The reaction of methyl radicals with neopentane in flow photolysis at 607–823 K

1984 ◽  
Vol 62 (6) ◽  
pp. 1203-1206 ◽  
Author(s):  
Hiroshi Furue ◽  
Kim C. Manthorne ◽  
Philip D. Pacey
Keyword(s):  
Heat Capacity ◽  
High Pressure ◽  
Arrhenius Plot ◽  
Flow System ◽  
Rate Coefficients ◽  
Methyl Radicals ◽  
Large Excess ◽  
Arrhenius Parameters ◽  
Temperature Range ◽  
Pressure Limit

Acetone was photolyzed in the presence of a large excess of neopentane in a flow system at total pressures between 7 and 150 Torr and at 607–823 K. For reactions[Formula: see text]and[Formula: see text]the quotient of rate coefficients, k12/k2, was calculated from CH4 and C2H6 yields and was extrapolated to the high pressure limit, k12/k2,x. Taking k2,x as 2.2 × 1010 L mol−1 s1, Arrhenius parameters for reaction [1] were found to be: log10A (L mol−1 s−1) = 10.0 ± 0.1, EA = 62( ± 2) kJ mol−1. In combination with data from the literature for the temperature range 365–953 K, the Arrhenius plot for k1/k2,x1/2 was strongly curved, with a heat capacity of activation of 71 ± 4 J K−1 mol−1.

scholarly journals The Pyrolysis of Tetramethyltin

1972 ◽  
Vol 50 (1) ◽  
pp. 50-54 ◽  
Author(s):  
R. P. Johnson ◽  
S. J. W. Price
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Flow System ◽  
Heterogeneous Reaction ◽  
Methyl Radicals ◽  
Product Analysis ◽  
First Order ◽  
Carrier Flow ◽  
Pressure Limit

The pyrolysis of tetramethyltin has been studied in a toluene carrier flow system from 803–941 °K using total pressures of 10.6 to 52.4 mm. Contact times varied from 0.49 to 13.8 s and the amount of decomposition from 1.35–98.7%. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, and ethylbenzene formed. No appreciable heterogeneous reaction was detected and the first order rates constants appear to have been determined at the high pressure limit. The quantity of undecomposed alkyl was also measured and was found to be in agreement with the product analysis if four methyl radicals are released for each molecule undergoing reaction.Least squares analysis gives[Formula: see text]with an estimated uncertainty in E of ± 1 kcal mol−1. The activation energy should be a good approximation to D[(CH3)3Sn—CH3].

Kinetic study of the thermal isomerization of fulvene

1981 ◽  
Vol 34 (2) ◽  
pp. 449 ◽  
Author(s):  
BJ Gaynor ◽  
RG Gilbert ◽  
KD King ◽  
PJ Harman
Keyword(s):  
High Pressure ◽  
Reaction Mechanism ◽  
Kinetic Study ◽  
Low Pressure ◽  
Thermal Isomerization ◽  
Marcus Theory ◽  
Rate Coefficients ◽  
Arrhenius Parameters ◽  
Temperature Range ◽  
Concerted Reaction

The thermal unimolecular isomerization of fulvene to benzene was studied by the technique of very low-pressure pyrolysis. The observed fall-off regime rate coefficients (obtained over the temperature range of c. 1050-1150 K) were fitted by using RRKM (Rice-Ramsperger-Kassel-Marcus) theory (assuming a concerted reaction mechanism) to give high-pressure Arrhenius parameters in the range E∞ = 268-285 kJ mol-1, log(A/s-1) = 13-14.

The reaction of methyl radicals with formaldehyde in dimethyl ether pyrolysis

1978 ◽  
Vol 56 (10) ◽  
pp. 1307-1310 ◽  
Author(s):  
Kim C. Manthorne ◽  
Philip D. Pacey
Keyword(s):  
High Pressure ◽  
Dimethyl Ether ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Flow System ◽  
Methyl Radicals ◽  
Limiting Values

Dimethyl ether was pyrolyzed in a flow System at 788, 856, and 935 K and 38–401 Torr. Measurement of the yields of CH4 and C2H6 and of either H2 or CO enabled calculation of high pressure limiting values of the rate constant quotient k9k6−1/2, where reaction 9 is[Formula: see text]and reaction 6 is the recombination of two methyl radicals. Including literature data from 357–1005 K, the Arrhenius plot for this quotient is a curve.

The pyrolysis of trimethylarsine

1970 ◽  
Vol 48 (20) ◽  
pp. 3209-3212 ◽  
Author(s):  
S. J. W. Price ◽  
J. P. Richard
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Rate Constants ◽  
Flow System ◽  
Heterogeneous Reaction ◽  
Methyl Radicals ◽  
Product Analysis ◽  
First Order ◽  
Carrier Flow ◽  
Pressure Limit

The pyrolysis of trimethylarsine has been studied in a toluene carrier flow system from 764 to 858 °K using total pressures from 6.35 to 35.5 mm. Contact times varied from 0.9 to 3.7 s and the amount of decomposition, from 1.2 to 73 %. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, and ethylbenzene formed. No heterogeneous reaction was detected and the first order rate constants appear to have been determined at approximately the high pressure limit. In seven runs the undecomposed alkyl was also measured. The quantity found was in agreement with the product analysis if three methyl radicals are released for each molecule undergoing reaction.Least squares analysis of the results gives[Formula: see text]The activation energy should be a good approximation to D[(CH3)2As—CH3]. The product analysis and the values of k4/k51/2 are consistent with the simple consecutive release of three methyl radicals but thermodynamic and kinetic considerations may preclude this possibility.

The Initial Stages of the Pyrolysis of Dimethyl Ether

1975 ◽  
Vol 53 (18) ◽  
pp. 2742-2747 ◽  
Author(s):  
Philip D. Pacey
Keyword(s):  
Dimethyl Ether ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Flow System ◽  
Order Rate Constant ◽  
Chain Termination ◽  
Rate Coefficients ◽  
First Order ◽  
Order Rate ◽  
Initiation Reaction

Dimethyl ether was pyrolized in a flow system at 782–936 K and 25–395 Torr with conversions from 0.2–10%. Product analyses were consistent with a simple Rice–Herzfeld mechanism with most chain termination by the recombination of CH3 radicals. The rate coefficients for both the initiation and termination reactions appeared to be slightly pressure dependent. The first-order rate constant for the initiation reaction,[Formula: see text]calculated from the rate of C2H6 formation, was k1 = 1015.0±0.5exp (−318 ± 8 kJ mol−1/RT) s−1, corresponding to ΔHf0(CH3O) = −5 ± 8 kJmol−1. Comparison of CH4 and C2H6 yields enabled calculation of the rate constant for the reaction of CH3 with dimethyl ether. From 373−936 K, the Arrhenius plot for this reaction is a curve.

The Rate-Constant for the Recombination of Methyl Radicals

1986 ◽  
Vol 39 (8) ◽  
pp. 1257 ◽  
Author(s):  
NL Arthur ◽  
JC Biordi
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Rate Constant ◽  
Rate Constants ◽  
The Other ◽  
Methyl Radicals ◽  
Experimental Conditions ◽  
Temperature Range ◽  
Best Value ◽  
Limiting Value

Rate constants for the recombination of CH3 radicals have been measured by means of the rotating sector technique in the temperature range 373- 463 K, and at a pressure of 30 Torr . CH3 radicals were produced by the photolysis of acetone, and the experimental data were fitted to sector curves generated from Shepp's theory. The results give kb = (2.81�0.22)×1013 cm3 mol-1 s-1, which, under the chosen experimental conditions, is close to its high-pressure limiting value. A comparison is made with the other values of the rate constant reported in the literature, and a best value is suggested.

scholarly journals Pressure-Dependent Kinetics of Peroxy Radicals Formed in Isobutanol Combustion

2020 ◽  
Author(s):  
Mark Goldman ◽  
Nathan Wa-Wai Yee ◽  
Jesse Kroll ◽  
William H. Green
Keyword(s):  
High Pressure ◽  
Reaction Rates ◽  
State Theory ◽  
Rate Coefficients ◽  
Quantum Calculations ◽  
Peroxy Radicals ◽  
Alkoxy Radical ◽  
Pressure Limit ◽  
Combustion Properties ◽  
Quantum Chemistry Calculations

Bio-derived isobutanol has been approved as a gasoline additive in the U.S., but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy leading to better estimation of isobutanol’s combustion properties and its environmental impacts. This work examines 47 molecules and 38 reactions involved in the first oxygen addition to isobutanol’s three alkyl radicals located α, β, and γ to the hydroxide. Quantum calculations are mostly done at CCSD(T)-F12/cc-pVTZ-F12//B3LYP/CBSB7, with 1-D hindered rotor corrections obtained at B3LYP/6-31G(d). The resulting potential energy surfaces are the most comprehensive isobutanol peroxy networks published to date. Canonical transition state theory and a 1-D microcanonical master equation are used to derive high-pressure-limit and pressure-dependent rate coefficients, respectively. At all conditions studied, the recombination of α- isobutanol radical with O2 forms HO2 and isobutanal. The recombination of γ-isobutanol radical with O2 forms a stabilized hydroperoxy alkyl radical below 400 K, water and an alkoxy radical at higher temperatures, and HO2 and an alkene above 1200 K. The recombination of β-isobutanol radical with O2 results in a mixture of products between 700-1100 K, forming acetone, formaldehyde and OH at lower temperatures and forming HO2 and alkenes at higher temperatures. The barrier heights, high-pressure-limit rates, and pressure-dependent kinetics generally agree with the results from previous quantum chemistry calculations. Six reaction rates in this work deviate by over three orders of magnitude from kinetics in detailed models of isobutanol combustion, suggesting the rates calculated here can help improve modeling of isobutanol combustion and its environmental fate.

The Reaction of Methyl Radicals with Molecular Hydrogen

1974 ◽  
Vol 52 (21) ◽  
pp. 3665-3670 ◽  
Author(s):  
Peter C. Kobrinsky ◽  
Philip D. Pacey
Keyword(s):  
Rate Constant ◽  
Molecular Hydrogen ◽  
Arrhenius Plot ◽  
Flow System ◽  
Methyl Radicals

Mixtures of neopentane and hydrogen were pyrolyzed in a flow system at 826–968 K and 27–400 mm Hg. Measurements of the yields of CH4 and C2H6 at various conditions enabled calculation of the rate constant for[Formula: see text]at 926 and 829 K. The Arrhenius plot of these and earlier measurements from 372 to 1370 K is a curve, which can be represented by[Formula: see text]

Reactions of methyl radicals. V. Hydrogen abstraction from hydrogen sulfide

1983 ◽  
Vol 36 (11) ◽  
pp. 2195 ◽  
Author(s):  
H Arican ◽  
NL Arthur
Keyword(s):  
Hydrogen Sulfide ◽  
Rate Constant ◽  
Hydrogen Abstraction ◽  
Methyl Radicals ◽  
Arrhenius Parameters ◽  
Temperature Range

Hydrogen abstraction from H2S by CH3 radicals, produced by the photolysis of azomethane, has been studied in the temperature range 334-432 K. The rate constant, based on the value 1013.34 cm3 mol-1 s-1 for the recombination of CH3 radicals, is given by log k4 = (11.00 � 0.01) - (8760 � 80)/19.145T where k4 is in cm3 mol-1 s-1 and E is in J mol-1. The previous data reported for this reaction are discussed and best values for its Arrhenius parameters are recommended. The results indicate that CH3 radicals react faster than CF3 radicals with H2S; this confirms the importance of polar effects in the hydrogen abstraction reactions of CF3 radicals.

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