Alkenes peracid epoxidation

At that period of time, this rather primitive transition structure for the peracid epoxidation of ethylene was sufficiently novel to warrant publication as a communication Today, calculating transition structures for epoxidation of a variety of complex alkenes with the actual peracid used experimentally, such as meta-chloroperoxybenzoic acid m-CPBA), is commonplace . ... 

The most convincing evidence for an essentially synchronous peracid epoxidation of simple alkenes came from a combined experimental and theoretical study by Singleton, Honk and coworkers. Experimental KIEs for the reaction of m-CPBA with 1-pentene, determined by the clever methodology developed by Singleton and Thomas utilizing the combinatorial high-precision determination of C and H KIEs at natural abundance, confirmed the symmetrical or nearly symmetrical nature of this epoxidation TS. These data were corroborated by B3LYP/6-31G calculations on propylene that supported a synchronous transition state for peroxyformic acid epoxidation. 

Several general conclusions may be drawn concerning the mechanism of peracid epoxidation of alkenes ... 

Conversion of alkenes to epoxides The simplest epoxide, ethylene dioxide, is prepared by catalytic oxidation of ethylene, and alkenes are also oxidized to other epoxides by peracid or peroxy acid (see Section 5.7.2). 

Metal-Catalyzed Epoxidation. Hydrogen peroxide is able to convert alkenes to epoxides in the presence of metal catalysts. Several metal oxides (Mo03, W03, Se02, V205) are known to catalyze such epoxidations.2,245,278,279 All these catalysts form stable inorganic peracids, and these peracids are supposedly involved in epoxidation in a process similar to organic peracids. 

The diastereoselectivity of the addition of hypohalous acids and esters to alkenes is potentially even more susceptible to polar effects than peracid epoxidations124 they correlate to the electronegativity of the halogen and of the oxygen substituent. The derived epoxide normally has the opposite configuration to that resulting from the polar effect on peracid epoxidation, e.g., formation of the epoxide 2 with various acyl hypohalites38. 

Surprisingly, JV-methylation of the alanyl group in one of these alkenes has been reported to retain the very high syn selectivity of peracid epoxidation (Table 9, entries 10 and 11) from the stereochemical outcome of these two epoxidations it has been argued that a second NH hydrogen... 

The oxidation of amines, acylhydrazines, and alkoxy amines described in this section involves the formation of nitrenes or other intermediates, depending on the nature of the nitrogen substituent and the oxidant, although lead tetraacetate is commonly employed. For example, a nitrenium ion or an amino lead derivative was proposed as the intermediate in the oxidation of alkoxyamines with lead tetraacetate 2. However, evidence has been provided that the jV-acetoxy species is the intermediate in the aziridination of alkenes with V-aminophthal-imide and /V-aminoquinazolinone, where a mechanism analogous to the Bartlett mechanism for the peracid epoxidation of alkenes should be operating3,4. 

In contrast with other electrophilic additions, the peracid epoxidation is syn-stereospecific. With sterically strongly hindered alkenes the reaction takes place on the less sterically hindered side. In other cases, the stereochemistry of the reaction is affected by polar effects or the geometry of the transition state. Important conclusions regarding the mechanism of the reaction can be drawn from the steric pathways in the synthesis of the oxiranes. This has been dealt with comprehensively by Berti, who reviewed the topic up to 1971, with special emphasis on the peracid oxidation. A noteworthy account of the topic of peracid epoxidation is given in a review by Rebek. ... 

Other phenol derivatives that are used to form the backbone of an epoxy resin include bisphenol E, bisphenol F, resorcinol, brominated bisphenols, and more highly functionalized molecules such as tetrakisphenylolethane. Alcohols, amines, and carboxylic acids may be combined with epichlorohydrin to give a range of diglycidyl ether based epoxy resins. Non-aromatic, commercially available epoxides are produced by peracid epoxidation of alkenes and dienes, such as vinyl cyclohexene and esters of cyclohexane carboxylic acids [23]. The chemical formulas for two common uncured polymers are shown below ... 

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