The importance of peroxy radical chain-breaking reactions in the cool flame domain

1979 ◽  
Vol 34 ◽  
pp. 153-159 ◽  
Author(s):  
K.A. Sahetchian ◽  
A. Heiss ◽  
G.M.L. Dumas ◽  
R.I. Ben-Aim
Keyword(s):  
Peroxy Radical ◽  
Radical Chain ◽  
Cool Flame ◽  
Chain Breaking

The non-isothermal oxidation of 2 -methylpentane. - III. The reaction at high pressure

1969 ◽  
Vol 313 (1513) ◽  
pp. 261-297 ◽  
Keyword(s):  
High Temperatures ◽  
Isothermal Oxidation ◽  
Gas Liquid Chromatography ◽  
Labile Hydrogen ◽  
Chain Process ◽  
Unimolecular Decomposition ◽  
Hydrogen Atoms ◽  
Radical Chain ◽  
Cool Flame ◽  
Alkylperoxy Radicals

The non-isothermal oxidation of 2-methylpentane has been studied at pressures of 1-4 MN m -2 and temperatures of 440 to 660 °C in an arrested-piston rapid-compression machine. The variations with pressure and temperature of the induction periods leading to cool-flame reaction and hot ignition have been determined, and the products of the reaction have been analysed by gas-liquid chromatography. At high temperatures and pressures the cool-flame reaction occurs by a free-radical chain process in which homogeneous isomerization and subsequent decomposition of alkylperoxy radicals propagate the chain. The resulting propa­gation cycle is substantially the same as that which has been established at lower tempera­tures and subatmospheric pressures. At high temperatures and pressures the reaction is, however, even more unselective, and oxidation of β -hydroperoxyalkyl radicals competes more successfully with their unimolecular decomposition, thus leading to the formation of β -ketoaldehydes. These compounds, together with the conjugated unsaturated carbonyl compounds, account quantitatively for the absorption of ultraviolet light by reacting 2-methylpentane/air mixtures. The mechanism of chain branching in the cool-flame reaction probably involves the pyrolysis of hydroperoxides. In the second stage of two-stage ignition, the propagation cycle is the same as that occurring in the cool flame but the important difference is that the cool flame has formed substantial concentrations of compounds with labile hydrogen atoms; these react readily with alkylperoxy radicals to form hydroperoxides, the pyrolysis of which again branches the chain.

Antimalarial Drugs Exacerbate Rat Liver Microsomal Lipid Peroxidation in the Presence of Oxidants

2001 ◽  
Vol 21 (3) ◽  
pp. 353-359 ◽  
Author(s):  
E. Olatunde Farombi ◽  
Stanley Adoro ◽  
Samuel Uhunmwangho
Keyword(s):  
Lipid Peroxidation ◽  
Rat Liver ◽  
Lipid Hydroperoxide ◽  
Antimalarial Drugs ◽  
Oxygen Species ◽  
Radical Chain ◽  
Microsomal Lipid Peroxidation ◽  
Hydroperoxide Formation ◽  
Chain Breaking

The study was undertaken to evaluate the effect of prior treatment of rats with the antimalarial drugs amodiaquine (AQ) mefloquine (MQ) and halofantrine (HF) on rat liver microsomal lipid peroxidation in the presence of 1 mM FeSO4, 1 mM ascorbate and 0.2 mM H2O2 (oxidants). Ingestion of α-tocopheral, a radical chain-breaking antioxidant was also included to assess the role of antioxidants in the drug treatment. In the presence of oxidants AQ, MQ and HF elicited 288%, 175% and 225% increases in malondialdehyde (MDA) formation while the drugs induced 125%, 63% and 31% increases in the absence of oxidants respectively. Similarly, AQ, MQ and HF induced lipid hydroperoxide formation by 380%, 256%, 360% respectively in the presence of oxidants and 172%, 136% and 92% in the absence of exogenously added oxidants respectively. α-tocopherol reduced AQ, MQ and HF-induced MDA formation by 40%, 55% and 52% respectively and lipid hydroperoxide formation by 53%, 59% and 54% respectively. Similarly, α-tocopherol attenuated the AQ, MQ and HF-induced MDA formation by 49%, 51% and 51% in the presence of oxidants and lipid hydroperoxide formation by 61%, 62% and 47% respectively. The results indicate that rat liver microsomal lipid peroxidation could be enhanced by antimalarial drugs in the presence of reactive oxygen species and this effect could be ameliorated by treatment with antioxidants.

The Role of Certain Organic Sulfur Compounds as Preventive Antioxidants

1974 ◽  
Vol 47 (4) ◽  
pp. 949-959 ◽  
Author(s):  
J. Reid Shelton
Keyword(s):  
Oxidative Degradation ◽  
Polymeric Materials ◽  
Chain Scission ◽  
Peroxy Radicals ◽  
Radical Chain ◽  
Organic Sulfur Compounds ◽  
Chain Breaking ◽  
Degradation Of Properties ◽  
Free Radical Chain Reaction ◽  
Crosslinking Reactions

Abstract The mechanism of autoxidation of organic materials by elemental oxygen is a free radical chain reaction initiated by hydroperoxide decomposition to form alkoxy and peroxy radicals. Chain scission and crosslinking reactions occur, along with the formation of hydroperoxide, resulting in degradation of properties of polymeric materials. The presence of unsaturation in natural and synthetic rubbers makes them particularly vulnerable to autoxidation, and antioxidants are thus essential to provide protection against oxidative degradation. There are two ways in which antioxidants can function to retard autoxidation. Preventive antioxidants act in some way to reduce the rate of initiation, while chain-breaking antioxidants intercept the chain-propagating peroxy free radicals and thus terminate the chain mechanism. Both types include a variety of compounds and possible modes of action as indicated in the following classification:

scholarly journals Trace explosives detection by cavity ring-down spectroscopy (CRDS)

2021 ◽  
Author(s):  
Bobbi Stromer ◽  
Anthony Bednar ◽  
Milo Janjic ◽  
Scott Becker ◽  
Tamara Kylloe ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Limit Of Detection ◽  
Peroxy Radical ◽  
Peak Height ◽  
Expected Value ◽  
Explosives Detection ◽  
Triacetone Triperoxide ◽  
Radical Chain ◽  
Cavity Ring Down Spectroscopy ◽  
Cavity Ring Down

We built three successive versions of a thermal decomposition cavity ring-down spectrometer and tested their response to explosives. These explosive compound analyzers successfully detected nitroglycerine, 2,4,6-trinitrotoluene (TNT), pentaerythryl tetranitrate, hexahydro-1,3,5-trinitro-s-triazine and triacetone triperoxide (TATP). We determined the pathlength and limits of detection for each, with the best limit of detection being 13 parts per trillion (ppt) of TNT. For most of the explosive tests, the peak height was higher than the expected value, meaning that peroxy radical chain propagation was occurring with each of the explosives and not just the peroxide TATP.

Phenolic betalain as antioxidants: meta means more

2020 ◽  
Vol 92 (2) ◽  
pp. 243-253 ◽  
Author(s):  
Letícia C. P. Gonçalves ◽  
Nathana B. Lopes ◽  
Felipe A. Augusto ◽  
Renan M. Pioli ◽  
Caroline O. Machado ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom Transfer ◽  
Antioxidant Potential ◽  
Human Consumption ◽  
Ph Effects ◽  
Radical Chain ◽  
Proton Coupled Electron Transfer ◽  
Chain Breaking ◽  
The Relationship ◽  
Transfer Mechanisms

AbstractBetalains are phytochemicals of nutraceutical importance that emerged as potent antioxidants, preventing radical chain propagation and the deleterious health effects of oxidative stress. However, despite the wide application of betalains as color additives in products for human consumption, little is known about the relationship between their structure and antioxidant potential. Here we investigate the mechanism of antioxidant action of three regioisomeric phenolic betalains and show that the meta isomer has higher antiradical capacity than most natural betalains, anthocyanins and flavonoids. Structural and pH effects on redox and antiradical properties were investigated and the results are rationalized in light of quantum chemical calculations. Our results demonstrate that hydrogen atom transfer/proton-coupled electron transfer or sequential proton loss electron transfer mechanisms are plausible to explain the radical chain breaking properties of phenolic betalains in water. Furthermore, mesomeric effects are responsible for the stabilization of the resulting radical phenolic betalains. These findings are useful for the design of biocompatible antioxidants and for the development of novel additives for functional foods and cosmetics with high antioxidant potential.

Radical Chain Breaking Bis( ortho ‐organoselenium) Substituted Phenolic Antioxidants

2021 ◽  
Vol 16 (8) ◽  
pp. 966-973
Author(s):  
Aditya Upadhyay ◽  
Bhagat Singh Bhakuni ◽  
Rahul Meena ◽  
Sangit Kumar
Keyword(s):  
Phenolic Antioxidants ◽  
Radical Chain ◽  
Chain Breaking

Metal complexes as antioxidants. 7. Kinetics of inhibition of styrene autoxidation by zinc di-isopropyldithiophosphate

1980 ◽  
Vol 58 (1) ◽  
pp. 92-95 ◽  
Author(s):  
J. A. Howard ◽  
S-B. Tong
Keyword(s):  
Chain Transfer ◽  
Peroxy Radical ◽  
Chain Termination ◽  
Oxygen Absorption ◽  
Reaction Products ◽  
Radical Chain ◽  
Chain Initiation ◽  
Styrene Concentration ◽  
Kinetics Of ◽  
Kinetics Of Inhibition

Rates of oxygen absorption by styrene (RH) containing 2,2,3,3-tetraphenylbutane and zinc di-isopropyldithiophosphate at 30 °C obey the rate law [Formula: see text] where Ri is the rate of free-radical chain initiation. This order with respect to the styrene concentration implies extensive chain transfer from the poly(peroxystyryl)peroxy radical to a radical derived from the inhibitor. Reaction products confirm the displacement of a di-isopropyldithiophosphoryl radical in the chain termination reaction.Diethyldithiophosphoric acid also inhibits styrene autoxidation by a mechanism which involves extensive chain transfer.

Alkylperoxy radical rearrangements during the gaseous oxidation of isobutene

1963 ◽  
Vol 273 (1354) ◽  
pp. 427-434 ◽  
Keyword(s):  
Methyl Ethyl Ketone ◽  
Peroxy Radical ◽  
Methyl Ethyl ◽  
Isotopic Tracer ◽  
Cool Flame ◽  
Cool Flames ◽  
Tracer Techniques ◽  
Slow Combustion ◽  
Flame Region ◽  
Subsequent Decomposition

Isotopic tracer techniques have been used to elucidate the mechanism of production of ketones in the gaseous oxidation of isobutane. Both acetone and methyl ethyl ketone are formed from this hydrocarbon, the former predominating in the products of slow combustion and the latter in the products of cool flames. Addition of [1,3- 14 C] acetone to reacting isobutane + oxygen mixtures has established that none of the methyl ethyl ketone formed in the cool-flame region and only 25% of that formed during slow combustion arises from further reactions of acetone. The formation of methyl ethyl ketone probably involves predominantly rearrangement and subsequent decomposition of the tert .-butyl peroxy radical and this indeed appears to be the almost exclusive fate of this radical under cool-flame conditions.

Sulfamides Direct Radical-Mediated Chlorination of Aliphatic C–H Bonds

2019 ◽  
Author(s):  
Melanie Short ◽  
Mina Shehata ◽  
Matthew Sanders ◽  
Jennifer Roizen
Keyword(s):  
Hydrogen Atom ◽  
Transfer Reaction ◽  
Hydrogen Atom Transfer ◽  
Chain Propagation ◽  
Propagation Mechanism ◽  
Atom Transfer ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Transfer Processes ◽  
Unusual Position

Sulfamides guide intermolecular chlorine transfer to gamma-C(sp<sup>3</sup>) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage in otherwise rare 1,6-hydrogen-atom transfer processes. The disclosed chlorine-transfer reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp<sup>3</sup>)-H bonds.

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