Abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by methyl radicals and chlorine atoms: photochlorination of 1-methylbicyclo[2.1.1]hexane

1969 ◽  
Vol 47 (10) ◽  
pp. 1627-1631 ◽  
Author(s):  
R. Srinivasan ◽  
F. I. Sonntag
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Methyl Radicals ◽  
Absolute Rate ◽  
Methyl Radical ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Chlorine Atoms ◽  
Exponential Factor ◽  
Highly Strained

Photolysis of acetone has been used as a source of methyl radicals to study the abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by methyl radicals. The reaction was found to have an activation energy of 10.3 kcal/mole and a pre-exponential factor that is typical of other abstraction reactions. The absolute rate of abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by chlorine atoms at room temperature was measured to be 8.1 × 1010 l mole−1 s−1. The photochlorination of 1-methylbicyclo-[2.1.1]hexane in solution gave both the 1-chloromethyl and 2- or 3-chloro-1-methylbicyclohexanes. The relative rates of attack at the methyl and the 2- or 3- position were determined to be 1:2.1. It is pointed out that the rate parameters for the abstraction of an H atom from bicyclo[2.1.1]hexane by a methyl radical are slower than for cyclopentane, as would be expected for a highly strained hydrocarbon, whereas the abstraction by chlorine is slightly faster than the rate for cyclopentane.

THE REACTION OF METHYL RADICALS WITH FORMALDEHYDE

1959 ◽  
Vol 37 (9) ◽  
pp. 1462-1468 ◽  
Author(s):  
A. R. Blake ◽  
K. O. Kutschke
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Addition Reactions ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
A Value ◽  
Abstraction Reaction ◽  
Butyl Peroxide

The pyrolysis of di-t-butyl peroxide has been reinvestigated and used as a source of methyl radicals to study the abstraction reaction between methyl radicals and formaldehyde. At low [HCHO]/[peroxide] ratios the system was simple enough for kinetic analysis, and a value of 6.6 kcal/mole was obtained for the activation energy. At higher [HCHO]/[peroxide] ratios the system became very complicated, possibly due to the increased importance of addition reactions.

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

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.

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 PHOTO-OXIDATION OF AZOMETHANE

1955 ◽  
Vol 33 (3) ◽  
pp. 496-506 ◽  
Author(s):  
G. R. Hoey ◽  
K. O. Kutschke
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Room Temperature ◽  
Major Product ◽  
Steric Factor ◽  
Primary Process ◽  
Methyl Radicals ◽  
Low Oxygen ◽  
Secondary Product ◽  
Photo Oxidation

The photo-oxidation of azomethane has been studied at low oxygen pressures (0.02 to 1 mm.) in the temperature range ca. 25 °C. to 161 °C. The primary process in the normal photolysis of azomethane is essentially unaffected by the presence of oxygen. Carbon monoxide is probably a secondary product of the oxidation of methyl radicals. Carbon dioxide formation is quite small, and therefore neither methyl radicals nor CH3N=N—CH2 radicals are oxidized appreciably to carbon dioxide. Nitrous oxide, which is a major product of the oxidation, is most likely formed from the oxidation of CH3N=NCH2 radicals. The suggested mechanism of N2O formation is:[Formula: see text] The reaction of methyl radicals with oxygen was found to proceed with a negligible activation energy and a steric factor of the order of 10−2. Evidence for the occurrence of the reactions[Formula: see text]at room temperature was obtained.

THE REACTION OF ACTIVE NITROGEN WITH ETHANOL

1965 ◽  
Vol 43 (4) ◽  
pp. 935-939 ◽  
Author(s):  
P. A. Gartaganis
Keyword(s):  
Flow System ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Active Nitrogen ◽  
Condensed Discharge ◽  
Preliminary Study ◽  
Fast Flow ◽  
Ethyl Radicals ◽  
Water Hydrogen

The reaction of active nitrogen with ethanol has been investigated in the range 300 to 593 °K using a modified condensed-discharge Wood–Bonhoeffer fast-flow system. The only condensable products found in appreciable amounts were hydrogen cyanide and water. Hydrogen was the main noncondensable product. A very small amount of acetaldehyde was also formed along with traces of ethane, ethylene, methane, acetonitrile, cyanogen, and probably carbon monoxide. The overall activation energy is 3.4 kcal/mole. It is postulated that the mechanism consists of the formation of two fragments NC2H5 and OH, from which the condensable products result as follows:[Formula: see text]A number of products found in trace quantities are produced by concomitant reactions of the hydrogen atoms with methyl radicals, and with ethanol as well as by disproportionation of ethyl radicals to produce ethane and ethylene. A preliminary study of the reaction of active nitrogen with isopropanol indicated that the energy of activation is in line with the energies of activation of methanol and ethanol.

THE REACTION OF HYDROGEN ATOMS WITH METHYL CYANIDE

1955 ◽  
Vol 33 (12) ◽  
pp. 1814-1818 ◽  
Author(s):  
W. Forst ◽  
C. A. Winkler
Keyword(s):  
Discharge Tube ◽  
Hydrogen Cyanide ◽  
Main Product ◽  
Initial Step ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Methyl Cyanide ◽  
Secondary Reactions

Hydrogen atoms produced in a discharge tube were found to react with methyl cyanide to produce hydrogen cyanide as the main product, together with smaller amounts of methane and ethane. The proposed mechanism involves the formation of hydrogen cyanide and a methyl radical in the initial step; methane and ethane are attributed to secondary reactions of the methyl radicals.

Primary process(es) in the mercury-photosensitized decomposition of dimethyl ether at 2537 Å

1968 ◽  
Vol 46 (16) ◽  
pp. 2693-2697 ◽  
Author(s):  
R. Payette ◽  
M. Bertrand ◽  
Y. Rousseau
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Light Intensity ◽  
Dimethyl Ether ◽  
Molecular Hydrogen ◽  
Room Temperature ◽  
Primary Process ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Radical Recombination

The mercury-photosensitized decomposition of dimethyl ether has been studied at room temperature and at pressures ranging from 10 to 200 Torr.The formation of an excited dimethyl ether (DME) molecule has been verified by following the rates of formation of methane, ethane, and carbon monoxide with various ether pressures.The study of the variation of the quantum yield of molecular hydrogen formation with absorbed light intensity at high ether pressures has shown that the primary process involves the dissociation of ether molecules into hydrogen atoms and methoxy methyl radicals:[Formula: see text]The results presented in this paper indicate that the excited DME molecule can originate in a radical recombination between hydrogen atoms and methoxy methyl radicals.

PHOTOSENSITIZED REACTIONS OF CARBON TETRAFLUORIDE

1950 ◽  
Vol 28b (5) ◽  
pp. 173-181 ◽  
Author(s):  
J. R. Dacey ◽  
J. W. Hodgins
Keyword(s):  
Activation Energy ◽  
Quantum Efficiency ◽  
Room Temperature ◽  
Hydrogen Atoms ◽  
Solid Product ◽  
Carbon Tetrafluoride ◽  
Measurable Rate

Hg (63P1) at room temperature and at 300 °C. and Hg (61P1) at room temperature fail to react with carbon tetrafluoride at a measurable rate. Xe (3P1) causes carbon tetrafluoride to decompose with a quantum efficiency of about unity to yield fluorine and an unidentified solid product. It is concluded that the energy necessary to break the first C–F bond m CF4 is more than 154 and less than 194 kcal. per mole. Hydrogen atoms produced from Hg (63P1) at room temperature and at 300 °C. and from Hg (61P1) at room temperature do not react with carbon tetrafluoride. It is concluded from this that the activation energy of the reaction CF4 + H → CF3 + HF is not less than 14 kcal. per mole.

THE VAPOR PHASE PHOTOLYSIS OF HEXAFLUOROACETONE IN THE PRESENCE OF METHANE AND ETHANE

1955 ◽  
Vol 33 (5) ◽  
pp. 743-749 ◽  
Author(s):  
P. B. Ayscough ◽  
J. C. Polanyi ◽  
E. W. R. Steacie
Keyword(s):  
Activation Energy ◽  
Vapor Phase ◽  
Activation Energies ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Photolytic Decomposition

The photolytic decomposition of hexafluoroacetone by light of wavelength 3130 Å has been used to produce trifluoromethyl radicals for a study of their reactions with methane and ethane. It has been shown that these radicals abstract hydrogen with greater facility than do methyl radicals. The activation energies for the two reactions[Formula: see text]and[Formula: see text]are found to be 10.3 ± 0.5 kcal./mole and 7.5 ±0.5 kcal./mole respectively, if one can assume zero activation energy for the recombination of trifluoromethyl radicals.

Sign in / Sign up

Export Citation Format

Share Document