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Peroxy-radicals

Some of the reactions of peroxy radicals were discussed in Section A.l of this chapter during our analysis of autooxidation reactions. These reactive intermediates also undergo many other processes of great importance in natural systems and also in treatment systems where high concentrations of free radicals are generated. [Pg.247]

There are few direct measurements of peroxy radical concentrations in the atmosphere (Mihelcic et al., 1978 Cantrell et al., 1984). Like many other atmospheric radical species, their numbers seem to be greatest when solar UV intensity is strongest. For 28 samples collected from flights over West Germany, values ranging from [Pg.247]

05 to 0.3 ppb were obtained (Mihelcic et al., 1982). In the atmosphere, oxidizing radicals such as RCH2OO are excellent scavengers for NO, converting it to NO2  [Pg.247]

Further reaction of the alkoxy radicals, formed in this step, with O2 affords aldehydes and hydroperoxy radicals (also capable of oxidizing NO with regeneration of OH)  [Pg.247]

Peroxy radicals can also react directly with NO2 to form pernitrate esters  [Pg.247]


Antioxidants markedly retard the rate of autoxidation throughout the useful life of the polymer. Chain-terminating antioxidants have a reactive —NH or —OH functional group and include compounds such as secondary aryl amines or hindered phenols. They function by transfer of hydrogen to free radicals, principally to peroxy radicals. Butylated hydroxytoluene is a widely used example. [Pg.1008]

Molecular oxygen contains two unpaired electrons and has the distinction of being capable of both initiating and inhibiting polymerization. It functions in the latter capacity by forming the relatively unreactive peroxy radical ... [Pg.396]

In the presence of any substantial amount of oxygen this reaction is extremely rapid, but the terminal peroxy radical formed reacts slowly with monomer and has a relatively rapid termination rate. [Pg.166]

Oxidation begins with the breakdown of hydroperoxides and the formation of free radicals. These reactive peroxy radicals initiate a chain reaction that propagates the breakdown of hydroperoxides into aldehydes (qv), ketones (qv), alcohols, and hydrocarbons (qv). These breakdown products make an oxidized product organoleptically unacceptable. Antioxidants work by donating a hydrogen atom to the reactive peroxide radical, ending the chain reaction (17). [Pg.436]

Carbon-centered radicals generally react very rapidly with oxygen to generate peroxy radicals (eq. 2). The peroxy radicals can abstract hydrogen from a hydrocarbon molecule to yield a hydroperoxide and a new radical (eq. 3). This new radical can participate in reaction 2 and continue the chain. Reactions 2 and 3 are the propagation steps. Except under oxygen starved conditions, reaction 3 is rate limiting. [Pg.334]

Under these conditions, a component with a low rate constant for propagation for peroxy radicals may be cooxidized at a higher relative rate because a larger fraction of the propagation steps is carried out by the more reactive (less selective) alkoxy and hydroxy radicals produced in reaction 4. [Pg.335]

Bimolecular reactions of peroxy radicals are not restricted to identical radicals. When both peroxy radicals are tertiary, reaction 15 is not possible. When an a-hydrogen is present, reaction 15 is generally the more effective competitor and predominates. [Pg.335]

Acids are usually the end products of ketone oxidations (41,42,44) but vicinal diketones and hydroperoxyketones are apparent intermediates (45). Acids are readily produced from vicinal diketones, perhaps through anhydrides (via, eg, a Bayer-ViUiger reaction) (46,47). The hydroperoxyketones reportedly decompose to diketones as well as to aldehydes and acids (45). Similar products are expected from radical— radical reactions of the corresponding peroxy radical precursors. [Pg.336]

Reaction 36 may occur through a peroxy radical complex with the metal ion (2,25,182). In any event, reaction 34 followed by reaction 36 is the equivalent of a metal ion-cataly2ed hydrogen abstraction by a peroxy radical. [Pg.343]

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... [Pg.269]

Oxidation. AH polyamides are susceptible to oxidation. This involves the initial formation of a free radical on the carbon alpha to the NH group, which reacts to form a peroxy radical with subsequent chain reactions leading to chain scission and yellowing. As soon as molten nylon is exposed to air it starts to discolor and continues to oxidize until it is cooled to below 60°C. It is important, therefore, to minimize the exposure of hot nylon to air to avoid discoloration or loss of molecular weight. Similarly, nylon parts exposed to high temperature in air lose their properties with time as a result of oxidation. This process can be minimized by using material containing stabilizer additives. [Pg.270]

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. [Pg.317]

Eor antioxidant activity, the reaction of aminyl radicals with peroxy radicals is very beneficial. The nitroxyl radicals formed in this reaction are extremely effective oxidation inhibitors. Nitroxides function by trapping chain-propagating alkyl radicals to give hydroxylamine ethers. These ethers, in turn, quench chain propagating peroxy radicals and in the process regenerate the original nitroxides. The cycHc nature of this process accounts for the superlative antioxidant activity of nitroxides (see Antioxidants). Thus, antioxidant activity improves with an increase in stabiUty of the aminyl and nitroxyl radicals. Consequendy, commercial DPA antioxidants are alkylated in the ortho and para positions to prevent undesirable coupling reactions. [Pg.243]

Propagation. Propagation reactions (eqs. 5 and 6) can be repeated many times before termination by conversion of an alkyl or peroxy radical to a nonradical species (7). Homolytic decomposition of hydroperoxides produced by propagation reactions increases the rate of initiation by the production of radicals. [Pg.223]

The reaction rate of molecular oxygen with alkyl radicals to form peroxy radicals (eq. 5) is much higher than the reaction rate of peroxy radicals with a hydrogen atom of the substrate (eq. 6). The rate of the latter depends on the dissociation energies (Table 1) and the steric accessibiUty of the various carbon—hydrogen bonds it is an important factor in determining oxidative stabiUty. [Pg.223]

Radical Scavengers Hydrogen-donating antioxidants (AH), such as hindered phenols and secondary aromatic amines, inhibit oxidation by competing with the organic substrate (RH) for peroxy radicals. This shortens the kinetic chain length of the propagation reactions. [Pg.223]

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). [Pg.225]

According to this mechanism, hindered-amiae derivatives terminate propagatiag reactioas (eqs. 5 and 6) by trappiag both the alkyl and peroxy radicals. In effect, NO competes with O2, and NOR competes with RH. Siace the nitroxyl radicals are not consumed ia the overall reactioas, they are effective at low coaceatratioas. [Pg.226]

The fimction of an antioxidant is to divert the peroxy radicals and thus prevent a chain process. Other antioxidants fimction by reacting with potential initiators and thus retard oxidative degradation by preventing the initiation of autoxidation chains. The hydroperoxides generated by autoxidation are themselves potential chain initiators, and autoxidations therefore have the potential of being autocatalytic. Certain antioxidants fimction by reducing such hydroperoxides and thereby preventing their accumulation. [Pg.685]

Process 4, conversion of peroxy radicals to hydroperoxides can be interrupted by traditional primary antioxidants (see Fig. 16). The fastest reacting primary antioxidants are the aromatic amines (e.g. Naugard 445). However, these materials yellow upon exposure to UV light which restricts their applieations. More common in adhesives are the hindered phenol types of which numerous types are available, with Irganox 1010 the most common choice for adhesives. [Pg.730]

The decomposition of the peroxyketals (53) follows a stepwise, rather than a concerted mechanism. Initial homolysis of one of the 0-0 bonds gives an aikoxy radical and an a-peroxyalkoxy radical (Scheme 3.36).306"08"210 This latter species decomposes by P-scission with loss of either a peroxy radical to form a ketone as byproduct or an alkyl radical to form a peroxyester intermediate. The peroxyester formed may also decompose to radicals under the reaction conditions. Thus, four radicals may be derived from the one initiator molecule. [Pg.91]

These additives are thus able to trap both alkyl and peroxy radicals. In this way they interfere with the propagating steps of the degradation process. Since overall the nitroxyl radicals are not consumed in this mechanism these additives are effective at low concentrations in the polymer. [Pg.124]

The endoperoxy hydroperoxide (36) results from the hydroperoxide (35) by sequential peroxy radical generation, (>-exo trig cyclisation and oxygen trapping <96SL349>. [Pg.305]


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Alkenes reactions with peroxy radicals

Alkyl peroxy radical reactivity

Alkyl peroxy radical reactivity compounds

Alkyl peroxy radicals

Alkyl peroxy radicals, atmosphere

Aryl peroxy radicals

Bicyclization, peroxy radical

Bond strengths in Vinyl, Allyl, and Ethynyl Peroxy Radicals

Branching ratios peroxy radical reactions

By Superoxide, Peroxy Radicals and Peroxide

Chain peroxy radicals

Chemical amplification, peroxy radical measurement

Chemical reactions peroxy radicals

Chemiluminescence, peroxy radical measurement

Chlorine peroxy radical, from

Cyclization peroxy! radical

Cyclohexene reaction + peroxy radicals

Direct studies of peroxy radical isomerizations

Fluorinated peroxy radicals

Formation of peroxy radicals

Formation of the peroxy polymer radical

Hindered amine light stabilizer peroxy radicals

Hydrogen bonding with peroxy radicals

Hydrogen peroxy radicals

Hydroxyalkyl peroxy radicals

Hydroxymethyl cyclohexadienyl peroxy radical

Intramolecular H-atom transfer to peroxy radicals

Intramolecular propagation with peroxy radicals

Lipid-peroxy radicals

Mass spectrometry peroxy radicals

Measurement methods, peroxy radicals

Measurement methods, peroxy radicals chemical conversion

Metal ions reactions with peroxy radicals

Methyl peroxy radical, hydrogen

Methyl peroxy radicals

Nitrate radical reaction with peroxy radicals

Organic peroxy radical

Organic peroxy radical reaction with

Oxidation of styrene. The peroxy radical addition mechanism

PTFE peroxy radicals

Peroxy

Peroxy acetyl radical

Peroxy alkyl radicals transfer reaction

Peroxy alkyl radicals, fragmentation

Peroxy compounds, radical formation

Peroxy esters free radicals from

Peroxy radical - reaction/source

Peroxy radical absorption spectra

Peroxy radical branching ratios

Peroxy radical formation

Peroxy radical generation

Peroxy radical generation mechanism

Peroxy radical isomerization

Peroxy radical reaction with

Peroxy radical scavenger

Peroxy radical self-reactions

Peroxy radicals INDEX

Peroxy radicals Peroxyacetyl nitrate

Peroxy radicals alkylperoxy

Peroxy radicals benzylperoxy

Peroxy radicals butylperoxy

Peroxy radicals chemical conversion

Peroxy radicals computer simulations

Peroxy radicals elimination reactions

Peroxy radicals epoxidation

Peroxy radicals hydrogen atom transfer from

Peroxy radicals hydroperoxides

Peroxy radicals ketone

Peroxy radicals reaction rate constants

Peroxy radicals reactions

Peroxy radicals reactions with organic compounds

Peroxy radicals reactivities

Peroxy radicals rearrangements

Peroxy radicals sources

Peroxy radicals spectroscopy

Peroxy radicals structures, cyclic

Peroxy radicals, chain termination

Peroxy radicals, disproportionation

Peroxy radicals, initiation

Peroxy radicals, initiation kinetics

Peroxy radicals, interaction

Peroxy-radical cation, triplet oxygen reactions

Peroxy-type radicals

Protein-peroxy radical

Rate constant peroxy radical with

Reactions of peroxy radicals with polyfunctional molecules

Reactivities of peroxy radicals toward

Rearrangements of peroxy radicals

Ring closures of peroxy radicals

Self-reactions of peroxy radicals

Structure and Molecular Motion of Peroxy Radicals in Polymer Matrices

Superoxide, Peroxy Radicals and Peroxynitrite

Tocopherol reaction with peroxy radical

Trichloromethyl peroxy radical

Unsaturated hydroperoxides, peroxy radicals from

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