Halogenated Epoxides

Furstoss and collaborators have shown that the partially purified recombinant EH from A. niger LCP 521 efficiently catalyzes the kinetic resolution of l-chloro-2-(2,4-difluorophenyl)-2,3-epoxypropane at a very high substrate concentration of 500 g/1 using a biphasic process [5]. The unreacted (S)-chloro-epoxide and the formed (R)-chloro-diol were obtained in nearly enantiopure form and nearly quantitative 5tield. Due to tiie fact that the formed (R)-chloro-diol was easily chemically transformed into tile (S)-chloro-epoxide, an enantioconvergent process could be set up. Using the difference in chemical reactivity between the oxirane ring and the chlorine 

Kinetic resolution of racemic epichlorohydrin using purified EH from Agrobacterium radiobacter, leading to the formation of enantiomerically pure (/ )-epichlorohydrin. 

Preparative hydrolytic resolution of rac-1-chloro- and 1-triazole-2(2,4-difluorophenyl)-2,3-epoxypropane using AnEH as a biocatalyst. The latter compound is a useful building block for the synthesis of enantiopure D0870. 

8 EPOXIDE HYDROLASES AND THEIR APPLICATION IN ORGANIC SYNTHESIS 

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Halogenated alkenes are transformed into halogenated epoxides by oxygen or hydrogen peroxide (equation 58) [1100],... 

Of the substituents listed in Table 2, fluorine deviates the most from the observed correlations its o, is 0.54, " whereas we would estimate it to be 0.38. Whereas fluorine is regarded as the most electronegative element, there is considerable experimental and theoretical evidence that it is limited in the total amount of electronic charge that it can accept. In earlier studies of halogenated epoxides,dibenzo-p-dioxins and naphthalenes, we have found chlorine to be more effective than fluorine in withdrawing charge from... 

Fig. 15. Primary thermograms for m-phenylenediamine-cured halogenated epoxides at various heating rates (26 ].

Cross-linked epoxy resins are combustible and their burning is self-supporting. They require mainly reactive flame-retardants, such as tetrachloro- or tetrabromobisphenol-A and various halogenated epoxides. Even the cross-linking agent may be flame-retardant, as in the case of chlorendic anhydride, tetrabromo- or tetrachloro-phthalic anhydride, or possibly phosphorus compounds. Halogenated agents can be supplemented with antimony trioxide. 

In conclusion, stilbenes involve in miscellaneous chemical reactions. For non-substituted stilbenes, the most chemically reactive part is double bond, which relatively easily undergoes the halogenation, epoxidation, oxidation, reduction, and addition. The chemistry of substituted stilbenes is in principle as rich as organic chemistry. Including stilbenes in dendrides, dextrins, polymers, and surfaces led to a sufficient change in their chemical, photochemical, photophysical, and mechanical properties and, therefore, establishes the basis for design of new materials. 

The earlier studies and the competition experiments [5b] with equivalent molar, enal, or enone 9-BBN (3-5% excess) reveal that enals or enones are selectively reduced to allylic alcohols (Eq. 25.9) in the presence of other organic functional groups such as nitro, halogen, epoxide, carboxylic acid, amide, ester, nitrile, sulfide, disulfide, sulfoxide, sulfone, tosylate, azo, etc. 

When such halogenated epoxides decompose at high temperatures, as is the case during combustion, various halogen-containing species are formed, which help to trap the free radicals formed and their removal snuffs out the flame. 

Finally, apart from using halogenated epoxide resins or additives, it is also possible to use halogenated curing agents, examples being... 

Figure 1.5 Ln versus 1/T for m-phenylenediamine-cured halogenated epoxide at the indicated values of W. Reproduced with permission from D.W. Levi, L. Reich and H.T. Lee, Polymer Engineering and Science, 1965, 5, 3, 135. 1965,...

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