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 A mixture of two organic compounds is decomposed, all the hydrogen in one of the compounds having been replaced by deuterium.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 The free radical polymerization of the vapours of certain vinyl derivatives

1946 ◽  
Vol 187 (1008) ◽  
pp. 37-53 ◽  
Keyword(s):  
Free Radical ◽  
Radical Polymerization ◽  
Vinyl Chloride ◽  
Free Radical Polymerization ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Kinetic Methods ◽  
Free Radical Mechanism ◽  
Vinyl Derivatives ◽  
Styrene Butadiene

The free radical polymerization of the vapours of vinyl chloride, acrylic nitrile, styrene, butadiene and methyl isopropenyl ketone has been investigated using methyl radicals from photo-decomposing acetone. Although all the reactions do not exhibit ideal behaviour it is possible by the application of kinetic methods to measure the ratio of the propagation to the termination coefficients for these polymerization reactions. In this way relative values of the quantitative tendency for a molecule to polymerize by a free radical mechanism can be computed.

Derivation of rate constants for steps in the free-radical chain decomposition of paraffins

1962 ◽  
Vol 268 (1332) ◽  
pp. 36-45 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Rate Constants ◽  
High Pressures ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Free Radical Mechanism ◽  
Standard Values

The Rice-Herzfeld free-radical mechanism for the thermal decomposition of saturated hydrocarbons, including both the uninhibited reaction and that partially inhibited by nitric oxide, involves the rate constants of various individual steps. If standard values are assumed for the rate constants of H -abstraction from n -pentane by methyl radicals, alkyl radical recombination, and addition of methyl to nitric oxide, then those of all the steps for a series of paraffins can be found. The method depends on measurements of the rate constant in the region where the chain reaction is of the first order, the inhibitory action of nitric oxide as a function of paraffin pressure, and the acceleration of paraffin decomposition rate produced by high pressures of nitric oxide. Values are derived for propane, three pentanes ( neo -, iso - and normal pentane) and three octanes ( normal octane, 2:3:4-trimethyl pentane and 2:2:4-trimethyl pentane), and the variations of the several rate constants with structure are discussed.

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.

Radiation Crosslinking of Rubber—Effect of Additives

1958 ◽  
Vol 31 (4) ◽  
pp. 737-746
Author(s):  
D. T. Turner
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Radiation Chemistry ◽  
High Energy ◽  
Radical Mechanism ◽  
Linear Polymers ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
Effect Of Additives ◽  
Free Radical Mechanism

Abstract Rubber is one of the linear polymers which may be crosslinked by high energy radiation. In this paper the effect of a range of additives on the cross-linking of rubber by pile and gamma radiation is reported. Many were found to retard crosslinking and this is of interest mechanistically and as an example of protection against high energy radiation. A major problem in radiation chemistry is the relative importance of ions, excited molecules, and free radicals. An ionic mechanism has been suggested for the crosslinking of polyethylene and both excitation transfer and free radical hypotheses of protection have been suggested in the radiolysis of polymethyl methacrylate. The adequacy of a free radical mechanism may be assessed by comparison of protective power and radical acceptance and in this work most of the additives were chosen because of their known, or reasonably inferred, reactivity towards free radicals and, in particular, of polyisoprenyl radicals.

THE DETECTION OF FREE RADICALS IN HYDROGEN ATOM REACTIONS WITH ORGANIC MOLECULES

1948 ◽  
Vol 26b (3) ◽  
pp. 343-355 ◽  
Author(s):  
G. M. Harris ◽  
A. W. Tickner
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Specific Activity ◽  
Reaction System ◽  
Radical Mechanism ◽  
Hydrogen Atoms ◽  
Experimental Conditions ◽  
Alkyl Radicals ◽  
Free Radical Mechanism ◽  
Positive Results

The Paneth–Rice free radical detection technique has been applied to the study of reactions of hydrogen atoms, produced by the discharge tube method, with two compounds, acetone and dimethyl mercury. Bismuth has been demonstrated to be a satisfactorily stable 'mirror metal' for the purpose, although some evidence was noted for the formation of a short-lived hydride of this metal under the adopted experimental conditions. A method has been devised for the preparation of radioactive bismuth mirrors of known specific activity, utilizing Bi210 ('Radium E'), obtained from uranium extraction residues, as the tracer. The hydrogen atom – acetone reaction system gave no evidence in the present work for the formerly postulated existence of free alkyl radicals. However, conclusive positive results were obtained in the case of the dimethyl mercury reaction. Studies in which the methane–ethane ratio in the products of the latter reaction was compared in presence and absence of the radical-sensitive mirror have further supported a previously proposed free radical mechanism.

THE REACTION OF 2-CYANO-2-PROPYL FREE RADICALS WITH OXYGEN: 2-CYANO-2-PROPYL HYDROPEROXIDE

1960 ◽  
Vol 38 (7) ◽  
pp. 1154-1157 ◽  
Author(s):  
M. Talât-Erben ◽  
Nevzat Önol
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Hydrogen Cyanide ◽  
Elevated Temperatures ◽  
Radical Mechanism ◽  
Acetone Cyanohydrin ◽  
Experimental Conditions ◽  
Polymerization Catalyst ◽  
Free Radical Mechanism ◽  
Induced Decomposition

The reaction with oxygen of cyanisopropyl free radicals generated by the polymerization catalyst 2,2′-azobisisobutyronitrile has been investigated. In xylene, or benzene, as solvent at 55° the products identified are: (1) a new compound, 2-cyano-2-propyl hydroperoxide; (2) acetone cyanohydrin; (3) hydrogen cyanide; (4) cyanogen; (5) acetone; (6) p-methyl benzaldehyde (in xylene only); and (7) tetramethylsuccinodinitrile. The hydroperoxide is surprisingly stable; its physical constants are: b.p. 37 °C at 1 mm Hg; m.p. −9 to −8°; [Formula: see text] 1.4138; d20 1.013 g/ml. In benzene under the same experimental conditions, only a very small amount of the hydroperoxide is obtained, the principal product being acetone cyanohydrin. A free-radical mechanism is proposed. The induced decomposition of the hydroperoxide, which is important in benzene, is almost completely inhibited in the presence of xylene. The new hydroperoxide can be used as a polymerization catalyst at moderately elevated temperatures.

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.

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