Double bond oxidation

Oxidation of olefins and dienes provides the classic means for syntheses of 1,2- and 1,4-difunctional carbon compounds. The related cleavage of cyclohexene rings to produce 1,6-dioxo compounds has already been discussed in section 1.14. Many regio- and stereoselective oxidations have been developed within the enormously productive field of steroid syntheses. Our examples for regio- and stereoselective C C double bond oxidations as well as the examples for C C double bond cleavages (see p. 87f.) are largely selected from this area. 

The second way in which fats deteriorate is oxidative lipolysis. This is an entirely different process in which oxygen free radicals add across double bonds. Oxidative rancidity can be prevented or reduced by several different routes. One way is to ensure that no double bonds are present. Another is to use anti-oxidants that act as free radical traps. Exposure to oxygen and ultraviolet light should be avoided. Reducing the temperature has no effect since free radical processes have a zero activation energy. 

The etherified starch was further transformed by hydrogenation of the double bonds to yield the corresponding linear octyl groups using [RhCl(TPPTS)3] catalyst soluble in EtOH-H20 mixtures. Complete hydrogenation was obtained at 40 °C under 30 bar of H2 after 12 h using 0.8-wt.% Rh-catalyst [84]. Other catalytic transformations such as double bond oxidation and olefin metathesis could possibly be used to prepare other modified starches for various applications. 

Hydrogenation/Reduction/Reductive Ring Cleavage of the N-0 Bond, 6.2 Hydroxylation of the Ring Carbon-Carbon Double Bond/Oxidation, 6.3 Ozonolysis. 6.4 Epoxidation... 

Hydroxylation of the Ring Carbon-Carbon Double Bond/Oxidation... 

Butenolide annotation. A new method was used to add the butenolide ring of the novel sesquiterpene colorata-4(13), 8-dienolide (5) to the ketone 1. Reaction of C6H5SCH2Li with 2 followed by hydrolysis gives 3 in 65% yield, but the hydrolysis at 20 requires about 4 weeks to prevent isomerization of the double bond. Oxidation of 3 followed by dehydration gives the thiophenylfurane 4. A similar slow hydrolysis (1 week) of 4 gives the desired 5. 

Eliminations to Form Carbon-Oxygen Double Bonds Oxidation Reactions... 

ELIMINATIONS TO FORM CARBON-OXYGEN DOUBLE BONDS OXIDATION REACTIONS... 

Pyridine could function as a nucleophile in ozonization. It is soluble in hydrocarbons and is rather stable towards ozone (8, 11). Pyridine does have a dramatic effect on the course of ozonization. Slomp and Johnson (13) in their work on the ozonolysis of 4,22-stigmastadien-3-one propose that two moles of aldehyde are formed for each mole of double bond oxidized and that pyridine is oxidized to pyridine oxide. They also propose that pyridine oxide oxidizes aldehyde to acid with regeneration of pyridine. 

The syn addition of BH3 across the double bond of norbornene takes place mostly from the more accessible outside (exo) face of the double bond. Oxidation gives a product with both the hydrogen atom and the hydroxyl group in exo positions. (The less accessible inner face of the double bond is called the endo face.)... 

A similar reactivity was observed for piperidino enamines of linear ketones which gave a-amino ketones, derived by rearrangement of the epoxide intermediates, and products of carbon-carbon double-bond oxidative cleavage33. 

Both chemical and enzymatic synthetic methods for the asymmetric oxidation of the carbon-carbon double bond have been developed [46], but the area of carbon-carbon double bond oxidations has been shaped by the breakthrough discovery of asymmetric epoxidation of allylic alcohols with the Katsuki-Sharpless method [47]. Catalytic asymmetric synthesis of epoxides from alkenes by Jacobsen... 

Acetoxylation of enol thioethers. The reaction of enol thioethers with lead tetraacetate (1,1 equiv.) in THF for 1 hour followed by addition of BFj etherate (or 5 N KOH-ether) results in allylic acetoxylation. The reaction is considered to involve bisacetoxylation of the double bond. Oxidation of sulfur is not observed. Examples ... 

Oxidative cleavage of an alkene breaks both the a and n bonds of the double bond to form two carbonyl groups. Depending on the number of R groups bonded to the double bond, oxidative cleavage yields either ketones or aldehydes. 

Oxidations by dioxygenases cw-hydroxylation of aromatic double bonds. Oxidations catalyzed by oxidases regio- and stereoselective oxidations of polyols oxidations of carbohydrates oxidations of hydroxy steroids oxidations of alkyl phenols to form chiral /7-hydroxybenzylic alcohols hydroxylation of phenols oxidation of amino acids to keto acids. 

Vitamin A with its five conjugated double bonds oxidizes to 5,8-epoxides (15) with subsequent loss of UV absorption at 325 nm. Thus, vitamin A was studied with the addition of various antioxidants (Table XI) in open bottles in thin layers. Although EMQ was the best, it is limited to use in vitamin A for animal feeds. AP activity was not great, but when added to a mixture of tocopherol, BHT, and diethanolamide, AP gave excellent protection. Klaui (16) has shown stability of vitamin A palmitate with tocopherol, AP, and an amine equal to 1300 h, compared to a control equal to 100 h. However, the antioxidants in the dry market form (beadlets) protect the vitamin A in the beadlets as well as the end use of the product. For example, spray-dried vitamin A can be pro-... 

In the synthesis of an ionophore antibiotic, a bicyclic sulfone made by oxidation of the corresponding sulfide with PhSeSePh/H202 to avoid double bond oxidation was coupled with an allylic bromide in 97% yield and high stereoselectivity. The sulfonyl group was finally eliminated in basic medium to create a trans-dxene (Scheme 66). 

Oxidative addition can also occur at C(sp2)-X bonds (i.e., at vinyl and aryl halides). It always occurs with retention of configuration about the double bond. Oxidative addition at C(sp2)-X obviously cannot proceed by an Sn2 mechanism. The SRN1 mechanism is a possibility. Another possibility is that the Pd coordinates first to the 77 bond of, say, vinyl iodide, to form a 7r complex. The metal-lacyclopropane resonance structure of the 77 complex can be drawn. An electro-cyclic ring opening of the metallacyclopropane (Chapter 4) can then occur. One Pd-C bond breaks, and I- leaves to give a new cationic Pd-vinyl complex. When I associates with the Pd, the overall result is oxidative addition. 

Oxidation of alcohol, carbonyl and acid functions, hydroxylation of aliphatic carbon atoms, hydroxylation of alicyclic carbon atoms, oxidation of aromatic carbon atoms, oxidation of carbon-carbon double bonds, oxidation of nitrogen-containing functional groups, oxidation of silicon, phosphorus, arsenic and sulfur, oxidative N-dealkylation, oxidative O- and S-dealkylation, oxidative deamination, other oxidative reactions... 

Case c (electrophilic character) allows one a direct attack of a double bond (oxidative breaking). 

The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction which occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds and the adjacent allylic functions are the sites of this chemical activity. Oil oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (18 3) with three double bonds is more susceptible to oxidation than linoleic (18 2) with only two double bonds, which is ten or more times as susceptible as oleic (18 1) with only one double bond. Oxidative deterioration results in the formation of hydroperoxides, which decompose into carbonyls, and dimerized and polymerized gums. It is accelerated by a rise in temperature, oxygen pressure, prior oxidation, metal ions, lipoxygenases, hematin compounds, loss of natural antioxidant, absence of metal deactivators, time and ultraviolet or visible light. Extensive oxidation will eventually destroy the beneficial components contained in many fats and oils, such as the carotenoids (vitamin A), the essential fatty acids (linoleic and linolenic), and the tocopherols (vitamin E). 

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