Absolute rate constants for hydrocarbon oxidation. XI. The reactions of tertiary peroxy radicals

1968 ◽  
Vol 46 (16) ◽  
pp. 2655-2660 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Chain Termination ◽  
Hydrogen Atom Abstraction ◽  
Hydrocarbon Oxidation ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Alkoxy Radical ◽  
Oxygen Chain ◽  
The Stability

Rate constants have been measured for the chain-terminating self-reactions of six tertiary peroxy radicals. The rate constants vary from ~ 1 × 103 M−1 s−1 for t-butylperoxy to ~ 6 × 104 M−1 s−1 for 1,1-diphenylethylperoxy radicals. It is suggested that the variation in the rate constants may be related to differences in the stability of the alkoxy radical products of tetroxide decomposition.Rate constants for hydrogen atom abstraction from aralkanes by tertiary peroxy radicals do not seem to be significantly affected by the structure of the attacking radical.In solution the triphenylmethylperoxy radical probably exists in equilibrium with the triphenylmethyl radical and oxygen. Chain termination in oxidations involving the triphenylmethylperoxy radical as the chain carrier occurs by the reaction of this radical with a triphenylmethyl radical.

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. XVII. The oxidation of some cyclic ethers

1969 ◽  
Vol 47 (20) ◽  
pp. 3809-3815 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Transfer Rate ◽  
Chain Transfer ◽  
Hydrogen Atom Abstraction ◽  
Cyclic Ethers ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Termination Rate

The propagation and termination rate constants have been determined for the autoxidation of 1,4-dioxan, tetrahydropyran, tetrahydrofuran, 2,5-dimethyltetrahydrofuran, and phthalan. The rate constants for α-hydrogen atom abstraction from some of the ethers by the tetralylperoxy radical and from tetralin by some ether peroxy radicals have been measured and compared. The chain transfer rate constants have been estimated for the reaction of the cumylperoxy radical with α-hydroperoxytetrahydrofuran, α-hydroperoxytetrahydropyran, and α-ethoxyethyl hydroperoxide.

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: IV. TETRALIN, CYCLOHEXENE, DIPHENYLMETHANE, ETHYLBENZENE, AND ALLYLBENZENE

1966 ◽  
Vol 44 (10) ◽  
pp. 1119-1130 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Chain Termination ◽  
Steric Effects ◽  
Hydrogen Atom Abstraction ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Oxidation Method ◽  
Oxidation Rates ◽  
Effect Of Solvents

Absolute rate constants have been measured for the autoxidation of five hydrocarbons under a variety of conditions. The propagation (kp) and termination (kt) rate constants at 30 °C (in l mole−1 s−1) are: tetralin in chlorobenzene 6.3 and 3.8 × 106 respectively, cyclohexene in chlorobenzene 6.1 and 2.8 × 106, diphenylmethane 4.8 and 8.0 × 107, ethylbenzene 0.11 and 2.0 × 107, and allylbenzene 10 and 2.2 × 108. Measurements on tetralin, α-methylstyrene, and allylbenzene in different solvents indicate that the effect of solvents on oxidation rates is mainly connected with changes in the rate of termination rather than propagation. Experiments with α,α-d2-diphenylmethane gave isotope effects kH/kD ~5.1 for kp and ~1.4 for kt. The rate constant for hydrogen atom abstraction from 2,6-di-t-butyl-4-methylphenol by peroxy radicals decreases in the order expected if steric effects are important, i.e., primary peroxy > secondary peroxy > tertiary peroxy radical.The co-oxidation method of estimating chain termination constants is criticized on the grounds that it can only be used to distinguish the fairly large changes in kt commonly encountered between hydrocarbons giving tertiary peroxy radicals and those giving secondary or primary radicals.The effect of hydrocarbon structure on bimolecular chain termination rate constants is reviewed. There is a gradation in kt from ~2 × 108] mole−1 s−1 for primary peroxy radicals, through the range 8 × 107 to 1 × 106 for secondary radicals, to the range from 3 × 105 to 3 × 102 for tertiary peroxy radicals.

Absolute rate constants for hydrocarbon oxidation. VIII. The reactions of cumylperoxy radicals

1968 ◽  
Vol 46 (6) ◽  
pp. 1017-1022 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold ◽  
M. Symonds
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Hydrogen Abstraction ◽  
Cumene Hydroperoxide ◽  
Hydrogen Atom Abstraction ◽  
Hydrocarbon Oxidation ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Substituent Constants ◽  
Deuterium Isotope Effects

Absolute rate constants have been measured for the reactions of cumylperoxy radicals with a number of hydrocarbons. The cumylperoxy radicals were produced from cumene hydroperoxide. Sufficient hydroperoxide was present to ensure that only cumylperoxy radicals were involved in the rate-determining propagation reaction.Primary and secondary deuterium isotope effects have been measured for propagation and termination in the oxidation of cumene. The rate of hydrogen atom abstraction from ring-substituted cumenes by cumylperoxy radicals can be correlated by the Hammett equation using σ+ substituent constants, ρ = −0.29. Primary and secondary peroxy radicals are about 3–5 times more reactive in hydrogen abstraction than tertiary peroxy radicals.

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. 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.

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