摘要:

AbstractThe negative temperature dependence, pressure dependence, and isotope effects of the self‐reaction of HO2are modeled, using RRKM theory, by assuming that the reaction proceeds via a cyclic, hydrogen‐bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO2self‐reaction is due to the approach to the high‐pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high‐pressure limit of the self‐reac

ISSN:0538-8066    

DOI:10.1002/kin.550170802

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractAbsolute rate constants and their temperature dependencies were measured for the reaction of tert‐butyl radicals with 24 substituted ethenes and several other compounds in 2‐propanol solution by time‐resolved electron spin resonance. At 300 K the rate constants cover the range from 60 M−1s−1(1,2‐dimethylene) over 16,500 M−1s−1(vinyl‐chloride) to 460,000 M−1s−1(2‐vinylpyridine). For the mono‐ and 1,1‐disubstituted ethenes logk300increases and the activation energy decreases with increasing electron affinity of the olefins. The frequency factors are in the range logA/M−1s−1= 7.5 ± 1.0 as typical for addition reactions, with minor exceptions. Electron affinity (polar) and steric effects on reactivity are separated for the addition of tert‐butyl to chloro‐ and methyl‐substituted ethylenes. A comparison with rate data for methyl, ethyl, 2‐propyl, and other radicals indicates both polar an

ISSN:0538-8066    

DOI:10.1002/kin.550170803

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550170804

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe oxidation of nitrogen monoxide has been studied extensively between 226 and 758 K at pressures of NO and O2ranging from about 0.2 to 30 torr. It has been shown that (i) the reaction is properly first order against oxygen and second order against nitrogen monoxide, as well under initial conditions as during the course of the reaction; (ii) the termolecular rate constant,k, first decreases with increasing temperature and reaches a minimum value at 600 K; (iii) the transition state theory is unable to describe this behavior correctly, (iv) under the present experimental conditionskcan be represented either by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k({\rm l}^{\rm 2} {\rm mol}^{ - 2} {\rm s}^{ - 1}) = - (5.18 \pm 1.00) + (2.70 \pm 0.25){\rm log}_{{\rm 10}} T + (700 \pm 50)/T $$\end{document}or by\documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm l}^{\rm 2} {\rm mol}^{ - 2} {\rm s}^{ - 1}) = (350 \pm 100)10^{(390 \pm 50)/T} + (8000 \pm 2000)10^{ - (440 \pm 50)/T} $$\end{document}The latter equation is compatabile with a multiple‐step mechanis

ISSN:0538-8066    

DOI:10.1002/kin.550170805

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low‐pressure flow reactor between 850–1280 K. Whereas CH3Cl is thoroughly stable, molecular chlorine readily dissociates by a first‐order process with an activation energy about a half of its bond energy. The decompositions of CH2Cl2and CCl4over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same condi

ISSN:0538-8066    

DOI:10.1002/kin.550170806

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe addition of water to 1‐(4‐Z‐2,6‐dinitrophenyl)‐3‐methylimidazolium chloride (Z = CN, NO2, and CF3) is catalyzed by carboxylate bases. There is a decrease in ρ with increasing basicity of the catalyst with ∂ρ/∂pKBH= −0.090. The results indicate that the mechanism of the reaction involves the addition of water to the aromatic substrates catalyzed by general bases. The changes in the structure‐reactivity parameters with changingpKof the catalysts or Z in the substrate are rationalized in terms of changing bond lengths in the transition state. The activation parameters and the kinetic solvent isotopic effect were determined for the water, acetate, and OH−catalyzed reactions and are consistent with

ISSN:0538-8066    

DOI:10.1002/kin.550170807

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe pyrolysis of 2‐methylbut‐1‐ene‐3‐yne (C5H6) has been studied from 375 to 450°C in a quartz reaction vessel in the absence and presence of O2or NO. From 375 to 425°C, the rates of disappearance of reactant and of formation of dimers are second order in C5H6. The major product is polymer, with the dimers accounting for about 3% of the C5H6consumed. In addition, toluene andp‐xylene are produced, their production coming, at least in part, from decomposition of the C5H6dimers (C10H12). Also, trace amounts of CH4, C2H4, C2H6, are formed. The rate coefficients for C5H6removal and C10H12formation in the absence of O2or NO are\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l}{\rm\rm\rm log\{ }k\{ {\rm C}_{\rm 5} {\rm H}_{\rm 6} {\rm \},M}^{ - 1} {\rm - s}^{ - 1} \} = 6.79 \pm 2.39 - (4179 \pm 1603)/T \\{\rm log\{ }k\{ {\rm C}_{{\rm 10}} {\rm H}_{{\rm 12}} \},{\rm M}^{ - {\rm 1}} {\rm - s}^{ - 1} \} = 7.40 \pm 2.32 - (5793 \pm 1555)/T \\\end{array} $$\end{document}where the uncertainties are one standard deviation. The reaction mechanism for dimer formation is analogous to that in vinyl acetylene (C4H4) pyrolysis (5), except that in the C4H4system cyclooctatetraene is seen as an unstable product that isomerizes to styrene, whereas in the C5H6system, the dimethylcyclooctatetraene apparently is too unstable to be detected. The dimers detected were 2,6‐dimethylstyrene (P4),p‐isopropenyltoluene (P5), and two other unidentified dimers (P3) with nearly identical gas chromatographic retention times. From the effect of the radical scavengers and by comparison of the C4H4and C5H6systems, the following mechanistic characteristics were determined: (1) The direct formation of styrene in the C4H4system comes from a head‐to‐head modified Diels‐Alder six‐member cycloaddition that proceeds through a diradical intermediate. (2) There is no positive evidence for a direct head‐to‐tail modified Diels‐Alder six‐member cycloaddition. However, if it does occur, it does not involve diradicals but must be concerted. (3) Cyclooctatetraene is formed in concerted, non‐free‐radical mechanisms that may proceed both by head‐to‐head and head‐to‐tail eight‐member cycloadditions. For the C5H6system, the head‐to‐head adduct isomerizes to P3, whereas the head‐to‐tail adduct isomerizes to P3, P4, and/or P5. and/or P5. Kinetic data suggest that P3 is not produced from the cyclooctatetraene intermediate, in which case, head‐to‐head addition would not occur. It appears that the head‐to‐head additions are free radical in nature and proceed mainly through a six‐membered ring intermediate, while head‐to‐tail additions are a concerted molecular p

ISSN:0538-8066    

DOI:10.1002/kin.550170808

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe ultraviolet absorption spectra of the acetyl and acetylperoxy radicals have been characterized in the range 195–280 nm. The acetyl radical was generated by the flash photolysis of Cl2in the presence of CH3CHO and was converted to the acetylperoxy radical in the presence of excess O2. The extinction coefficient of the acetylperoxy radical was measured to be 2300 L/mol cm at the maximum at 207 nm and the rate constant for the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ 2{\rm CH}_{\rm 3} {\rm CO}_{\rm 3} \to 2{\rm CH}_{\rm 3} {\rm + 2CO}_{\rm 2} {\rm + O}_{\rm 2} $$\end{document}was evaluated to bek5= (4.8 ± 0.8) × 109L/mo

ISSN:0538-8066    

DOI:10.1002/kin.550170809

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractUsing the method of freezing radicals in conjunction with ESR spectroscopic measurements, the kinetics of the thermal oxidation of methane has been studied under atmospheric pressure depending on the temperature, composition of the mixture, and nature of the surface of the reaction vessel. It has been shown that in a reactor treated with boric acid, the intermediates methylhydroperoxide and hydrogen peroxide are responsible for chain branching. It has been established that the leading active centers of the reaction are the HO2radicals, while chain branching occurs as a result of the decomposition of peroxy compounds—methylhydroperoxide and hydrogen peroxide. In reactors treated with potassium bromide, the concentrations of radicals and peroxy compounds were found to be lower than the sensitivity of the method of measurement. Computations were performed for the scheme of methane oxidation at 738 K for a reactor treated with boric acid. Satisfactory agreement was found between the experimental and computed kinetic curves of accumulation of main intermediates CH2O, H2O2, CH3OOH. The influence of their addition on the kinetics of the reaction has been considered. It has been shown that the addition of formaldehyde does not lead to chain branching, however; it contributes to the formation of those peroxy compounds that bring about chain branching. Mathematical modeling confirmed conclusions made on the basis of experimental data concerning the nature of the leading active centers and the products that are responsible for the degenerate chain branchin

ISSN:0538-8066    

DOI:10.1002/kin.550170810

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550170801

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY