Epoxides Oxiranes

Epoxides (or oxiranes) are cyclic ethers with a three-membered ring containing one oxygen atom. 

The most important commercial epoxide is ethylene oxide, produced by the silver-catalyzed air oxidation of ethylene. 

Worldwide production of ethylene oxide exceeds 30 billion pounds per year. Only rather small amounts are used directly (for example, as a fumigant in grain storage). Most of the ethylene oxide constitutes a versatile raw material for the manufacture of other products, the main one being ethylene glycol. 

The reaction in eq. 8.17 is suitable only for ethylene oxide. Other epoxides are usually prepared by the reaction of an alkene with an organic peroxyacid (often called simply a peracid). 

Peroxy acids are structurally related to hydrogen peroxide H—O—O—H, and peroxy acids are good oxidizing agents. On a large scale, peracetic acid (eq. 8.18, R = CH3) is used, whereas in the laboratory, organic peroxy acids such as m-chloroperbenzoic acid (R = m-chlorophenyl) are frequently used. 

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A quite different use of a thiocyanate salt is the conversion of an epoxide (oxirane) to an episulfide (thiirane) this normally heterogeneous reaction is markedly accelerated by the use of silica gel coated with, or finely ground with, potassium thiocyanate, rather than with the thiocyanate salt alone.17... 

Epoxides (oxirans) and 1,2-diols can also be looked upon as disguised ketones capable of being unmasked by acids. Since its development by Spencer et al49 the idea has been utilized by several other groups who used protic acids in work aimed at syntheses of methyl lambertianate,50 a rare furanoid fatty acid from an Exocarpus species,51 and a terpenoid furan,... 

We owe to Kato and his colleagues a considerable advance in furan copper reagents. They have demonstrated the formation of the lithium di(3-furyl) cuprate species 87 which is highly reactive and possesses hard properties that suit it to reaction at hard centers, mainly carbonyl carbon.223 The reagent is easily prepared in situ from 3-furyllithium and Cu2I2. Simple copper derivatives do not react with ketones, but this cuprate reacts well and quantitatively with acid chlorides. It also reacts well with some epoxides (oxirans). Moreover, there is another form prepared in the presence of... 

Preparation of epoxides (oxirans) on the commercial scale as resin or polymer components is widely practised. Careful control of conditions is necessary to avoid hazards, and the several factors involved are reviewed. 

Also known as glycol dinitrate. eth-o,len m,trat ethylene oxide orgchem 1. (CH2)20 A colorless gas, soluble in organic solvents and miscible in water, boiling point 11°C used in organic synthesis, for sterilizing, and for fumigating. 2. Also known as 1,2-epoxyethane epoxide oxirane eth-3,len ak,sTd ... 

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. 

The crucial methylenation step in this synthesis undoubtedly gave the 3,5-methylene acetal, not the 2,3-acetal (or the highly improbable 2,5-methylene acetal), because, otherwise, a 6-0-methyl-2(or 3)-0-p-tolylsulfonyl compound would have been obtained which could only have formed an epoxide (oxirane). The oxirane ring might have been opened under the conditions of the saponification the product would not then have been a dianhydride. 

Sulfur ylides react with aldehydes and ketones to form epoxides (oxiranes) ... 

Deoxygenation of epoxides Oxiranes are converted into alkenes with the same configuration by ISi(CH3)3 generated in situ. 

Epoxides (oxiranes) are three-membered cyclic ethers. The simplest and commercially most important example is ethylene oxide, manufactured from ethylene, air, and a silver catalyst. In the laboratory, epoxides are most commonly prepared from alkenes and organic peroxy acids. 

Know the meaning of epoxide, oxirane, organic peroxy acid, nucleophilic addition to epoxides, diethylene glycol. 

Oxacyclic monomers constitute the most widely investigated class of heterocyclic monomers regarding both academic and industrial interest. In particular, the coordination polymerisation of cyclic ethers such as epoxides (oxiranes) and of cyclic esters such as lactones, lactides and cyclic carbonates has been considered. 

Entropy change (AS) (Section 2.6) Entropy is a measure of disorder. Processes that increase the disorder in a system (AS > 0) are favored. Epoxide (oxirane) (Section 10.10) A three-membered cyclic ether. 

Epoxides (Oxiranes) We have already encountered some of the chemistry of epoxides in Section 8-12. Epoxides are three-membered cyclic ethers, usually formed by peroxyacid oxidation of the corresponding alkenes. The common name of an epoxide is formed by adding oxide to the name of the alkene that is oxidized. The following reactions show the synthesis and common names of two simple epoxides. 

The formation of polyfluoroalkoxyanions from perfluoroketones was discussed, along with other addition reactions of perfluoroketones, in Section IB, Subsection 2 similar anions can also be generated from acid fluorides and epoxides (oxiranes), as represented in Figure 8.46. 

Ethers (ROR ) may be considered to be the anhydrides of alcohols which are formed by the elimination of water from two alcohols (ROH and R OH). Epoxides (oxiranes) are a sub-set of ethers and share many of their characteristics which are derived from the presence of the oxygen lone pairs. However, their much greater reactivity arising from the strained nature of the three membered ring and their wider use in synthesis means that they are best considered separately. 

Sulfonium salts react in several ways. They may behave as a leaving group, undergoing substitution by a nucleophile or fragmenting with the formation of an alkene. However, the most important reaction of sulfonium salts involves the formation of an ylide in the presence of a base. The carbanion of this sulfur ylide is stabilized by the adjacent positively charged sulfonium ion. The reaction of the carbanion with a carbonyl group parallels that of a phosphonium ylide in the Wittig reaction. However, the decomposition of the intermediate dipolar species is different and leads to the formation of an epoxide (oxirane) rather than an alkene. 

Metabolic epoxidation of carbon-carbon double bonds in alkenes and arenes is a fundamentally important biotransformation of foreign compounds. The primary epoxide (oxirane) metabolites formed generally undergo further biotransformation to more polar and readily excreted metabolites via conjugation with glutathione or epoxide-hydrolase-mediated hydrolysis to diols. Thus, epoxidation can be considered the first step in a metabolic detoxification scheme. On the other hand, epoxidation is also a... 

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