Oxidation of double bonds

There are many ways to categorize the oxidation of double bonds as they undergo a myriad of oxidative transformations leading to many product types including epoxides, ketones, diols, endoperoxides, ozonides, allylic alcohols and many others. Rather than review the oxidation of dienes by substrate type or product obtained, we have chosen to classify the oxidation reactions of dienes and polyenes by the oxidation reagent or system used, since each have a common reactivity profile. Thus, similar reactions with each specific oxidant can be carried out on a variety of substrates and can be easily compared. 

Oxidation results from the interactions between atmospheric oxygen and the double bonds of unsaturated fatty acids. Several parameters can catalyze lipid oxidation, while others can prevent or slow down the reactions. Metals, light, moisture and heat can all enhance oxidation, while antioxidant compounds (e.g., BHT and vitamin E) can be utilized to retard oxidation. Oxidation of double bonds leads to intermediate peroxides that eventually break down into a variety of stable compounds. 

In some cases, oxidation of double bonds does not stop at the epoxide, but proceeds further to oxidative cleavage of the double bond. It was reported that the reaction of a-methyl styrene with H2O2 in the presence of TS-1 or TS-2 produces a-methyl styrene epoxide (15%), a-methyl styrene diol (10-40%) and acetophenone (40-60%) (Reddy, J. S. et al., 1992). However, results similar to those obtained with titanium silicates were obtained for many other catalysts, such as HZSM-5, H-mordenite, HY, A1203, HGa-silicalite-2, and fumed Si02. These materials have much different properties and differ significantly from titanium silicates thus, the results cast some doubt on the role of the catalyst in this reaction. Furthermore, the oxidation of styrene is reported to proceed with C=C cleavage and formation of benzaldehyde, in contrast to previous reports of the formation of phenylacetaldehyde with 85% selectivity (Neri et al., 1986). 

Oxidation of double bond-containing functional groups is a key method in synthesis which is used to form other functional moieties, especially in a stereocontrolled fashion. In this section the epoxidation and dihydroxylation of alkenes are covered in some detail. These are particularly common methods used for stereocontrolled elaboration of organic molecules. 

The most classical synthesis of the diacids concerns the oxidation of double bonds which are obtained by reactions of dehydrohalogenation or dehalogenation [12-16],... 

The liquid hydroxytelechelic polybutadiene admixtures increase the viscosity of synthetic or mineral oils 89). However, the oxidation of double bonds is followed by a fast ageing of the product. 

The fatty acid alkyl chain is susceptible to oxidation both at double bonds and adjacent allylic carbons. Eree-radical and photooxidation at aUylic carbons are responsible for deterioration of unsaturated oils and fats, resulting in rancid flavors and reduced nutritional quality, but they are also used deliberately to polymerize drying oils. Oxidation of double bonds is used in oleochemical production either to cleave the alkyl chain or to introduce additional functionality along the chain. Enzyme catalyzed oxidation is the initial step in the production of eicosanoids and jasmonates (biologically active metabolites in animals and plants respectively) but is not discussed further here. 

IV. Effect of Steric Factors on Reaction Rate 1. Oxidation of Double Bonds... 

The reaction of alkenes with peroxy acids provides for convenient and selective oxidation of double bonds. The peroxy acids most commonly used in the laboratory are m-chloroperoxybenzoic acid (mCPBA), monoperoxyphthalic acid magnesium salt (MMPP), peroxybenzoic acid, peroxyformic acid, peroxyacetic acid, trifluoroper-oxyacetic acid, and 7-butyl hydroperoxide f(CH3)3COOH]. The order of reactivity for... 

Saturation and Oxidation of Double Bonds It is known that radicals can directly add on double bonds [32], which leads in turn to saturation of the double bonds and formation of a new radical. After fixation of oxygen, a peroxy radical is formed followed an hydroperoxide by the classical hydrogen abstraction. Thermal and photochemical decomposition of the hydroperoxides gives alkoxy radicals (Scheme 15.4). 

Rats that are deprived of vitamin E become infertile, but the reasons for this effect are unknown. Vitamin E is known to prevent the oxidation of double bonds in the hydrocarbon tails of membrane lipids, and this may be its major function. Because oxidation reactions accelerate aging, some researchers believe that vitamin E may help to retard the aging process. The RDA for vitamin E is expressed in a-tocopherol equivalents (a-TE) because this is the most active form of vitamin E. The recommended daily intake is 10 a-TE for males and 8 a-TE for females. This is roughly the amount of vitamin E in a tablespoon of vegetable oil. 

Authors of works made also rather essential supervision connected to rather smaller or greater oxidability of double bonds, caused by influence of the neighboring substitutions, (oxymethylene groups, aldehyde and ketone groups) which is testified by publications of different years [7-9]. From peracids for oxidation of olefins apply peracetic acid [7, 10], pertri-fluoroacetic acid [11], m-chloroperbenzoic acid [10, 12] and perbenzoic acid [4, 13]. 

L-Ascorbic acid, an enediol, has been oxidized by sodium hypoiodite and by potassium permanganate to L-threonic acid (9). Such oxidation of double bonds does not occur in the enols alone, for D-arabinal is oxidized by H2O2 and OSO4 in er butanol to D-erythronic acid in addition to D-arabinose (10). Periodic acid and lead tetraacetate are useful for the cleavage of hexitols and glycosides to glyceraldehyde and glycolaldehyde (see Chapter... 

Products of degradation - chalking, oxidation of double bonds ... 

The oxidation of double bonds in polymers in a non-aqueous solvent leads to the formation of ozonides which, when acted upon by water, are hydrolysed to carbonyl compounds ... 

The basic difference between the latter type of resins and the alkyds is that they do not contain oil or oil-derived fatty acids which are otherwise an integral part of conventional baking alkyds. The absence of oil imparts a light colour to the resins and eliminates post-embrittlement caused by the oxidation of double bonds present in oils. Also, the elimination of long-chain fatty acids gives improved chemical resistance. A unique hardness-to-flexibility relationship with polyester resins made it possible to attain greater hardness with higher reverse impact than is possible with current systems. 

Epoxides are reactive entities due to the strain of the oxacyclopropane moiety. They can be formed from a variety of precursors but this chapter will be limited to the formation of epoxides by the oxidation of double bonds. If the double bond bears three or four different substitutes, epoxidation creates one or two chiral centers. In almost all epoxide-containing natural products these chiral centers were not created by chance and the products are nonracemic but contain an excess of one enantiomer. The chirality of the epoxides is caused by the chirality and the regioselectivity of the forming enzyme. This is a general attribute of enzymes making them ideal tools for enantiopure syntheses. 

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