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]

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 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 Reaction of Methyl Radicals with Neopentane

1973 ◽  
Vol 51 (15) ◽  
pp. 2415-2422 ◽  
Author(s):  
Philip D. Pacey
Keyword(s):  
Rate Constant ◽  
Flow Reactor ◽  
Arrhenius Plot ◽  
Reactor System ◽  
Methyl Radicals ◽  
Temperature Ranges ◽  
Initiation Reaction ◽  
Good Agreement

Neopentane was pyrolyzed in a flow reactor system at 793–953 K and 20–400 mm Hg. The rate constant for the initiation reaction,[Formula: see text]calculated from the observed C2H6 yield, was 1017.7±0.3 exp (−356 ± 6 kJ mol−1/RT)s−1, in good agreement with earlier determinations in other temperature ranges. The rate constant of the reaction,[Formula: see text]calculated from the observed CH4 and C2H6 yields, was 1010.5 ± 0.1 exp (−67 ± 2 kJ mol−1/RT) 1 mol−1 s−1, four to ten times faster than predicted on the basis of earlier work at 404–608 K. From 404–953 K, the Arrhenius plot for this reaction is strongly curved.

THE PYROLYSIS OF TRIMETHYLTHALLIUM

1965 ◽  
Vol 43 (7) ◽  
pp. 1961-1967 ◽  
Author(s):  
M. G. Jacko ◽  
S. J. W. Price
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Total Pressure ◽  
Flow System ◽  
Total Darkness ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Homogeneous Process ◽  
Carrier Flow ◽  
Reaction Proceeds

The pyrolysis of trimethylthallium has been studied in a toluene carrier flow system from 458 to 591 °K using total pressures from 5.6 to 33.0 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, and ethylbenzene formed and, in 21 runs, by direct thallium analysis. All preparative and kinetic work was carried out in total darkness where possible. A shielded 10 W lamp was used when some illumination was necessary.The decomposition is approximately 80% heterogeneous in an unconditioned vessel and 14–27% heterogeneous in a vessel pretreated with hot 50% HF for 10 min. The reaction proceeds by the simple consecutive release of three methyl radicals. The rate constant depends only slightly on the total pressure in the system so that the activation energy of the homogeneous process, 27.4 kcal/mole, may be equated to D[(CH3)2Tl—CH3].

Determination of the bond dissociation energy, D(CH3Hg—CH3), by the toluene carrier method

1969 ◽  
Vol 47 (6) ◽  
pp. 991-994 ◽  
Author(s):  
R. J. Kominar ◽  
S. J. Price
Keyword(s):  
Thermal Decomposition ◽  
Excellent Agreement ◽  
Rate Constant ◽  
Pressure Range ◽  
Arrhenius Equation ◽  
Flow System ◽  
Methyl Radicals ◽  
Exponential Factors ◽  
Pressure Independent

The thermal decomposition of Hg(CH3)2 has been studied in a toluene carrier flow system over the pressure range 4.5 to 323 mm at temperatures of 422 to 527 °C. The Arrhenius equation for the pressure independent region,[Formula: see text]is in excellent agreement with earlier work on the fully inhibited decomposition at lower temperatures. The region of fall off of the unimolecular rate constant is in agreement with a classical Kassel calculation using s = 16−18, but the rate of fall off requires the use of a curve with s = 3, displaced five log units to the left. This is consistent with the previous results for the dissociation of ethane into two methyl radicals and is further evidence of the inability of the classical Kassel equation to represent the behavior of systems with high pre-exponential factors.

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.

Reactions of free radicals with aromatic compounds in the gaseous phase. I. Kinetics of the reaction of methyl radicals with toluene

1964 ◽  
Vol 17 (12) ◽  
pp. 1329 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Flow System ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Benzyl Radical ◽  
Toluene Molecule ◽  
Benzyl Radicals ◽  
Butyl Peroxide ◽  
Kinetics Of

The kinetics of abstraction of hydrogen atoms from the methyl group of the toluene molecule by methyl radicals at 430-540�K have been determined. The methyl radicals were produced by pyrolysis of di-t-butyl peroxide in a stirred-flow system. The kinetics ,agree substantially with those obtained by previous authors using photolytic methods for generating the methyl radicals. At toluene and methyl-radical concentrations of about 5 x 10-7 and 10-11 mole cm-3 respectively the benzyl radicals resulting from the abstraction disappear almost entirely by combination with methyl radicals at the methylenic position. In this respect the benzyl radical behaves differently from the iso-electronic phenoxy radical, which previous work has shown to combine with a methyl radical mainly at ring positions. The investigation illustrates the application of stirred-flow technique to the study of the kinetics of free-radical reactions.

ChemInform Abstract: Comment: A Reevaluation of the Rate Constant for Abstraction of Hydrogen from Isobutane by Methyl Radicals

ChemInform ◽  
1990 ◽  
Vol 21 (33) ◽  
Author(s):  
H.-X. ZHANG ◽  
M. H. BACK
Keyword(s):  
Rate Constant ◽  
Methyl Radicals

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

1999 ◽  
Vol 14 (9) ◽  
pp. 3552-3558 ◽  
Author(s):  
P. Torri
Keyword(s):  
Activation Energy ◽  
Water Vapor ◽  
Oxidation Resistance ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Single Layer ◽  
Water Vapor Atmosphere ◽  
Oxidation Properties ◽  
Sputter Deposited ◽  
Sic Coatings

Oxidation of sputter-deposited nanocrystalline Mo–Si–N (MoSi2.2N2.5) coatings in oxygen–water vapor atmosphere has been studied in the temperature range 400–850 °C. In addition, the oxidation properties of nanolayered Mo–Si–N/SiC coatings at 700 °C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo–Si–N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 109 (1015 atoms/cm2)2/h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo–Si–N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.

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.

Sign in / Sign up

Export Citation Format

Share Document