The thermal decomposition of methane. III. Methyl radical exchange in CH4–CD4 mixtures

1977 ◽  
Vol 55 (10) ◽  
pp. 1624-1628 ◽  
Author(s):  
C.-J. Chen ◽  
M. H. Back ◽  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Shock Tube ◽  
Exchange Reaction ◽  
Rate Constant ◽  
Average Rate ◽  
Static System ◽  
Chain Mechanism ◽  
Methyl Radical ◽  
Radical Chain ◽  
Decomposition Of Methane

The thermal methyl-radical exchange reaction, CH4 + CD4 → CH3D + CD3H, has been studied in a static system at temperatures from 880 to 1103 K, with equimolar mixtures at a pressure of 440 Torr. The exchange occurs by a methyl-radical chain mechanism, propagated by the reactions CH3 + CD4 → CH3D + CD3, and CH3 + CD4 → CH3H + CD3. Values of an average rate constant for these reactions have been estimated; kx = 1.42 × 106 ℓ mol−1 s−1 at 995 K. Comparison with shock tube data and photochemical measurements, at higher and lower temperatures respectively, indicates pronounced non-Arrhenius behaviour.

THE THERMAL DECOMPOSITION OF HEXAFLUOROAZOMETHANE

1962 ◽  
Vol 40 (5) ◽  
pp. 930-934 ◽  
Author(s):  
Elizabeth Leventhal ◽  
Charles R. Simonds ◽  
Colin Steel
Keyword(s):  
Thermal Decomposition ◽  
High Pressure ◽  
Rate Constant ◽  
Static System ◽  
Homogeneous Reaction

The pyrolysis of hexafluoroazomethane has been studied in a static system between 0.3 mm and 73 mm and 572 °K and 634 °K by measuring the rate of nitrogen formation. The rate constant of the high-pressure homogeneous reaction is given by k = 1016.17±0.15 exp (−55,200 ± 400/RT) sec−1

The thermal decomposition of n-propyl bromide

1968 ◽  
Vol 21 (4) ◽  
pp. 973 ◽  
Author(s):  
JTD Cross ◽  
VR Stimson
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Order Reaction ◽  
Chain Mechanism ◽  
Initial Concentration ◽  
First Order ◽  
Reaction Proceeds ◽  
Atom Chain

Mechanisms already proposed or formally possible for the decomposition of n-propyl bromide as a 312-order reaction are shown to be unsatisfactory, and the reaction has been reinvestigated. Two reactions occur simultaneously: (a) a first-order reaction identifiable with the maximally inhibited reaction and presumably molecular; (b) a reaction second order in the initial concentration and somewhat autocatalysed as the reaction proceeds. The rate constant is given by k2 == 1018.1exp(-49300/RT)sec-1ml mole-1 Reaction (b) is catalysed by hydrogen bromide and inhibited by propene, and a bromine atom chain mechanism with hydrogen bromide catalysed initiation is proposed. Bromine-catalysed decomposition has also been studied. The mechanism of the inhibition is discussed.

Radiation-induced Oxidation of 2-Propanol by Nitrous Oxide in Alkaline Aqueous Solution

1972 ◽  
Vol 50 (11) ◽  
pp. 1751-1756 ◽  
Author(s):  
C. E. Burchill ◽  
G. P. Wollner
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Chain Mechanism ◽  
Radical Chain ◽  
Kinetic Isotope ◽  
Alkaline Aqueous Solution ◽  
Radiation Induced ◽  
Solution Proceeds

The radiation-induced oxidation of 2-propanol to acetone by N2O in alkaline aqueous solution proceeds via a free radical chain mechanism independent of pH above 12.5. The results are explained by abstraction of H from 2-propanol by O− at both the α and β positions (85% α attack). Chain propagation is by reaction of the α radical anion, (CH3)2ĊO−, with N2O with a rate constant of (3.8 ± 0.4) × 104 M−1 s−1 and by reaction of the β radical, ĊH2(CH3)CHOH, with 2-propanol to give the α radical with a rate constant of 430 ± 30 M−1 s−1.The conclusions are supported by the demonstration of kinetic isotope effects for selectively deuterated alcohols.

The thermal decomposition of trimethylacetyl bromide

1970 ◽  
Vol 23 (3) ◽  
pp. 525 ◽  
Author(s):  
BS Lennon ◽  
VR Stimson
Keyword(s):  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Hydrogen Bromide ◽  
Transition States ◽  
Volume Ratio ◽  
Reaction Vessel ◽  
Chain Mechanism ◽  
Radical Chain ◽  
First Order ◽  
Polar Transition

Trimethylacetyl bromide decomposes at 298-364� into isobutene, carbon monoxide, and hydrogen bromide in a first-order manner with rate given by k1 = 138 x 1014exp(-48920/RT) sec-1 The rate is unaffected by addition of the products or of inhibitors, or by increase of the surface/volume ratio of the reaction vessel. The likely radical chain mechanism is considered and rejected. The reaction is believed to be a molecular one, and possible cyclic and polar transition states are discussed.

The Thermal Decomposition of Methane. I. Kinetics of the Primary Decompositionto C2H6 + H2; Rate Constant for the Homogeneous Unimolecular Dissociation of Methane and its Pressure Dependence

1975 ◽  
Vol 53 (23) ◽  
pp. 3580-3590 ◽  
Author(s):  
C.-J. Chen ◽  
M. H. Back ◽  
R. A. Back
Keyword(s):  
Rate Constant ◽  
Flow System ◽  
Quantitative Agreement ◽  
Radical Mechanism ◽  
Unimolecular Dissociation ◽  
Static System ◽  
System Data ◽  
Decomposition Of Methane ◽  
Kinetics Of ◽  
Good Agreement

The pyrolysis of methane has been studied in a static system at temperatures of 995, 1038, 1068, and 1103 K and pressures from 25 to 700 Torr. It was concluded that the initial stages of the reaction can be described by a simple homogeneous, nonchain radical mechanism:[Formula: see text]Initial rates of reaction were measured, based on analysis of hydrogen, ethane, and ethylene, and k1 was found to be pressure dependent and homogeneous. Quantitative agreement was obtained with values of k1 calculated by R.R.K.M. theory. Values of A∞ = 2.8 × 1016 s−1 and E∞ = 107.6 kcal/mol were obtained, the latter appreciably greater than the value of E0 = 103 kcal/mol used in the calculations. Comparison of previous shock-tube and flow-system data at temperatures up to 2200 K showed good agreement with values of k1 obtained by extrapolation of the present R.R.K.M. calculations. It was concluded that in all previous studies, the initial dissociation was in its pressure-dependent region. Estimates were also made of the rate constant for the reverse of [1] and showed fair agreement with recent experimental measurements.

Rate constant for chlorine abstraction from CCl4 by the 5-hexenyl radical

1987 ◽  
Vol 65 (2) ◽  
pp. 311-315 ◽  
Author(s):  
Deborah Rae Jewell ◽  
Lukose Mathew ◽  
John Warkentin
Keyword(s):  
Free Radical ◽  
Double Bond ◽  
Chlorine Atom ◽  
Rate Constant ◽  
Methyl Ethyl ◽  
Chain Mechanism ◽  
Secondary Product ◽  
Radical Chain ◽  
Alkyl Radicals ◽  
Primary Products

Cyclization of the 5-hexenyl free radical to the cyclopentylmethyl free radical was used to clock chlorine atom abstraction by 5-hexenyl from carbon tetrachloride in solution. The source of 5-hexenyl radicals was 5-hexenyl[1-hydroxy-1-methyl-ethyl]diazene ((CH3)2C(OH)N=N(CH2)4CH=CH2), which decomposes thermally in CCl4 by a radical chain mechanism to afford chloroform, acetone, nitrogen, 6-chloro-1-hexene, cyclopentylchloromethane, 1-hexene, and methylcyclopentane as primary products. 6-Chloro-1-hexene is converted, in part, to a secondary product, 1,1,1,3,7-pentachloroheptane, by radical chain addition of CC14 to the double bond. The rate constant for chlorine atom abstraction, kCl, was calculated from the product composition and the known rate constant for cyclization of the 5-hexenyl radical. For the temperature range 274–353 K, kCl is given by log (kCl/M−1 s−1) = (8.4 ± 0.3) − (6.2 ± 0.4)/θ where θ = 2.3 RT kcal mol−1, which leads to [Formula: see text]. This value is significantly smaller than recently reported estimates for other primary alkyl radicals.

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