Epoxides scission

Epoxide scission in rigid, six-membered rings generally gives the product having the substituents oriented diaxially (Ftirst-Plattner rule). ... 

The first synthesis of a thio sugar by epoxide scission to be reported was the preparation of 1,2-0-isopropylidene-6-thio-D-glucose (67, R = H) from 5,6-anhydro-l,2-0-isopropylidene-a-D-glucofuranose (66) by the action of hydrogen sulfide. The product was isolated as the crystalUne... 

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). 

The quantitative bulk conversion of unsaturated functional groups in PHAs to epoxides has been achieved by reaction with m-chloroperbenzoic acid as the chemical reagent [107]. No chain scission of the macromolecular chain was observed. Epoxy-modified PHAs are chemically even more reactive than unsaturated PHAs and therefore could be useful in further chemical reactions (e.g. grafting of therapeutic important substances) [108]. 

In vitro studies of DNA interactions with the reactive ben-zo[a]pyrene epoxide BPDE indicate that physical binding of BPDE occurs rapidly on a millisecond time scale forming a complex that then reacts much more slowly on a time scale of minutes (17). Several reactive events follow formation of the physical complex. The most favorable reaction is the DNA catalyzed hydrolysis of BPDE to the tetrol, BPT (3,5,6,8,17). At 25°C and pH=7.0, the hydrolysis of BPDE to BPT in DNA is as much as 80 times faster than hydrolysis without DNA (8). Other reactions which follow formation of physical complexes include those involving the nucleotide bases and possibly the phosphodiester backbone. These can lead to DNA strand scission (9 34, 54-56) and to the formation of stable BPDE-DNA adducts. Adduct formation occurs at the exocyclic amino groups on the nucleotide bases and at other sites (1,2,9,17,20, 28,33,34,57,58). The pathway which leads to hydrocarbon adducts covalently bound to the 2-amino group of guanine has been the most widely studied. 

The resulting polyol resembles the product that is hypothesized for the oligomerization of triglycerides via air oxidation, with the exception that there is a large increase in the hydroxyl content of the polyol product, and there is very little, if any, of the starting epoxide left unreacted. In addition, the epoxidation process does not produce low molecular weight chain scission products, which are a by-product of the blown oil process. The hydroxylation of epoxidized triglycerides is illustrated in Fig. 17. 

Copolymerization of 3-chlorostyrene with glycidyl methacrylate to form GMC, resulted in G(x) increasing from 0.61 to 1.02 and G(s) from 0.16 to 0.42. Polyalkylmethacrylates are well-known to undergo main chain scission upon irradiation (10,23-6) e.g., polymethylmethacrylate has a G(x) =0 and G(.y) = 1.4(27). The increase in G(s) can therefore be attributed entirely to the presence of the methacrylate moiety. The enhanced G(x) value of GMC arises from the epoxide ring opening upon exposure and initiating cross-linking. 

Cvetanovic67 was concerned with oxygen atom reactions with unsaturated hydrocarbons. The oxygen atoms were obtained in his experiments by mercury-photosensitized decomposition of N20. Cvetanovi6 came to the conclusion that the reaction of oxygen atoms with ethylene proceeded essentially with scission of the hydrocarbon bond, while with higher olefins this was not observed. Corresponding oxides (epoxides) and carbonyl compounds were formed in the course of the reaction. 

Alkenes may also react with certain oxidizing agents to result in anti hydroxyla-tion. Treatment with peroxycarboxylic acids435 leads initially to an epoxide. Ring scission of the latter via an SN2 reaction in an anti manner with the corresponding carboxylic acid or water gives the trans monoester or tram diol, respectively. Complete anti stereoselectivity and high yields in the oxidation of cycloalkenes are... 

Epoxide rings in sugars have been opened by the action of halogen acids. Both possible products of ring scission were observed in the reaction of methyl 2,3-anhydro-4,6-O-benzylidene-a-D-alloside 8 with hydrobromic... 

Alkyl hydroperoxides. Peroxymercuration of alkenes proceeds cleanly and in good yield. These products previously were reduced to the desired alkyl hydroperoxides with alkaline sodium borohydride. This reduction proceeds in reasonable yield in the case of terminal alkenes, but scission to form epoxides of the original alkene predominates among products from nonterminal alkenes. This difficulty is now overcome by use of tri-n-butyltin hydride for reduction.18... 

Mode of synthesis A. cyanohydrin, by way of 2-nmino-2-deoxy-aldonic acid B. scission of sugar derivative epoxide with ammonia C. interconversion of hexosamine series D. hemihydrogenation of a-amino nitrile466 E. rearrangement of ketosyl-amine F. Removal of last carbon atom of hexosamine G. Hydrazinolysis (with inversion) of 2-0-tosyl-pentose. 6 Physical constants taken from this reference. c Derivatives (only) isolated. 

Oxametallacycle formation from aliphatic alkoxides could occur via C-H scission at the p position, or from epoxides by C-O scission to open the ring. The subsequent C-H and C-C bond activation steps are less clear than those of the aldehydes above. For the oxametallacycle formed from the ethoxide, C-C scission must release CH2 or perhaps CH... 

Decarbonylation of higher oxygenates on the Rh(l 11) surface leads to volatile hydrocarbons only in the case of aldehydes. Higher alcohols do not form adsorbed aldehydes, but appear to undergo (J-CH scission toformsurfaceoxametallacycles. These postulated intermediates can also be formed by C-0 scission in epoxides. Of the ten C2 and C3 oxygenates examined, elimination of atleastfivedifferenthydrocarbonligandsmustbeinvolvedintiiedecarbonylation step to explain the variations observed in the identity of adsorbed and volatile products. 

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