bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine‐T in aqueous solution
Authors: Mahadevappa D. S. , Jadhav M. B. , Naidu H. M. K.
Published: January 2005

The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine‐T (CAT) is studied in HClO4 and NaOH media with OsO4 as a catalyst in the latter medium. In acid medium, the rate law is ‐d [CAT]/dt = k [CAT][DMSO][H+]. Alkali retards the reaction and the rate law takes the form ‐d [CAT]/dt = k [CAT][DMSO][OsO4]/[NaOH], but is reduced to ‐d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied.

The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO4 which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine‐T and the substrate.
A new mechanism for the reaction of ozone with olefins
Authors: Dodge Marcia C. , Arnts Robert R.
Published: January 2005

A mechanism for ozone–olefin reactions is developed that is consistent with the recent findings of several investigations. These findings suggest a reaction sequence leading to the production of fewer free radical species than has been assumed in the past. Computer simulations using the new mechanism reproduce experimental results obtained from the ozonolysis of propylene in air.
A simple preparation of stable, nonreactive surfaces for gas kinetic studies of reactions of hydrogen atoms
Authors: Sepehrad Abolghassem , Marshall Roger M. , Purnell Howard
Published: January 2005

A quartz surface has been prepared for which γ, the mean collisional efficiency for removal of hydrogen atoms, is given by

over the temperature range from 315 to 818 K. The preparation “cleans” the surface by contact with 10M aqueous NaOH for ˜ 15 hr and then deactivates it by contact with 10M aqueous HNO3 for ˜15 hr. The surface is stable and long‐lived even after prolonged contact with air. Preliminary results show that a similar result can be obtained using Pyrex glass surfaces.
Kinetics of the reaction HO2 + NO2(+M) = HO2NO2 using molecular modulation spectrometry
Authors: Cox R. A. , Patrick K.
Published: January 2005

Rate constants for the reaction HO2 + NO2(+ M) = HO2NO2(+ M) have been obtained from direct observations of the HO2 radical using the technique of molecular modulation ultraviolet spectrometry. HO2 was generated by periodic photolysis of Cl2 in the presence of excess H2 and O2, and k1 was determined from the measured concentrations and lifetime of HO2 with NO2 present. k1 increased with pressure in the range of 40–600 Torr, and a simple energy transfer model gave the following limiting second‐ and third‐order rate constants at 283 K: k1∞ = 1.5 ± 0.5 × 10−12 cm3/molec·sec and k1III = 2.5 ± 0.5 × 10−31 cm6/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195–265 nm; it showed a broad feature with a maximum at 200 nm, σmax = 4.4 × 10−18 cm2.
Abstraction of chlorine atoms from chloroalkanes. V. The liquid‐phase reaction between Et3SiH radicals and CH2Cl2, CHCl3, CCl4, and CCl3CN
Authors: Aloni R. , Rajbenbach L. A. , Horowitz A.
Published: January 2005

The kinetics of chlorine transfer from CH2Cl2, CHCl3, CCl4, and CCl3CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1‐bromopentane was used as a reference. The following Arrhenius parameters were determined:magnified imagewhere the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et3Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.
The kinetics of the solvolysis of propylene and cyclopropane in concentrated aqueous sulfuric acid relative energies of the 2‐propyl cation and protonated cyclopropane
Authors: Viviani Donn , Levy Joseph B.
Published: January 2005

The rates of solvolysis of propylene and cyclopropane in 6.49M H2SO4 have been measured as a function of temperature. From the data, calculations of the relative heats of formation in solution of the 2‐propyl cation and protonated cyclopropane have been made. The heat of formation of protonated cyclopropane has been found to be 6.4 kcal/mol greater than that of the 2‐propyl cation. The implications of this result are discussed.
Very low‐pressure pyrolysis (VLPP) of hex‐1‐ene. Kinetics of the retro‐ene decomposition of a mono‐olefin
Authors: King Keith D.
Published: January 2005

The thermal unimolecular decomposition of hex‐1‐ene has been investigated over the temperature range of 915–1153 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C3−C4 fission and retro‐ene elimination, with the latter dominant at low temperatures and the former at high temperatures. This behavior results in an isokinetic temperature of 1035 K under VLPP conditions (both reactions in the unimolecular falloff regime). RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters given by log k1 (sec−1) = (12.6 ± 0.2) ‐(57.7 ± 1.5)/θ for retro‐ene reaction, and log k2 (sec−1) = (15.9 ± 0.2) ‐ (70.8 ± 1.0)/θ for C‐C fission, where θ = 2.303 RT kcal/mol. The A factors were assigned from the results of a recent shock‐tube study of the decomposition in the high‐pressure regime, and the activation energies were found by matching the RRKM calculations to the VLPP data. The parameters for C‐C fission are consistent with the known thermochemistry of n‐propyl and allyl radicals. A clear measure of the importance of the molecular pathway in the decomposition of a mono‐olefin has been obtained.
The kinetics of the gas‐phase thermal isomerization and decomposition of Trans‐ and Cis‐1,2‐Bis(trifluoromethyl)‐1,2,3,3‐tetrafluorocyclopropane
Authors: Ferrero Juan C. , Staricco Eduardo H.
Published: January 2005

The kinetics of the gas‐phase thermal isomerization between trans‐ and cis‐1,2‐bis(trifluoromethyl)‐1,2,3,3‐tetrafluorocyclopropane as well as their decomposition to trans‐ and cis‐perfluoro‐2‐butene, respectively, and CF2, was studied in the temperature range of 473–533°K, with an initial pressure of reactant of 1.5 to 7.0 Torr. Some runs were also made with the addition of SF6 as an inert gas up to a total pressure of 100 Torr. The reactions are first order and homogeneous. The rate constants for the geometrical isomerization fit the following Arrhenius relations:

and the corresponding equations for the decomposition of the trans and cis‐cyclopropane are

.
The reaction of CH3O2 radicals with NO2
Authors: Adachi Hiroyuki , Basco Norman
Published: January 2005

The rate constant for the reaction CH3O2 + NO2 → (products) has been measured directly by flash photolysis and kinetic spectroscopy. At room temperature and at total pressures between 53 and 580 Torr, k3 = (9.2 ± 0.4) × 108 liter/mole sec so that the rate of formation of the probable primary product peroxymethyl nitrate (CH3O2NO2) may be significant in urban atmospheres.
A reinvestigation of the temperature dependence of the rate constant for the reaction O + O2+ M → O3+ M (for M = O2, N2, and Ar) by the flash photolysis resonance fluorescence technique
Authors: Klais Odo , Anderson Philip C. , Kurylo Michael J.
Published: January 2005

The flash photolysis resonance fluorescence technique has been used to reinvestigate the kinetics of the oxygen atom–oxygen molecule combination reaction. Third‐order rate constants for O2, N2, and Ar as deactivant molecules were determined over the temperature range of 219–368 K. The results presented herein are the most extensive data sets available for atmospheric modeling and are used to formulate a recommendation for such purposes. The recommended rate expressions areorComparisons of these results with existing literature data are presented.
Kinetics of formation of HCN during pyridine pyrolysis
Authors: Houser Thomas J. , Hull Mitchell , Alway Robert M. , Biftu Tesfaye
Published: January 2005

The rate of HCN evolution during the inert pyrolysis of pyridine in the temperature range of 900–1000°C was determined in a flow system using a stirred‐flow reactor. The data indicated that HCN was formed through a sequence of reactions rather than during the initial step(s) involving the disappearance of pyridine. The Arrhenius parameters for the first‐order step yielding HCN were 39.5 kcal/mol and 6.8 for the activation energy and log frequency factor, respectively. The mechanistic implications of the rate data are discussed, and these are related to the overall pyridine pyrolysis mechanism.
A computational analysis of the alkane pyrolysis mechanism: Sensitivity analysis of individual reaction steps
Authors: Edelson D. , Allara D. L.
Published: January 2005

The previously reported extensive mechanism for the pyrolysis of propane and n‐butane around 800 K is reexamined in the light of a recent reevaluation of the rate constant data base, and the sensitivity of model simulations to variations in the rate parameters is studied. The pyrolysis rates of butane and the product distribution of propane remain in good agreement with the available experiments, while the rate of propane and the product distribution of butane now show significant differences. The linear sensitivity analysis of the reaction matrix demonstrates an intimate coupling between initiation, hydrogen abstraction, radical decomposition, and recombination reactions as primarily responsible for the overall behavior of the mechanism. The role of unsaturated radicals in the self‐inhibition of the pyrolysis process is quantitatively established. The study of the sensitivity coefficients for butane product formation has permitted pinpointing those specific reaction steps in the mechanism which are most likely responsible for the remaining discrepancies between model and experiment. This particular example demonstrates the usefulness of sensitivity calculations for the isolation of reactions for which improvements in rate parameter values are needed.
Kinetics of the reaction Cl + HO2 = HCl + O2, using molecular modulation spectrometry
Authors: Cox R. A.
Published: January 2005

The rate constant for the reaction (1), Cl + HO2 → HCl + O2, was measured using molecular modulation spectrometry to investigate HO2 radical kinetics in the modulated photolysis of Cl2;H2O2 mixtures at 760 torr pressure. HO2 was monitored directly in absorption at 220 nm, and k1 was determined from computer simulations of the observed kinetic behavior of HO2, using a simple chemical model. The results gave

where k4 is the rate constant for the reaction of Cl with H2. A consensus value of k4 gave k1 = 6.9 × 10−11 cm3/molecule sec, independent of temperature in the range of 274–338 K with an overall uncertainty of ±50%. The relative importance of reaction (1) for the conversion of Cl to HCl in the stratosphere is discussed briefly.
Kinetics and mechanism of the germane decomposition
Authors: Newman C. G. , Dzarnoski J. , Ring M. A. , O'Neal H. E.
Published: January 2005

The homogeneous gas‐phase thermal decomposition kinetics of germane have been measured in a single‐pulse shock tube between 950 and 1060 K at pressures around 4000 torr. The initial decomposition is GeH4 → GeH2 + H2 in its pressure‐dependent regime, with log k = 13.83 ± 0.78 – 50,750 ± 3570 cal/2.303RT. RRKM calculations suggest that the high‐pressure Arrhenius parameters are log k GeH4(M → ∞) = 15.5 – 54,300 cal/2.303RT. Extrapolations to static system pyrolysis conditions (T ∼ 600 K, P ∼ 200 torr) give homogeneous reaction rates which are much slower than those observed, hence the static system pyrolysis of germane must be predominantly heterogeneous. Shock‐initiated pyrolysis reaction stoichiometry is 2 mol H2 per mole GeH4, suggesting that the subsequent decomposition of germylene is essentially quantitative. Investigations of the hydrogen product yields for pyrolysis of GeD4 in øCH3 further indicate that the germylene decomposition reaction is mainly GeH2 → H2 + Ge, but that a small amount of reaction to H atoms may also occur.
Mutual interactions of the methyl and methylperoxy radicals studied by flash photolysis and kinetic spectroscopy
Authors: Adachi Hiroyuki , Basco N. , James D. G. L.
Published: January 2005

The decadic extinction coefficient of the methyl radical at 216.4 nm and the rate constant for mutual combination were redetermined as:

. The application of the Beer–Lambert law to these measurements was justified experimentally. The absorption spectrum of the methylperoxy radical was characterized as a weak, broad, structureless band, having a maximum at 240 nm with ϵ(240) = 1.55 × 103 l./mol cm. The mutual interaction of methylperoxy radicals leads to the generation of methoxy and hydroperoxy radicals as a consequence of the nonterminating interaction

. Each derivative radical may consume a significant fraction of the methylperoxy radicals, and either of these cross interactions may be made predominant by a suitable choice of oxygen pressure. The mutual interaction was studied under both conditions. The overall mechanism was analyzed by a precise computational method, and the rate constant of the total mutual interaction

was estimated as

.
The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media
Authors: Brusa M. A. , Colussi A. J.
Published: January 2005

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K

was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = ‐d[Br2]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br2[(2.7–13.6) × 10−3M], H+ (0.03–2.0M), and Br− (up to 0.6M). The mechanism
equation image
with k1 = 20.2 ± 1.2 M−1 sec−1, pK2 = 3.76, pK3 = −1.20, accounts for all experimental observations. Br3− and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.
Effect of brownian diffusion on chemical kinetics
Authors: Sitarski M.
Published: January 2005

A new method of theoretical prediction of the kinetic rate constants of fast chemical reactions in solutions is presented. It takes into account the effect of finite diffusive displacements of the reacting molecules. The approach is based on the solution of the steady‐state Fokker–Planck equation by the moments method of Grad developed in the theory of coagulation of aerosol particles. A comparison of the predicted rate constants with the experimental data provided by Schuh and Fischer for the self‐reaction of tert‐butyl radicals in n‐alkanes shows a good correspondence.
Kinetic studies of free radical reactions by mass spectrometry. II. The reactions of SO + ClO, SO + OClO and SO + BrO
Authors: Clyne Michael A. A. , Macrobert Alexander J.
Published: January 2005

The rates of several novel elementary reactions involving ClO, BrO and SO free radicals in their ground states were studied in a discharge‐flow system at 295 K, using mass spectrometry. The rate constant k2 was determined from the decay of SO radicals in the presence of excess ClO radicals:

The SO + OClO overall reaction has a complex mechanism, with the primary step having a rate constant k5 equal to (1.9 ± 0.7) × 10−12 cm3 sec−1:

A lower limit for the rate constant of the rapid reaction of SO radicals with BrO radicals was determined:
Effect of cyano group substitution on metathetical reactions. IV. Substituent effects on the rates of cyanomethyl radical reaction with haloalkanes
Authors: Gonen (Geliebter) Y. , Horowitz A. , Rajbenbach L. A.
Published: January 2005

Gamma radiation‐induced free radical chain reactions in liquid mixtures of BrCH2CN, eyelohexane (RH), and haloalkanes (XCCl3) were studied. The kinetics of hydrogen and chlorine atom abstraction from CHCl3, CH3CCl3, CH2ClCCl3, CHCl2CCl3, CF3CCl3, C2Cl6, CCl3CN, and CCl4 by CH2CN radicals were investigated by a competitive method. The reactions investigated were
equation image
Rate constant ratios k3/k2, k5/k6, k7/k2, and k3/k7 were determined at 180°C. In the CCl4RHBrCH2CN system k3/k2 was determined in the temperature range of 100–180°C, yielding log k2 k3 = −0.11 ± 0.2 −(3.34 ± 0.39/θ): where θ = 2.3RT in kcal/mol. The value E2E3 was combined with existing data on E3 to yield E2(CCl4) = 17.57 kcal/mol. The reactivity trend of CH2CN is compared with that of R radicals. It is shown that in spite of a difference of about four orders of magnitude in kCl values, the reactive cyclohexyl radical is somewhat more selective than CH2CN. It is proposed that the relative reactivities log[k2(XCCl3)/k2(CH3CCl3)] can be correlated in terms of a dual‐parameter Taft equation which takes into account both resonance and inductive substituent effects.
Very low‐pressure pyrolysis (VLPP) of pentynes. I. Kinetics of the retro‐ene decomposition of pent‐1‐yne
Authors: King Keith D.
Published: January 2005

The thermal unimolecular decomposition of pent‐1‐yne has been investigated over the temperature range of 923–1154 K using the technique of very low‐pressure pyrolysis (VLPP). Under the experimental conditions the reaction proceeds predominantly via a molecular retro‐ene pathway to yield allene and ethylene. There was some evidence for the occurrence of the higher energy C3C4 bond fission pathway at the high end of the temperature range. Interpretation of the data with the aid of RRKM theory and taking into account a decrease in gas‐wall collision efficiency with temperature yields the following high‐pressure rate constant expression for the retro‐ene pathway:

at 1100 K where θ = 2.303 RT kcal/mol and the A factor was assigned from the results of shock‐tube studies of similar molecules. These rate parameters are independent of the inclusion of the bond fission pathway in the RRKM calculations. The results are compared with previous data on the retro‐ene decomposition of alkynes.
An indirect measurement of the absolute rate constant of the self‐reaction of tert‐butoxy radicals
Authors: Wong S. King
Published: January 2005

No reliable rate constant is available for the self‐reaction of tert‐;butoxy radicals. We have set up a competition between hydrogen abstraction and self‐reaction of tert‐butoxy radicals in a flash photolysis electron spin resonance study to extract this information. Experimental values of hydrogen abstraction product radical concentrations under various hydrogen donor concentrations were then compared with theoretically calculated values with different values of 2k4 to obtain the best fit. Hydrogen donors such as cyclopentane, anisole, methyl tert‐butyl ether, and methanol were chosen for the study. A value of (1.3 ± 0.5) × 109M−1 sec−1 for the rate constant of the self‐reaction of tert‐butoxy radicals has been determined at 293°K.
Kinetics of acid catalyzed and Ag(I) catalyzed decomposition of peroxodisulfate in aqueous medium
Authors: Singh U. Chandra , Venkatarao K.
Published: January 2005

The mechanism of acid catalyzed decomposition of peroxodisulfate, (S2O) in aqueous perchlorate medium involves the hydrolysis of the species H2S2O8 and HS2O and the homolysis of the species H2S2O8, HS2O and S2O at the OO bond. The overall rate law when 1.4M > [HClO4] > 0.1M is

The constants k′ and k″ contain the hydrolysis and homolysis rate constants of HS2O8− and H2S2O8, respectively. With added Ag(I), the acid catalyzed and Ag(I) catalyzed reactions take place independently. Ag(I) catalyzed decomposition appears to involve the species AgS2O (aq).
The rate of reaction of methyl radicals with ozone
Authors: Ogryzlo E. A. , Paltenghi R. , Bayes Kyle D.
Published: January 2005

The absolute rate constant for the reaction of methyl radicals with ozone has been measured as a function of temperature. Small concentrations of CH3 were generated by flash photolyzing CH3NO2 at 193 nm with an ArF laser. A photoionization mass spectrometer was used to follow the rate of decay of CH3 at various ozone concentrations. The resulting rate constants could be fit by the expressions

over the temperature range of 243–384 K. These rate constants can be modeled by simple transition state theory using reasonable parameters for the activated complex. Use of this rate constant shows that less than 1% of the methyl radicals formed in the stratosphere react with ozone.
The √t law in solid‐phase reactions. Analysis of the hypothesis on rate constant distribution
Authors: Zaskul'nikov V. M. , Vyazovkin V. L. , Bol'shakov B. V. , Tolkatchev V. A.
Published: January 2005

The reaction C2H5 + O2 → C2H5O2 in glassy methanol‐d4 and the H‐atom abstraction by CH3, C2H5, and n‐C4H9 radicals in C2H5OH + C2D5OH and CD3CH2OH + C2D5OH glassy mixtures have been studied by electron spin resonance. The analysis of the dependence of the reaction rates on the concentration of O2 (oxidation) and C2H5OH, CD3CH2OH (H‐atom abstraction) has shown that the √t law is not conditioned by the existence of regions characterized by different rate constants.
The kinetics of radiation‐induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclohexene
Authors: Alfassi Zeev B. , Feldman Liviu
Published: January 2005

The kinetics of hydrogen abstraction from cyclohexene by CCl3 radicals were studied in CCl4 solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl3 radicals were produced both by radiolysis of CCl4 and by photolysis of CCl3Br. The rate constant for the reaction
equation image
was found to be given by the equation

where θ = 2.303 RT kcal/mol. This activation energy leads to CH bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C‐C6H11 radical.
Temperature dependence of rate constants for the reaction of atomic oxygen with hydrogen chloride
Authors: Singleton Donald L. , Cvetanovi R. J.
Published: January 2005

A phase‐shift method has been used to determine the rate constant for the reaction of ground state oxygen atoms with HCl over the temperature range of 330–600 K. Oxygen atoms were generated by modulated mercury photosensitized decomposition of N2O, and monitored by the chemiluminescence from their reaction with NO. After correction for diffusion of oxygen atoms from the viewing zone, the rate constants can be represented by the Arrhenius equation k1 = (3.06 ± 1.43) × 1012 exp[(−3160 ± 184)/T] cm3/mol·s. The indicated uncertainties are 95% confidence limits for 15 degrees of freedom. Also, the third‐body efficiency of HCl relative to N2O in the reaction O + NO + M ← NO2 + M was determined to be 1.9 ± 0.2 over the temperature range of 298–360 K.
Mechanistic details of the Belousov–Zhabotinsky oscillations IV. Sensitivity analysis
Authors: Edelson David
Published: January 2005

The sensitivity of the period of the Belousov–Zhabotinsky oscillations to the rate constants and initial conditions of our previously proposed mechanism is computed by the technique recently developed for this purpose and shown to be valid in our analysis of the Oregonator. The principal rate‐controlling steps for the determination of the period are found to be the enolization and bromination of malonic acid. Dependence of the period on initial conditions qualitatively agrees with available experimental data, except for the hydrogen ion, where a large discrepancy exists. It is suggested that this may be due to deficiencies in the organic reactions in the mechanism, or to a hydrogen‐ion catalyzed bromination mechanism for malonic acid. Other components of the mechanism, which participate in characterizing the period and amplitude of the oscillations, are discussed.
Estimation of rate constants from growth and decay data
Authors: Carrington Tucker
Published: January 2005

Many experiments in chemical kinetics are initiated by a fast pulse, such as electric discharge, shock wave, flash lamp, or laser. After this pulse one observes the production and subsequent decay of a reactive intermediate. One then postulates a mechanism and adjusts the associated rate constants so as to minimize the difference between the results of the experiment and the prediction of the mechanism. The parameters to be estimated are usually strongly correlated, so that it is not possible to determine them separately. These estimated parameters are of little value unless we can also estimate statistically valid confidence limits for them. The difficulties are discussed which frequently arise in estimating parameters and confidence limits for a kinetic mechanism which is widely used in interpreting laser excitation and fluorescence measurements, that is, first‐order production and decay. These difficulties, and methods for dealing with them, are illustrated with realistic data. The estimation problem is particularly ill conditioned when the production and loss rates are nearly equal. In some experimental systems this can be avoided, but in others it is inevitable.
A completely inorganic oscillating system of the Belousov–Zhabotinskii type
Authors: Adamčíková Ľubica , Ševčíak Peter
Published: January 2005

An inorganic compound, NaH2PO2, has been found to generate temporal chemical oscillations in Belousov–Zhabotinskii type reactions when it is substituted for the organic reducing material. Gaseous products were removed by a constant flow of nitrogen carrier gas. Periodic Br2 evolution was measured polarographically.
Kinetics of the reactions of OH radicals with n‐alkanes at 299 ± 2 K
Authors: Atkinson R. , Aschmann S. M. , Carter W. P. L. , Winer A. M. , Pitts J. N.
Published: January 2005

Relative rate constants for the reaction of OH radicals with a series of n‐alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n‐butane of 2.58 × 10−12 cm3 molecule−1s−1, the rate constants obtained are (X1012 cm3 molecule−1 s−1): propane 1.22 ± 0.05, n‐pentane 4.13 ± 0.08, n‐heptane 7.30 ± 0.17, n‐octane 9.01 ± 0.19, n‐nonane 10.7 ± 0.4, and n‐decane 11.4 ± 0.6. The data for propane, n‐pentane, and n‐octane are in good agreement with literature values, while those for n‐heptane, n‐nonane, and n‐decane are reported for the first time. These data show that the rate constant per secondary C—H bond is ∽40% higher for —CH2— groups bonded to two other —CH2— groups than for those bonded to a —CH2— group and a —CH3 group.
Basic hydrolysis of glyceryl nitrate esters. I. 1‐glyceryl and 2‐glyceryl nitrate esters
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 1‐glyceryl mononitrate (1‐MNG) and 2‐glyceryl mononitrate (2‐MNG) 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. Both glyceryl nitrate esters hydrolyzed via second‐order reaction at 25°C. 2‐MNG in calcium hydroxide solution isomerized to 1‐MNG, which subsequently hydrolyzed to form NO. In strongly basic aqueous solutions of NaOH (30%), 2‐MNG is converted to glycidol and NO.
Quantitative treatment of the effect of counterions on ctab‐catalyzed reactions of stabilized carbonium ions with cyanide ion
Authors: Srivastava S. K. , Katiyar Sarvagya S.
Published: January 2005

The reactions of stabilized carbonium ions of setoglaucin, methyl violet, and ethyl violet with cyanide ions are largely catalyzed by the cationic micelles of cetyltrimethylammonium bromide (CTAB) in aqueous media. Added counterions (anions in this case) have strong inhibitory effects on the CTAB‐catalyzed reactions in the following order: N > NO > Br− > Cl− > F− > no salt. The inhibitory effects of the counterions have been attributed to the exchange between added anions and reagent (CN−) in the micellar media. The data have been analyzed by the model schemes, and mathematical formulations were developed. Various parameters associated with the exchange process, such as equilibrium exchange constant, number of surfactant molecules per substrate molecule, number of added anions, and a factor related to the binding of additives to the catalytic micellar aggregates, have been evaluated.
Studies in nickel(IV) chemistry. Part 6. Kinetics of electron transfer from phenylhydrazine to tris‐(dimethylglyoximato) nickelate(IV) in aqueous medium
Authors: Acharya S. , Neogi G. , Panda R. K. , Ramaswamy D.
Published: January 2005

The kinetics of electron transfer from phenylhydrazine(S) to tris‐(dimethylglyoximato) nickelate(IV), Ni(dmg) (dmg2− = dimethylglyoximate dianion), have been studied in aqueous medium in the range of 6.21 ⩽ pH ⩽ 12.2. The kinetics exhibit a pseudo‐first‐order disappearance of Ni(dmg) when excess S is present. The pseudo‐first‐order rate constants kobs are almost linearly dependent on [S]0 for varying concentrations of the reductant. At constant [S]0, the kobs−pH profile is U shaped. The kobs values register a decrease as the [H+] is increased in the pH range of ∽12.2–9.5, remain almost constant (minimum) in the range of ∽9–8, and then again linearly increase as [H+] is increased in the pH range of ∽7–6.21. Results are interpreted in terms of a probable mechanism involving outer‐sphere electron transfer from the phenylhydrazine and phenylhydrazinium cation species to the unprotonated and one‐protonated species of the Ni(IV) complex. The reduction rate appears to be dependent on the nature of the species (unprotonated and one‐protonated) of the oxidant Ni(IV) complex. The phenylhydrazinium cation reduces the Ni(IV) complex at least one order of magnitude faster than does the neutral reductant species. The major product of the oxidation of phenylhydrazine by the Ni(IV) complex is 4‐hydroxyazobenzene with a small amount of phenol.
Induced heterogeneity, a novel technique for the study of gas‐phase reactions. Part I. Determination of the arrhenius parameters for CC bond scission in propane
Authors: Kanan Khalid , Purnell Howard , Smith Eileen
Published: January 2005

It is shown that, by deliberate activation of the reaction vessel, heterogeneous reaction at the wall can be made to dominate chain termination in a complex gas‐phase reaction. For a homogeneous process, characterized, as is often the case, by multiple terminations, this has the effect of simplifying the mechanism and allowing explicit solution of the relevant steady‐state equations so that the rate constants of some individual steps can be evaluated without assumption as to the values of those of others.

The pyrolysis of propane, in the vicinity of 500°C, has been used as an example of this approach. Enhancement of the wall activity leads to the reaction
equation image
providing, almost exclusively, chain termination. As a result, rate constants for the initiation step
equation image
can be directly determined. The results of this study provide the Arrhenius equation

In combination with current thermochemical values this result gives k−1 = 1013.40 cm3/mol·s which, in turn, implies, via the geometric mean rule, kEt‐Et = 1012.9 cm3/mol·s for ethyl–ethyl recombination, in good accord with the most recent determinations and compatible with the newly proposed value of the enthalpy of formation of ethyl.

The first‐order wall constant k8 has been evaluated as k8<104.2 s−1. This appears to be the first occasion on which a wall constant has been evaluated from data for a high‐temperature complex gas reaction.
Kinetics of the gas‐phase reactions of OH radicals with a series of α,β‐unsaturated carbonyls at 299 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Pitts James N.
Published: January 2005

Relative rate constants for the reaction of OH radicals with a series of α,β‐unsaturated carbonyls have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with propene of 2.52 × 10−11 cm3/molec·s, the rate constants obtained are (× 1011 cm3/molec·s: acrolein, 1.83 ± 0.13; crotonaldehyde, 3.50 ± 0.40; methacrolein, 2.85 ± 0.23; and methylvinylketone, 1.88 ± 0.14). These data, which are necessary input to chemical computer models of the NOx–air photooxidations of conjugated dialkenes, are discussed and compared with literature values.
Kinetics of the reaction: 2C2H4 → C2H5 + C2H3· heat of formation of the vinyl radical
Authors: Ayranci G. , Back M. H.
Published: January 2005

The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 800 K have been measured in the presence and absence of the additives neopentane and ethane. It has been shown that in the absence of the additive the main initiation process is
equation image
while in the presence of neopentane and ethane the following additional initiation processes occur:
equation image
From the ratios of the rates of formation of the major products in the presence and absence of the additive the ratios kN/k1 and kE/k1 were measured over the temperature range of 750–820 K. Taking values from the literature for kN and kE, the following value was obtained for k1:

Previous results using butene‐1 as additive were rexamined and shown to be consistent with this measurement. From this measurement the following values were derived: ΔHf(C2H3) = 63.4 ± 2 kcal/mol and D(C2H3H) = 103 kcal/mol.
Kinetics of benzene photochlorination
Authors: Ledakowicz S. , Perkowski J.
Published: January 2005

An empirical approach to the kinetic investigations of photo‐initiated liquid‐phase chlorination of benzene is presented. Reaction order and the reaction constants for chlorine consumption and for the production of hexachlorocyclohexane isomers were evaluated from experimental data.
Investigation of the thermal isomerization of 1α,25‐dihydroxycholecalciferol by nuclear magnetic resonance spectroscopy
Authors: Grant Anne , Bhattacharyya Pranab K.
Published: January 2005

This investigation of the kinetics and thermodynamics of the thermal isomerization reaction of 1α,25‐dihydroxycholecalciferol, the physiologically active metabolite of vitamin D3, is based on the simultaneous determinations of 1α,25‐(OH)2D3 and its previtamin analog by nuclear magnetic resonance spectroscopy which distinguishes these compounds from possible impurities. The kinetics at different temperatures are used to obtain the activation parameters for the sigmatropic [1,7] thermal interconversion process which is shown to be compatible with a reaction that is unimolecular and concerted. The nature of the transition state of the activated complex, the reaction energetics, and the relative stabilities of 1α,25‐(OH)2D3 and vitamin D3 are discussed.
The kinetics and mechanisms of elementary NF2reactions with O and N atoms
Authors: Gershenzon Yu. M. , Il'in S. D. , Kishkovitch O. P. , Malkhasyan R. T. , Rozenshtein V. B. , Umanskii S. Ya.
Published: January 2005

A combined EPR–LMR spectrometer with a fast‐flow system has been used to investigate the kinetics and mechanisms of NF2reactions with O and N atoms at 298 K. The overall rate constants of these reactions are:k0= (2.8 ± 0.4) × 10−11cm3/s andkN= (5.7 ± 0.8) × 10−11cm3/s. The stoichiometry of the reactions with respect to O, N, NF2, F, and NO has been determined. The statistical theory of bimolecular reactions has been used for interpretation of the results obtained.
Kinetics of gas‐phase decomposition of oxetan and oxetan‐2,2‐d2
Authors: Zalotai L. , Hunyadi‐zoltán Zs. , Bérces T. , Márta F.
Published: January 2005

The pressure dependence of the first‐order rate coefficient of oxetan and oxetan‐2,2‐d2 decomposition has been studied in the pressure range from about 7 kPa down to 0.01 kPa at various temperatures between 673 and 758 K. Experimental data were analyzed using RRKM theory. Interpretation of the fall‐off curves lends support to the high‐pressure Arrhenius parameters A = 1015.42s−1 and EA = 259.5 kJ/mol derived from measurements made in the pressure‐independent range. Decomposition of oxetan is found to occur via biradical intermediates. Data for the kinetic isotope effect were used to derive kinetic parameters for the ring‐opening elementary steps in oxetan and oxetan‐d2 decomposition.
Kinetics of the thermal gas‐phase dimerization of hexafluoropropene
Authors: Robinson Peter J. , Skelhorne Graham G.
Published: January 2005

The reversible thermal gas‐phase dimerization of hexafluoropropene to the four isomeric cyclobutanes has been studied by pressure change and by gas‐liquid chromatographic analysis in the temperature range of 645–708 K with initial pressures of olefin from 802 to 4820 mm Hg. The reaction was accurately second order at low conversions of olefin to dimers, and at higher conversions it gave a very good fit to the rate equation for opposing second‐ and first‐order reactions. The rate constants for the dimerization, calculated from initial rates of reaction, yielded the least‐mean‐squares Arrhenius equation (95% confidence limits):

where k2 is defined by

Studies carried out in a packed vessel showed no evidence of heterogeneity. The rate constants found in this work are in excellent agreement with those found at lower pressures by Atkinson and Tsiamis, and the combined results give the Arrhenius equation
Kinetics of the gas‐phase reaction between iodine and monogermane and the bond dissociation energy D(H3GeH)
Authors: Noble Paul N. , Walsh Robin
Published: January 2005

The title reaction has been investigated in the temperature range of 403–446 K. Monoiodogermane and di‐iodogermane together with hydrogen iodide were the main products, although at high conversions at least one other product was formed. GeH3I is clearly the primary product. Initial rates were found to obey the rate law

over a wide range of initial iodine and monogermane pressures. Secondary reactions (of GeH3I with I2) affect the subsequent kinetics, although at sufficiently high initial reactant ratios ([GeH4]0/[I2]0 ≥ 100) an integrated rate equation fits the data with the same rate constants as the initial rate expression.

The observed kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step

log k1 (dm3/mol·s) = (11.03 ± 0.13) – (52.3 ± 1.0 kJ/mol)/RT ln 10 has been deduced. From this the bond dissociation energy D(GeH3H) = 346 ± 10 kJ/mol (82.5 kcal/mol) is obtained. The significance of this value, together with derived values for Ge–Ge and Ge–C bond strengths, is discussed.
Rate constants of the reaction of ozone with trans‐1,2‐dichloroethene and vinyl chloride in air
Authors: Zhang Jian , Hatakeyama Shiro , Akimoto Hajime
Published: January 2005

Kinetic studies on reactions of ozone with trans‐1,2‐dichloroethene (DCE) and vinyl chloride (VC) were performed in air. In the presence of scavengers of radicals, such as CH3CHO, the rates for both reactions are second order (first order in each reactant). Observed rate constants are (1.80 ± 0.29) X 10−19 cm3/molecule·s for DCE and (2.45 ± 0.45) × 10−19 cm3/molecule·s for VC. In the presence of CH3CHO, propene ozonide
\documentclass{article}\pagestyle{empty}\begin{document}$ ({\rm CH}_3 \overline {{\rm CHOOCH}_2 {\rm O}}) $\end{document} was observed as a product in the case of VC. Peroxyformic acid (HC)O(OOH) was detected in both reactions. The Criegee mechanism was proposed to play a major role in the reaction of ozone with chloroolefins. The branching ratio of O3 + CH2=CHCl → CH2OO + HCOCl (6a), CHClOO + HCHO (6b) was obtained as 76:24, and the fraction of the stabilized CH2OO was estimated to be 0.25 of that produced in reaction (6a).
Effects of ring strain on gas‐phase rate constants. I. Ozone reactions with cycloalkenes
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L. , Pitts James N.
Published: January 2005

Rate constants for the gas‐phase reactions of O3 with a series of cycloalkenes and with cis‐2‐butene have been determined at 297 ± 1 K. The rate constants obtained were (in units of 10−16 cm3/molecule·s): cis‐2‐butene, 1.38 ± 0.16; cyclopentene, 2.75 ± 0.33; cyclohexene, 1.04 ± 0.14; cycloheptene, 3.19 ± 0.36; 1,3‐cyclohexadiene, 19.7 ± 2.8; 1,4‐cyclohexadiene, 0.639 ± 0.074; bicyclo[2.2.1]‐2‐heptene, 21.4 ± 3.5; bicyclo[2.2.1]‐2,5‐heptadiene, 46.8 ± 12.9; and bicyclo[2.2.2]‐2‐octene, 0.728 ± 0.090. These data for cis‐2‐butene, cyclopentene, and cyclohexene are compared with previous literature data, and the effects of ring strain on the rate constants are discussed.
Couloamperometry. A fast kinetic technique for halogenations. I. Bromination rate constants of highly reactive enol ethers
Authors: Ruasse M. F. , Poupard D. , Dubois J. E.
Published: January 2005

A new couloamperometric apparatus has been designed to extend the range of this kinetic technique to the measurement of very high rate constants, 108M−1s−1, by using TFCR‐EXSEL conditions (TFCR—very low reactant concentration; EXSEL—salt excess), which give half‐lives of a few seconds for very fast second‐order reactions. Very low faradaic currents, in the nanoampere range for halogens, corresponding to very low reactant concentrations of 10−8–10−9M, are measured selectively by compensating the eddy currents, principally the residual and the induced currents. When the electroactive species is bromine, the concentration is demonstrated to be linearly related to the limiting reduction current in the very low concentration range. The upper limit of this technique for bromination is at present 3 × 108M−1s−1. The method is applied to the kinetic study of highly reactive enol ethers EtO‐C(R) = CH‐R′, where R and R′ are H or Me. A value of 2.2 × 108M−1s−1 is obtained for k, the rate constant for free bromine addition to EtO‐CH = CH2, by extrapolating the kinetic bromide ion effects to [Br−] = 0. An α‐methyl effect (kα‐Me/kH)EtO of 15 is found; this is a small decrease in the methyl effect compared to the marked increase in the double bond reactivity. For the enol acetate MeCOO‐CH = CH2, whose rate constant is 6 × 102M−1s−1, (kα‐Me/kH)OCOMe is 21. The dependence of substituent effects on reactivity is discussed in terms of the Hammond effect on the transition state position and of charge delocalization by group G of olefins G‐CH = CH2.
Electron transfer to trans‐dihydroxotetraoxoosmate(VIII). II. Kinetics of the oxidation of dimethylsulfoxide in aqueous alkaline media
Authors: Neogi G. , Acharya S. , Panda R. K. , Ramaswamy D.
Published: January 2005

The kinetics of the oxidation of dimethylsulfoxide by oxohydroxoosmate(VIII) complex ions in alkaline media follow pseudo‐first‐order disappearance in Os(VIII). The values of the observed pseudo‐first‐order rate constant are linearly dependent on initial dimethylsulfoxide concentrations in a fortyfold range, and increase with increasing [OH−], leveling off at higher relative [OH−]. The results are interpreted in terms of outer sphere interactions involving dimethylsulfoxide and various species of the Os(VIII) complex. The more nucleophilic dihydroxotetraoxoosmate(VIII) ion reacts about 50 times faster than the trihydroxotrioxoosmate(VIII) species.
Kinetics of the reaction F + 1,2‐dibromo‐1,1,2‐trifluoroethane
Authors: Forst Wendell , Pavaday Harold
Published: January 2005

The title reaction was studied in a standard flow system with F atoms produced by RF discharge in F2‐He mixture. Analysis was by gas chromatography using electron capture detection. There were two major products, identified as CF2BrCF2H and CF2BrCF2Br, plus presumably HF which was not detectable. The overall rate of disappearance of reactant was found to be of mixed one and one‐half order, indicating a complex reaction. A mechanism is proposed comprising six steps and involving two radical species CF2BrċFBr (R1) and CF2BrċF2. The 300 K rate constant for the initial step F + reactant → HF + R1 is evaluated to be 2.2 × 10−13 cm3/molec·s, which fits in with rates of other saturated hydrocarbon reactants containing one hydrogen atom, thus supporting the view that in this class of reactants the rates of reactions of the type F + saturated hydrocarbon depend mainly on the number of hydrogen atoms in the reactant.
Nonlinear structure–reactivity correlations. The hydrolysis of 2,4,6‐trinitrophenyl acetate catalyzed by general bases
Authors: De Rossi Rita H. , Nuñez Alberto
Published: January 2005

The hydrolysis of 2,4,6‐trinitrophenyl acetate was studied in the presence of several carboxylic bases and tertiary amines. Carboxylic bases pyridine and imidazole react as nucleophilic catalysts, while 2,4‐dimethyl and 2,4,6‐trimethyl pyridine react as general‐base catalysts. The nonlinear structure–reactivity correlations (log kcat versus log kOH and log kcat versus pK of the leaving group) for the series of aryl acetates are discussed, and it is suggested that there is a change in transition‐state structure along the series.
Third‐order rate constants of atmospheric importance
Authors: Patrick Roger , Golden David M.
Published: January 2005

Input data and results are presented for the calculation of a number of third‐order rate constants of atmospheric interest using Troe′s approximate method. A comparison with experimental data indicates that this approach provides a reliable method for predicting unknown rate constants and estimating temperature dependences. These calculations form the basis of the recommendations of the NASA review panel for third‐order rate constants to be used in atmospheric modeling.
The gas‐phase decomposition of methylsilane. Part II. Mechanisms of decomposition under static system conditions
Authors: Sawrey B. A. , O'Neal H. E. , Ring M. A.
Published: January 2005

The static system pyrolysis of methylsilane (T ∼ 700 K, PT ∼ 150 torr), pure and in the presence of ethylene, propylene, and acetylene, has been investigated. It is proposed that in the uninhibited system, the major products (silane and dimethylsilane) are produced by free radical processes, and that the free radicals are formed at the walls from methylsilylenes. In the presence of olefins, the free radicals are trapped to form methylsilane adducts. In acetylene, trapping of methylsilylenes prevents free radical production and eliminates the free radical produced products of the pure and the olefin inhibited systems. Rates of initiation correlate with rates of reactant loss in acetylene inhibited systems, and with rates of hydrogen formation in olefin inhibited systems. Rough estimates of primary dissociation process yields give for the 1,1‐H2 elimination ϕ1,1 ≅ 0.78, for the 1,2‐H elimination ϕ1,2 ≅ 0.16, and for the methane elimination ϕCH4 ≅ 0.06 at 700 K. Deuteration lowers initial step kinetics by about 15%.
Reaction of carbon monoxide with ozone and oxygen atoms
Authors: Toby Sidney , Sheth Shailesh , Toby Frina S.
Published: January 2005

The reaction between ozone and carbon monoxide was reinvestigated in the range of 80–160°C. The previously reported rate law −d[O3]/dt = ka[O3][CO] + kb[O3]2 was confirmed and simulated using a mechanism based on an impurity‐initiated chain reaction. When the CO was sufficiently purified, kb tended to zero and ka reduced to the value expected for the thermal decomposition of O3. Subsequent reactions of O atoms with CO produced chemiluminescence which was used to measure k3 for

as 10−14.0±0.3 exp[−(1630 ± 325)/T] cm3 molecule−1 s−1. The implications of this are discussed.