ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. α-METHYLSTYRENE, β-METHYLSTYRENE, AND INDENE

1966 ◽  
Vol 44 (10) ◽  
pp. 1113-1118 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
Propagation Rate ◽  
Absolute Rate ◽  
Order Process ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Process Rate Constant ◽  
Propagation Rate Constant

Absolute rate constants for the copolymerization of α-methylstyrene and oxygen have been measured from 13 to 50 °C. The propagation and termination rate constants can be represented by[Formula: see text]Experiments with 2,6-di-t-butyl-4-methylphenol at 65 °C have shown that C6H5C(CH3):CH2 and C6H5C(CD3):CD2 have the same propagation rate constant but that chain termination involves a deuterium isotope effect (kt)H/(kt)D ≈ 1.5.Absolute rate constants for the copolymerization of oxygen with β-methylstyrene and with indene at 30 °C showed that a significant fraction of the oxidation chains were terminated by a kinetically first order process (rate constant kx). The rate constants for β-methylstyrene and indene at 30 °C are kp = 51 and 142 l mole−1 s−1, kt = 1.6 × 107 and 2.5 × 107 l mole−1 s−1, and kx = 0.61 and 1.2 s−1, respectively. The propagation rate constant for indene can be separated into a rate constant for the copolymerization with oxygen (kadd = 128 l mole−1 s−1) and a rate constant for hydrogen atom abstraction (kabstr = 14 l mole−1 s−1). In the presence of heavy water the first order process for indene had a deuterium isotope effect (kx)/(kx)D2O ≈ 3.

Absolute rate constants for hydrocarbon autoxidation. XV. The induced decomposition of some t-hydroperoxides

1969 ◽  
Vol 47 (20) ◽  
pp. 3797-3801 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
The Self ◽  
Absolute Rate ◽  
Alkoxy Radical ◽  
Deuterium Isotope Effect ◽  
Alkoxy Radicals ◽  
Induced Decomposition ◽  
Alkylperoxy Radicals

The radical induced decomposition of several t-hydroperoxides at 30° has been studied. In the self reaction of t-alkylperoxy radicals the ratio of the rates of alkoxy radical diffusion from the cage to combination in the cage is essentially independent of the size of the t-alkyl group.The rate constant for abstraction from hydroperoxides of the hydroperoxidic hydrogen by alkoxy radicals is about 4 × 106 M−1 s−1 at 30°. This reaction has a deuterium isotope effect, kH/kD ≈ 5.The 1,1-diphenylethoxy radical undergoes a 1,2-phenyl shift to yield the 1-phenyl-1-phenoxyethyl radical more rapidly that it undergoes β-scission.

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.

Quantitative studies of the autoxidation of linoleate monomers sequestered in phosphatidylcholine bilayers. Absolute rate constants in bilayers

1985 ◽  
Vol 63 (10) ◽  
pp. 2633-2638 ◽  
Author(s):  
Lawrence Ross Coates Barclay ◽  
Steven Jeffrey Locke ◽  
Joseph Mark MacNeil ◽  
Joann Vankessel
Keyword(s):  
Linoleic Acid ◽  
Methyl Linoleate ◽  
Rate Constant ◽  
Rate Constants ◽  
Homogeneous Solution ◽  
Propagation Rate ◽  
Water Soluble ◽  
Peroxyl Radicals ◽  
Absolute Rate ◽  
Hydrophobic Region

The kinetics of autoxidation of linoleic acid in dimyristoylphosphatidylcholine (DMPC) bilayers were studied at 30 °C and pH 7 under 760 Torr O2. Reactions were initiated using either the lipid-soluble di-tert-butylhyponitrite (DBHN) or water-soluble azobis(2-amidinopropane)•HCl (ABAP). Rates of chain initiation, Ri, were measured with a lipid-soluble antioxidant, a-tocopherol, or a water-soluble one, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). The slightly higher oxidizability obtained [Formula: see text] compared to methyl linoleate in chlorobenzene [Formula: see text] is attributed to a moderate polar solvent effect on ionized linoleate near the bilayer surface. A low initiator efficiency, e = 0.0895 for DBHN in DMPC, is attributed to the cage effect in the bilayer of high microviscosity. Similar autoxidation experiments on methyl linoleate in DMPC bilayers gave a lower oxidizability [Formula: see text], indicating that the ester is sequestered deeper in the hydrophobic region of DMPC than is ionized linoleate. Some absolute rate constants are determined using the rotating sector technique for linoleic acid in 0.50 M SDS micelles, and egg lecithin and dilinoleoylphosphatidylcholine (DLPC) bilayers. A hundredfold decrease in the termination rate constant, 2kt for DLPC bilayer compared to homogeneous solution is attributed to chain termination in a bilayer region of high polarity. A concomitant reduction (up to tenfold) in the propagation rate constant, kp, is attributed to diffusion of polar peroxyl radicals away from the oxidizable region of the bilayer.

scholarly journals ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: I. STYRENE

1965 ◽  
Vol 43 (10) ◽  
pp. 2729-2736 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Chain Termination ◽  
Chain Propagation ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Chain Initiation ◽  
First Order

Absolute rate constants for the uninhibited oxidation of styrene have been obtained by the rotating sector technique. The rate constants for the propagation (kp), bimolecular termination (kt), and a kinetically first order termination (kx) for 2 M styrene In chlorobenzene can be represented by[Formula: see text]The rate constant for the reaction of poly(peroxystyryl) peroxy radicals with 2,6-di-t-butyl-4-methylphenol can be represented by[Formula: see text]Chemically inert solvents can affect the rate of chain initiation and the rate of chain propagation but they do not appear to affect the rate of chain termination.

scholarly journals The influence of crown ethers on the kinetics of E1cB and E2 β-elimination reactions of di(4-nitrophenyl)fluoroethanes with sodium methoxide in methanol

1982 ◽  
Vol 60 (24) ◽  
pp. 3077-3080
Author(s):  
Kenneth T. Leffek ◽  
Grzegorz Schroeder
Keyword(s):  
Isotope Effect ◽  
Crown Ethers ◽  
Rate Constant ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Activation Parameters ◽  
Deuterium Isotope Effect ◽  
Kinetic Order ◽  
Elimination Reactions ◽  
Kinetics Of

The addition of crown ethers 1,4,7,10,13-pentaoxacyclopentadecane (15C5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18C6) in quantities equimolar to the base, to β-elimination reactions of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane and 1-fluoro-2,2-di(4-nitrophenyl)ethane promoted by sodium methoxide in methanol, has been investigated. In the E2 reaction of the monofluoro compound, the crown ethers caused no change in the kinetic order and only small changes in the second-order rate constants and activation parameters. The primary deuterium isotope effect was also unaltered by the presence of crown ethers.For the (E1cB)R reaction of the trifluoro compound, no change in kinetic order was found, but slightly larger rate constant changes and an increase in the isotope effect from kH/kD = 1.0 to 1.25 at 25 °C was observed. This is interpreted as an alteration in mechanism from (E1cB)R towards (E1cB)I.

Spectrochemical Behavior of Carcinogenic Polycyclic Aromatic Hydrocarbons in Biological Systems. Part II: A Theoretical Rate Model for BaP Metabolism in Living Cells

1996 ◽  
Vol 50 (11) ◽  
pp. 1352-1359 ◽  
Author(s):  
Ping Chiang ◽  
Kuang-Pang Li ◽  
Tong-Ming Hseu
Keyword(s):  
Rate Constant ◽  
Living Cells ◽  
Rate Model ◽  
Number Density ◽  
Order Process ◽  
Irreversible Reaction ◽  
First Order ◽  
Metabolism Rate ◽  
Polycyclic Aromatic ◽  
Kinetics Of

An idealized model for the kinetics of benzo[ a]pyrene (BaP) metabolism is established. As observed from experimental results, the BaP transfer from microcrystals to the cell membrane is definitely a first-order process. The rate constant of this process is signified as k1. We describe the surface–midplane exchange as reversible and use rate constants k2 and k3 to describe the inward and outward diffusions, respectively. The metabolism is identified as an irreversible reaction with a rate constant k4. If k2 and k3 are assumed to be fast and not rate determining, the effect of the metabolism rate, k4, on the number density of BaP in the midplane of the microsomal membrane, m3, can be estimated. If the metabolism rate is faster than or comparable to the distribution rates, k2 and k3, the BaP concentration in the membrane midplane, m3, will quickly be dissipated. But if k4 is extremely small, m3 will reach a plateau. Under conditions when k2 and k3 also play significant roles in determining the overall rate, more complicated patterns of m3 are expected.

Substituent effects of rate constants for thermal [4π + 2π] cycloreversion of spiro-fused β-lactam oxadiazolines

1993 ◽  
Vol 71 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Michel Zoghbi ◽  
John Warkentin
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Substituent Effects ◽  
Ground States ◽  
Phenyl Substituent ◽  
First Order ◽  
Average Value ◽  
Carbonyl Ylide

Twelve Δ3-1,3,4-oxadiazolines in which C-2 is also C-4 of a β-lactam moiety (spiro-fused β-lactam oxadiazoline system) were thermolyzed as solutions in benzene. Substituents in the β-lactam portion affect the rate constant for thermal decomposition of the oxadiazolines to N2, acetone, and a β-lactam-4-ylidene. The total spread of first-order rate constants at 100 °C was 47-fold and the average value was 6.7 × 10−4 s−1. A phenyl substituent at N-1 or at C-3 was found to be rate enhancing, relative to methyl. At C-3, H and Cl were also rate enhancing, relative to methyl. The data are interpreted in terms of the differential effects of substituents on the stabilities of the ground states, and on the stabilities of corresponding transition states for concerted, suprafacial, [4π + 2π] cycloreversion. The first products, presumably formed irreversibly, are N2 and a carbonyl ylide. The latter subsequently fragments to form acetone (quantitative) and a β-lactam-4-ylidene.

Absolute rate constants for hydrocarbon autoxidation. 32. On the self-reaction of 1,1-diphenylethylperoxyl in solution

1982 ◽  
Vol 60 (20) ◽  
pp. 2566-2572 ◽  
Author(s):  
J. A. Howard ◽  
J. H. B. Chenier ◽  
T. Yamada
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
The Self ◽  
Absolute Rate ◽  
Radical Process ◽  
First Order ◽  
Hydroperoxide Decomposition ◽  
Solvent Cage ◽  
Induced Decomposition ◽  
Free Radical Process

The major products of the self-reaction of 1,1-diphenylethylperoxyl have been determined from product studies of the autoxidation of 1,1-diphenylethane, induced decomposition of 1,1-diphenylethyl hydroperoxide, and decomposition of 2,2,3,3-tetraphenylbutane under an atmosphere of oxygen. Overall self-reaction is a complex free-radical process involving the intermediacy of 1,1-diphenylethoxyl and 1-phenyl-1-phenoxyethoxyl which undergo H-atom abstraction, β-scission and, in the case of the former radical, rearrangement. Hydroperoxide decomposition under an atmosphere of 36O2 has shown that 1,1-diphenylethylperoxyl undergoes β-scission faster than α-cumylperoxyl at 303 K in solution. The values of the rate constants for self-reaction of Ph2C(Me)O2• relative to those for tert-butylperoxyl are, however, not affected by this reaction. Furthermore they are not affected to any appreciable extent by the efficiency with which Ph2C(Me)O•, formed in nonterminating self-reactions, escape from the solvent cage. They are influenced principally by the first-order rate of decomposition of Ph2C(Me)OOOOC(Me)Ph2.

The lifetime of hydrogen adsorbed on a slightly oxidized nickel surface

1957 ◽  
Vol 240 (1222) ◽  
pp. 423-436 ◽  
Keyword(s):  
Oxide Film ◽  
Mass Spectrometer ◽  
Rate Constant ◽  
Molecular Beam ◽  
Copper Surface ◽  
Solid Surfaces ◽  
Nickel Surface ◽  
Order Process ◽  
Adsorbed Molecules ◽  
First Order

A method for investigating the lifetimes of adsorbed molecules on solid surfaces is described. A molecular beam of hydrogen was projected on to the surface of a spinning nickel disk, and the hydrogen evaporating from the surface at different times after deposition was collected and measured with a mass spectrometer. On a slightly oxidized nickel surface all the hydrogen was adsorbed. The subsequent evaporation was a first-order process with a rate constant of 4·5 x 10 11 exp ( -11·5 kcal/ RT ) S -1 . With a mixed molecular beam of hydrogen and deuterium no exchange was produced by the adsorption, which is considered to be molecular. Attempts to remove the oxide film from the nickel surface gave an un­stable surface on which no clear results were obtained. The lifetime of hydrogen on a copper surface was too short to measure.

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