Initiation mechanisms in radical polymerizations : Reaction of cumyloxy radicals with methyl methacrylate and styrene

1982 ◽  
Vol 35 (10) ◽  
pp. 2013 ◽  
Author(s):  
E Rizzardo ◽  
AK Serelis ◽  
DH Solomon
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Methyl Methacrylate ◽  
Rate Constants ◽  
Polymer Structure ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Constant Rate ◽  
Radical Generation

Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60�) of dicumyl hyponitrite in methyl methacrylate and styrene. The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxyl. Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate. Styrene underwent only double-bond addition by both cumyloxy and methyl radicals. Some possible implications of these results for polymer structure are discussed. A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave k=7.7 × 1014exp(-13600/T) s-1 for the rate constant. Rate constants for the addition of cumyloxyl to methyl methacrylate (k ≈ 2 × 104 dm3 mol-1 s-1) and styrene (k≈2 × 105 dm3 mol-1 s-1) at 60�have been estimated.

Influence of the double bond on the hydrogen abstraction reactions of methyl esters with hydrogen radical: an ab initio and chemical kinetic study

RSC Advances ◽  
2015 ◽  
Vol 5 (84) ◽  
pp. 68314-68325 ◽  
Author(s):  
Quan-De Wang ◽  
Weidong Zhang
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Kinetic Study ◽  
Rate Constants ◽  
Methyl Esters ◽  
Hydrogen Abstraction ◽  
Chemical Kinetic ◽  
Hydrogen Atom Abstraction ◽  
Hydrogen Radical

This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydrogen radical on the isomers of unsaturated C6 methyl esters.

Structure and Reactivity of Methyl Radical — Cyanide Ion Pairs in Crystal I and Crystal II of Acetonitrile

1974 ◽  
Vol 52 (15) ◽  
pp. 2840-2844 ◽  
Author(s):  
Estel Dean Sprague ◽  
Keiji Takeda ◽  
Jih Tzong Wang ◽  
Ffrancon Williams
Keyword(s):  
Hydrogen Atom ◽  
Hyperfine Splitting ◽  
Radical Anion ◽  
Strong Dependence ◽  
Ion Pairs ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Cyanide Ion ◽  
Radical Reactivity

The extent of interaction between methyl radicals and cyanide ions produced in pairs by dissociative electron capture in the two solid phases of acetonitrile has been studied by e.s.r. using CD313CN. Although no interaction is observed when the radical–anion pairs are generated by photobleaching the acetonitrile dimer radical anion in Crystal I, a very weak interaction as evidenced by an isotropic 13C hyperfine splitting of 3.4 G is found for the corresponding species produced from the acetonitrile monomer radical anion in Crystal II. The rate of hydrogen atom abstraction by the methyl radical in Crystal I is at least a factor of 10 greater than in Crystal II at the same temperature over the range 77–113 K. These results show that the weak perturbation of the methyl radical by the cyanide ion does not enhance methyl radical reactivity in hydrogen atom abstraction. Evidence from 13C hyperfine splitting measurements on [Formula: see text] indicates that the configuration of the methyl radical is planar in these radical–anion pairs. It is emphasized that quantum mechanical tunneling provides a satisfactory explanation for the low apparent activation energies, the curved Arrhenius plots, and the abnormally large deuterium isotope effects which characterize hydrogen atom abstraction reactions by methyl radicals in glassy and crystalline solids at low temperatures. Moreover, since the tunneling rate is extremely sensitive to the width of the barrier, methyl radical reactivity is expected to show a very strong dependence on the precise geometry of the reacting partners in the solid state.

scholarly journals A cross-dehydrogenative C(sp3)−H heteroarylation via photo-induced catalytic chlorine radical generation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chia-Yu Huang ◽  
Jianbin Li ◽  
Chao-Jun Li
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Evolution ◽  
Alkyl Radical ◽  
Cobalt Catalyst ◽  
Alkylation Reaction ◽  
Hydrogen Atom Abstraction ◽  
Dehydrogenative Coupling ◽  
Radical Generation ◽  
Limited Scope

AbstractHydrogen atom abstraction (HAT) from C(sp3)–H bonds of naturally abundant alkanes for alkyl radical generation represents a promising yet underexplored strategy in the alkylation reaction designs since involving stoichiometric oxidants, excessive alkane loading, and limited scope are common drawbacks. Here we report a photo-induced and chemical oxidant-free cross-dehydrogenative coupling (CDC) between alkanes and heteroarenes using catalytic chloride and cobalt catalyst. Couplings of strong C(sp3)–H bond-containing substrates and complex heteroarenes, have been achieved with satisfactory yields. This dual catalytic platform features the in situ engendered chlorine radical for alkyl radical generation and exploits the cobaloxime catalyst to enable the hydrogen evolution for catalytic turnover. The practical value of this protocol was demonstrated by the gram-scale synthesis of alkylated heteroarene with merely 3 equiv. alkane loading.

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.

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.

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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