Chain propagation, in oxidation

Peroxyl radicals can undergo various reactions, e.g., hydrogen abstraction, isomerization, decay, and addition to a double bond. Chain propagation in oxidized aliphatic, alkyl-aromatic, alicyclic hydrocarbons, and olefins with weak C—H bonds near the double bond proceeds according to the following reaction as a limiting step of the chain process [2 15] ... 

Chain propagation in oxidized 1,2-substituted ethylenes proceeds via addition of dioxygen followed by the elimination of the hydroperoxyl radical [156] ... 

The reaction of hydrogen atom abstraction by the alkylhydroxyperoxyl radical from alcohol limits chain propagation in oxidized alcohol [8,9]. 

The analysis of alcohol reactivities in reactions with the peroxyl radicals will be discussed later. The values of the rate constants of chain propagation in oxidized alcohols are collected in Table 7.4. 

As a result, two different peroxyl radicals take part in chain propagation in oxidized alcohol, namely, alkylhydroxyperoxyl and hydroperoxyl radicals. 

Chain propagation in oxidized alcohols proceeds with the participation of a mixture of H02 and R(0H)02 radicals. Using the data of Table 7.4 and Table 7.7 we can compare the activity of the H027H0R02 mixture and alkylperoxyl radicals toward the same alcohol (R OO is the peroxyl radical of cyclohexene, T = 333 K). 

Let us compare the competition of intermolecular and intramolecular chain propagations in oxidized dibenzyl ether. The rate constant A p(R02 + RH) = 95 L mol-1s-1 (T = 303 K, Table... 

In SBR the compounding ingredients can be (1) reinforcing fillers, such as carbon black and silica, which improve tensile strength or tear strength (2) inert fillers and pigments, such as clay, talc, and calcium carbonate, which make the polymer easier to mold or extrude and also lower the cost (3) plasticizers and extenders, such as mineral oils, fatty acids, and esters (4) antioxidants, basically amines or phenols, which stop the chain propagation in oxidation and (5) curatives, such as sulfur for unsaturated polymers and peroxides for saturated polymers, which are essential to form the network of cross-links that ensure elasticity rather than flow. 

Rate Constants of Chain Termination and Propagation in Oxidized Alcohols... 

In addition to two peroxyl radicals, H02 and R1R2C(0H)00 , participating in chain propagation in the oxidized alcohols, there are three reactions that are guilty of chain termination in the oxidized alcohols. The most probable reaction between them is disproportionation. 

Chain propagation in an oxidized aldehyde is limited by the reaction of the acylperoxyl radical with the aldehyde. The dissociation energy of the O—H bond of the formed peracid is sufficiently higher than that of the alkyl hydroperoxide. For example, in hydroperoxide PhMeCHOOH, Z)0 H = 365.5 kJ mol-1 and in benzoic peracid... 

Rate Constants for Chain Propagation in the Oxidation of Aldehydes... 

Of these reactions, the reaction of the peroxyl radical with phosphite is the slowest. The rate constant of this reaction ranges from 102 to 103 L mol 1 s 1 which is two to three orders of magnitude lower than the rate constant of similar reactions with phenols and aromatic amines. Namely, this reaction limits chain propagation in the oxidation of phosphites. Therefore, the chain oxidation of trialkyl phosphites involves chain propagation reactions with the participation of both peroxyl and phosphoranylperoxyl radicals ... 

By using the differential form of the copolymer composition equation (26, 28) the products of oxidation of mixtures at low conversions permit comparison of rates of chain propagation in autoxidations of various compounds, essentially free from effects of chain initiation, chain termination, and over-all rates. 

The alkylperoxy radical isomerization and alkene-hydroperoxy radical addition theories of chain propagation in the oxidation of alkyl radicals at ca. 300°C. have been combined into a single comprehensive reaction scheme. 

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