of Thallium(III) acetate, cyclohexene, and a reaction complex. The value of k2 has been evaluated as 0.00027 and (k−1 + k2) as 0.0385k1. For low thallium(III) acetate concentrations the reaction kinetics follow the rate law:

where α = the excess concentration of cyclohexene over thallium(III) triacetate. For thallium(III) acetate concentrations above 0.02 M, double salt formation of thallium(III) acetate with product thallium(I) acetate removes thallium(III) acetate from the reaction and a modified rate law is observed. Runge–Kutta numerical solutions to the differential equations provide confirmation that the rate expressions are valid in predicting the observed concentrations of thallium(III) acetate.
Molecular beam sampling mass‐spectrometric study of high‐temperature benzene oxidation
Authors: Rotzoll G.
Published: January 2005

The oxidation of benzene has been investigated with a high‐temperature alumina flow reactor in the temperature range of 950–1150 K at residence times of ca. 1 ms and pressures of ca. 400 mbar. Analysis of the reaction products at various stages of the reaction was carried out by direct expansion of the reacting gas yielding a molecular beam that was analyzed by a mass spectrometer. Product identification studies were made by comparing the results from the oxidations of C6H6 and C6D6. Besides the products found in previous studies a number of new oxygenated intermediate species were identified, namely benzoquinone, cyclopentadienone, acrolein, and a C4H4O species. In addition, some higher hydrocarbons have been found even at high oxygen excess. The role of the intermediates within the current ideas of the reaction mechanism is discussed.
Uses of the transit time distribution in kinetic flow systems
Authors: Lambert Mark , Sadowski C. M. , Carrington Tucker
Published: January 2005

We investigate the distribution of transit or residence times of a trace reactant in laminar flow. We present measurements of this distribution for hydrogen atoms in a typical flow system, and show that the results are consistent with known theory and previous measurements of the diffusion coefficient. The use of the measured distribution as a diagnostic of flow behavior is discussed. It is also shown that the measured or calculated transit time distribution can provide a convenient means of correcting results of kinetic measurements for the departure from plug flow. In the case of firstorder, and also second‐order decay of a single reactant, this correction is a useful approximation to the more rigorous solution of the partial differential equation for diffusion and reaction in laminar flow. Effects of the deviation from plug flow on a complex rection system are illustrated qualitatively for the H + NO2titration system.
Kinetics and mechanism of copper(II) induced decomposition of 9‐diazofluorene
Authors: Ahmad Iftikhar
Published: January 2005

The kinetics and products of the decompositon of 9‐diazofluorene by copper(II) tetrafluoroborate in acetonitrile solvent have been investigated. The reaction is first order with respect to both 9‐diazofluorene and copper(II) tetrafluoroborate. A reaction mechanism has also been proposed.
Self‐Reaction of HO2 and DO2: Negative temperature dependence and pressure effects
Authors: Mozurkewich Michael , Benson Sidney W.
Published: January 2005

The negative temperature dependence, pressure dependence, and isotope effects of the self‐reaction of HO2 are modeled, using RRKM theory, by assuming that the reaction proceeds via a cyclic, hydrogen‐bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO2 self‐reaction is due to the approach to the high‐pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high‐pressure limit of the self‐reaction of HO2.
Structure‐Reactivity correlations in the addition of water to aromatic substrates
Authors: De Rossi Rita H. , Veglia Alicia
Published: January 2005

The addition of water to 1‐(4‐Z‐2,6‐dinitrophenyl)‐3‐methylimidazolium chloride (Z = CN, NO2, and CF3) is catalyzed by carboxylate bases. There is a decrease in ρ with increasing basicity of the catalyst with ∂ρ/∂pKBH = −0.090. The results indicate that the mechanism of the reaction involves the addition of water to the aromatic substrates catalyzed by general bases. The changes in the structure‐reactivity parameters with changing pK of the catalysts or Z in the substrate are rationalized in terms of changing bond lengths in the transition state. The activation parameters and the kinetic solvent isotopic effect were determined for the water, acetate, and OH− catalyzed reactions and are consistent with the proposed mechanism.
Kinetics and mechanism of oxidation of fumarate, acrylate, cinnamate, and maleate anions by hexavalent manganese in aqueous alkaline medium
Authors: Sreenivasulu P. V. , Adinarayana M. , Sethuram B. , Rao T. Navaneeth
Published: January 2005

Kinetics of oxidation of fumarate, acrylate, cinnamate, and maleate anions by hexavalent manganese has been studied in aqueous alkaline medium. The order in [oxidant] was unity while that in [substrate] was fractional. The order of reactivity of anions is fumarate → acrylate → cinnamate → maleate. The reactions followed Michaelis–Menten kinetics suggesting the formation of a cyclic intermediate between Mn(VI) and the substrate followed by its disproportionation in a slow step. The equilibrium constant (K) for the preequilibrium step and the rate constant (k) for the slow disproportionation step have been calculated from the intercept and the slope values of the linear plot of 1/kobs versus 1/[substrate]. Activation parameters are also presented and discussed. A convenient iodometric method is reported for the estimation of Mn(VI).
The agent of the autocatalytic thermal decomposition of aliphatic nitrate ester explosives
Authors: Batten J. J.
Published: January 2005

The condensed‐phase thermal decomposition of aliphatic nitrate ester explosives is generally autocatalytic. The object of this article is to show that the agent of the autocatalysis is not the product NO2, as is generally believed, but to suggest that it may be the product formaldehyde.