Ethers, Epoxides, and Peroxides

Because di-/ fZ-alkyl peroxides are less susceptible to radical-induced decompositions, they are safer and more efficient radical generators than primary or secondary dialkyl peroxides. They are the preferred dialkyl peroxides for generating free radicals for commercial appHcations. Without reactive substrates present, di-/ fZ-alkyl peroxides decompose to generate alcohols, ketones, hydrocarbons, and minor amounts of ethers, epoxides, and carbon monoxide. Photolysis of di-/ fZ-butyl peroxide generates / fZ-butoxy radicals at low temperatures (75), whereas thermolysis at high temperatures generates methyl radicals by P-scission (44). 

Reagent for deoxygenation of epoxides and peroxides, and desulfurizations of thiiranes, and polysulfides. Ligand for metals of Groups IB, IIB, IVB, VB, VIB, VIII. Used as C H soln. for extraction-separation of In (as ion-associate with InBr4 , diisopropyl ether). Liq. with garlic-like odour. Misc. org. solvs. Fp 40°. Bp 240°, Bp2o 130°. 1.4635. 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

When analysing these different lists one realises that the different sources do not agree with each other. So far as the NFPA reactivity code is concerned, codes 2 and 3 have been attributed to epoxides and ethers that are unsaturated. Their purpose is to inform the reader about dangerous polymerisation and not peroxidation risks. The accidents described below also involve compounds such as dibutyl ether that are not considered as dangerous in the regulations or NFPA Extracting a fatty substance and a floor wax with diethyl ether gives rise to a detonation. 

The application of modern surface analysis techniques, such as XPS, to the analysis of modified polymer surfaces, has demonstrated that in most of the above processes the polymer is oxidized. Many functional groups such as hydroxyl, carbonyl, ether, carboxyl, ester, peroxide, epoxide, etc., have been detected by direct XPS analysis or after derivatization of functional groups. The interaction between evaporated metal films and several of such functional groups has been clearly demonstrated (3). 

As a resirlt of the differences in polarity between the carbon fluorine and the carbon-hydrogen bond, fluorocarbon chemistry is wrought with more differences than similarities to hydrocarbon chemistry despite their similarities in van der Waal s radii (1.20 vs. 1.35 A). A great body of chemistry for the functionalized fluorocarbons has been developed in the areas of perfluoroalkenes, halofluoroalkanes, ethers, epoxides, peroxides, ketones, acids, and esters. 

Oxyfluorides of Carbon. The literature on compounds containing only carbon, oxygen, and fluorine is extensive, numerous reviews are available, and many compounds are of industrial importance. Functional groups included under this classification are ketones, acid fluorides, ethers, epoxides, peroxides, and hypofluorites. Only very simple molecules are mentioned here as representatives of this large class of compounds. 

Based on enantioselective epoxidation and subsequent ring opening and closing, the so-called Achmatowicz reaction was developed. This is an organocatalytic one-pot cascade for the annulation of a,(J-unsaturated aldehydes, hydrogen peroxide, p-carbonyl compounds and NBS, which furnish optically active 3-pyrones. Other chiral heterocycles were also assembled by organocatalytic cascade reactions using diaiylprolinol silyl ethers as catalysts. ... 

Cyclo-octa-2,4-dien-l-ol is converted into anti -2,3-epoxycyclo-oct-4-enol (91 %) on treatment with m-chloroperoxybenzoic acid, whereas t-butyl peroxide-VO(acac)2 gives the bicyclic ether (163 78 %). 2,6,6-Trimethylcyclohepta-2,4-dienol is converted into syn-2,3-epoxy-2,6,6-trimethylcyclohept-4-enol (65 %) by m-chloroperoxybenzoic acid and into (164 86%) by t-butyl per oxide-VO(acac)2- As the syn-epoxycyclo-heptenol gave (164) on treatment with VO(acac)2, it was suggested that in the t-butyl peroxide-VO(acac)2 epoxidations the bicyclic ethers were formed via the syn-2,3-epoxides and subsequent transannular S 2 substitution. The nature of the products obtained from reactions of epoxides with lithium diethylamide is solvent dependent. Thus the mono-epoxide of cyclo-octa-1,5-diene gives cyclo-oct-3-enone in benzene or ether and bicyclo[5,l,0]oct-2-en-syn-6-ol in HMPT the exocyclic... 

Silyl enol ethers are a class of electron-rich, nonaromatic compounds that easily form reactive radical cations on one electron oxidation. The silyl enol ether functional group is closely related to the carbonyl function and consequently, syntheses of silyl enol ethers generally make use of enolates. In addition, silyl enol ethers can be described as masked enols or enolates since their reactions often yield ketones. A number of oxidation reactions of silyl enol ethers making use of oxygen or oxygen-containing reagents such as peroxides, peracids (known as Rubottom oxidation), dioxirane, osmium tetraoxide, or triphenyl phosphite ozonide have been described in the literature. In all cases either a-hydroxy-ketones or the silyl enol ether epoxides are formed. 

Tetrafluoroethylene undergoes addition reactions typical of an olefin. It bums in air to form carbon tetrafluoride, carbonyl fluoride, and carbon dioxide (24). Under controlled conditions, oxygenation produces an epoxide (25) or an explosive polymeric peroxide (24). Trifluorovinyl ethers,... 

Although the first and still most important epoxide resins are of the glycidyl ether type, other epoxide resins have been commercially marketed in recent years. These materials are generally prepared by epoxidising unsaturated compounds using hydrogen peroxide or peracetic acid. 

The reaction of allenes with peracids and other oxygen transfer reagents such as dimethyldioxirane (DM DO) or hydrogen peroxide proceeds via allene oxide intermediates (Scheme 17.17). The allene oxide moiety is a versatile functionality. It encompasses the structural features of an epoxide, an olefin and an enol ether. These reactive intermediates may then isomerize to cyclopropanones, react with nucleophiles to give functionalized ketones or participate in a second epoxidation reaction to give spirodioxides, which can react further with a nucleophile to give hydroxy ketones. 

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