Epoxidation definition

CAS 8013-07-8 EINECS/EEINCS 232-391-0 Synonyms Epoxidized soya oil ESBO ESO Soybean oil, epoxidized Definition Modified oil obtained from soybean oil by epoxidation Properties Clear pale yel. liq., low odor sol. < 0.1% in water sp.gr. 0.99 ... 

More definitive evidence for the formation of an oxirene intermediate or transition state was presented recently by Cormier 80TL2021), in an extension of his earlier work on diazo ketones 77TL2231). This approach was based on the realization that, in principle, the oxirene (87) could be generated from the diazo ketones (88) or (89) via the oxocarbenes 90 or 91) or from the alkyne (92 Scheme 91). If the carbenes (90) (from 88) and (91) (from 89) equilibrate through the oxirene (87), and if (87) is also the initial product of epoxidation of (92), then essentially the same mixture of products (hexenones and ketene-derived products) should be formed on decomposition of the diazo ketones and on oxidation of the alkyne this was the case. 

All unsolvated TSs lie in a narrow range of 2 kcal/mol relative to 5 + propenol. From the point of view of a qualitative analysis, it is disappointing that we were unable to identify any structural characteristic that might definitely favor or disfavor one TS with respect to the others. Would the reaction occur via unsolvated TSs, all eight of them are expected to contribute to some extent to the formation of the final epoxide. 

As discussed above, the activation barrier of solvated complexes (type b) is larger, since the starting complex is more stabilized than the TS. Notwithstanding this barrier increase, solvated TSs reside at much lower (absolute) energies than their unsolvated counterparts. However, hydrated TSs are entropically disfavored (by 9 kcal/mol in the gas phase) with respect to the corresponding water-free TSs. These observations prevent a definitive decision whether 5 or 5b is the active epoxidant species in solution. 

The problem of the role of acidity in the oxidation reaction has been examined. To this end silicalites containing both Ti(IV) and Al(III),- or Fe(III) or Ga(III) have been synthesized [24-26] and used in the epoxidation of propylene. It is well known that trivalent elements introduced in the framework impart definite acidic character to the material. The results obtained under very similar experimental conditions are given in Table 2. 

Epimerization of sugar, mechanisms 778 Epimers, definition of 163 Epinephrine (adrenaline) 542,553, 553s Episomes. See plasmid Epithelial cells 29 Epitheliocytes 25 Epoxides, alkyation by 254 Epoxide hydrolases 591 EPR (electron paramagnetic resonance) spectroscopy 398, 399 of glutamate mutase 873 in study of phosphotransferases 639 EPSP (enolpyruvoylshikimate-3-phosphate) 687s... 

The epoxide ring of methyl crotonate has been reposted to undergo addition of methanol on the carbon atom furthest from the u l<-r function (Eq. 574), giving methyl 2-hydroxy-3-methoxybutyrato.4"5 Alcoholysis of 1,1 -dioarbethoxy-1.2-epoxypropane in the presence of acid has also been carriod cut.1310 Although not definitely established, it is nevertheless probable that addition likewise takes plaoe at thr epoxide carbon atom farthest removed from the ester substituents. 

Before commencing, the attention of the reader is drawn to the terms enantiofacial selectivity and diastereoselectivity. The usage in this chapter does not conform to the strictest possible definitions of these terms. In particular, enantiofacial selectivity is used with reference to the selection and delivery of oxygen by the epoxidadon catalyst to one face of the olefin in preference to the other. This usage extends to chiral allylic alcohols (primarily the 1-substituted allylic alcohols) when the focus of the discussion is on face selection in the epoxidation process. Diastereoselectivity is used in the discussion of kinetic resolution when the generation of diastereomeric compounds is emphasized. 

The [3-hydroxy amines are a class of compounds falling within the generic definition of Eq. 6A.6. When the alcohol is secondary, the possibility for kinetic resolution exists if the Ti-tartrate complex is capable of catalyzing the enantioselective oxidation of the amine to an amine oxide (or other oxidation product). The use of the standard asymmetric epoxidation complex (i.e., T2(tartrate)2) to achieve such an enantioselective oxidation was unsuccessful. However, modification of the complex so that the stoichiometry lies between Ti2 (tartrate) j and Ti2(tartrate)1 5 leads to very successful kinetic resolutions of [3-hydroxyamines. A representative example is shown in Eq. 6A.11 [141b,c]. The oxidation and kinetic resolution of more than 20 secondary [3-hydroxyamines [141,145a] provides an indication of the scope of the reaction and of some... 

Epoxidation of aromatic hydrocarbons is an important method for the preparation of arene oxides. m-Chloroperbenzoic acid (MCPBA) is used in a two-phase system that involves treating the hydrocarbon with a large excess ( 10-fold) of MCPBA in methylene chloride-aqueous sodium bicarbonate at room temperature. The yields are moderate (10-60%). Because the arene oxides are sensitive to acids, the presence of sodium bicarbonate buffer is necessary. A number of K-region (see Section VII for a definition) epoxides like phenanthrene 9,10-oxide (1, 59%), 9,10-dimethylphenanthrene 9,10-oxide (2,40%), 9-phenylphenanthrene 9,10-epoxide (3,50%), pyrene 4,5-oxide (4, 14%), and chrysene 4,5-oxide (5,9%) have been prepared by this method.9... 

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