bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractKinetics 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

AbstractRate 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

AbstractPotassium 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

AbstractIt 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

AbstractThe 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

AbstractThe 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

AbstractSmall 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

AbstractRates 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

AbstractThe 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

AbstractUsing 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

AbstractBy 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

AbstractVinyl 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractKinetics 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

AbstractThe 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.