REACTION OF DEUTERIUM ATOMS WITH ETHANE—MECHANISM OF METHANE EXCHANGE

1958 ◽  
Vol 36 (6) ◽  
pp. 983-989 ◽  
Author(s):  
R. Berisford ◽  
D. J. Le Roy
Keyword(s):  
Methane Molecule ◽  
Methane Formation ◽  
Methyl Radicals ◽  
Third Body ◽  
Ethyl Radical ◽  
Ethane Molecule ◽  
Body Concentration

The reaction of deuterium atoms with ethane has been studied at 25 °C. by the method of mercury (3P1) photosensitization. Methane formation takes place by the addition of D atoms to methyl radicals in the presence of a third body. From the dependence of methane exchange on third-body concentration the lifetime of the excited methane molecule is estimated to be of the order of 10−9 sec. The lifetime of the excited ethane molecule formed by the addition of a D atom to an ethyl radical is estimated to be considerably less than 10−9 sec.

The reaction of hydrogen atoms with ethylene

1970 ◽  
Vol 316 (1527) ◽  
pp. 575-591 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Recombination Reaction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Cracking Reaction ◽  
Computer Calculations ◽  
First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

THE THERMAL DECOMPOSITION OF ETHANE: PART II. THE UNIMOLECULAR DECOMPOSITION OF THE ETHANE MOLECULE AND THE ETHYL RADICAL

1966 ◽  
Vol 44 (20) ◽  
pp. 2357-2367 ◽  
Author(s):  
M. C. Lin ◽  
M. H. Back
Keyword(s):  
High Pressure ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Methyl Radicals ◽  
Unimolecular Decomposition ◽  
First Order ◽  
Order Rate ◽  
Ethyl Radical ◽  
Lower Temperature ◽  
Ethyl Radicals

The rate of the elementary dissociation of ethane into two methyl radicals has been measured in its pressure-dependent region at temperatures from 913–999 °K and at pressures from 1–200 mm. The high-pressure first-order rate constant obtained by extrapolation was in agreement with that obtained at lower temperatures,[Formula: see text]Comparison with calculated Kassel curves showed that the best fit of the data was obtained with the Kassel parameter s = 12 ± 1. The high-pressure first-order rate constant for the decomposition of the ethyl radical was obtained by extrapolation of the data reported in Part I, assuming the rate constant for combination of ethyl radicals is independent of temperature.[Formula: see text]From the measured constant for the dissociation of ethane, the rate constant for the combination of methyl radicals was calculated and compared with the values measured in a lower temperature region. Differences in the values of the rate constants and in the shapes of the unimolecular falloff curves are discussed.

Third Body Effects in the Combination of Methyl Radicals

1964 ◽  
Vol 68 (9) ◽  
pp. 2492-2497 ◽  
Author(s):  
S. Toby ◽  
B. H. Weiss
Keyword(s):  
Methyl Radicals ◽  
Third Body

Hydrogen abstraction from toluene by methyl radicals and the pressure dependence of the recombination of methyl radicals

1970 ◽  
Vol 48 (8) ◽  
pp. 1269-1272 ◽  
Author(s):  
A. N. Dunlop ◽  
R. J. Kominar ◽  
S. J. W. Price
Keyword(s):  
Pressure Dependence ◽  
Reasonable Agreement ◽  
Pressure Range ◽  
Hydrogen Abstraction ◽  
Methyl Radicals ◽  
Third Body ◽  
Kcal Mole

Using dimethylzinc, dimethylmercury, and trimethylbismuth as sources of methyl radicals, values of k1/k21/2[Formula: see text]have been calculated from 338 to 610 °C over the pressure range 4.5–204 mm. M is predominantly toluene. The observed pressure dependence of reaction [2] is in agreement with that found when M = benzene, but is somewhat greater, and the fall-off occurs at higher pressures, than for ethane dissociation. However, reasonable agreement is obtained if it is assumed that the efficiency of toluene as a third body in reaction [2] is about 1/10th that of ethane.Extrapolation to infinite pressure, where it is assumed that E2 = 0and A2 = 1013.34 cm3 mole−1 s−1, gives E1 = 8.0 ± 0.3 kcal mole−1 and A1 = 1011.07 cm3 mole−1 s−1.

The combination of methyl radicals: photolysis of acetone at low pressures

1954 ◽  
Vol 223 (1154) ◽  
pp. 283-295 ◽  
Keyword(s):  
Relative Rate ◽  
Methyl Radicals ◽  
Third Body ◽  
Low Pressures ◽  
Kinetics Of ◽  
Photo Decomposition ◽  
Activated Complex

The kinetics of the photo-decomposition of acetone at low pressures (20 to 0.2 mm) are consistent with the participation of a third body in the recombination of methyl radicals. Various added gases increase the relative rate of formation of ethane; approximate values, relative to acetone, are given for their efficiencies in deactivating excited ethane molecules by collision. The rate of spontaneous redissociation of the activated complex is less than 6 x 10 7 s -1 at 520° K, and increases with temperature.

Kinetics and mechanisms of the thermal decomposition of propane I. The Uninhibited of reaction

1962 ◽  
Vol 270 (1341) ◽  
pp. 242-253 ◽  
Keyword(s):  
Radical Mechanism ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Third Body ◽  
Third Order ◽  
First Order ◽  
The Third ◽  
Free Radical Mechanism ◽  
Pressure Region ◽  
Initiation Reaction

The uninhibited pyrolysis of propane was investigated from 530 to 670 °C and at pressures up to 600 mm. In an unpacked vessel the reaction was of the first order at lower temperatures and higher pressures. A transition to 3/2 order at higher temperatures and lower pressures was observed. The rates were somewhat reduced in a packed vessel, and an apparent order of 1.25 was obtained. The activation energy of the reaction in its first-order region was 67.1 kcal and that of the f-order reaction was 54.5 kcal. Added carbon dioxide had no effect on the rates either in the first-order or 3/2-order region. On the basis of this evidence, and of theoretical arguments, it is concluded that the reaction is largely homogeneous and occurs by a free-radical mechanism. The initiation reaction is considered to be the dissociation of propane into a methyl radical and an ethyl radical, this reaction being in its second-order low-pressure region under the conditions of the experiments. The termination reaction when the overall order is unity is concluded to be the recombination of a methyl and a propyl radical in the presence of a third body. In the 3/2-order region the termination reaction is believed to be the recombination of two methyl radicals, also in the third-order region. These mechanisms are shown to give a satisfactory interpretation of the overall behaviour.

Mercury-photosensitized decomposition of dimethyl ether. Part III. The combination of radicals

1967 ◽  
Vol 45 (22) ◽  
pp. 2775-2783 ◽  
Author(s):  
Leon F. Loucks
Keyword(s):  
Dimethyl Ether ◽  
Rate Constant ◽  
Pressure Dependence ◽  
Rate Coefficient ◽  
Methyl Radicals ◽  
Methyl Ethyl ◽  
Methyl Radical ◽  
Unimolecular Decomposition ◽  
Third Body ◽  
Methyl Ethyl Ether

As part of the study of the mercury-photosensitized decomposition of dimethyl ether, the combination of methyl radicals has been investigated in the temperature range 200 to 300 °C and at pressures between 3 and 300 mm Hg. For pressures of less than 100 mm the second-order rate coefficient for the combination of methyl radicals shows a pressure dependence. The pressure dependence agrees qualitatively with that observed by others, but occurs at somewhat higher pressures. Calculations for the Kassel equation using the Arrhenius parameters for ethane decomposition and fitted to the pressure dependence of the methyl radical combination show that the number of effective modes for ethane decomposition is 8 or 9. Carbon dioxide was found to be a quite ineffective third body for energy transfer. The results for the mercury-photosensitized decomposition of dimethyl ether have also been analyzed to obtain information about the combination of methyl radicals with methoxymethyl radicals. The combination of these radicals becomes pressure dependent at pressures less than about 15 mm. Kassel integrations based on the rate constant [Formula: see text]for the unimolecular decomposition of methyl ethyl ether at the C—C bond, and fitted to the observed pressure dependence of the combination reaction, lead to s = 10 for these reactions.The rate constant for the abstraction of a hydrogen atom by a methyl radical from dimethyl ether was found to be [Formula: see text]

The thermal dissociation and pyrolysis of ethane

1963 ◽  
Vol 275 (1361) ◽  
pp. 190-199 ◽  
Keyword(s):  
Free Radical ◽  
Thermal Dissociation ◽  
Experimental Results ◽  
Methane Formation ◽  
Methyl Radicals ◽  
Order Process ◽  
Radical Chain ◽  
Chain Decomposition ◽  
First Order ◽  
Kinetics Of

The kinetics of methane formation during the pyrolysis of ethane have been examined experimentally. It has been shown that under the conditions commonly used for the pyrolysis of hydrocarbons, the dissociation of ethane into methyl radicals is a first-order process of velocity constant log 10 k 1 = (17.45 ±0.82) - 91740 ±1400/2.303 RT (S -1 ) The kinetics of the free-radical chain decomposition of ethane are interpreted in the light of this and other experimental results.

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