bluuebunny/crossref_metadata_2025 huggingface dataset:
Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro‐n‐propyl and ethyl radicals revisited
Authors: Pritchard G. O. , Abbas S. H. , Kennedy J. M. , Paquette S. J. , Hudson D. B. , Meleason M. A. , Shoemaker D. D.
Published: January 2005

A redetermination of the disproportionation/combination ratio for n–C3F7 and C2H5 radicals gives a value of Δ(n–C3F7, C2H5) = 0.13 ± 0.01, independent of the temperature. The radicals were produced by the photolysis of n–C3F7COC2H5. The previous determinations of this ratio are discussed and are found to be largely incorrect. The values for Δ(CF3, C2H5) and Δ(C2F5, C2H5) are also re‐evaluated, and the recommended values are 0.10 ± 0.02 and 0.12 ± 0.02, respectively. Systems involving perfluoroalkyl and ethyl radicals are complicated due to rapid perfluororadical addition to the ethylene formed in the disproportionation process. The extent of this reaction, and its consequences, are discussed and evaluated. The role of the propionyl (C2H5CO) radical in the room temperature photolysis is also assessed. However, it is found that the Δ values determined by the intercept method used in this work are not affected by the secondary reactions that occur. It is concluded that high cross‐combination ratios are general to perfluoroalkyl‐alkyl radical interactions. For C3F7 and C2H5 radicals the ratio is 2.7–2.8. Above 100°C ratios exceed 3 due to secondary reactions.
A study of the reactions of NO3 radicals with organic sulfides: Reactivity trend at 298 K
Authors: Daykin E. P. , Wine P. H.
Published: January 2005

A laser flash photolysis‐long path laser absorption technique has been employed to investigate the kinetics of NO3 reactions with CH3SCH3(𝓀1), CD3SCD3(𝓀2), and C2H5SC2H5(𝓀3) in 500 torr air at 298 K. The dependence of 𝓀1 on total pressure (20–500 torr) and oxygen partial pressure (0—100 torr) has also been investigated, with no dependence observed. Measured rate coefficients in units of 10−13 cm3 molecule−1 s−1 are 𝓀1 = 13 ± 3, 𝓀2 = 3.4 ± 0.8, and 𝓀3 = 48 ± 12, where the quoted uncertainties are 2σ estimates of absolute accuracy. The magnitude of NO3 + sulfide rate coefficients and negative activation energies for 𝓀1 (reported by other investigators) suggest that reaction does not proceed via a direct hydrogen abstraction mechanism. However, the reactivity trend observed in this study provides evidence that the reaction mechanism does involve breaking a carbon‐hydrogen bond.
Initiation in hydrocarbon autoxidation at elevated temperatures
Authors: Jensen R. K. , Korcek S. , Zinbo M. , Johnson M. D.
Published: January 2005

Kinetic and mechanistic investigations of liquid phase autoxidation of hexadecane at 120 to 190°C have shown that, in the early stages of oxidation, the initiation process involves homolytic decomposition of hydroperoxides. The values of a composite first order rate constant for this decomposition, 𝓀1, have been determined in stirred flow reactor experiments from the rate of formation of termination products and in batch reactor studies using inhibitor methods. Arrhenius parameters derived from these studies (log (A/s−1) = 8.5 and Ea = 26 kcal mol−1) allow calculation of 𝓀1 as a function of temperature. This permits determination of the rate of initiation as a function of hydroperoxide concentration and facilitates determination of absolute rate constants for other oxidation reactions occurring in this system.
Substituent effects in the gas‐phase thermolysis of aryl tert‐butyl ethers and sulfides
Authors: Martin Gonzalo , Martinez Henry , Ascanio Julian
Published: January 2005

The pyrolyses of p‐nitrophenyl t‐butyl ether, p‐methoxyphenyl t‐butyl ether, p‐aminophenyl t‐butyl ether, p‐nitrophenyl t‐butyl sulfide, and propargyl t‐butyl sulfide have been studied in a stirred‐flow reactor over the temperature range 430–530°C and pressures in the range 7–14 torr, using toluene as carrier gas. The reactions yielded between 90 and 99% isobutene plus the corresponding phenol, thiophenol, or thiol as products. The first order rate coefficients for reactant consumption, based on isobutene production, followed the Arrhenius equations

p‐nitrophenyl t‐butyl ether

p‐methoxyphenyl t‐butyl ether

p‐aminophenyl t‐butyl ether:

p‐nitrophenyl t‐butyl sulfide

propargyl t‐‐butyl sulfide:

The results support a unimolecular elimination of the isobutene involving polar, four‐center cyclic transition states.
A kinetic study of the decomposition of N‐bromoserine
Authors: Antelo Juan M. , Arce Florencio , Crugeiras Juan , Franco Julia , Rodriguez Pilar , Varela Angel
Published: January 2005

This article reports the kinetics of the decomposition of N‐bromoserine formed rapidly by bromation of serine by BrO−. The main decomposition products are glycolaldehyde, ammonia, carbon dioxide, and bromide ions at pH < 11.5, and β‐hydroxypyruvic acid, ammonia, and bromide ions at pH > 11.5. The reaction is of order one with respect to N‐bromoserine, and is independent of ionic strength and excess serine. The rate constant increases with increasing pH at pH > 11 and with decreasing pH at pH < 8, and over the range pH 8–11 has the constant value 1.67 × 10−3 s−1 at 298 K.
Rate constant and products of the BrO + BrO reaction at 298 K
Authors: Lançar I. T. , Laverdet G. , Bras G. Le , Poulet G.
Published: January 2005

The overall rate coefficient k of the self recombination of BrO radicals has been measured at 298 K with use of the discharge flow/mass spectrometry technique. The rate coefficient k2 for the reaction channel forming Br2 has been also determined. The results are: k = (3.2 ± 0.5) × 10−12 and k2 = (4.7 ± 1.5) × 10−13 (in cm3 molecule−1 s−1). These results are discussed with respect to previous literature data.
The mechanism of thermal eliminations. Part XXVIII [1]: Thermal decomposition of benzoylformic acid
Authors: Taylor Roger
Published: January 2005

The thermal decomposition of benzoylformic acid into carbon dioxide and benzaldehyde is a unimolecular first‐order reaction which takes place according to the rate equation log k = 15.3–42,500/4.575 K. At 600 K the reaction takes place 18 times faster than the corresponding decomposition of pyruvic acid into carbon dioxide and acetaldehyde. This is consistent with the 4‐center process proposed previously for pyruvic acid, in which a partial negative charge develops on the carbon of the α‐carbonyl group in the transition state. Benzoylformic acid is considerably less reactive towards thermal elimination than is oxalic acid, which also accords with the proposed mechanism.
Pd(II) complexes of amino alcohols and their reaction with chloramine‐T: A kinetic study
Authors: Shukla Anju , Gupta Sushma , Upadhyay Santosh K.
Published: January 2005

The kinetics of reaction of amino alcohols viz. 2‐aminoethanol, 3‐aminopropanol, and triethanolamine with chloramine‐T have been studied in perchloric acid medium with palladous chloride as catalyst. The formation of {Pd(II)‐(aminoalcohol)} and {Pd(II)‐(aminoalcohol)2} complexes and resistance of {Pd(II)‐(aminoalcohol)2} complex to react with chloramine‐T have been observed. A suitable mechanism consistent with the kinetic data is proposed and discussed.
Atmospheric oxidation of reduced sulfur species
Authors: Tyndall Geoffrey S. , Ravishankara A. R.
Published: January 2005

The kinetics of elementary gas phase reactions involved in the oxidation of reduced sulfur species, H2S, CS2, OCS, CH3SH, CH3SCH3, and CH3SSCH3, to SO2 (or other products) are reviewed. The reactions with OH and NO3 which are the processes that initiate the degradation of the above compounds have been evaluated. Reactions of key intermediates, HS, HSO, CH3S, and CH3SO, are discussed. Whenever possible, recommendations for the rate coefficients are made and the need for further work indicated. The review has been carried out with the atmospheric chemistry in mind by looking at the laboratory based kinetics data. This review also provides information that will help model the Earth's sulfur cycle.
Kinetics and mechanisms of the oxidation by permanganate of L‐Phenylalanine
Authors: Insausti M. J. , Mata‐Perez F. , Alvarez‐Macho M. P.
Published: January 2005

The oxidation of L‐Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first‐order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first‐order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are proposed.
Activation energy barriers in the molecular relaxation dynamics of Li+ interacting with acyclic and cyclic polyethers in acetonitrile
Authors: Xu Meizhen , Eyring Edward M. , Petrucci Sergio
Published: January 2005

Ultrasonic relaxation spectra of LiClO4 plus the open chain polyether triglyme (TG) at CLiClO4 ≃ 0.8 M, molar ratio R = [TG]/[LiClO4] = 1, and at temperatures of 15, 25, 35, and 45°C in dry acetonitrile are reported. Corresponding spectra for LiClO4 plus the macrocycle 12‐crown‐4 (12C4) at R = [12C4]/[LiClO4] = 1, at 10, 15, 20, 25, 30, and 40°C, and CLiClO4 = 0.32 M in acetonitrile are also reported.

Both relaxation envelopes, for the two systems, have been fitted by two Debye relaxation processes and interpreted by the Eigen‐Winkler reaction scheme:

where “PE” symbolizes the polyether, Li+ … PE is a solvent separated species and LiPE+ and (LiPE)+ are two complex species. The temperature dependence of the relaxation spectra permits the calculation of the activation parameters for the forward and reverse processes for the system LiClO4 + TG and for one of the two processes for the LiClO4 + 12C4 system.

Comparisons between the two sets of data lead to the conclusion that the much slower second relaxation process, in the case of the macrocycle, is attributable to a combination of an enthalpic and an entropic effect on the energy barrier for the present systems.
Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane
Authors: Roscoe J. M. , Blatt C. , Back R. A.
Published: January 2005

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C2H6 and N2, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C3H8 (3.5 × 10−3), C2H4 (3.2 × 10−4), CH4 (3 × 10−3), and n‐C4H10 (trace). Quantum yields of H2 of 4 × 10−5 and 2 × 10−5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively.

The minor hydrocarbon products can be accounted for by reactions of CH3 and C2H5 radicals following hydrogen abstraction from azomethane by CH3. The H2 product observed represents an upper limit for the H2 elimination from vibrationally excited C2H6 formed by CH3 combination in the system, corresponding to a rate of elimination ca. 5 × 10−5 times the competing rate of dissociation to 2CH3. Assuming a frequency factor of 1013 s−1 for the H2 elimination, a lower limit of about 90 kcal mol−1 was estimated for the energy barrier.
Hydrolysis of schiff bases, 1: Kinetics and mechanism of spontaneous, acid, and base hydrolysis of N‐(2/4‐hydroxybenzylidene)‐2‐aminobenzothiazoles
Authors: Misra Pramila , Mishra Bijaya K. , Behera Gopa B.
Published: January 2005

The rate of hydrolysis of title schiff bases was studied in the pH range 4–13 in 10% dioxanewater system, CTAB, NaLS micellar solutions. The hydrolysis was found to be due to ‘water’ and ‘hydroxide’ reactions and hence the rate constants in different pH were computed and analyzed with an intermediate involving a water molecule being positioned with the help of 2‐OH group and the thiazolyl C–N pi bond. The ‘hydroxide’ reaction was due to a direct nucleophilic attack of hydroxide ion at the aldimine linkage of the reactant. The influence of cationic and anionic micelles supports the mechanistic picture in the entire pH range.
A shock tube study of H + HNCO → NH2 + CO
Authors: Mertens John D. , Kohse‐Höinghaus Katharina , Hanson Ronald K. , Bowman Craig T.
Published: January 2005

The reaction of atomic hydrogen with isocyanic acid (HNCO) to produce the amidogen radical (NH2) and carbon monoxide,
equation image
has been studied in shock‐heated mixtures of HNCO dilute in argon. Time‐histories of the ground‐state NH2 radical were measured behind reflected shock waves using cw, narrowlinewidth laser absorption at 597 nm, and HNCO time‐histories were measured using infrared emission from the fundamental v2‐band of HNCO near 5 μm. The second‐order rate coefficient of reaction (2(a)) was determined to be:

cm3 mol−1 s−1, where f and F define the lower and upper uncertainty limits, respectively.

An upper limit on the rate coefficient of
equation image
was determined to be:
The kinetics and mechanisms of methyl 2‐bromopropionate and 2‐bromopropionic acid pyrolyses under maximum inhibition
Authors: Chuchani Gabriel , Dominguez Rosa M. , Rotinov Alexandra
Published: January 2005

The kinetics of the gas phase pyrolyses of methyl 2‐bromopropionate and 2‐bromopropionic acid were studied in a seasoned, static reaction vessel and under maximum inhibition of the free radical suppressor toluene. The working temperature and pressure range was 310–430°C and 26.5–201.5 torr, respectively. The reactions proved to be homogeneous, unimolecular, and obeys a first‐order rate law. The rate coefficients are expressible by the following equations: for methyl 2‐bromopropionate, log k1(s−1) = (13.10 ± 0.34) − (211.4 ± 4.4)kJ mol−1(2.303RT)−1; for 2‐bromopropionic acid, log k1(s−1) = (12.41 ± 0.29) − (180.3 ± 3.4)kJ mol−1(2.303RT)−1. The bromoacid yields acetaldehyde, CO and HBr. Because of this result, the mechanism is believed to proceed via a polar five‐membered cyclic transition state.
Electron transfer. 109. The reaction of dimeric molybdenum(V) with carboxylato‐bound chromium(V). A third mechanistic variation
Authors: Ghosh M. C. , Gould E. S.
Published: January 2005

The bridged dimer of molybdenum(V), Mo2O42+ (aq) is oxidized to Mo(VI) by carboxylato‐bound chromium(V). Reaction of bis(chelated) Cr(V) with excess (MoV)2 yields a chelated Cr(III) complex, but this conversion proceeds through a pink Cr(IV) intermediate, indicating that the oxidation of (MoV)2 entails a series of le− steps, passing through a reactive transient, the mixed valence complex, MoVMoVI. When experiments are carried out in buffers of the ligating acid, 2‐ethyl‐2‐hydroxybutanoic acid, two stages of ligation of (MoV)2 by the ligand anion, characterized by rate constants near 104 and 0.14 M−1 s−1 (19°C; pH 3.0; μ = 0.6 M) must be considered. In quick mixing experiments, the first, but not the second, of these proceeds before the redox reaction gets under way, and autocatalytic redox profiles are observed. If the slower ligation is allowed to reach completion before Cr(V) is added, reduction to Cr(IV) is greatly accelerated and conforms to the superposition of two processes, whereas the reduction of Cr(IV) to Cr(III) is slow and exhibits a rate independent of [CrIV]. A proposed sequence applicable to the latter conditions includes reductions of Cr(V) at two ligation levels, slow unimolecular conversion of (MoV)2 to an activated form, and rapid reduction of the latter with Cr(IV). Here Cr(IV) has assumed the role of a scavenger for the reactive form of (MoV)2.
Kinetics of the gas‐phase reactions of β‐phellandrene with OH and NO3 radicals and O3 at 297 ± 2 K
Authors: Shorees Basima , Atkinson Roger , Arey Janet
Published: January 2005

Rate constants for the gas‐phase reactions of the biogenically emitted monoterpene β‐phellandrene with OH and NO3 radicals and O3 have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm3 molecule−1 s−1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10−10; for reaction with the NO3 radical, (7.96 ± 2.82) × 10−12; and for reaction with O3, (4.77 ± 1.23) × 10−17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β‐phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O3 reaction as a loss process for β‐phellandrene during daylight hours.
Decomposition of hydrogen peroxide in aqueous solutions at elevated temperatures
Authors: Lin C. C. , Smith F. R. , Ichikawa N. , Baba T. , Itow M.
Published: January 2005

Decomposition of hydrogen peroxide in high‐purity water has been measured at temperatures ranging 100 to 280°C in a laboratory test loop. A first‐order decomposition kinetics has been observed in all cases, but the decomposition rates were found to vary widely, depending on the material used in the reaction chamber. In a 4 mm ID stainless steel tubing, the decomposition rate constant is determined to be k = 2 × 105 exp(−14800/RT). This decomposition rate is approximately 100 times faster than that observed in a Teflon tubing.

The variation of decomposition rate in different reaction chambers is attributed to the heterogeneous catalytic effects. There is no evidence of reaction between H2 and H2O2 in the highpurity water at temperatures up to 280°C.
A shock tube study of the reaction of methyl radicals with hydroxyl radicals
Authors: Bott J. F. , Cohen N.
Published: January 2005

The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol‐s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (≃75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol‐s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure.
Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies
Authors: Baggott J. E. , Blitz M. A. , Frey H. M. , Lightfoot P. D. , Walsh R.
Published: January 2005

The reactions of dimethylsilylene, SiMe2, generated by laser flash photolysis from pentamethyldisilane and octamethyltrisilane, and detected via its 457.9 nm absorption, have been investigated with a number of oxygen containing molecules, including oxygen itself, carbon monoxide, water, alcohols, and ethers at 295 K. Some substrate molecules were deuterated. Apart from CO, all molecules reacted with SiMe2 with second order rate constants (in cm3 molecule−1 s−1) in the range 7.7 ± 10−14 to 4.7 ± 10−11.

While most of the reactions of SiMe2 studied went to completion those with dimethylether and tetrahydrofuran were partially reversible. The reaction of SiMe2 with oxirane was pressure dependent.

The data are generally consistent with a mechanism involving initial formation of a donoracceptor, zwitterionic complex. In the case of reaction with alcohols, there is a small overall isotope effect, suggesting formation of a complex followed by rapid H‐transfer, which only marginally affects the rate. In the case of ethers, complexes are formed which (i) may react further (Me2Si…oxetane), (ii) may react further but also reversibly decompose (Me2Si…oxirane), or (iii) do not seem to react further (Me2Si…OMe2, Me2Si…THF) but partially redissociate. The donor‐acceptor bond strength has been estimated in these last cases to be ca. 40 kJ mol−1. Supporting arguments and mechanistic details of all reactions investigated are presented.
Effect of solvent on the reactions of coordination complexes: Part 16. Kinetics and mechanism of complexation of oxalatopentaammine‐cobalt(III) with nickel(II) in methanol‐water medium
Authors: Dash Anadi C. , Pradhan Jyotshamayee
Published: January 2005

The kinetics of reversible complexation of oxalatopentaammine cobalt(III) with Ni2+ has been investigated in MeOH + water media (0–50 (v/v) % MeOH) at 15.0–35.0°C and I = 0.10 mol dm−3. Analysis of rate data indicates that the monobonded complex [(NH3)5 · CoOCOCO2Ni]3+ in which Ni2+ is bound to the end carboxylate group is the possible reaction intermediate. The formation and dissociation rates of such a species are rate limiting for the overall formation and dissociation of the binuclear species, in which Ni2+ is chelated by the oxalate moiety. The rate and activation parameters for formation and dissociation of the binuclear species are moderately solvent sensitive and solvent structural effects are discernible in the nonlinear variations of ΔH≠ and ΔS≠ with solvent composition. The log kr vs. Grunwald Winstein parameter (Y) plot for the dissociation of the binuclear species is markedly nonlinear.
Effects of solvent on the reactions of coordination complexes: Part 17. Kinetics and mechanism of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt (III) in methanol + water and dimethylsulphoxide + water media
Authors: Dash Anadi C. , Das Prafulla K.
Published: January 2005

The base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ⩽ t°C ⩽ 35.0 and I = 0.10 mol dm−3 (ClO4−). The phenoxide species [(tetren)CoO2CC6H4O]+ undergoes both OH−‐independent and OH−‐catalyzed hydrolysis via SN1ICB and SN1CB mechanism, respectively. The OH−‐independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH−‐catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, ΔH≠ and ΔS≠, with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in ΔH≠ vs. ΔS≠ plot accomodating all data for k1 and k2 paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory.
Pressure dependence of the reaction Cl + C2H2 over the temperature range 230 to 370 K
Authors: Kaiser E. W.
Published: January 2005

The pressure dependence of reaction (1), Cl + C2H2 + M → C2H2Cl + M, has been measured by a relative rate technique using the pressure independent abstraction reaction (2), Cl + C2H6 → C2H5 + HCl, as the reference. Values of k1/k2 were measured at pressures between 25 and 1300 torr at four temperatures ranging from 252 to 370 K, using air, N2, or SF6 diluent gases. Low pressure measurements (10–50 torr) were performed at 230 K. Assuming a temperature‐independent center broadening factor of 0.6 in the Troe formalism and using the established value of k2, these data can be used to determine the temperature dependent high and low pressure limiting rate constants over the range of conditions studied in air for reaction (1): k∞(1) = 2.13 × 10−10 (T/300)−1.045 cm3/molecule‐s; and k0(1) = 5.4 × 10−30 (T/300)−2.09 cm6/molecule2‐s. Use of these expressions yields rate constants with an estimated 20% accuracy including uncertainty in the reference reaction. The data indicate that the rate constant for a typical stratospheric condition at 30 km altitude is approximately 50% of that previously estimated.
Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane
Authors: DóBé S. , Turányi T. , Iogansen A. A. , Bérces T.
Published: January 2005

The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k1 = (1.17 ± 0.15) × 10−16 T3/2 exp[−(1037 ± 87) kcal mol−1/RT] cm3 molecule−1 s1 and k2 = (5.06 ± 0.57) × 10−16 T3/2 exp[−(228 ± 78) kcal mol−1/RT] cm3 molecule−1 s−1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure‐reactivity correlations involving kinetic and energetic parameters.
CH and C‐atom time histories in dilute hydrocarbon pyrolysis: Measurements and kinetics calculations
Authors: Dean Anthony J. , Hanson Ronald K.
Published: January 2005

CH and C‐atom concentration‐time histories were measured during pyrolysis of highly dilute mixtures (6 to 100 ppm) of ethane or methane in argon behind reflected shock waves over the temperature range 2500 to 3800 K and pressure range 0.5 to 1.3 atm. CH was detected using narrow‐linewidth laser absorption at 431 nm. C‐atom concentrations were measured using atomic resonance absorption spectroscopy (ARAS) at 156.1 nm. These data allow improved understanding of dilute hydrocarbon pyrolysis.

A pyrolysis reaction mechanism was developed which fits essential characteristics of the CH and C‐atom profiles (time to peak, peak concentration, and 50% decay time) within ±25%. Critical reactions for which rate coefficient data were not previously available are:

equation image

Best‐fit rate coefficients, valid over the range 2500 to 3800 K, are: k4 = 5.0 × 1015 exp(−42800 K/T), k5 = 4.0 × 1015 exp(−41800 K/T), k6 = 1.3 × 1014 exp(−29700 K/T), and k7 = 1.9 × 1014 exp(−33700 K/T) cm3 mol−1 s−1
Mono‐complex formation kinetics of 2‐acetylcyclohexanonatochromium(III) in aqueous solution
Authors: Blanco Carlos A. , Hernando José M. , Mateo Manuel
Published: January 2005

The kinetics and mechanism of the reaction of complexation of chromium(III) with 2‐acetyl‐cyclohexanone has been investigated spectrophotometrically in aqueous solution at 50°C and ionic strength 0.5 mol dm−3 NaClO4. The equilibrium constants of the complex have been determined. The mechanism proposed to account for the kinetic data involves a double reversible pathway where both Cr3+ and Cr(OH)2+ react with the enol tautomer of the ligand with rate constants of 9.6 × 10−3 dm3 mol−1 s−1, and 3.69 × 10−2 dm3 mol−1 s−1, respectively. Some discussions are made on the basis of Eigen‐Wilkins theory considering the effect of solvent exchange on the complex formation.
Kinetics of the solvolysis of [Co(3Rpy)4Cl2]+ ions (R = Me or Et) in Water + t‐butyl alcohol mixtures
Authors: El‐Subruiti Gehan M. , Wells Cecil F. , Sidahmed Ibrahim M.
Published: January 2005

Rates of solvolysis of complex ions [Co(3Rpy)4Cl2]+ with R = Me and Et have been determined in mixtures of water with t‐butyl alcohol over a range of temperatures. Extrema found in the enthalpy ΔH* and entropy ΔS* of activation are correlated with the physical properties of the solvent mixtures which are influenced by changes in the solvent structure and these extrema are compared with those found for the solvolysis of related complexes in water + alcohol mixtures. Isokinetic plots over wide ranges of ΔH* and ΔS* are compared for the solvolysis of CoIII complexed to a variety of ligands. The application of a free energy cycle shows that the emergent cobalt (III) cation in the transition state becomes increasingly stabilized in water‐rich mixtures relative to the cobalt (III) cation in the initial state as the mol fraction of t‐butyl alcohol increases.
Kinetics of formation, dissociation, and redox reactions of the benzyl radical‐Cu(II) ion complex in a 10% acetonitrile‐90% water mixture
Authors: Mayouf Ahmed , Lemmetyinen Helge , Sychttchikova Irina , Koskikallio Jouko
Published: January 2005

The rate constant of formation, dissociation, and redox reaction of the benzyl radical‐copper(II) ion complex have been determined at temperatures from 274 K to 333 K by laser flash photolysis of 1,3‐diphenyl‐2‐propanone (DBK) in a 10% acetonitrile‐90% water mixture containing copper(II)perchlorate. Rate constants were calculated from time resolved absorbances of both benzyl radicals (Bz) at 315 nm and benzyl‐copper complexes (BzCu2+) at 375 nm. Values of the rate constants of the formation of BzCu2+ complex were fitted to the equation

and the rate constant of the reverse reaction of BzCu2+ complex to the equation

The rate constant of the redox reaction of BzCu2+ complex to benzyl alcohol and copper(I) ion can be described by the equation

The first order rate constant of dissociation of phenylacetyl radical formed initially in the flash photolysis of DBK is given by the equation
The unimolecular decomposition and isomerization of chemically activated 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane
Authors: Arbilla G. , Ferrero J. C. , Staricco E. H.
Published: January 2005

The reaction of CH2(1A1) with 1,1,2,2‐tetrafluorocyclopropane was studied at 300 K and at pressures between 9.0 and 365.0 torr. Chemically activated 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane was formed and two competitive reaction paths, namely decomposition and isomerization, were observed. By fitting the experimental results to calculated values from RRKM theory, we estimated the Arrhenius parameters for both reaction processess as well as the heat of formation of 1‐methyl‐2,2,3,3‐tetrafluorocyclopropane. © John Wiley & Sons, Inc.
Kinetics and mechanism of oxidation of hydroxylamine by peroxomonosulphate
Authors: Sharma Madhu , Prasad D. S. N. , Gupta K. S.
Published: January 2005

The kinetics of the reaction (1) obey the rate law (2) in acetate buffered solutions. A comparison with H2O2 and S2O82− shows the reactivity order to be H2O2 < HSO5− > S2O82−. © John Wiley & Sons, Inc.

equation image
Reactions of the nitrate radical with a series of reduced organic sulphur compounds in air
Authors: Jensen N. R. , Hjorth J. , Lohse C. , Skov H. , Restelli G.
Published: January 2005

A 480 L evacuable reaction chamber, equipped with FT‐IR spectroscopy on‐line and ion chromatography off‐line, has been used to study the gas phase reaction between the nitrate radical, NO3, and the reduced organic sulphur compounds CH3CH2SH, (CH3CH2)2S, (CH3CH2)2S2, and CH3CH2SCH3 in air. The products CH3CH2SO3H, SO2, H2SO4, CH3CHO, and CH3CH2ONO2 were identified and quantified in the reactions of the first three compounds, CH3CH2SH, (CH3CH2)2S, and (CH3CH2)2S2. The reaction products were CH3CH2SO3H, CH3SO3H, SO2, H2SO4, CH3CHO, and CH2O in the reaction of CH3CH2SCH3. On the basis of identified reaction products and intermediates observed in the infrared spectra, mechanisms are proposed for the reactions between the NO3 radical and the four reduced organic sulphur compounds. The results of this study, together with those from previous experiments performed in this laboratory on CH3SCH3, CH3SH, and CH3SSCH3 lead to the conclusion that all these species, in the reaction with the NO3 radical, follow a similar degradation mechanism producing SO2, H2SO4, RSO3H, RCHO, and RCH2ONO2, as the main reaction products. The inital step of the reaction of NO3 with RSR and RSH type (R = CH3, CH2CH3) reduced organic sulphur compounds was found to be H‐atom abstraction, probably after the formation of an initial adduct. For the reaction between NO3 and RSSR type compounds, evidence for an addition‐decomposition reaction, as the initial steps, was obtained. RS·, RS(O)·, and RS(O)2· appear to be formed as intermediates in all the reactions. © John Wiley & Sons, Inc.
Kinetics and mechanism of sulfite oxidation by permanganate in basic medium
Authors: Ernst Teresa , Cyfert Maria , Wilgocki Michal
Published: January 2005

The kinetics of the permanganate‐sulfite redox reaction has been studied in the alkaline medium using a stopped‐flow technique. In the pH range 10 to 12 the reaction was found to obey the rate expression: −½d[MnO4−]/dt = (k1 + k2[OH−]) [MnO4−] [SO32−]. Mechanisms for the two paths involving the formation of a (O3MnOSO3)3− complex prior to the rate‐determining step are consistent with the data. © John Wiley & Sons, Inc.
Enzymic oxidation of dopamine by polyphenol oxidaze
Authors: Tan T. C. , Chen Y.
Published: January 2005

The kinetics of the enzymic oxidation of dopamine (A) by polyphenol oxidaze (E) was studied by spectrophotometrically monitoring the concentration of the reaction product, 2,3‐dihydroindole‐5, 6 quinone, at 470 nm. The kinetics model proposed for the reaction and the effect of pH agreed with the experimental data and the resulting rate equation is given by

where [A] is the concentration of dopamine (mM), [Eo] the concentration of polyphenol oxidaze (mg/1) and [H+] the concentration of hydrogen ion (M) in the reaction mixture. © John Wiley & Sons, Inc.
Oxidation with permanganate in strong alkaline medium. Oxidation of pyruvic and lactic acids
Authors: Jáky Miklós , Kozhevnikov Ivan V. , HÖFt Eugen
Published: January 2005

The reaction of permanganate ion with pyruvic acid and lactic acid has been studied in aqueous solutions containing 0.10–2.0 mol dm−3 alkali. In this range of HO− concentration the reaction

is followed slowly by the reduction of manganate, thus, the above process can be studied separately. In the case of lactic acid (LA), the reactive species is alkoxy anion, and the deprotonation constant could be calculated from the kinetic data. A mechanism based on electron abstraction from the alkoxy anion has been proposed. In the case of pyruvic acid (PA) oxidation may proceed with participation of enolate anion, or hydrate anion, or an adduct. These three possibilities have been investigated. © John Wiley & Sons, Inc.
Chlorine initiated photooxidation studies of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs): Results for HCFC‐22 (CHClF2); HFC‐41 (CH3F); HCFC‐124 (CClFHCF3); HFC‐125 (CF3CHF2); HFC‐134a (CF3CH2F); HCFC‐142b (CClF2CH3); and HFC‐152a (CHF2CH3)
Authors: Edney E. O. , Driscoll D. J.
Published: January 2005

Data on the tropospheric degradation of proposed substitutes for ozone depleting CFCs were obtained by conducting photochemical oxidation studies of HCFCs and HFCs using long path Fourier transform infrared spectroscopy. The hydrogen abstraction reactions were initiated using Cl radicals rather than OH radicals because of the rather unreactive nature of the compounds. The experimental product yields at T = 25 ± 3°C and 700 Torr of dry air were: CHClF2 (1.11 ± 0.06 C(O)F2); CClFHCF3 (1.00 ± 0.04 CF3C(O)F); CF3CHF2 (1.09 ± 0.05 C(O)F2); CClF2CH3 (0.98 ± 0.03 C(O)F2); CHF2CH3 (1.00 ± 0.05 C(O)F2); CF3CH2F (0.16 ± 0.03 CF3CF(O), and 0.83 ± 0.22 HFC(O)), where all standard deviations are 2σ. For each compound, the critical step in determining the oxidation products was the decomposition of a halogenated alkoxy radical. For HCFC‐22 and HCFC‐124, the major alkoxy radical decomposition route was Cl elimination. The HFC‐125 product data were consistent with CC cleavage of a two carbon alkoxy radical as the major decomposition route whereas both CC cleavage and H abstraction by O2 were significant contributors to the decomposition of the HFC‐134a alkoxy radical. Secondary Cl reactions in the HCFC‐142b and HFC‐152a experiments prevented an unambiguous determination of the decomposition modes; the data are consistent with both CC bond scission and Cl reactions with halogenated aldehydes producing the oxidation product C(O)F2. With the exception of the HFC‐134a and HFC‐125 data, the proposed mechanisms can account for the major oxidation products. For HFC‐134a and HFC‐125, a number of product bands could not be identified. The bands are likely due to products from reactions involving the CF3O2 radical. © John Wiley & Sons, Inc.
Study of the kinetics of the reactions of NO3 with HO2 and OH
Authors: Mellouki A. , Talukdar R. K. , Bopegedera A. M. R. P. , Howard Carleton J.
Published: January 2005

The Absolute rate constants for the gas‐phase reactions of NO3 with HO2 and OH have been determined using the discharge flow laser magnetic resonance method (DF‐LMR). Since OH was found to be produced in the reaction of HO2 with NO3, C2F3Cl was used to scavenge it. The overall rate constant, k1, for the reaction, HO2 + NO3 → products, was measured to be k1=(3.0 ± 0.7)×10−12 cm3 molecule−1 s−1 at (297 ± 2) K and P=(1.4 – 1.9) torr. This result is in reasonable agreement with the previous studies. Direct detection of HO2 and OH radicals and the use of three sources of NO3 enabled us to confirm the existence of the channel producing OH:HO2+NO3→OH+NO2+O2 (1a); the other possible channel is HO2+NO3→HNO3+O2 (1b). From our measurements and the computer simulations, the branching ratio, k1a/(k1a + k1b), was estimated to be (1.0). The rate coefficient for the reaction of OH with NO3 was determined to be (2.1 ± 1.0) × 10−11 cm3 molecule−1 s−1. © 1993 John Wiley & Sons, Inc.
Extrapolating H‐atom transfer rate constants via thermochemical kinetics: The effect of tunneling
Authors: Rodgers Alan S.
Published: January 2005

One of the important applications of chemical kinetics is the attempt to understand complex processes through kinetic modeling. This process frequently requires that rate constants be obtained by extrapolation of data either to higher or lower temperatures than the experimental, or by estimation or correlation with such data. Thermochemical kinetics combined with conventional transition state theory forms a framework from which this may be done. However, rate data for H transfer reactions may have a significant contribution from tunneling. In this work, a one dimensional approach to tunneling, consistent with conventional transition state theory, is taken to show how tunneling affects the extrapolation and correlation of rate constants in thermochemical kinetics. It is concluded that extrapolation and correlation are both quite good even when tunneling comprises 80% of the reaction. However, this is not without limitations, which are discussed. © 1993 John Wiley & Sons, Inc.
A relative rate study of the reaction of chlorine atoms (Cl) and hydroxyl radicals (OH) with a series of ethers
Authors: McLoughlin Peter , Kane Rosaleen , Shanahan Imelda
Published: January 2005

Rate constants for the gas phase reactions of hydroxyl radicals and chlorine atoms with a number of ethers have been determined at 300 ± 3 K and at a total pressure of 1 atmosphere. Both OH radical and chlorine atom rate constants were determined using a relative rate technique. Values for the rate constants obtained are as follows.

compound
kOH×1012(cm3 molecule−1 s−1)
kC1×1011(cm3 molecule−1 s−1)

Hexane
5.53 ± 1.55
—

2‐Chloro ethyl methyl ether
4.92 ± 1.09
14.4 ± 5.0

2,2‐Dichloro ethyl methyl ether
2.37 ± 0.50
4.4 ± 1.6

2‐Bromo ethyl methyl ether
6.94 ± 1.38
16.3 ± 5.4

2‐Chloro,1,1,1‐trifluoro ethyl ethyl ether
<0.3
0.30 ± 0.10

Isoflurane
<0.3
<0.1

Enflurane
<0.3
<0.1

Di‐i‐propyl ether
11.08 ± 2.26
16.3 ± 5.4

Diethyl ether
—
25.8 ± 4.4

The above relative rate constants are based on the values of k(OH + pentane)=[3.94 ± 0.98]×10−12 and k(OH + diethyl ether)=[13.6 ± 2.26] × 10−12 cm3 molecule−1 s−1 in the case of the hydroxyl reactions. In the case of the chlorine atom reactions, the above rate constants are based on values of k(Cl + ethane)=[5.84 ± 0.88] × 10−11 and k(Cl + diethyl ether)=[25.4 ± 8.05] × 10−11 cm3 molecule−1 s−1. The quoted errors include ±2σ from a least squares analysis of our slopes plus the uncertainty associated with the reference rate constants.

Atmospheric lifetimes calculated with respect to reaction with OH radicals are based on a tropospheric OH radical concentration of (7.7 ± 1.4) × 105 radicals cm−3, and lifetimes with respect to reaction with Cl atoms are based on a tropospheric Cl atom concentration of 1 × 103 atoms cm−3. Observed trends in the relative rates of reaction of hydroxyl radicals and chlorine atoms with the ethers studied is discussed. The significance of the calculated tropospheric lifetimes is also reviewed. © 1993 John Wiley & Sons, Inc.
Rate constants for reactions of SO4˙− radicals in acetonitrile
Authors: Padmaja S. , Alfassi Z. B. , Neta P. , Huie R. E.
Published: January 2005

Rate constants have been measured for the reactions of the sulfate radical, SO4˙−, with alkanes, alkenes, alcohols, ethers, and amines in 95% acetonitrile solution. The rate constants were in the range of 106 L mol−1 s−1 for the abstraction reactions and 107−109 L mol−1 s−1 for the addition and electron transfer reactions. These values are 20 to 80 times lower than those measured in aqueous solutions. Furthermore, the rate constants for the reactions of SO4˙− with the primary alcohols increase with the number of carbon atoms and then level off, in contrast to the behavior observed in aqueous solution, where the rate constant increases more sharply for the larger alcohols. © 1993 John Wiley & Sons, Inc.
A kinetic study of the oxidation of L‐ascorbic acid by chromium(VI)
Authors: Perez‐Benito Joaquin F. , Arias Conchita
Published: January 2005

The reaction between chromium(VI) and L‐ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is

where Kp is the equilibrium constant for protonation of chromate ion and kr is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L‐hydrogenascorbate ion). The activation parameters associated with rate constant kr are Ea = 20.4 ± 0.9 kJ mol−1, ΔH≠ = 17.9 ± 0.9 kJ mol−1, and ΔS≠=−152 ± 3 J K−1 mol−1. The reaction thermodynamic magnitudes associated with equilibrium constant Kp are ΔH0 = 16.5 ± 1.1 kJ mol−1 and ΔS0 = 167 ± 4 J K−1 mol−1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.
Kinetic isotope effect for hydrogen/deuterium abstraction by chlorine atoms from (CH3)2NNO2 and (CD3)2NNO2
Authors: Lazarou Yannis G. , Papagiannakopoulos Panos
Published: January 2005

The kinetic isotope effect for the abstraction of hydrogen/deuterium from dimethylnitramine and dimethylnitramine‐d6 by chlorine atoms has been studied in the temperature range 273–353 K. The rate constant ratio kH0/kD is given by the Arrhenius expression, kH/kD=(0.92 ± 0.07)exp(286 ± 250/RT), where R is expressed in cal mol−1 K−1. The absolute rate constant for the deuterium abstraction reaction is extrapolated as kD=(1.50 ± 0.90) × 10−10 exp(−1,486 ± 370/RT) cm3 molecule−1 s−1. The temperature dependence of the kinetic isotope effect was calculated using the conventional transition‐state theory, and the obtained values for kH/kD and ΔEH, D are in good agreement with the experimental value for a bent transition state geometry, with two new vibrational frequencies of 340 cm−1 (272 cm−1) corresponding to the in‐plane and out‐of‐plane motions of hydrogen (deuterium) atoms in the Cl…H…C arrangement. © 1993 John Wiley & Sons, Inc.
CO2 laser‐induced decomposition of ethanol
Authors: Holbrook K. A. , Oldershaw G. A. , Shaw C. J.
Published: January 2005

The multiple photon absorption and decomposition of ethanol irradiated by pulsed 9P18 infrared radiation (1048.7 cm−1) from a TEA CO2 laser has been studied in the fluence range 15 to 5 J cm−2. The absorption cross‐section is pressure‐dependent due to rapid collisional rotational hole‐filling. At low pressures the only important decomposition channel following absorption is molecular dehydration of ethanol to yield ethene, but at higher pressures hydrogen, methane, carbon monoxide, ethane, and ethyne are also produced. In the irradiation of pure ethanol under ‘collision‐free’ conditions, thermal decomposition following collisional redistribution of energy makes only a small contribution to the overall decomposition yield at fluences above 3.5 J cm−2 but may become more significant at lower fluences. Modelling using RRKM calculations has been employed to link measured absorbed energies to extents of decomposition of ethanol. Both these calculations and the absorption measurements indicate that at low pressures only a fraction of the irradiated ethanol molecules absorb the 9P18 radiation. © 1993 John Wiley & Sons, Inc.
Photolysis of N‐nitrosamines in neutral media
Authors: Fiz Nemesio , Usero José L. , Casado Julio
Published: January 2005

The photolysis of N‐nitrosamines in solutions of acetonitrile follows a first‐order reaction with respect to the concentration of nitrosamine. Quantum yields are very low (≈ 0.1) and depend on the concentration of nitrosamine, with the observation of a linear correlation between the reciprocal of quantum yield and the reciprocal of nitrosamine concentration. For all the nitrosamines studied, the final product of the photolysis appears to be unique, alkylidenimine, which in the case of nitroso methyl benzyl amine undergoes a relatively rapid hydrolysis, giving rise to benzaldehyde, following second order kinetics. A provisional model consistent with the experimental results obtained in this work is proposed. © 1993 John Wiley & Sons, Inc.
Kinetic investigation of the collisional behavior of ground state atomic carbon, C(2p2(3PJ)), with halogenated olefins and aromatic compounds studied by time‐resolved atomic resonance absorption spectroscopy in the vacuum ultra‐violet
Authors: Haider Nazre , Husain David
Published: January 2005

A kinetic investigation is described of the reaction of ground state atomic carbon, C(2p2(3PJ)), monitored by time‐resolved atomic resonance absorption spectroscopy, with a wide range of halogenated olefins and aromatic compounds. Atomic carbon was generated by the repetitive pulsed irradiation (λ > ca. 160 nm) of C3O2 in the presence of excess helium buffer gas and the added reactant gases in a slow flow system, kinetically equivalent to a static system. C(23PJ) was then monitored photoelectrically by time‐resolved atomic resonance absorption in the vacuum ultra‐violet (λ = 166 nm, 33PJ ← 23PJ) with direct computer interfacing for data capture and analysis. The following absolute second‐order rate constants for the reactions of C(23PJ) with the following reactants are reported:

Reactant
kR/cm3 molecule−1 s−1 (300 K)

C2F4
(1.9 ± 0.1) × 10−10

C2Cl4
(10.6 ± 0.5) × 10−10

CH2CF2
(4.3 ± 0.2) × 10−10

CHClCCl2
(7.9 ± 0.4) × 10−10

C6H6
(4.8 ± 0.3) × 10−10

C6F6
(4.9 ± 0.3) × 10−10

C6HF5
(5.0 ± 0.3) × 10−10

C6H2F4
(4.4 ± 0.2) × 10−10

C6H5—CH3
(5.5 ± 0.3) × 10−10

C6F5—CF3
(5.4 ± 0.3) × 10−10

These results, constituting the first reported body of absolute rate data for reactions of ground state carbon with these reactants, are compared with the analogous body of absolute rate data for atomic silicon in its Si(3p2(3PJ)) ground state, also determined hitherto by time‐resolved atomic resonance absorption spectroscopy and demonstrating similar kinetic behavior. © 1993 John Wiley & Sons, Inc.