Molecular oxygen, oxidation rearrangements

A chemical transformation, on the other hand, produces new substances. For example, when magnesium metal bums in air, elemental magnesium metal and molecular oxygen combine chemically to form magnesium oxide, a white solid containing Mg and O atoms in 1 1 ratio. This is a chemical transformation that rearranges the atoms in Mg and O2 to yield MgO. 

As described in the preceding paragraphs, oxidation products of carotenoids can be formed in vitro as a result of their antioxidant or prooxidant actions or after their autoxidation by molecular oxygen. They can also be found in nature, possibly as metabolites of carotenoids. Frequently encountered products are the monoepoxide in 5,6- or 5, 6 -positions and the diepoxide in 5,6 5, 6 positions or rearrangement products creating furanoid cycles in the 5,8 or 5, 8 positions and 5,8 5, 8 positions, respectively. Products like apo-carotenals and apo-carotenones issued from oxidative cleavages are also common oxidation products of carotenoids also found in nature. When the fission occurs on a cyclic bond, the C-40 carbon skeleton is retained and the products are called seco-carotenoids. 

Oxidation to CO of biodiesel results in the formation of hydroperoxides. The formation of a hydroperoxide follows a well-known peroxidation chain mechanism. Oxidative lipid modifications occur through lipid peroxidation mechanisms in which free radicals and reactive oxygen species abstract a methylene hydrogen atom from polyunsaturated fatty acids, producing a carbon-centered lipid radical. Spontaneous rearrangement of the 1,4-pentadiene yields a conjugated diene, which reacts with molecular oxygen to form a lipid peroxyl radical. 

Isoquinoline Reissert compounds of type 12 could be easily converted to the corresponding 1-cyanoisoquinolines (13) by simple base treatment (4,5) (Scheme 3). This transformation also takes place with high yields when type 12 compounds are oxidized with molecular oxygen in a two-phase system in the presence of phase-transfer catalysts (12-14). It should be mentioned that similar oxidation of dihydro Reissert compounds of type 14 afforded the corresponding dihydroisocarbostyril derivatives (15) (12-14). Base treatment of isoquinoline Reissert eompounds followed by intramolecular rearrangement, due to the absence of a proper intermolecular reaction partner, results in 1-acylisoquinoline derivatives (18) (3). 

Molecular oxygen reacts with the free-radical, giving a peroxy radical of atrazine as shown in Equation (6.137). This is reduced by Fe2+ to form a hydroperoxide. The rearrangement of the hydroperoxide forms amide through oxidation of secondary C with loss of a water molecule, as shown in Equation (6.139). 

A novel and unusual oxidative rearrangement of 6-methoxypyran-2-ones to form highly functionalized cr,/3-buteno-lides has been reported <20050L3705>. The oxidation occurs at 20 °C in the presence of molecular oxygen. A mechanism was proposed for this transformation and is shown in Scheme 21. 

The biopterin product is recycled by elimination of water, reduction using NADPH as the reagent, and reaction with molecular oxygen. The other product, the phenylalanine oxide, rearranges with a hydride shift followed by the loss of a proton to give tyrosine. 

Caprolactam can be made by the Beckmann rearrangement of the oxime f of cyclohexanone. (Check that you can draw the mechanisms, of both these reactions and look at Chapters 14 and 37 if you find you can t.) Cyclohexanone used to be made by the oxidation of cyclohexane with molecular oxygen until the explosion at Fiixborough in Lincolnshire on 1 June 1974 that killed 28 people. Now cyclohexanone is made from phenol. 

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