Oxidation of epoxides

Electrochemical oxidation of epoxides in absence of nucleophiles, catalyses a rearrangement to the carbonyl compound. The electrolyte for this process is dichlo-romethane with tetrabutylammonium perchlorate. Reaction, illustrated in Scheme 8.7, involves the initial formation of a radical-cation, then rearrangement to the ketone radical-cation, which oxidises a molecule of the substrate epoxide. The process is catalytic and requires only a small charge of electricity [73]. 

As the oxidation of epoxides with PCC is relatively slow, it is possible to adjust the oxidation conditions so as to selectively transform an alcohol into an aldehyde or ketone in the presence of an epoxide.292... 

The role of the acid catalyst during the oxidation of epoxides with DMSO has been explored by DFT studies of three acids, namely H30+, Li+, and Mg2+. Stationary points have been obtained at the B3LYP/6-31+- -G(d,p) level of theory and the reaction barriers have been evaluated through tree-energy calculations. The mechanism proceeds in two steps, namely ring opening followed by an intramolecular proton transfer that leads to an a-hydroxy carbonyl compound.88 The epoxidation... 

An important factor in the oxidation of epoxides by BP" to their corresponding radical cations would certainly be the much longer lifetime of BP compared to... 

Antoniotti and Dunach have reviewed the stoichiometric and catalytic oxidation of epoxides and their scope in organic synthesis, with particular focus on the Bi/02-catalyzed oxidation developed in their group. Such reactions can lead to either the oxidative cleavage of the epoxy carbon-carbon bond (giving carbonyl compounds or carboxylic acids (Scheme 57, Equation 14) or alternatively the formation of a-functionalized ketones when the C-C bond of the epoxide remains uncleaved (Scheme 57, Equation 15) <2003S2753>. 

The oxidation of epoxides by chromium(VI) oxide can be used to prepare ketolsfrom trisubstituted epoxides. 

The presence of induction periods in the thermooxidative destruction of epoxide resins indicates an autocatalytic character of the reaction. By analogy with other polymers, the authors proposed that the oxidation of epoxide resins is a chain reaction with degenerate branches, which are related to decomposition of the hydroperoxides formed during the oxidation process. 

Villemind and Hammadi (1995) used DMSO in presence of KSF for the oxidation of epoxide into a-hydroxyketones under microwave irradiation. The a-hydroxyketones were produced in good yields (55-90%). 

Futamura, S., Kusunose, S., Ohta, H., and Kamiya, Y, Formation of ozonides via 9,10-dicyanoan-thracene-sensitized photo-oxidation of epoxides,/. Chem. Soc., Chem. Commun., 1223, 1982. 

Acid-catalyzed oxidation of epoxides with HBp4-OMe2/ DMSO results in the formation of a-hydroxy ketones (eq 6). This procedure in an acidic medium complements the a-hydroxylation of ketone enolates under strongly basic conditions. 

Regioselectivity of C—C double bond formation can also be achieved in the reductiv or oxidative elimination of two functional groups from adjacent carbon atoms. Well estab llshed methods in synthesis include the reductive cleavage of cyclic thionocarbonates derivec from glycols (E.J. Corey, 1968 C W. Hartmann, 1972), the reduction of epoxides with Zn/Nal or of dihalides with metals, organometallic compounds, or Nal/acetone (seep.lS6f), and the oxidative decarboxylation of 1,2-dicarboxylic acids (C.A. Grob, 1958 S. Masamune, 1966 R.A. Sheldon, 1972) or their r-butyl peresters (E.N. Cain, 1969). 

Three membered rings that contain oxygen are called epoxides At one time epox ides were named as oxides of alkenes Ethylene oxide and propylene oxide for exam pie are the common names of two industrially important epoxides... 

Benzene with no alkyl side chain and no benzyhc hydrogens undergoes a different reaction under these conditions Oxidation of the ring occurs to convert benzene to its epoxide... 

This kind of chemical reactivity of epoxides is rather general Nucleophiles other than Gng nard reagents react with epoxides and epoxides more elaborate than ethylene oxide may be used All these features of epoxide chemistry will be discussed m Sections 16 11-16 13... 

Overall the stereospecificity of this method is the same as that observed m per oxy acid oxidation of alkenes Substituents that are cis to each other m the alkene remain CIS m the epoxide This is because formation of the bromohydrm involves anti addition and the ensuing intramolecular nucleophilic substitution reaction takes place with mver Sion of configuration at the carbon that bears the halide leaving group... 

We saw an example of nucleophilic ring opening of epoxides in Section 15 4 where the reaction of Grignard reagents with ethylene oxide was described as a synthetic route to primary alcohols... 

As we ve just seen nucleophilic ring opening of ethylene oxide yields 2 substituted derivatives of ethanol Those reactions involved nucleophilic attack on the carbon of the ring under neutral or basic conditions Other nucleophilic ring openings of epoxides like wise give 2 substituted derivatives of ethanol but either involve an acid as a reactant or occur under conditions of acid catalysis... 

The use of epoxides as alkylating agents for diethyl malonate provides a useful route to y lactones Wnte equations illustrating such a sequence for styrene oxide as the starting epoxide Is the lactone formed by this reaction 3 phenylbutanohde or is it 4 phenylbutanohde ... 

The direct oxidation of fluoroalkenes is also an excellent general synthesis procedure for the preparation of perfluoroepoxides (eq. 8). This method exploits the low reactivity of the epoxide products to both organic and inorganic free radicals. 

Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

Aldehydes react with alkenylborates to give 1,3-diols upon oxidation of the intermediate (300). Alkynylborates ate transformed by epoxides into homoallyhc alcohols and alkenylborates into 1,4-diols (300,301). Carbon dioxide reacts with alkenylborates to yield catboxyhc acids (302). The scope of these transformations is further extended by the use of functionalized electrophiles and borates, often reacting with high stereoselectivity. For example, in the... 

An oxirane process utilizes ethylbenzene to make the hydroperoxide, which then is used to make propylene oxide [75-56-9]. The hydroperoxide-producing reaction is similar to the first step of cumene LPO except that it is slower (2,224,316—318). In the epoxidation step, a-phenylethyl alcohol [98-85-1] is the coproduct. It is dehydrated to styrene [100-42-5]. The reported 1992 capacity for styrene by this route was 0.59 X 10 t/yr (319). The corresponding propylene oxide capacity is ca 0.33 x 10 t/yr. The total propylene oxide capacity based on hydroperoxide oxidation of propylene [115-07-1] (coproducts are /-butyl alcohol and styrene) is 1.05 x 10 t/yr (225). 

Alkoxide-Type Initiators. Using the guide that an appropriate initiator should have approximately the same stmcture and reactivity as the propagating anionic species (see Table 1), alkoxide, thioalkoxide, carboxylate, and sUanolate salts would be expected to be usehil initiators for the anionic polymeri2ation of epoxides, thikanes, lactones, and sUoxanes, respectively (106—108). Thus low molecular weight poly(ethylene oxide) can be prepared... 

Obsolete uses of urea peroxohydrate, as a convenient source of aqueous hydrogen peroxide, include the chemical deburring of metals, as a topical disinfectant and mouth wash, and as a hairdresser s bleach. In the 1990s the compound has been studied as a laboratory oxidant in organic chemistry (99,100). It effects epoxidation, the Baeyer-Villiger reaction, oxidation of aromatic amines to nitro compounds, and the conversion of sodium and nitrogen compounds to S—O and N—O compounds. 

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