Absolute rate constants for hydrocarbon autoxidation. XIX. Oxidation of some α-substituted toluenes

1970 ◽  
Vol 48 (14) ◽  
pp. 2165-2172 ◽  
Author(s):  
J. A. Howard ◽  
S. Korcek
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Bromine Atom ◽  
Peroxy Radical ◽  
Phenyl Radical ◽  
Absolute Rate ◽  
Termination Rate ◽  
Substituted Toluenes

Absolute propagation and termination rate constants have been measured for the liquid phase autoxidation of some α-substituted toluenes at 30 °C. Rate constants for reaction of α-substituted toluenes with their own peroxy radical and with the t-butylperoxy radical have been compared. It would appear that the reactivity of an α-substituted benzylperoxy radical depends on the nature of the α-substituent.Reactivities of α-substituted toluenes towards the t-butylperoxy radical, the bromine atom, and the phenyl radical have been compared.

Absolute Rate Constants for Hydrocarbon Autoxidation. XXII. The Autoxidation of some Vinyl Compounds

1972 ◽  
Vol 50 (14) ◽  
pp. 2298-2304 ◽  
Author(s):  
J. A. Howard
Keyword(s):  
Rate Constants ◽  
Addition Reaction ◽  
Peroxy Radical ◽  
Stabilization Energy ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Termination Rate ◽  
Vinyl Compound ◽  
Rate Constants For Addition

Absolute propagation and termination rate constants have been determined for the autoxidation of some vinyl compounds at 30°. Rates of propagation depend on the structure of both the peroxy radical and the vinyl compound. The reactivity of peroxy radicals towards addition increases as the electron-withdrawing capacity of the α-substituent increases. Rate constants for addition of t-butylperoxy radicals to vinyl compounds, [Formula: see text] fit the equation[Formula: see text]where Es is the estimated stabilization energy of the β-peroxyalkyl radical (in kcal/mol) formed in the addition reaction.

Absolute Rate Constants for Hydrocarbon Autoxidation. Part XX. Oxidation of Some Organic Sulfides

1971 ◽  
Vol 49 (12) ◽  
pp. 2178-2182 ◽  
Author(s):  
J. A. Howard ◽  
S. Korcek
Keyword(s):  
Liquid Phase ◽  
Hydrogen Atom ◽  
Rate Constants ◽  
Hydrogen Atom Abstraction ◽  
Absolute Rate ◽  
Organic Sulfides

Absolute rate constants for the liquid phase autoxidation of some organic sulfides at 30 °C have been measured. The reactivities of organic sulfides towards t-butylperoxy radicals are equal to or somewhat less than the reactivities of structurally analogous ethers. The α-alkylthiylalkylperoxy radicals appear to be about 3–5 times more reactive in hydrogen atom abstraction than the α-alkoxyalkylperoxy radicals.

Absolute rate constants for hydrocarbon autoxidation. VI. Alkyl aromatic and olefinic hydrocarbons

1967 ◽  
Vol 45 (8) ◽  
pp. 793-802 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Peroxy Radical ◽  
Electron System ◽  
Chain Termination ◽  
The Self ◽  
Hydrogen Atom Abstraction ◽  
Peroxy Radicals ◽  
Absolute Rate

Absolute rate constants have been measured for the autoxidation of a large number of hydrocarbons at 30 °C. The chain-propagating and chain-terminating rate constants depend on the structure of the hydrocarbon and also on the structure of the chain-carrying peroxy radical. With certain notable exceptions which are mainly due to steric hindrance, the rate constants for hydrogen-atom abstraction increase in the order primary < secondary < tertiary; and, for compounds losing a secondary hydrogen atom, the rate constants increase in the order unactivated < acyclic activated by a single π-electron system < cyclic activated by a single Π-system < acyclic activated by two π-systems < cyclic activated by two π-systems. The rate constants for chain termination by the self-reaction of two peroxy radicals generally increase in the order tertiary peroxy radicals < acyclic allylic secondary  [Formula: see text] cyclic secondary  [Formula: see text] acyclic benzylic secondary < primary peroxy radicals < hydroperoxy radicals.

Absolute rate constants for hydrocarbon autoxidation. 25. Rate constants for hydrogen atom abstraction from alkanes by the tert-butylperoxy radical

1978 ◽  
Vol 56 (24) ◽  
pp. 3047-3053 ◽  
Author(s):  
J. H. B. Chenier ◽  
S. B. Tong ◽  
J. A. Howard
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Kinetic Isotope Effect ◽  
Peroxy Radical ◽  
Hydrogen Atom Abstraction ◽  
Labile Hydrogen ◽  
Absolute Rate ◽  
Steric Strain ◽  
Kinetic Isotope ◽  
Tert Butyl Hydroperoxide

Rate constants for abstraction of secondary and tertiary hydrogens from structurally different alkanes by the tert-butylperoxy radical in solution at 30 °C have been determined by competitive experiments in the presence of tert-butyl hydroperoxide. Rate constants fall in the range 1 × 10−4to 9 × 10−4and 1 × 10−3–2 × 10−2 M−1 s−1 for secondary and tertiary aliphatic C—H bonds, respectively. The most reactive secondary hydrogen is, therefore, almost as reactive as the least reactive tertiary hydrogen. Differences in reactivity within a type of aliphatic C—H bond are governed by differences in steric hindrance to attack by the peroxy radical and by relief of steric strain upon removal of the labile hydrogen. Rate constants for reaction of perdeuterated methylcyclohexane and 3-methylpentane are much smaller than the values calculated from the maximum primary kinetic isotope effect for this reaction.

Absolute rate constants for hydrocarbon autoxidation. XVIII. Oxidation of some acyclic ethers

1970 ◽  
Vol 48 (6) ◽  
pp. 873-880 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Propagation Rate ◽  
Phenyl Ether ◽  
Isopropyl Ether ◽  
Benzyl Ether ◽  
Absolute Rate ◽  
Butyl Ether ◽  
Termination Rate ◽  
Benzyl Phenyl Ether

Propagation and termination rate constants have been measured for autoxidation of benzyl phenyl ether, benzyl-t-butyl ether, isopropyl ether, and benzyl ether. In the case of isopropyl ether and benzyl ether, estimates have been made of inter- and intramolecular propagation rate constants. Reactivities of acyclic ethers towards the t-butylperoxy radical have been determined. Rate constants for autoxidation of cyclic and acylic ethers have been summarized and compared.

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: II. DEUTERO STYRENES AND RING-SUBSTITUTED STYRENES

1965 ◽  
Vol 43 (10) ◽  
pp. 2737-2743 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Peroxy Radical ◽  
Propagation Rate ◽  
Chain Termination ◽  
Absolute Rate ◽  
First Order ◽  
Oxidation Rates ◽  
Deuterium Substitution ◽  
Termination Process

The effect of deuterium substitution on the absolute rate constants for the bimolecular chain termination process in the oxidation of styrene indicates that the α-hydrogen is abstracted in this reaction. The first order chain termination process is suppressed both by deuteration of styrene at the α-position and by the addition of heavy water. A possible mechanism for this termination is proposed. There appear to be small secondary deuterium isotope effects in the propagation reaction.The overall oxidation rates and the propagation rate constants are increased by the addition to the aromatic ring of both electron-attracting and electron-releasing substituents. This is attributed in the former case to the increased stability of the resulting styryl radicals and in the latter case to the increased stability of a dipolar transition state. In hydrogen atom abstraction from 2,6-di-t-butyl-4-methylphenol, the peroxy radical from 3-chlorostyrene is more reactive than that from styrene which, in turn, is more reactive than the peroxy radical from 4-methoxy-styrene.

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