bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic studies of free radical reactions by mass spectrometry. I. The reactions SO + NO2 and ClO + NO
Authors: Clyne Michael A. A. , Macrobert Alexander J.
Published: January 2005

A novel technique is described for forming ground‐state SO X3Σ radicals free of reactive impurities in a discharge‐flow system. Mass spectrometric detection of SO and ClO free radicals has been used to study the kinetics of the following reactions at 295 K:
equation image
The √t law in solid‐phase reactions verification of the √t law stability in h‐atom abstraction reactions
Authors: Bol'shakov B. V. , Stepanov A. A. , Tolkatchev V. A.
Published: January 2005

The law c = c0 exp(K √t) in the alkyl radical abstraction reaction is affected by neither the matrix annealing nor the way of the radical generation. If the reaction runs at varying temperature, a dimensionless time τ which does determine unambiguously the degree of conversion can be introduced.
A concerted hydrogen‐transfer reaction in the gas phase
Authors: Lalonde P. J. , Back M. H.
Published: January 2005

The kinetics of the thermal reaction of mixtures of ethylene and cyclopentene has been examined for the occurrence of a concerted hydrogen‐transfer reaction,

. The main products of the reaction were ethane and cyclopentadiene, and the rate of formation of ethane was first order in each reactant over a 2500‐fold change in the ratio of concentrations of the reactants. An increased surface‐to‐volume ratio of the reaction vessel or additions of oxygen and nitric oxide had little effect on the rate of formation of ethane, and it was concluded that the dominant reaction in the system was the concerted hydrogen‐transfer process. The rate constant for the reaction, measured over the temperature range of 325–505°C, was represented as
Micellar effects upon electron transfer from ferrocenes
Authors: Bunton Clifford A. , Cerichelli Giorgio
Published: January 2005

The oxidations of ferrocene (FcH) and n‐butylferrocene (FcBu) by ferric salts (nitrate or bromide) are strongly inhibited by aqueous cetyltrimethylammonium bromide and nitrate (CTABr and CTANO3, respectively). The kinetics of inhibition fit a model in which the substrates are distributed between water, and the micelles and binding constants Ks to the micelle can be estimated. The oxidations are strongly catalyzed by micelles of sodium lauryl sulfate (NaLS), and the kinetics can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase and the rate constants in that pseudophase, which for both substrates are very similar to those in water. Some added salts reduce the micellar catalysis by excluding ferric ions from the micelle. The oxidations of FcH and FcBu by ferricyanide ions are too fast to be followed in water, but they are inhibited by anionic micelles of NaLS. By analyzing the rate surfactant profiles using independently measured values of Ks the second‐order rate constants in water have been estimated.
On the effect of copper (II) and chloride ions on the iodate‐hydrogen peroxide reaction in the presence and absence of manganese (II)
Authors: Cooke David O.
Published: January 2005

The effect of copper (II) and chloride ions on the manganese (II) catalyzed iodate‐peroxide reaction has been examined with reference to the hydrogen peroxide‐iodic acid‐manganese (II)‐organic species oscillatory reaction. The observations are considered to provide evidence for iodine dioxide as the key intermediate in the manganese (II) catalyzed reaction. Kinetic data for the copper (II) catalyzed reaction are reported.
The kinetic isotope effect for carbon and oxygen in the reaction CO + OH
Authors: Stevens C. M. , Kaplan Louis , Gorse Robert , Durkee Susan , Compton Michael , Cohen Sidney , Bielling Karen
Published: January 2005

The kinetic isotope effect (KIE) for carbon and oxygen in the reaction CO + OH has been measured over a range of pressures of air and at 0.2 and 1.0 atm of oxygen, argon, and helium. The reaction was carried out with 21–86% conversion under static conditions, utilizing the photolysis of H2O2 as a source of OH radicals. The value of the KIE for carbon varies with pressure and the kind of ambient gas; for air the ratio of the reaction rates 12k/13k has the value 1.007 at 1.00 atm and decreases to 0.997 at 0.2 atm; for oxygen and argon over the same pressure range the values are 1.002–0.994 and 1.000–0.991, respectively. The value of the KIE for the CO oxygen atom is 16k/18k = 0.990 over the pressure range 0.2–1.0 atm and is independent of the kind of ambient gas. No exchange of the oxygen atoms in the activated complex, followed by decomposition to the starting molecules, was observed. From the mechanistic standpoint the normal KIE observed for carbon at the high pressure is attributed to the initial formation of the activated HOCO radical, whereas the inverse KIE observed at low pressures is a result of the KIE for the reverse reaction HOCO† → CO + OH being greater than that for the forward reaction HOCO† → CO2 + H. The derived isotopic equilibrium constant for HOCO ⇄CO favors the enrichment of 13C in the more strongly bound HOCO.
An FTIR study of the Cl atom‐initiated oxidation of CH2Cl2 and CH3Cl
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P.
Published: January 2005

The Cl atom‐initiated oxidation of CH2Cl2 and CH3Cl was studied using the FTIR method in the photolysis of mixtures typically containing Cl2 and the chlorinated methanes at 1 torr each in 700 torr air. The results obtained from product analysis were in general agreement with those reported by Sanhueza and Heicklen. The relative rate constant for the Cl atom reactions of CH2Cl2 and CH3Cl was determined to be k(Cl +CH3Cl)/k(Cl + CH2Cl2) = 1.31 ± 0.14 (2σ) at 298 ± 2 K.
Ion pair catalysis of the autooxidation of pyridine and benzil in emulsion systems
Authors: Franklin Thomas C. , Ogiya Naoyuki
Published: January 2005

It was found that the rates of absorption of oxygen by pyridine–aqueous sodium hydroxide emulsions and the same emulsions containing benzil were catalyzed by the addition of quaternary salts and followed the same rate law:

. It was concluded that the autooxidation of benzil in pyridine‐aqeuous sodium hydroxide emulsions has as its rate‐determining step a step in the autooxidation of pyridine. Possibly the superoxide formed in the autooxidation of pyridine is the oxidizing agent in the oxidation of benzil.
An overall and detailed kinetic study of the pyrolysis of propane
Authors: Hautman D. J. , Santoro R. J. , Dryer F. L. , Glassman I.
Published: January 2005

Overall and detailed kinetic descriptions of the pyrolysis of C3H8 have been proposed as a result of a turbulent flow reactor investigation in the temperature range of 1110–1235 K and at atmospheric pressure. The overall reaction was described by a first‐order rate expression with an activation energy of 58.65 kcal/mol and a preexponential factor of 3.2 × 1012 sec−1. This expression agrees with previously reported rate data. In addition, a kinetic mechanism involving 13 chemical species and 32 elementary reactions has been postulated to describe the kinetics. Experimental data from the present flow reactor experiments and from static vessel and shock tube experiments reported in the literature were used to verify the mechanism. Agreement over the temperature range of 800–1400 K and over the pressure range of 0.1–8.5 atm was obtained by adjusting three rate constants. Previously reported values for these rate constants appear to require reexamination. The reactions in question are the following:
equation image
The sum of the rate constants for reactions (2a) and (2b) and the rate constant for reaction (23) are best represented by

and

which differ with the expressions in the literature.
The rate constant for t‐C4H9 → H + i‐C4H8 and the thermodynamic parameters of t‐C4H9
Authors: Canosa Carlos E. , Marshall Roger M.
Published: January 2005

The rate of the reverse reaction of the system
equation image
has been measured in the range of 584–604 K from a study of the azomethane sensitized pyrolysis of isobutane. Assuming the published value for the rate constant of recombination of t‐butyl we obtain

Combination with our published data for k1 permits the evaluation

We have modified a previously published structural model of t‐butyl by the inclusion of a barrier to free rotation of the methyl groups in order to calculate values of the entropy and enthalpy of t‐butyl as a function of temperature. Using standard data for H and for i‐C4H8 we obtain

We have obtained other, independent values of this quantity by a reworking of published data using our new calculations of the entropy and enthalpy of t‐butyl. There is substantial agreement between the different values with one exception, namely, that derived from published data on the equilibrium

which is significantly lower than the other values.

We conclude that the value

obtained from the present work and a reworking of published data which involves the use of experimental data on t‐butyl recombination is incompatible with the result based on iodination data.
The hydrolysis of phosphoranes in aqueous dioxane
Authors: Queen A. , Lemire A. E. , Janzen A. F.
Published: January 2005

The entropy of activation for the hydrolysis of pentaphenoxyphosphorane in 25% aqueous dioxane is −188 J/mol deg. The enthalpy of activation is 22.5 kJ/mol, which is small for the relatively slow reaction. This suggests that the reaction is a multistep process having a preliminary equilibrium with a negative heat of reaction. This conclusion is supported by the results obtained for the hydrolysis of C6H5
equation image
[OCH(CF3)2]2. A kinetic isotope effect kH2O/kD2O of 3.46 was found for the latter reaction. Orders in water were obtained, and a mechanism of hydrolysis is proposed.
Persulfate and perphosphate oxidation of 2‐propanol: A relative rate study
Authors: Levey Gerrit , Bida Gerald , Edwards John O.
Published: January 2005

A competitive reaction study for two isoelectronic peroxides (peroxodisulfate S2O and peroxodiphosphate P2O) interacting with the free radical ·Clpar;CH3)2OH is described. The radical formation is initiated by photolysis, the amounts of peroxide remaining analyzed volumetrically. It is found that persulfate reacts with the organic radical over 100 times more rapidly than does perphosphate. Mechanistic consequences in relation to previous work are briefly discussed.
Kinetics of the gas‐phase reaction between iodine and monosilane and the bond dissociation energy D(H3SiH)
Authors: Doncaster Alan M. , Walsh Robin
Published: January 2005

The title reaction has been investigated in the temperature range of 494–545 K. During the early stages of reaction the only observed products were silyl iodide and hydrogen iodide. Initial rates were found to obey the rate law
equation image
over a wide range of initial iodine and monosilane pressures. Secondary reactions, most probably of SiH3I with I2, became more important as the reaction progressed. However, provided [SiH4]0/[I2]0 > 20, these secondary processes had a negligible effect on the kinetics, and an integrated rate expression could be used. These kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step
equation image
has been deduced. From this the bond dissociation energy D(SiH3H) = 378 ± 5 kJ/mol (90 kcal/mol) is obtained. The kinetic and thermochemical implications of this value, especially to the pyrolysis of monosilane, are discussed.
Photolysis of ethyl‐iodide in lithium chloride glassy aqueous solutions with light, λ = 254 nm at 77 K
Authors: Burbo E. M. , Gurman V. S.
Published: January 2005

The photolysis of C2H5I in a glassy salt matrix (5M, 7.5M, 10M) of aqueous LiCl at 77 K with light of λ = 254 nm has been conducted, product analysis being by ESR and UV spectroscopy. The electrolytic medium causes the ionization of product HI, and I− concentrations can be continuously determined. During photolysis [I−] is less than the amount of C2H5I decomposed. But after photolysis thaw‐freeze cycling is accompanied by progressive growth in [I−] until the yield matches the C2H5I loss, the quantum yields being 0.26, 0.20, and 0.17 for the three LiCl solutions, respectively. The quantum yield of unionized HI is unchanged, however, at around 0.36, the overall change being due to a fall in the extent to which the HI is ionized in the direct photolysis (ø = 0.22, 0.16, and 0.11). It is proposed that this is a consequence of the density increase of matrix packing as the LiCl concentration is increased so that fewer HI are in contact with the aqueous medium and cage recombination is favored.

The results establish that the primary reaction is essentially exclusive:
equation image
and that substantial aggregates of C2H5I exist within which HI are caged and cannot be ionized. The direct reaction

occurs only to a trivial extent, ø; = 10−4, C2H5 arising virtually totally via
The estimation of a factors for atom fissions in polyatomics
Authors: Ghibaudi E. , Colussi A. J.
Published: January 2005

It is shown that A factors for atom fissions in polyatomics can be reliably estimated by an improved version of the restricted free rotor model (RFRM). No adjustable parameters are used in the evaluation of A factors for the dissociation of the ROF bond (R: NO2, SF5, CF3, FSO2), and the authors' predictions are compared with high‐pressure kinetic data for these reactions. In the case of O2NOF, for which full spectroscopic information is available, RFRM reproduces the observed value Am well within a factor of 2. Similar agreement is reached for F5SOF and FO2SOF, assigning reasonable limits to their OF torsional frequencies. For F3COF, Am and the calculated back reaction rate constant, which is independent of the model, are both much too small to be plausible, suggesting falloff effects rather than a failure of RFRM.
Infrared photochemistry of cyclobutyl chloride
Authors: Francisco J. S. , Steinfeld J. I.
Published: January 2005

The decomposition of cyclobutyl chloride following multiple infraredphoton excitation has been investigated. The primary photolysis products are butadiene, from elimination of HCl, and ethylene and vinyl chloride, fromring scission. The vinyl chloride undergoes secondary decomposition to acetylene and HCl. In addition to these products, known from thermal VLPP experiments, we also find 1‐butene, which may arise from a higher energy CCl homolysis channel. Collisions with either reactant molecules oradded buffer gas lead to cooling of the laser‐produced vibrational energy distributions. The average amount of energy removed per collision is 15–20 kcal/mol for self‐collisions and 2–4 kcal/mol with argon.
The kinetics and the mechanism of the thermal decomposition of bis(trifluoromethyl) trioxide. The influence of carbonmonoxide on its decomposition
Authors: Czarnowski J. , Schumacher H. J.
Published: January 2005

The kinetics of the thermal decomposition of CF3O3CF3 has been investigated in the pressure range of 15–599 torr at temperatures between 59.8 and 90.3°C and also in the presence of CO between 42 and 7°C. The reaction is homogeneous. In the absence of CO the only reaction products are CF3O2CF3 and O2. The rate of reaction is strictly proportional to the trioxide pressure, and is not affected by the total pressure, the presence of inert gases, and oxygen.

The following mechanism explains the experimental results:
equation image

In the presence of CO there appear CO2, (CF3OCO)2, and CF3O2C(O)OCF3 as products. With increasing temperature the amount of peroxicarbonate decreases, while the amounts of oxalate and CO2 increase. The rate of decomposition of the trioxide above a limiting pressure of about 10 torr CO is strictly first order and independent of CO pressure, total pressure, and the pressure of the products.

equation image
The addition of larger amounts of O2 to the CO containing system chaqnges the course of the reaction.
The temperature coefficient of the rates in the system Cl + CH4 ⇆ CH3 + HCl, thermochemistry of the methyl radical
Authors: Heneghan Shawn P. , Knoot Peter A. , Benson Sidney W.
Published: January 2005

The bimolecular rate constant for the title reaction has been measured by very‐low‐pressure reactor techniques at 233 < T K < 338. The equilibrium constant has also been measured between 253 and 338 K. Our rate constants are in excellent agreement with recent measurements using very different techniques and reaction conditions, and the general agreement probably makes this one of the most accurately measured rateconstants. Transition state models of the reaction rule out a bent TS in favor of a TS with colinear Cl···H···C bonds. The curvature at higher temperatures (>350 K) is quantitatively accounted for by transition state theory analysis. Tunneling is shown not to play a role. The measured values of K1 allow an experimental value of S° (CH3) to be fixed to only ±2.4 e.u. However, using known values of S° for all species gives ΔH°f298(CH3.) = 35.1 plusmn; 0.1 kcal/mol in excellent agreement with other measured values.
Comparison of the kinetics of cathodic H2 evolution from the unhydrated H3O+ ion and its hydrated form H9O: Frequency factor effects and modes of activation
Authors: Conway B. E. , Tessier D. F.
Published: January 2005

Experiments are described in which the kinetics of cathodic hydrogen evolution from the unhydrated H3O+ ion in pure CF3SO H3O+ are compared with those from an aqueous solution of CF3SO3H where the proton is mainly in a fully hydrated state as H9O. From the acid hydrate, which exists mainly as the ionic compound CF3SOH3O+, rates of H2 evolution at Ni, Pt, and Hg electrodes, measured at a given overpotential or expressed as exchange current densities, are between about 3.5 and 20 times slower than those from the same electrolyte in dilute (1.0M) aqueous solution. Allowing for the concentration differences in these two types of system and double‐layer effects, the rate constants are between about 9.4 and 216 times smaller for the reaction from H3O+ than from H9O at the above electrodes.

The evaluation of apparent heats of activation for H2 evolution from the two types of proton sources allows ratios of real frequency factors to be calculated for discharge from H3O+ and H9O. These data have a bearing on the theoretical conclusions regarding proton discharge mechanisms and show that frequency factor effects can be as important as activation energy differences in determining the rates of proton discharge from different proton sources.

The results are discussed in terms of current ideas about electron and proton transfer in electrochemical reactions, the state of hydration of H+, and the role of discharge from paired CF3SO and H3O+ ions. In particular, the molecular mechanics of discharge of the proton from the molecular ion H3O+ can be different from that from the fully hydrated H+ ion where many more HO‐ vibrational and librational modes can be involved in the process of activation of the H9O entity.
Quasi‐classical trajectory calculations on the H + O2 reaction
Authors: Bottomley Margaret , Bradley John N. , Gilbert James R.
Published: January 2005

Quasi‐classical trajectory calculations have been performed on the H + O2 system. Significant reaction probabilities are obtained when the initial energy is in rotation or vibration, or a combination of the two, but not when the initial energy is in translation. The opacity function shows a bimodal dependence on the impact parameter, with a small peak at 0.9 Å < b < 1.5 Å and a very prominent peak at 2.5 Å < b < 3.3 Å. The product scattering angles and product energy distributions also depend on b and to a limited extent on the initial energy distribution.

The observations can be largely interpreted in terms of the nature of the motion on the potential energy surface, while the effects of rotational energy on the reaction follow qualitatively from statistical phase‐space theory.
Electron transfer between trans‐dihydroxotetraoxoosmate(VIII) and thiosulfate. A kinetic study in aqueous alkaline media
Authors: Panda Rama Krushna , Neogi Gautam , Ramaswamy D.
Published: January 2005

The kinetics of oxidation of thiosulfate to tetrathionate by trans‐dihydroxotetraoxoosmate(VIII) in aqueous alkaline media have been studied. The oxidation follows a rate expression

where KOs is the formation constant of trans‐dihydroxotetraoxoosmate (VIII), and K2 and k3, respectively, represent the formation constants of the intermediate complex involving Os(VIII) and S2O and its decomposition constant. The KOs, K2, and k3 values have been computed to be (19.5 ± 3) dm3/mol, (6.12 ± 0.5) and (3.32 ± 0.3) × 10−1 dm3/mol s at 303 K, and I = 0.32 mol/dm3, respectively. The rate law is consistent with a mechanism envisaging the equilibrium formation of an intermediate complex involving Os(VIII) and S2O, followed by a rate‐determining decomposition of the complex with concomitant electron transfer.
Unimolecular activation–deactivation: Impulsive collision theory
Authors: Schranz Harold W. , Nordholm Sture
Published: January 2005

A theory of collisional energy transfer based on microcanonical relaxation in the limit of infinitesimal collision lifetimes is developed. In distinction to the recently formulated ergodic collision theory the potential energy is now frozen due to the short time scale, and only kinetic energy is available for redistribution. As a consequence, the rate of energy transfer is decreased, and agreement with experimentally based estimates generally improved.
Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation
Authors: Horiguchi Hiroyuki , Tsuchiya Soji
Published: January 2005

The bimolecular reaction of HI in CO2, which was excited vibrationally by irradiation of a continuous‐wave CO2 laser light, was investigated in the temperature range of 721–980 K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:1 HICO2 mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO2 laser (50 W) at 1 torr. However, in the HI‐SF6 mixtures the decomposition rate of HI was not accelerated by irradiation of the CO2 laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser‐excited CO2 (00°1). At lower total pressures or at lower partial pressures of HI in HI‐CO2 mixtures the enhancement was more significant because of inefficient vibrational deactivation of excited HI. A model calculation gave the result in agreement with the experimental one if the effective activation energy is assumed as Ea† = Ea ‐ αEvib, where Ea is the activation energy for the thermal reaction, Evib is the vibrational energy of two colliding HI molecules, and α is estimated to be about 0.7. This means that a part of the vibrational energy of reacting HI is employed to reduce the activation energy for the translational or rotational degree of freedom.
O(3P) + HOONO2 → products: Temperature‐dependent rate constant
Authors: Chang Jenq‐sian , Trevor Paula L. , Barker John R.
Published: January 2005

The title reaction was studied in a stirred‐flow reactor at six temperatures ranging from 228 to 297 K and for pressures near 2 torr. The experiments were performed under O‐atom‐rich conditions, and the HOONO2 concentration was monitored with a modulated molecular‐beam mass spectrometer. O‐atom concentrations were measured by titration with NO2 and by monitoring the portion of O2 dissociated in the microwave discharge. A weighted least‐squares analysis gives (k ± 1σ) = (7.0 ± 12.2) × 10−11 exp(‐3369 ± 489/T) cm3/s, where the uncertainties are 1 standard deviation (six temperatures) the covariance was σAB = 5.97 × 10−8. Due to the possible presence of systematic errors, the uncertainty in the rate constant could be as great as a factor of 2 over the entire temperature range.
Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato‐O)‐chromium(2+) ion
Authors: Hansen Peter J. , Birk James P.
Published: January 2005

The kinetics of the aquation of (H2O)5Cr(O2CCCl3)2+ have been examined at 35–55°C and 1.00M ionic strength with [H+] = 0.01−1.00M. The reaction follows the rate equation ‐d ln [Crtotal]/dt = (a[H+]−1 + b + c[H+])/(1 + d[H+]), where [Crtotal] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10−7M/s, b = (1.66 ± 0.02) × 10−5 s−1, c = (7.0 ± 0.8) × 10−5M−1·S−1 and d = 2.3 ± 0.3M−1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady‐state intermediates. Equilibrium and activation parameters were determined.
The kinetics of isotope exchange reactions: Use of initial rates to measure isotope effects on carbon acid ionization
Authors: Kresge A. J. , Powell M. F.
Published: January 2005

Multistep hydrogen isotope exchange reactions, such as the íonization of a carbon acid via a carbanion intermediate in a protic solvent, when conducted using an isotopic tracer to monitor the exchange, have the unusual feature that their rate‐determining steps always refer to the transfer of the tracer isotope and never to the isotope present in macroscopic amounts. This property of these reactions is discussed and rationalized using a free energy versus reaction coordinate diagram. It is further shown that this property does not invalidate a commonly used method of measuring kinetic isotope effects on carbon acid ionization in which rates of incorporation of tritium tracers into RH and RD substrates are compared, despite the fact that tritium transfer is rate determining in both exchanges, but it is valid only if initial rate measurements are used. When the comparison is made in a protio solvent, e.g., H2O, the portion of the initial reaction which may be used depends strongly on the magnitude of the isotope effect. It ranges from less than 1% tritium incorporation for large isotope effects to 10% or more for isotope effects near unity. On the other hand, when a deuterated solvent, e.g., D2O, is used, the range of validity of the method for large isotope effects is extended dramatically.
Vibrational energy transfer from chemically activated 1,4‐cyclohexadiene
Authors: Orchard S. Walter , Ramsden Jennifer
Published: January 2005

The thermal isomerization ofcis,anti,cis‐tricyclo[3.1.0.02,4] hexane was used to produce highly vibrationally excited 1,4‐cyclohexadiene. The competition between unimolecular decomposition of the energized diene (to benzene and hydrogen) and collisional stabilization was studied using the parent compound, SF6, CO2, N2, and He as quenching gases. Quenching efficiencies decreased in the order given above. By applying RRKM theory to the isomerization and decomposition reactions, it was possible to calculate the step size in a stepladder model of the deactivation of cyclohexadiene. The step sizes 〈ΔE〉 deduced (at 528 K and in units of kJ/mol) were: parent compound and SF6, 7; CO2, 5; N2, 4; He, 2. The study confirmed the utility of this unimolecular chemical activation system for energy transfer studies.
Intramolecular isotopic effect in the pyrolysis of ethyl‐2d1 chloride
Authors: Papagiannakopoulos P. J. , Benson S. W.
Published: January 2005

The thermal decomposition of deuterated ethyl chloride CH2DCH2Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high‐pressure limit and in the temperature range of 670–1100 K was found to be

The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratio kH/kD was found to decrease with increasing pressure. The RRKM‐theory calculations describe the experimental data well.

The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression

when kH and kD are the rate constants for the HCl and DCl channels of elimination.

The Arrhenius A factors obtained at the high‐pressure limit together with the temperature‐dependent expression of the branching ratio provided additional experimental data for an assignment (fine‐tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH2DCH2Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the transition‐state model.
A novel wall reaction of OH
Authors: Glass G. P. , Chaturvedi B. K.
Published: January 2005

A moderately fast second‐order reaction between OH and atomic hydrogen, which occurred on the halocarbon‐coated or acid‐washed walls of a standard discharge‐flow apparatus, has been investigated using epr spectroscopy. The reaction that occurred in a halocarbon‐coated flowtube was found to be unusual in that it produced a reactive product, namely, atomic oxygen.
Gas‐phase chlorine‐initiated photooxidation of methanol and isopropanol
Authors: Ohta Tomohiro , Bandow Hiroshi , Akimoto Hajime
Published: January 2005

The photolysis of CH3OH/Cl2/air, CH3OH/Cl2/NO2/air, and (CH3)2CHOH/Cl2/NO2/air at 28 ± 2°C was studied using the long‐path FTIR method. The primary reactions of methanol and isopropanol with Cl atoms were α‐hydrogen abstraction (100%), and α hydrogen (85%), and α‐hydrogen abstraction (15%), respectively. The failure to detect hydroxyalkyl‐peroxy nitrates suggested that the oxygen addition to α‐hydroxy radicals is not important. From the product distribution an upper limit of the ratio of oxygen addition to CH2OH and CH3CHOH was estimated to be about 6 and 7%, respectively. The oxygen addition ratio to (CH3)2COH was very low. The reaction mechanism is also discussed.
Nucleophilic character of the tert‐butyl radical. Absolute rate constants for the reactions with substituted toluenes
Authors: Dütsch H. R. , Fischer H.
Published: January 2005

The decay of photochemically generated tert‐butyl radicals is studied at 48°C in 11 m‐ and p‐substituted toluenes by time‐resolved electron spin resonance spectroscopy. It is governed by the second‐order self‐termination perturbed by a pseudo‐first‐order reaction of the radical with the toluenes. The first‐order lifetimes yield the rate constants kA for hydrogen transfer from toluenes to tert‐butyl. Substituent effects on the rate constants confirm the nucleophilic character of the radical.
Base‐catalyzed isomerization of phenylpropenes
Authors: Hassan M. , Nour A. R. O. Abdel , Satti A. M. , Kirollos K. S.
Published: January 2005

The prototropic rearrangement of 3‐phenyl‐1‐propenes to the corresponding 1‐phenyl‐1‐propenes was investigated in basic media utilizing 0.1M sodium ethoxide in absolute ethanol at 81°C. It was found that the effect of substituents on the rate of such isomerizations follows the order: p‐NO2 > o‐Cl > m‐Cl ≥ m‐F > p‐Br > o‐CH3 > m‐CH3 > m‐CH(CH3)2 > p‐CH(CH3)2 ≥ p‐C(CH3)3 > o‐OCH3. This is consistent with first‐order kinetics and “BS” mechanism. Quantitative treatment in terms of Hammett's equation showed a straight line, with a slope (p value) of +2.25. An increase in the strength of the base was also found to cause an increase in the rate of isomerization.
Small effect on the rate of complexation of some dialkyl‐2,2′‐bipyridyl‐5,5′‐dicarboxylates with the ion of Ni(II) in methanol
Authors: A. Dagoberto Pacheco , De O. Francesca Creazzola , B. Jesús A. Sequera , Medina José D. , De Santis De M Vienna
Published: January 2005

The kinetics of formation of the 1:1 complexes of some dialkyl‐2,2′‐bipyridyl‐5,5′‐dicarboxylates with the ion of Ni(II) have been determined by the stopped‐flow spectrophotometric method. Second‐order formation rate constants have been correlated with the Taft modification of the Hammett equation. A linear regression has been found (P = 0.95 confidence) with the following characteristics: slope = ‐0.6 ± 0.1; intercept = 1.32 ± 0.02 (log k0). An inductive effect of the alkyl groups upon the reaction of the complexation is proposed.
The liquid‐phase reaction of CCl3 radicals with primary alcohols
Authors: Feldman Liviu , Alfassi Zeev B.
Published: January 2005

The kinetics of gamma‐radiation‐induced free‐radical reactions in carbon tetrachloride solutions of ethanol and n‐pentanol were studied in the range of 0.05–0.80M and 25–170°C. The rate constant for the reaction

was found as

The activation energy is larger by 0.8 kcal/mol than for secondary alcohols, while the A1 factors are about the same.
High‐temperature kinetics of the reactions of SO2 and SO3 with atomic oxygen
Authors: Smith Owen I. , Tseregounis Spyros , Wang Shie‐Ning
Published: January 2005

A nozzle‐beam‐skimmer sampling system is used to measure species concentration profiles for a lean one‐dimensional premixed COO2Ar flame, into which small amounts of sulfur dioxide are introduced. The net formation rate for sulfur trioxide is obtained from the flux fraction profile for this species. The kinetic scheme
equation image

equation image

is then utilized, along with the measured temperature profiles, to evaluate the rate coefficients k1 and k2 over the temperature range of 1435–1850 K. The most satisfactory agreement between the measured net formation rate for SO3 and that calculated on the basis of reactions (1) and (2) is obtained with the rate coefficients

Reactions (1) and (2) are found to be nearly balanced in a substantial region of the flame. Here the data are more sensitive to the difference in activation energies, as opposed to a particular value for either. Implications of this observation on the uncertainty of the deduced temperature dependence for each reaction are discussed, as are some of the procedures used in the data analysis.
The oxidation of diethylhydroxylamine by nitrogen dioxide
Authors: Gleim Jeffrey , Heicklen Julian
Published: January 2005

Diethylhydroxylamine, (C2H5)2NOH, was oxidized by NO2 at 25°C in a long‐path‐length infrared gas cell. The measured products of the reaction were HONO and CH3CHO. The reaction scheme which explains the reaction is magnified image was oxidized by NO2, and the reaction was found to be very rapid with k1 > 10−16 cm3/s. The products of the reaction were verified by both infrared absorption (CH3CHO, C2H5NO) and gas chromatography (CH3CHO, NO).
Electron transfer reactions of V(IV) with Cl(I), Br(I) and I(I). A kinetic study
Authors: Radhakrishnamurti P. S. , Janardhana C. , Behera G. P. , Mohanty G. K.
Published: January 2005

A kinetic study on the oxidation of V(IV) by chloramine‐T (CAT) at pH 6.85 by N‐bromo succinimide (NBS) in aqueous acetic acid–perchloric acid media and by N‐iodo succinimide (NIS) in aqueous perchloric acid medium has been carried out. In all the systems studied the order with respect to the oxidant is unity. NBS and CAT oxidation reactions exhibited Michaelis–Menten type kinetics, and the NIS study indicated unit dependence on [substrate]. Independence on acidity has been observed in the case of CAT and NBS reactions, but NIS reactions exhibited inverse unit dependence on [acid]. Novel solvent influences have been noticed in the case of CAT reactions, but with NIS and NBS reactions retardation in the rate has been observed with an increase in the percentage of acetic acid. Plausible mechanisms consistent with the results have been postulated, and suitable rate laws in consonance with the postulated mechanisms have been derived.
The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pKa of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure
Authors: Buncel Erwin , Chuaqui Claudio , Wilson Harold
Published: January 2005

A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p‐nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pKa of HOOH in methanol at 25°C as 15.8 ± 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH3O− + H2O2 ⇄ CH3OH + HO were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo‐first‐order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such a corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant kHOO‐for the reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio k/k = 8.8 ± 2.2. This confirms the existence of an α effect at saturated carbon in this system.
A reexamination of the pyrolysis of bis trifluoromethyl peroxide
Authors: Batt L. , Walsh R.
Published: January 2005

The literature results for the pyrolysis of bis trifluoromethyl peroxide are reexamined and compared with those for dimethyl peroxide. The thermochemistry yields the result that the π‐bond energy in carbonyl fluoride is 96 ± 10 kcal/mol compared to 74 kcal/mol for that in formaldehyde. Thermodynamic additivity contributions are derived for the C(F)3(O) and O(C)(F) groups. Some conclusions are drawn in relation to the oxidation of halogeno methyl radicals and the chemistry of the atmosphere.
Photolysis of carbon tetrachloride in the presence of alkanes
Authors: Matheson Ian , Tedder John , Sidebottom Howard
Published: January 2005

The photolysis of carbon tetrachloride in the presence of a number of alkanes has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the alkane. The data have been used to determine Arrhenius parameters for hydrogen abstraction from the series of alkanes CH4, C2H6, C3H8, and i‐C4H10 by trichloromethyl radicals, magnified image The rate data obtained are used to explain why termination reactions involving alkyl radicals become less significant as the alkane becomes more complex.
A double‐barreled chemical oscillator
Authors: Cooke David O.
Published: January 2005

A chemical system, based on the Briggs–Rauscher reaction, which unperturbed undergoes rhythmic activity followed by a long period of iodine production–consumption prior to return of the rhythmic activity, is described. The effect of the various variables on the system is reported.
Reaction between U(IV) and H2O2 in hydrochloric acid medium
Authors: Bhattacharyya P. K. , Saini R. D. , Ruikar P. B.
Published: January 2005

Kinetic investigations on the reaction between U(IV) and H2O2 have been carried out at different acidities in chloride medium at an ionic strength of 2M. The observed bimolecular rate constant has been found to be dependant on [H+]−1.3. The activation energy of the overall reaction has been found to vary from 13.4 ± 0.7 to 18.0 ± 0.8 kcal/mol in the range of acidity from 0.3 to 1.5M. The results have been explained on the basis of three parallel rate‐controlling reactions involving unhydrolyzed species of U(IV) and hydrolyzed species UCl(OH)2+ and UO2+. The values of the rate constants for these three reaction paths have been found to be of the order of 3.95, 5.59 × 103, and 1.49 × 105M−1 min−1, respectively.
Kinetics and mechanism of chlorination of toluene and some substituted toluenes by chloramine‐T
Authors: Radhakrishnamurti P. S. , Pati Subas C. , Dev B. R.
Published: January 2005

The kinetics of chlorination of toluene, o‐methyl toluene, p‐methyl toluene, m‐methyl toluene, and m‐chlorotoluene by chloramine‐T(CAT) in aqueous acetic acid in the presence of HClO4 have been studied. The reaction is first order with respect to [CAT] as well as [H+]. The order with respect to the substrate is unity in the case of toluene and m‐chlorotoluene, fractional in the case of o‐methyl toluene and p‐methyl toluene, and zero order in the case of m‐methyl toluene. Nuclear halogenation has been observed with m‐methyl toluene, while nuclear and side‐chain halogenation for p‐methyl toluene and o‐methyl toluene, and sidechain halogenation for toluene and m‐chlorotoluene are the pathways. An increase in the proportion of acetic acid accelerates the rate. Added acetate ions inhibit the reaction, and added p‐toluene sulfonamide causes a pronounced retardation. A mechanism involving AcO+HCl as the important electrophile is discussed.
Thermal reaction of hydrogen–butene‐2‐cis mixtures at 500°C: Hydrogenation, hydrogenolysis, and thermal reaction of the olefin
Authors: Collongues C. , Richard C. , Martin R.
Published: January 2005

The thermal reaction of hydrogen–butene‐2‐cis mixtures has been studied in a static system at low extent of reaction around 500°C. Hydrogen does not affect the thermal reaction itself of the olefin, but gives rise to new stoichiometries of hydrogenolysis and hydrogenation, which are specified:

The reaction is described in terms of a molecular and free‐radical mechanism. It is shown that the key process for the hydrogenolysis–hydrogenation reaction is
equation image
and that the rate constant of this process can be determined from either propylene, or methane, or butene‐1 formations:

with θ = 4.57 × 10−3 T kcal/mol. Other rate constants are estimated and agree with literature data.
Kinetics of the reactions of O3 and OH radicals with furan and thiophene at 298 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L.
Published: January 2005

Rate constants for the reactions of O3 and OH radicals with furan and thiophene have been determined at 298 ± 2 K. The rate constants obtained for the O3 reactions were (2.42 ± 0.28) × 10−18 cm3/molec·s for furan and <6 ×10−20 cm3/molec·s for thiophene. The rate constants for the OH radical reactions, relative to a rate constant for the reaction of OH radicals with n‐hexane of (5.70 ± 0.09) × 10−12 cm3/molec·s, were determined to be (4.01 ± 0.30) × 10−11 cm3/molec·s for furan and (9.58 ± 0.38) × 10−12 cm3/molec·s for thiophene. There are to date no reported rate constant data for the reactions of OH radicals with furan and thiophene or for the reaction of O3 with furan. The data are compared and discussed with respect to those for other alkenes, dialkenes, and heteroatom containing organics.
Mechanism and thermochemistry of oxidation of HCl and HBr at high temperatures. The heat of formation of HO2
Authors: Shum Lilian G. S. , Benson Sidney W.
Published: January 2005

Using currently available thermochemical and kinetic data and estimation methods to analyze the thermochemistry and the kinetic parameters of the elementary reactions involved in the oxidation of HCl and HBr, reaction mechanisms are proposed which account for the previously reported reaction products, the rate law, and the kinetic data. For oxidation of HCl, two competitive pathways, the radical initiation by hydrogen abstraction and the fourcenter reaction pathway, were invoked to account for the observations. In the oxidation of HBr one must invoke a fast surface reaction of the type

to account for the reaction.
Complex rate law for the cerium(IV) oxidation of glycolic acid in the medium HClO4–Na2SO4–NaClO4
Authors: Calvaruso Giuseppe , Cavasino F. Paolo , Sbriziolo Carmelo , Triolo Roberto
Published: January 2005

The kinetics of the cerium(IV) oxidation of glycolic acid have been studied in the medium HClO4Na2SO4NaClO4 at varying organic substrate (HL), hydrogen, and bisulfate ion concentrations at 25.0°C and ionic strength 2.0M. Under the experimental conditions used (0.03 ⩽ [H+] ⩽ 0.5M; 0.02 ⩽ [HSO4−] ⩽ 0.1M; 0.01 ⩽ [HL] ⩽ 0.1M) the observed pseudo‐first‐order rate constant kobs has been found to follow the complex expression
equation image
where the values of the various constants have been estimated by a nonlinear least‐squares method. According to this expression the oxidation process occurs significantly through three simultaneous pathways. Moreover three equilibria involving cerium(IV) and HSO4− (or SO42−) ions are important from a kinetic point of view, whereas only two equilibria involving the corresponding complexes with the organic substrate are predominant.
A reexamination of the pyrolysis of bis trifluoromethyl peroxide. Addendum: Concerning D(CF3O2‐CF3) and D(CF3‐O2)
Authors: Batt L. , Walsh R.
Published: January 2005

Earlier arguments concerning D(CF3O2‐CF3) and D(CF3‐O2) are shown to be probably wrong. New values of 86 and 49 kcal/mol, respectively, are derived. C–O bond strengths are compared between CF3‐ and CH3‐containing compounds.
Kinetic analysis of an extended single‐path sequence of first‐order reactions. The reaction of mesitonitrile in sulfuric acid
Authors: Al‐ka′bi Ja′far , Gore Peter H. , Saad Esmat F. , Waters David N. , Moxon Gerald F.
Published: January 2005

The system of a sequence of five first‐order reactions, A → B → C → D → E → F, has been analyzed kinetically. An actual example is proposed in the reaction of mesitonitrile in 89.8% (w/w) sulfuric acid at 98.3°C. The analysis provides estimates of concentration ratios as functions of time, and the progress of the buildup and decay of the intermediate species can be monitored. The kinetics have been measured for the hydration of mesitonitrile, the hydrolysis of mesitamide, and the sulfonation of mesitylenesulfonic acid in 89.8% sulfuric acid. The calculated values of the concentration ratios of mesitylenedisulfonic acid as a function of time were satisfactorily close to those found in experiment.
Reaction of CF3 radicals with H2O and D2O
Authors: Pasteris Leonor , Oexler Elena V. , Staricco Eduardo H.
Published: January 2005

The reaction of CF3 radicals with H2O (D2O) has been studied over the range of 533–723 K using the photolysis and the pyrolysis of CF3I as the free radical source. Arrhenius parameters for the reactions

where X = H or D, relative to CF3 radical recombination are given by

where k/k is in cm3/2/mol1/2·s1/2 and θ = 2.303RT/cal/mol. The activation energy and the primary kinetic isotope effect have been compared with those derived from the BEBO method.
Studies in nickel(IV) Chemistry. Kinetics of the aquacopper(II)‐catalyzed oxidation of phenylhydrazine by tris(dimethylglyoximato)‐nickelate(IV) in aqueous medium
Authors: Acharya S. , Neogi G. , Panda R. K.
Published: January 2005

The kinetics of electron transfer in the redox system containing phenylhydrazine (S) and tris(dimethylglyoximato)nickelate(IV), in the presence of catalytic amounts of added Cu(II)aq, have been studied in aqueous medium at an ionic strength of 0.25M in the pH range of 6.01–9.06. The kinetics exhibit pseudo‐zero‐order disappearance of Ni(IV) when an excess of [S]0 and small amounts of Cu(II) are present. While the pseudo‐zero‐order rate constants are almost linearly dependent on [S]0 at constant [Cu(II)] and pH tending to become non‐linearly dependent on higher relative [S]0, they are linearly dependent on [Cu(II)] in a 20‐fold range. The pH‐rate profiles with low [S]0 and [Cu(II)] show a monotonic decrease in rates with increasing pH, the rates tending to attain limiting values at higher relative pH. Results are interpreted in terms of a probable mechanism involving the formation of precursor complexes of phenylhydrazine and Cu(II) species in the medium, followed by the rate‐determining breakdown of the precursors with concomitant electron transfer. The hydrolyzed species of Cu(II) reacts more slowly than does the aquacopper(II). Ni(IV) does not appear to have any kinetic role in the redox system and is involved only in rapid product formation steps. The oxidation product of phenylhydrazine is 4‐hydroxyazobenzene.