Autoxidation of olefin

Allylic hydroperoxides are primary products in the autoxidation of - olefins, and lack of definite information on their reactivity and chemical behavior has hampered efforts to understand olefin oxidation mechanisms (2). This deficiency is most strongly felt in determining the relative rates of addition and abstraction mechanisms for acyclic olefins since assignment of secondary reaction products to the correct primary source is required. Whereas generalizations about the effect of structure on the course of hydroperoxide decompositions are helpful, most questions can be answered better by directly isolating the hydroperoxides involved and observing the products formed by decomposition of the pure compounds. 

Autoxidation of Olefins Accompanying a Novel Hydrogen Transfer in a Silent Discharge... 

Propose a pathway to account for the formation of epoxides in autoxidation of olefins. 

There are additional possibilities for chain propagation in the autoxidation of olefins. These reactions involve the addition of the alkylperoxy radical to the double bond... 

Further evidence against initiation by direct oxygen activation in the oxidation of olefins is provided by the following two observations.185 First, no reaction was observed between olefins (e.g., cyclohexene, 1-octene, and styrene) and metal-dioxygen complexes, such as I, II, and V, when they were heated in an inert atmosphere (nitrogen). Second, no catalysis was observed with these metal complexes in the autoxidation of olefins, such as styrene, that cannot form hydroperoxides. 

In support of the electron transfer mechanism [Eqs. (139)—(141)], the ESR spectra of various radical cations have been observed during reaction of alkenes with Co(III) in trifluoroacetic acid mixtures.218 However, a very different situation may obtain in the cobalt-catalyzed autoxidation of olefins in neutral non-... 

Homolytic autoxidations of hydrocarbons often give complex mixtures of products-the autoxidation of olefins is a prime example. There is a great incentive, therefore, to search for catalysts that can promote the selective oxidation of olefins by essentially nonradical mechanisms. For example, there is no method available for carrying out the selective epoxidation or oxidative cleavage of olefins (see Section III.C) by molecular oxygen. In order to be successful, any heterolytic pathway for the metal-catalyzed oxidation of a substrate must, of course, be considerably faster than the ubiquitous homolytic processes for autoxidation. Thus, the metal catalysts discussed in the following sections, in addition to being able to promote heterolytic oxidations, are also able to catalyze homolytic processes. 

Ethylene oxide is prepared industrially by the vapor phase oxidation of ethylene over a supported silver catalyst at elevated temperatures.49la c Application of this reaction to higher olefins results in complete oxidation of the olefin to carbon dioxide and water. In general, autoxidations of olefins are notoriously unselective because of the many competing reactions of the intermediate peroxy radicals in these systems. 

Metalloporphyrins catalyze the autoxidation of olefins, and with cyclohexene at least, the reaction to ketone, alcohol, and epoxide products goes via a hydroperoxide intermediate (129,130). Porphyrins of Fe(II) and Co(II), the known 02 carriers, can be used, but those of Co(III) seem most effective and no induction periods are observed then (130). ESR data suggest an intermediate cation radical of cyclohexene formed via interaction of the olefin with the Co(III) porphyrin this then implies possible catalysis via olefin activation rather than 02 activation. A Mn(II) porphyrin has been shown to complex with tetracyanoethylene with charge transfer to the substrate (131), and we have shown that a Ru(II) porphyrin complexes with ethylene (8). Metalloporphyrins remain as attractive catalysts via such substrate activation, and epoxidation of squalene with no concomitant allylic oxidation has been noted and is thought to proceed via such a mechanism (130). Phthalocyanine complexes also have been used to catalyze autoxidation reactions (69). 

Classical (metal-catalyzed) autoxidation of olefins is facile but not synthetically useful owing to competing oxidation of allylic C-H bonds and the olefinic double bond, leading to complex product mixtures [105]. Nonetheless, the synthetic chemist has a number of different tools for the allylic oxidation of olefins available. 

Autoxidation of olefins Olefins react with oxygen at the -position to the double bond. This can yield, not merely the hydroperoxide with the double bond in the original position, but also isomeric hydroperoxides resulting from migration of the double bond. According to Farmer and his co-workers the cause of this is mesomerism of the, / -unsaturated radical first formed (oc-methylene mechanism) ... 

An expression for the reaction rate r, may be described in terms of two reactants with reaction order m and n. Such an expression is applicable to the autoxidation of olefins. 

Early reports on rhodium(I) catalyzed autoxidation of olefins indicated attack of coordinated dioxygen at the allylic position... 

It is reported that the mixture of disulfide and thiosulfinate, such as 5-(4-methox3q)henyl) benzenethiosulfinate, can be used as an antioxdant for the retardation of autoxidation of olefins. ... 

Hydroperoxide chemistry had its heyday in the decade 1950-1960, following the firm establishment of these compounds as reactive intermediates in the autoxidation of olefins. Afterward, many reports regarding vinyl polymerization involving hydroperoxide alone or coupled with a suitable reducing agent have appeared in the literature. 

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