The reaction of free radicals with trichlorosilane

1967 ◽  
Vol 20 (8) ◽  
pp. 1545 ◽  
Author(s):  
TN Bell ◽  
BB Johnson
Keyword(s):  
Free Radicals ◽  
Quantitative Study ◽  
Rate Constant ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Experimental Conditions ◽  
Chlorine Atoms

Trifluoromethyl radicals generated from the photolysis of hexafluoroacetone abstract hydrogen atoms from trichlorosilane; the competitive abstraction of chlorine atoms does not occur under the experimental conditions. The rate of the abstraction ������� �����������������CF3 + SiHCl3 → CF3N + SiCl3 has been measured in comparison with the known rate for the recombination of trifluoromethyl radicals, to yield a rate constant, ������������������ k = 1012.13exp(-6850/RT) ml mole-1 sec-1 Methyl radicals similarly abstract hydrogen to yield methane. A quantitative study of this reaction proved impractical, due to complications using acetone as a radical source.

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 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.

Photolyse du méthyl-2-butène-1, du méthyl-3-butène-1 et du cis-pentène-2 à 174, 163 et 147 nm

1979 ◽  
Vol 57 (8) ◽  
pp. 863-869 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers ◽  
Sylvain Auclair
Keyword(s):  
Double Bond ◽  
Photon Energy ◽  
Rate Constant ◽  
Pressure Effect ◽  
Low Pressure ◽  
Decomposition Process ◽  
Fragmentation Process ◽  
Quantum Yields ◽  
Methyl Radicals ◽  
Hydrogen Atoms

Photolysis of 2-methyl-1-butene (M2B1), cis-2-pentene (CP2), and 3-methyl-1-butene (M3B1) has been systematically studied at 163 nm. Pressure effect has been measured at 147, 163, and 174 nm. The main fragmentation process of the photoexcited olefine is the C—C split of the bond located in position β relative to the double bond:[Formula: see text] α-Methallyl radicals obtained in the M3B1 and CP2 photolysis decompose partly at low pressure, giving rise to the formation of 1,3-butadiene and hydrogen atoms. β-Methallyl radicals decompose also at low pressure into allene and methyl radicals. Butadiene and allene quantum yields follow the Stern–Volmer law, and this allows us to determine the ratio of the rate constant of dissociation relative to the rate constant of stabilization, kd/ks, through collision of the α- and β-methallyl radicals. From these values, we conclude that the excess of photon energy is not statistically distributed into the fragments, and that the decomposition process follows one (or several) particular law(s).

Reactions of methyl radicals. I. Hydrogen abstraction from dimethyl sulphide

1976 ◽  
Vol 29 (7) ◽  
pp. 1483 ◽  
Author(s):  
NL Arthur ◽  
M Lee
Keyword(s):  
Free Radicals ◽  
Rate Constant ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Reverse Reaction ◽  
Thermochemical Data ◽  
Methyl Radicals ◽  
Dimethyl Sulphide ◽  
Temperature Range

Hydrogen abstraction from (CH3),S and CH3COCH3 by CH3 radicals CH3+CH3SCH3 → CH4+CH3SCH2 CH3 + CH3COCH3 → CH4 + CH3COCH2 has been studied in the temperature range 120-245�. The rate constants, based on the value of 1013.34cm3 mol-l s-1 for the recombination of CH3 radicals, are given by (k in cm3 mol-1 s-1, E in kJ mol-1, R = 0.008314 kJ K-1 mol-1): logk1 = (11.62 � 0.08) ? (38.35 � 0.68)/2.303RT logk3 = (11.61 � 0.05) ? (40.48 � 0.46)/2.303RT Combination of the results for (1) with thermochemical data gives a calculated value of Logk-1 = (11.8 -63.7/2.303RT for the rate constant of the reverse reaction. The results for CH3+(CH3)2S are compared with all of the available data for hydrogen abstraction by free radicals from both sulphur-containing compounds, and molecules of the type (CH3)xM.

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.

FREE RADICALS IN ORGANIC DECOMPOSITION REACTIONS: I. THE THERMAL DECOMPOSITION OF MIXTURES OF METHYL ETHER AND DEUTERO-ACETONE

1937 ◽  
Vol 15b (7) ◽  
pp. 295-304
Author(s):  
E. W. R. Steacie ◽  
W. A. Alexander
Keyword(s):  
Free Radicals ◽  
Methyl Ether ◽  
Experimental Error ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Decomposition Reactions ◽  
Free Radical Mechanism ◽  
Insight Into ◽  
Organic Decomposition

A new method of obtaining information concerning the participation of free radicals in decomposition reactions is described. A mixture of two organic compounds is decomposed, all the hydrogen in one of the compounds having been replaced by deuterium. By an examination of the distribution of deuterium among the products, it is possible to obtain considerable insight into the mechanism of the process.Mixtures of deutero-acetone and dimethyl ether have been decomposed at 590 °C. It is found that the hydrogen in the products is entirely "light" within the experimental error. This precludes the possibility that formaldehyde (which is the source of the hydrogen) decomposes by a free radical mechanism, HCHO = H + CHO, as otherwise reaction of hydrogen atoms with deutero-acetone would lead to the formation of HD.It is also concluded that it is unlikely that formaldehyde formed in the methyl ether decomposition is decomposed by sensitization from methyl radicals from the ether decomposition. If this were the case we would expect to have the reactions[Formula: see text]and again hydrogen atoms by reaction with deutero-acetone would yield HD.The method of investigation seems to have interesting possibilities and to be of wide applicability.

scholarly journals Dynamics of platelet-activating-factor release and uptake in a human neutrophil suspension

1991 ◽  
Vol 278 (2) ◽  
pp. 453-459 ◽  
Author(s):  
M Cluzel ◽  
C A Rohde ◽  
D W MacGlashan ◽  
B J Undem ◽  
F H Chilton
Keyword(s):  
Cellular Uptake ◽  
Rate Constant ◽  
Exponential Function ◽  
Human Neutrophil ◽  
Platelet Activating Factor ◽  
Mathematical Functions ◽  
Experimental Conditions ◽  
Zero Baseline ◽  
Factor Release

The present study has examined the dynamics of platelet-activating-factor (PAF) synthesis, release and uptake in order to understand better the trafficking of PAF between cells and medium. Initial experiments indicated that the amount of PAF found on the outside of the cell remained constant well after the synthesis from a precursor had apparently stopped, and in spite of a continued capacity of the cell to take up and catabolize PAF. These results suggested that PAF produced and stored within the cell is eventually released to the outside of the cell at a rate proportional to that of cellular uptake. In order to estimate the amount of PAF released from the cell, the processes of PAF release and uptake were modelled using simple mathematical functions. It was found that, under the experimental conditions used in this study, the uptake of PAF could be expressed as an exponential function tending to a non-zero baseline. Utilizing this rate constant for the uptake of PAF with the amount of PAF outside the cell, the amount of total PAF released from the cell was estimated. Data from the model suggested PAF was released in amounts 10-fold higher than could actually be measured over 30 min. In fact, the model predicted more PAF could be released from the cell than is synthesized, suggesting that a portion of the PAF which is released is taken up and then released again to the outside of the cell. The potential for PAF and/or its intermediates to be recycled was verified by demonstrating that a large proportion of exogenously provided 1-alkyl-2-lyso-sn-glycero-3-phosphocholine is taken up by the neutrophil, converted into PAF and then released again by the cell. These results suggest that PAF trafficking between the cell and medium is complex and involves many processes, which include synthesis, release, uptake, catabolism and recycling.

Electron transfer between ferrocene and hexacyanoferrate(III) across the water/1,2-dichloroethane interface

1988 ◽  
Vol 53 (5) ◽  
pp. 903-911 ◽  
Author(s):  
Josef Hanzlík ◽  
Jan Hovorka ◽  
Zdeněk Samec ◽  
Štefan Toma
Keyword(s):  
Electron Transfer ◽  
Aqueous Phase ◽  
Rate Constant ◽  
Potential Range ◽  
Ion Transfer ◽  
Potential Sweep ◽  
Experimental Conditions ◽  
Chemical Decomposition ◽  
Kinetics Of

Kinetics of electron transfer between ferrocene or its derivative (1,1'-diethyl- or 1,1'-distearoylferrocene) in dichloroethane and hexacyanoferrate(III) in water was studied by means of convolution potential sweep voltammetry. Within the accessible range of experimental conditions no effect of either the potential or concentrations of reactants on the rate constant of electron transfer from the organic to the aqueous phase (ko→w = 1 . 10-7 m4 mol-1 s-1) was observed. Electron transfer was shown to occur far from the potential range, in which the ferricenium ion transfer can take place. However, the reaction was complicated by the chemical decomposition of ferricenium in dichloroethane (k = 0·346 s-1).

Reactions of hydrogen atoms with hexafluoroacetone

1978 ◽  
Vol 56 (20) ◽  
pp. 2638-2645 ◽  
Author(s):  
D. W. Grattan ◽  
K. O. Kutschke
Keyword(s):  
Rate Constant ◽  
Cross Sections ◽  
The Other ◽  
Hydrogen Atoms ◽  
Kinetics Of

Attempts were made to study the kinetics of the reaction of atomic H with (CF3)2CO vapour (HFA). Atomic H was generated from H2 by mercury photosensitization in the presence of C2H4 and HFA but the system was complicated by the loss of C2H5 radicals by addition to HFA and the kinetic results were intractable. When atomic H was generated from C3H8, the kinetics again were obscured by some unidentified reaction(s) which became more important at higher [HFA]/[C3H8]. An estimate of the rate constant for the addition of H to HFA obtained at low [HFA]/[C3H8] yielded k9 = 8.5 × 105 l mol−1 s−1. Trifluoroacetaldehyde was identified with some reliability but many of the other heavier products formed in the H2 + HFA reaction could not be identified. Quenching cross-sections were determined for C2H4, C3H8, C4H10, and HFA relative to that for N2O.

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