Epoxidations, of alkenes and

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

The most important oxirane syntheses are by addition of an oxygen atom to a carbon-carbon double bond, i.e. by the epoxidation of alkenes, and these are considered in Section 5.05.4.2.2. The closing, by nucleophilic attack of oxygen on carbon, of an OCCX moiety is dealt with in Section 5.05.4.2.1 (this approach often uses alkenes as starting materials). Finally, oxirane synthesis from heterocycles is considered in Section 5.05.4.3 one of these methods, thermal rearrangement of 1,4-peroxides (Section 5.05.4.3.2), has assumed some importance in recent years. The synthesis of oxiranes is reviewed in (B-73MI50500) and (64HC(19-1U). 

The reaction is carried out using a titanium silicalite-1 (TS-1) zeolite catalyst [30, 122]. This type of catalyst is known to accelerate the selective oxidation of alcohols, epoxidation of alkenes and hydroxylation of aromatics. These reactions have importance for fine-chemical production. 

Khenkin, A.M. and Neumann, R. (2000). Aerobic photochemical oxidation in meso-porous Ti-MCM-41 epoxidation of alkenes and oxidation of sulfides. Catal. Lett. 68(1-2), 109-111... 

Based on these calculations, one can conclude that TSs for epoxidation of alkenes and allylic alcohols with peroxy acids, dioxiranes, and Re-peroxo complexes share a spiro geometry in which the plane of the attacking peroxo... 

Epoxides (oxiranes) can be reduced in different ways. So-called deoxygenation converts epoxides to alkenes. Such a reaction is very useful since it is the reversal of epoxidation of alkenes, and since both these reactions combined represent temporary protection of a double bond. 

SCHEME 85. Epoxidation of alkenes and alkenols with a perfluorinated quaternary ammonium salt of a polyoxometalate catalyst... 

Co(ni) alkyl peroxides have been prepared and used by Mimoun and coworkers in the hydroxylation of hydrocarbons with this metal a Haber-Weiss type of reactivity is suggested. Square-planar Pt(II) complexes, of the type [(dppe)Pt(CF3)(solv)], used by Strukul in the epoxidation of alkenes and in Baeyer-Villiger oxidations of ketones (Schemes 8 and 9), are effective catalysts also in the direct hydroxylation of aromatics with hydrogen peroxide. The reactivity increases in the presence of electron releasing substituents in the aromatic ring. Ortho and para derivatives are practically the only products observed and interesting selectivity toward the ortho products has been detected (equation 85). 

In mammalian liver microsomes, cytochrome P-450 is not specific and catalyzes a wide variety of oxidative transformations, such as (i) aliphatic C—H hydroxylation occurring at the most nucleophilic C—H bonds (tertiary > secondary > primary) (ii) aromatic hydroxylation at the most nucleophilic positions with a characteristic intramolecular migration and retention of substituents of the aromatic ring, called an NIH shift,74 which indicates the intermediate formation of arene oxides (iii) epoxidation of alkenes and (iv) dealkylation (O, N, S) or oxidation (N, S) of heteroatoms. In mammalian liver these processes are of considerable importance in the elimination of xenobiotics and the metabolism of drugs, and also in the transformation of innocuous molecules into toxic or carcinogenic substances.75 77... 

The oxidative properties of chromium-oxo complexes towards organic substrates have been thoroughly investigated, and several reviews have appeared in recent years.270 276 We will only briefly consider the oxidation of alcohols to carbonyl compounds, the epoxidation of alkenes and the hydroxylation of hydrocarbons. 

In the presence of ascorbate coreducing agent and under phase-transfer conditions, manganese porphyrins have recently been shown to activate oxygen by catalyzing epoxidation of alkenes and hydroxylation of alkanes to alkanol-one mixtures.484... 

Epoxidation of alkenes and hydroxylation of alkanes can be achieved under mild conditions with iron porphyrin catalysts and iodosylbenzene as the oxidant.497 499,488... 

The molybdenum complex 227 is an effective catalyst for epoxidation of alkenes and has allowed the development of the polystyrene-supported peptide-linked epoxidation catalyst 228351. 

Iodine-catalysed hydroperoxidation of cyclic and acyclic ketones with aqueous hydrogen peroxide in acetonitrile is an efficient and eco-friendly method for the synthesis of gem -dihydroperoxides and the reaction is conducted in a neutral medium with a readily available low-cost oxidant and catalyst.218 Aryl benzyl selenoxides, particularly benzyl 3,5-bis(trifluoromethyl)phenyl selenoxide, are excellent catalysts for the epoxidation of alkenes and Baeyer-Villiger oxidation of aldehydes and ketones with hydrogen peroxide.219 Efficient, eco-friendly, and selective oxidation of secondary alcohols is achieved with hydrogen peroxide using aqueous hydrogen bromide as a catalyst. Other peroxides such as i-butyl hydroperoxide (TBHP), sodium... 

The enzymes reductively activate dioxygen using NADPH as an electron source. One oxygen atom is then reduced to water and the other atom is transferred to a substrate, resulting in the hydroxylation of alkenes and arenes, the epoxidation of alkenes and the formation of N-oxides and S-oxides from amino and sulphur compounds. Other P-450 reactions include N-dealkylation, O-dealkylation and reductase-like dehalogenation of halocarbons. Typical P-450 reactions are summarised in Ihble 5-4. 

Hill and co-workers have reported that TMSP is effective for the epoxidation of alkenes and the oxygenation of alkanes by use of f-BuOOH and PhIO as oxidants [67]. The characteristics of TMSP in alkene epoxidation, compared with those of metalloporphy-rins, Schiff base complexes, and triflate salts, are as follows [67] ... 

It is immediately apparent from Table 3 why hydrophobic TS-1 is an excellent catalyst for the epoxidation of alkenes and why a polar solvent, like methanol or water, is preferable. On a qualitative basis, it can be understood why the apolar hydrocarbon has a greater affinity for the hydrophobic surface of the pores, whereas water (and methanol) has an affinity for the external polar solution. The concentration of the former in the proximity of active sites is high, while that of the latter is small. It is also predicted that a longer chain olefin (or paraffin) is oxidized faster than a shorter one, as is found experimentally. 

Epoxidation. In the presence of catalytic amounts of 18-crown-6 and an acyl chloride, KO, can effect epoxidation of alkenes and of some polycyclic arenes derived from phenanthrene. The most effective acyl chlorides are phosgene and benzoyl chloride. The highest yields of epoxides are formed from fran,v-stilbene (89%) and cyclohexene (80%). The 9,10-epoxide of phenanthrene is obtained in 38% yield. 

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