摘要:

AbstractThe rates of gas‐phase thermolysis reactions of 2‐acetylcyclopentanone 1,2‐acetylcyclohexanone 2,N‐acetylcaprolactam 3,2‐acetylbutyrolactone 4,2‐acetyl‐2‐methylbutyrolactone 5, and 3‐acetyl‐2‐oxazolidinone 6 have been measured over a temperature range of 50 K. They undergo unimolecular first‐order elimination reactions for which logA= 11.7, 11.7, 11.2, 11.4, 11.5, and 11.1 s−1and Ea= 193.4, 189.5, 153.2, 201.0, 206.8, and 176.1 kJ mol−1, respectively. The effect of the ring size together with the effect of a heteroatom in the ring on the rate of thermolysis reactions for compound 1–6 is the subject of this work

ISSN:0538-8066    

DOI:10.1002/kin.550270902

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe elimination kinetics of the title compounds have been examined over the temperature range of 270–320°C and pressure range of 19–117 torr. The reactions, carried out in seasoned vessels, with the free‐radical suppressor toluene always present, are homogeneous, unimolecular, and follow a first‐order rate law. The products of 2‐hydroxy‐2‐methylbutyric acid are 2‐butanone, CO, and H2O; while of 2‐ethyl‐2‐hydroxybutyric acid are 3‐pentanone, CO, and H2O. The rate coefficient is expressed by the following Arrhenius equation: for 2‐hydroxy‐2‐methylbutyric acid, logk1(s−1= (12.87 ± 0.19) − (171.2 ± 2.1) kJ mol−1(2.303RT)−1; and for 2‐ethyl 2‐hydroxybutyric acid, logk1s−1) = (12.13 ± 0.34) − (159.4 ± 3.7) kJ mol−1(2.303RT)−1. Augmentation of alkyl bulkiness at the 2‐position of the 2‐hydroxycarboxylic acids showed an increase in the rate of dehydration. The electron release of alkyl groups, rather than steric acceleration, appears to enhance the pyrolysis decomposition of these substrates. These reactions are believed to proceed through a semi‐polar five‐membered cy

ISSN:0538-8066    

DOI:10.1002/kin.550270903

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractKinetic modeling and sensitivity analyses for the reaction CH3+ C2H2→ CH3C2H2(4) have been performed according to the experimental conditions and results of Mandelcorn and Steacie, Garcia Dominguez and Trotman–Dickenson, and Holt and Kerr. The kinetically modeled results show that Mandelcorn and Steacie overestimated the rate constant of reaction (4) whereas Garcia Dominguez and Trotman‐Dickenson underestimated it, and that there could be significant uncertainty in the steady‐state treated results of Holt and Kerr. Reanalysis of Garcia Dominguez and Trotman–Dickenson's experimental data by kinetic modeling with the proper mechanism gives a more reliable rate constant for reaction (4). The improved rate constant (k4) is in good agreement with our theoretically predicted values. © 1995 John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550270904

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics and mechanism of the thermal reduction of NO by H2have been investigated by FTIR spectrometry in the temperature range of 900 to 1225 K at a constant pressure of 700 torr using mixtures of varying NO/H2ratios. In about half of our experimental runs, CO was introduced to capture the OH radical formed in the system with the well‐known, fast reaction, OH + CO → H + CO2. The rates of NO decay and CO2formation were kinetically modeled to extract the rate constant for the rate‐controlling step, (2) HNO + NO → N2O + OH. Combining the modeled values with those from the computer simulation of earlier kinetic data reported by Hinshelwood and co‐workers (refs. [3] and [4]), Graven (ref.[5]), and Kaufman and Decker (ref. [6]) gives rise to the following expression:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 \, = \,\,10^{12.93\, \pm \,0.13} \,{\rm exp}\left[ { - {{\left({14,890\, \pm \,360} \right)} \mathord{\left/ {\vphantom {{\left({14,890\, \pm \,360} \right)} T}} \right. \kern-\nulldelimiterspace} T}} \right]\,{\rm cm}^{\rm 3} \,{\rm mol}^{ - 1} \,{\rm s}^{ - 1} $$\end{document}.This encompasses 45 data points and covers the temperature range of 900 to 1425 K. RRKM calculations based on the latest ab initio MO results indicate that the reaction is controlled by the addition/stabilization processes forming the HN(O)NO intermediate at low temperatures and by the addition/isomerization/decomposition processes producing N2O + OH above 900 K. The calculated value ofk2agrees satisfactorily with the experimental result. © 1995 John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550270905

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractReaction experiments on mixtures of N2O/H2O/N2were performed in a variable pressure flow reactor over temperature, pressure, and residence time ranges of 1103–1173 K, 1.5–10.5 atm, and 0.2–0.8 s, respectively. Mixtures of approximately 1% N2O in N2were studied with the addition of varying amounts of water vapor, from background to 3580 ppm. Experimentally measured profiles of N2O, O2, NO, NO2, H2O, and temperature were compared with predictions from detailed kinetic modeling calculations to assess the validity of a reaction mechanism developed from currently available literature thermochemical and rate constant parameters. Sensitivity and reaction flux analyses were performed to determine key elementary reaction path processes and rates.Reaction rate constants for the uni‐molecular reaction, N2O → N2+ O, were determined at various pressures in order to match overall experimental and numerical decomposition rates of N2O. The numerical model included a newly determined rate constant for N2O + OH → HO2+ N2with an upper limit of 5.66 × 108cm3mol−1sec−1at 1123 K. This is considerably smaller than presently reported in the literature. The experimentally observed rate of N2O decomposition was found to be slightly dependent on added water concentration. The rate constant determined for the elementary decomposition is strongly dependent on the choice of rate constants for the N2O + O ⇔ N2+ O2and N2O + O ⇔ NO + NO reactions. In the absence of accurate data at the temperatures of this work, and based on these and other experiments in this laboratory, we presently recommend rate constants from the review of Baulch et al. The basis for this recommendation is discussed, including the impact on the rate constants derived for elementary nitrous oxide decomposition. The uncertainties in the rate constants as reported here are ±30%.The present mechanism was applied to previously reported high‐pressure shock tube data and yields a high‐pressure limit rate constant a factor of three larger than previously reported at these temperatures. The following expressions for the elementary decomposition reaction are recommended:k 0, N 2= 9.13 × 1014exp (−57, 690/RT) cm3mol−1s−1andk∞= 7.91 × 1010exp(−56020/RT) s−1. Simple Lindemann fits utilizing these parameters reproduce the pressure dependent rate constants measured he

ISSN:0538-8066    

DOI:10.1002/kin.550270906

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPropagating reaction fronts generated in the autocatalytic oxidation of formaldehyde by nitric acid have been investigated. The experimental values of the wave velocity ν and those of the maximal reaction ratermat a given spatial coordinate have been described by the formulae ν = 2(Dk[CH2(OH)2]0)1/2andrm= 0.247 ×k[CH2(OH)2]02, respectively, (Dandkconstants). Similarities and differences to other nitric acid oxidations have been discussed. © 1995 John Wiley&Sons,

ISSN:0538-8066    

DOI:10.1002/kin.550270907

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractKinetics of regioselective N2 alkylation of a series of 5‐(R‐phenyl)tetrazoles with isopropyl alcohol has been studied in 88.2, 94.3, and 98.3% (w/w) sulfuric acid at 25°. The true rate constants were evaluated, logarithms of which were found to correlate with σ° constants of phenyl substituents as logk= −0.488 σ° − 0.417. Small value of Hammett constant ρ is evidence of a considerable isolation of the reaction center from the influence of the substituent at position C5 of the heteroring. This conclusion is confirmed by results of MNDO quantum chemical calculations of a series of 5‐substituted tetrazolium cations. A correlation between logarithms of the true rate constants and the calculated net effective charges on atoms N2(N3) for 5‐(R‐phenyl)tetrazolium cations has been revealed. © 1995

ISSN:0538-8066    

DOI:10.1002/kin.550270908

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe second‐order rate constant for the oxidation of NADH by methylene blue at pH 9.0 and 25°C under aerobic conditions is 4.21 M−1s−1. © 1995 John Wiley&So

ISSN:0538-8066    

DOI:10.1002/kin.550270909

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe formation constants of the Schiff bases of pyridoxal 5′‐phosphate with polyallylamine were determined over the pHrange of the acetic‐acetate buffer (3.9–5.5) at an ionic strength of 0.1 M and a temperature of 25°C. The results were consistent with the rapid formation of an ionized carbinolamine,T+, followed by deprotonation, in the rate‐determining step, to a neutral carbinolamine,T°. Subsequent dehydration ofT° in a rapid step yields the final Schiff base. The formation ofT+is a concerted process subject to specific acid catalysis. © 1995 John Wi

ISSN:0538-8066    

DOI:10.1002/kin.550270910

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550270901

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY