Three epoxides

The similar magnitudes of the rate coefficients k0 (Table 9) for three epoxides are in agreement with the simple SN 2 mechanism. Similar magnitudes of rate coefficients have been found also for the uncatalyzed reaction of ethylene oxide and the primary carbon in propylene oxide with chloride ion (Table 9). In the case of the two-step mechanism, methyl substitution would increase the basicity of the oxygen in the ring, favoring formation of the protonated intermediate, and exert a small influence on the Sn 2 reactivity of the primary carbon. The overall effect would be a rate increase. However, the experimental data do not agree with this expectation and, consequently, the two-step mechanism may be ruled out. 

The research of Warrener et al. in this area has yielded a number of interesting oxabicyclopentane derivatives. In their epoxidation of the Cookson ester (30) a mixture of the two monoepoxides (31) and (32) was isolated (Equation (1)) <94TL1075>. Epoxidation of Nenitzescu s ester (33) with MCPBA, contrary to an earlier report <83JOU1390, 83ZOR1543), delivers a mixture of the three epoxides (34), (35), and (36) (Equation (2)). Several research groups have directed interest toward the synthesis of Dewar furan (5-oxabicyclo[2.1,0]pent-2-ene) and its derivatives these have been... 

In a similar approach polyacrylates bearing alcoholic hydroxyl groups (hy-droxyethyl methacrylate) was mixed with a small molecule functionalized with two or three epoxides and a PAG [382]. 

When the preceding three epoxides were mixed with the catalysts (maleic anhydride or m-phenylenediamine), except for the AG-13E/C1 and UC Endo isomer/CL, all the mixtures exhibited two exothermic peaks and only one... 

The incubation of the same substrate (265) in M. plumbeus ATCC 4740 in high-iron-rich medium gave 270, which was obtained from C. lunata mentioned earlier, 268, 272, 273, 277,278, and 279. In low-iron medium, this fungus converted the same substrate 265 into three epoxides (274 276), a tetraol (280) with common metabolites (268, 273, 277,278), and 271, which was the same metabolite used by C. lunata (Collins et al., 2002a). It is interesting to note that only epoxides were obtained from the substrate (265) by Mucor fungus in low iron medium (Figure 20.83). 

Fig. 5 Relation between log 17 and log <7 for three epoxide oligomers ( ) Epikote 828 (O) Epikote 1001 ( ) Epikote 1004.

Fatty acids with polar substituents also retard the migration of triacylglycerols on TLC adsorbents, and those from seed oils that contain epoxy fatty acids can be separated into simpler species that contain from zero to three epoxide residue per mole. For example, silica gel layers and a solvent system of hexane-diethyl ether (3 1, v/v) were used to isolate such fractions from seed oils (Figure 9.1(B)) [192], Similar separations have been achieved with triacylglycerols that contain hydroxyl, estolide and other functional groups in the fatty acids. 

Here, the sample is suspended from a balance and located in an oven. Weight changes are recorded as temperature increases. Its particular use is in observing thermal degradation of adhesives. An example is taken from the work of Xu and Dillard (2003), which is shown in O Fig. 18.18. Data are for three epoxide adhesives made electrically conductive by the addition of about 80% by weight of powdered silver. It can be seen that they all begin to decompose at about 400° C. 

To a mixture of 100 ml of THF and 0.10 mol of the epoxide (note 1) was added 0.5 g Of copper(I) bromide. A solution of phenylmagnesium bromide (prepared from 0.18 mol of bromobenzene, see Chapter II, Exp. 5) in 130 ml of THF was added drop-wise in 20 min at 20-30°C. After an additional 30 min the black reaction mixture was hydrolysed with a solution of 2 g of NaCN or KCN and 20 g of ammonium chloride in 150 ml of water. The aqueous layer was extracted three times with diethyl ether. The combined organic solutions were washed with water and dried over magnesium sulfate. The residue obtained after concentration of the solution in a water-pump vacuum was distilled through a short column, giving the allenic alcohol, b.p. 100°C/0.2 mmHg, n. 1.5705, in 75% yield. 

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... 

Unlike most ethers epoxides (compounds m which the C—O—C unit forms a three membered ring) are very reactive substances The principles of nucleophilic sub stitution are important m understanding the preparation and properties of epoxides... 

Thus epoxides like cyclopropanes have significant angle strain They tend to undergo reactions that open the three membered nng by cleaving one of the carbon-oxygen bonds... 

Epoxides typically exhibit three bands Two bands one at 810-950 cm and the other near 1250 cm correspond to asymmetric and symmetric stretching of the ring respectively The third band appears m the range 750-840 cm ... 

Section 16 11 Epoxides are much more reactive than ethers especially m reactions that lead to cleavage of their three membered nng... 

Although epoxides are always considered to have their oxygen atom as part of a three membered ring the prefix epoxy in the lUPAC system of nomenclature can be used to denote a cyclic ether of vanous sizes Thus... 

Perfluoroepoxid.es were first prepared ia the late 1950s by Du Pont Co. Subsequent work on these compounds has taken place throughout the world and is the subject of a number of reviews (1 5). The main use of these epoxides is as intermediates in the preparation of other fluorinated monomers. Although the polymerisation of the epoxides has been described (6—12), the resulting homopolymers and their derivatives are not significant commercial products. Almost all the work on perfluoroepoxides has been with three compounds tetrafluoroethylene oxide (TFEO), hexafluoropropylene oxide (HFPO), and perfluoroisobutylene oxide (PIBO). Most of this work has dealt with HFPO, the most versatile and by far the most valuable of this class of materials (4). 

Three peroxyacids are produced commercially for the merchant market peroxyacetic acid as a 40 wt % solution in acetic acid, y -chloroperoxybenzoic acid, and magnesium monoperoxyphthalate hexahydrate. Other peroxyacids are produced for captive use, eg, peroxyformic acid generated in situ as an epoxidizing agent. 

Propylene oxide and other epoxides polymerize by ring opening to form polyether stmctures. Either the methine, CH—O, or the methylene, CH2—O, bonds ate broken in this reaction. If the epoxide is unsymmetrical (as is PO) then three regioisomers are possible head-to-tad (H—T), head-to-head (H—H), and tad-to-tad (T—T) dyads, ie, two monomer units shown as a sequence. The anionic and... 

PO—SM Coproduction. The copioduction of propylene oxide and styrene (40—49) includes three reaction steps (/) oxidation of ethylbenzene to ethylbenzene hydroperoxide, (2) epoxidation of ethylbenzene hydroperoxide with propylene to form a-phenylethanol and propylene oxide, and (3) dehydration of a-phenylethanol to styrene. 

In terms of cost, the effectiveness of the catalytic cycle in the ring closure makes this process economical in palladium. The first three steps in the reaction sequence -- ring opening of an epoxide by a Grignard reagent, converison of an alcohol to an amine with inversion, and sulfonamide formation from the amine — are all standard synthetic processes. 

NB Daia for the three important ihermosetting materials (phenolics, aminoplastics and epoxide resins) were not covered in the 1998 review on which the 1997 data was based. The 1987 figures for these materials do include a substantial percentage of use in adhesive, surface coating and laminate applications. 

The chapter is divided into three sections, devoted to the discussion of the synthesis of (1) oxiranes (epoxides), (2) aziridines (ethylene imines) and (3) thiiranes (episulfides). 

Three possible mechanisms for the Serini reaction were originally suggested. These proceed via (a) a A -enol acetate, (b) a A -epoxide, or (c) a cyclic orthoester ... 

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