摘要:

AbstractThe low temperature gas‐phase oxidation of CH3CHO and C2H5CHO have been investigated as an example of heterogeneous‐homogeneous reaction. It has been shown that with the increase of S/V (surface/volume) ratio of the reaction vessel the maximum rate of the process increases and the heterogeneous consumption of aldehyde prevails over the homogeneous one. Peroxy radicals have been discovered by EPR method in vessels with different S/V ratios. The concentration of peroxy radicals and the accumulation rate of peracid in the gas phase did not change with the increase of S/V ratio in the same interval. Under the conditions of these experiments excluding the homogeneous propagation of chains the aldehydes oxidized heterogeneously. The peroxy radicals initiate this heterogeneous process which indicate the existence of short chains on the surface. The reaction between the peroxy radicals and aldehyde on the solid surface (SiO2, KCl/SiO2) has been shown by EPR, IR‐spectroscopy, and mass‐spectrometry methods. A conclusion has been drawn that the solid surface takes part in the chain propagation stage of aldehydes oxidation. © 1994 John Wiley&S

ISSN:0538-8066    

DOI:10.1002/kin.550260602

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe kinetics of the gas‐phase reaction of the NO3radical with naphthalene have been investigated at 150 torr O2+ 590 torr N2and 600 torr O2+ 140 torr N2at 298 ± 2 K. Relative rate measurements were carried out in reacting NO3N2O5‐naphthalene‐propene‐O2N2mixtures by longpath Fourier transform infrared absorption spectroscopy. A rate constant ratio for the reactions of O2and NO2with the NO3‐naphthalene adduct ofk O 2/k NO 2<4 × 10−7was obtained from the competition between O2and NO2for reaction with the NO3‐naphthalene adduct and thermal decomposition of the adduct back to reactants. Atmospheric pressure ionization MS/MS measurements of the nitronaphthalene products of the NO3radical‐initiated reaction of naphthalene are consistent with the proposed reaction mechanism, and the atmospheric implications of the data are discussed

ISSN:0538-8066    

DOI:10.1002/kin.550260603

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractUV spectra of SF5and SF5O2radicals in the gas phase at 295 K have been quantified using a pulse radiolysis UV absorption technique. The absorption spectrum of SF5was quantified from 220 to 240 nm. The absorption cross section at 220 nm was (5.5 ± 1.7) × 10−19cm2. When SF5was produced in the presence of O2an equilibrium between SF5, O2, and SF5O2was established. The rate constant for the reaction of SF5radicals with O2was (8 ± 2) × 10−13cm3molecule−1s−1. The decomposition rate constant for SF5O2was (1.0 ± 0.5) × 105s−1, giving an equilibrium constant ofKeq= [SF5O2]/[SF5][O2] = (8.0 ± 4.5) × 10−18cm3molecule−1. The SF5O2bond strength is (13.7 ± 2.0) kcal mol−1. The SF5O2spectrum was broad with no fine structure and similar to the UV spectra of alkyl peroxy radicals. The absorption cross section at 230 nm was found to (3.7 ± 0.9) × 10−18cm2. The rate constant of the reaction of SF5O2with NO was measured to (1.1 ± 0.3) × 10−11cm3molecule−1s−1by monitoring the kinetics of NO2formation at 400 nm. The rate constant for the reaction of F atoms with SF4was measured by two relative methods to be (1.3 ± 0.3) × 10−11cm3

ISSN:0538-8066    

DOI:10.1002/kin.550260604

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Arrhenius parameters for the thermal decomposition of ferrocenyl azide in isooctane areA= (5.1 ± 1.4) × 1012s−1andEact= 113.1 ± 0.9 (kJ mol−1) and the rate is relatively insensitive to solvent (isooctane, benzene, acetonitrile: 1:1.7:2.4). The results indicate a relatively nonpolar transition state which is considerably “tighter” than for a normal bond fission reaction. The Arrhenius parameters are comparable to those for aromatic azides and do not offer any support for anchimeric assistance by the iron atom. A kinetic scheme is presented which accounts for the observed products: Nitrogen, ferrocene, aminoferrocene, azoferrocene, and insoluble material. Rates of hydrogen abstraction by the intermediate ferrocenyl nitrene from cyclohexane, benzene, and acetonitrile are used to show that the nitrene is nucleophilic. © 1994 John Wile

ISSN:0538-8066    

DOI:10.1002/kin.550260605

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe dynamical aspects of some α‐diazoketones (DZ) photolysis are investigated within the framework of statistical theories (RRKM formulation). On the whole, the results agree satisfactorily with the gas‐phase experimental observations (quantum yields). In particular, the reactions DZ +hv→ α‐ketocarbene (KC) + N2, appear to be mainly governed by statistical behavior. The two channel isomerizations KC → ketene (KE), i.e, the Wolff Rearrangement, and KC → α,β‐unsaturated ketone (ON) are also considered. It is suggested that the trapping of the α‐ketocarbenes and oxirenes (OX) species would be favored under appropriate conditions (among them the irradiation wavelength and the relaxation processes involved in the reactive medium). The parametrization of the model relies on semi‐empirical quantum calculations and is improved by some adjustments with experimental data. © 19

ISSN:0538-8066    

DOI:10.1002/kin.550260606

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe violet superoxo complex, [(H2O)4(OH)RhIII(O2)RhIII(OH)(H2O)4]3+, formed by treatment of (RhII)24+with O2in HClO4, is converted to a le−reduction product, the corresponding μ‐peroxo complex, by the reductants I−, IrCl63−, and the trinuclear aquamolybdenum(III) cation, (MoIII)3. Each reaction is first‐order in both redox partners, and the le−reduction by IrCl63−is followed by a much slower conversion to a peroxide‐free complex. Among the rapid reductions of the superoxo derivative examined here and in a previous study, only that by IrCl63−is accelerated by increases in acidity; the rate law for this reaction features both an acid‐independent and a [H+]‐proportional component, the latter stemming from partial conversion of the oxidant to its conjugate acid (pKA<−1.0). Rate laws for reductions by other metal‐center reagents generally exhibit inverse‐[H+] terms, reflecting deprotonation of the reductant. All reductions thus far observed involving this superoxo species appear to be outer‐sphere. Treatment of acid‐independent rate constants within the framework of the Marcus model, allows estimates of the self‐exchange rate,k11, for the (RhIII)2‐bound superoxo‐peroxo couple. Because values ofk11calculated from the several reductions span a range of 104.5, reductions of the superoxo complex cannot be taken to conform satisfactorily to the Marcus treatment, being in this respect comparable to the systems VO(OH)+/2+, Mn2+/3+, Eu2+/3+, and Ti(OH)2+/3+, each of which exhibits similar divergences. The wide range of calculated self‐exchange rates appears to invalidate an earlier suggestion that reduction of the superoxo complex by Fe2+proceeds primarily through a b

ISSN:0538-8066    

DOI:10.1002/kin.550260607

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe absolute rate constants for the intermolecular hydrogen abstraction reactions of secondary hydrogens by secondary alkylperoxy radicals in hexadecane autoxidation,k3, have been determined in the temperature range of 120–190°C using the stirred flow reactor technique. Absolute rate constants determined in this study for hexadecane are in good agreement with those determined for other hydrocarbons in liquid phase, on a per hydrogen basis, at lower temperatures. Arrhenius parameters fork3/H derived from this study are A = 108.6M−1s−1andEa= 16.0 kcal/mol. The values of these parameters provide experimental confirmation for previous estimates made from both lower temperature reactions in the liquid phase and higher temperature reactions in the gas phase. © 1994 John Wiley&So

ISSN:0538-8066    

DOI:10.1002/kin.550260608

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550260601

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY