Showing papers on "Epoxide published in 1995"

Methylrhenium trioxide as a catalyst for oxidations with molecular oxygen and for oxygen transfer

Abstract: Methylrhenium trioxide (MTO) was found to be a good catalyst for the oxidation of tertiary phosphines by molecular oxygen at room temperature. Evidence is given that an intermediate Re(V) compound — CH3ReO2, or the adduct CH3ReO2·OPPh3 — is involved. The deoxygenation of epoxides, sulfoxides, N-oxides, triphenylarsine oxide and triphenylstibine oxide at room temperature was also catalyzed by MTO, with triphenylphosphine as the oxygen acceptor. A plausible reaction mechanism involves phosphine attack at a compound formed between MTO and the epoxide or other oxygen-donor compound.

Polycyclic aromatic hydrocarbons: chemistry of DNA adduct formation.

Abstract: Polycyclic aromatic hydrocarbon carcinogens are usually activated for DNA binding by the metabolic formation of bay region dihydrodiol epoxides with R,S,S,R stereochemistry. Such metabolites from planar hydrocarbons reacted preferentially with the amino groups of deoxyguanosine residues, whereas those from nonplanar hydrocarbons were more efficiently trapped by DNA and reacted preferentially with the amino groups of deoxyadenosine residues, in some cases. Molecular modeling and NMR measurements indicated that the conformations of DNA adducts depend upon the hydrocarbon involved and the cis or trans opening of the epoxide ring during adduct formation. The structural characterization of carcinogen-DNA adducts and investigations of relationships between specific adducts and biological effects represent an important background that can be valuable in molecular epidemiological approaches.

Polyether-containing double metal cyanide catalysts

Abstract: Improved double metal cyanide (DMC) catalysts are disclosed. The catalysts comprise a DMC compound, an organic complexing agent, and from about 5 to about 80 wt. % of a polyether polyol that has tertiary hydroxyl groups. Compared with other DMC catalysts, those of the invention have excellent activity for epoxide polymerization, and they can be used to make polyols having very low unsaturation even at high epoxide polymerization temperatures.

Stereocontrolled Hydrolysis of the Linoleic Acid Monoepoxide Regioisomers Catalyzed by Soybean Epoxide Hydrolase

Abstract: Soybean fatty acid epoxide hydrolase (EC 3.3.2.3) was found to possess remarkable and unique stereochemical features. After complete hydrolysis, this enzyme converts racemic or enantiomerically enriched cis-9,10-epoxy-12(Z)-octadecenoic and cis-12,13-epoxyocta-9(Z)-decenoic acids, i.e. the two regioisomers of linoleic acid monoepoxides, into their corresponding 9R, 10R- and 12R, 13R-dihydrodiols with a high enantiomeric excess (> 90%). A straightforward chiral-phase HPLC technique was developed that gives an easy access to the stereochemistry of these reaction products. These results are discussed in terms of a possible model for the substrate binding site of this enzyme.

The synthesis and study of the photoinitiated cationic polymerization of novel cycloaliphatic epoxides

Abstract: The synthesis of a series of difunctional epoxides bearing two epoxycyclohexyl groups linked together by an alkylene ether group has been carried out. Subsequently, the reactivities of these novel monomers was investigated and compared to the reactivity of the cycloaliphatic epoxide, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate (I) in photoinitiated cationic polymerization. It was observed that alkylene oxide linking the two epoxycyclohexyl groups was short and the monomers are more reactive than I. The effects of the photoinitiator structure and the experimental conditions of the cationic photopolymerization on the rates was also studied using real-time infrared spectroscopy. 1995 John Wiley & Sons, Inc.

Hyperbranched macromolecule from epoxide nucleus and hydroxy-functional carboxylic acid chain extenders

Abstract: A hyperbranched macromolecule of polyester type comprising a central monomeric or polymeric nucleus and at least one generation of a branching chain extender having at least three reactive sites of which at least one is a hydroxyl or hydroxyalkyl substituted hydroxyl group and at least one is a carboxyl or terminal epoxide group. The nucleus is an epoxide compound having at least one reactive epoxide group. Optionally, the macromolecule comprises at least one generation consisting of at least one spacing chain extender having two reactive sites of which one is a hydroxyl or hydroxyalkyl substituted hydroxyl group and one is a carboxyl or terminal epoxide group. The macromolecule may be terminated by means of at least one chain stopper.

Oxidation of [60]fullerene by cytochrome P450 chemical models

Abstract: Reaction of [60]fullerene in cytochrome P450 (P450) chemical model systems gives several oxidation products; sequential epoxidation occurs, and the second and third oxygen atoms are each introduced at a double bond adjacent to an existing epoxide.

On the mechanism of catalytic alkene oxidation by molecular oxygen and halogenated iron porphyrins

Abstract: The halogenated porphyrin, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyriato-iron(III) chloride, [Fe(TFPPBr8)Cl], catalyzes the oxidation of cyclohexene in the presence of molecular oxygen or iodosobenzene. With PhIO, 77% epoxide is observed, consistent with a mechanism involving a high-valent metal-oxo species. With dioxygen, however, allylic alcohol and ketone are observed, suggesting a different mechanism. The relatively high activity of the [Fe(TFPPBr 8 )Cl] O 2 system suggests that the reaction involves the formation and decomposition of alkyl peroxides.

Selective oxidation of propylene by O2 with visible light in a zeolite

Abstract: Propylene and O2 loaded into zeolite BaY were found to react upon irradiation with green or blue light in a single photon process. In situ monitoring by FT-infrared spectroscopy showed that allyl hydroperoxide is the predominant product at −100°C. At room temperature, acrolein, propylene oxide, and allyl hydroperoxide were observed in comparable amounts. The aldehyde and epoxide are shown to emerge from secondary thermal chemistry of the allyl hydroperoxide photoproduct. The selectivity in terms of the hydroperoxide photoproduct is very high (98% at room temperature) even at high propylene conversion. Diffuse reflectance spectra show that access to the mild oxidation path is made possible by a zeolite-induced shift of the propylene O2 charge-transfer absorption from the UV into the visible region.

Highly active double metal cyanide catalysts and epoxide polymerization

Abstract: Highly active double metal cyanide (DMC) catalysts are disclosed. The catalysts comprise a DMC complex, and organic complexing agent, and from about 5 to about 80 wt. %, based on the amount of catalyst, of a polyether having a number average molecular weight greater than about 500. A method of preparing the catalysts is also disclosed. The catalysts are easy to prepare, have exceptional activity, and are readily removed, if desired, from polymer products. The catalysts are used for polymerizing epoxides.

Polymer Reaction of Epoxide and Carbon Dioxide. Incorporation of Carbon Dioxide into Epoxide Polymers

Abstract: Polymeric epoxides can be converted to corresponding five-membered cyclic carbonates effectively by the reaction with carbon dioxide. For instance, poly(glycidyl methacrylate) (PGMA) was quantitatively converted to a polymethacrylate bearing a five-membered cyclic carbonate group (PDOMA) by the polymer reaction with carbon dioxide using alkali metal or quaternary ammonium halide salt as a catalyst. The salts having more Lewis acidic cation and more nucleophilic anion acted as more effective catalysts. Kinetic analyses of the polymer reaction show that the reaction rate can be expressed by the empirical equation : -d[epoxide]/dt = k[epoxide][catalyst] m , where m depends on the Lewis acidity of the catalyst and molecular weight of the epoxide. The rate of the reaction is independent of the pressure of carbon dioxide. Further, various polymeric epoxides such as GMA copolymers, poly(glycidyl acrylate), and poly(vinylbenzyl glycidyl ether) could be converted to the corresponding polymers bearing five-membered cyclic carbonate moieties by the reaction with carbon dioxide, whereas the presence of an aromatic group in the structure of the polymer could retard the reaction with carbon dioxide.

Isolation of a highly enantioselective epoxide hydrolase from Rhodococcus sp. NCIMB 11216

Abstract: Whole cells of Rhodococcus sp. NCIMB 11216 catalyze the asymmetric hydrolysis of racemic epoxides giving access to chiral epoxides and diols, which are important chiral building blocks for the synthesis of bioactive compounds. Employing a four-step purification procedure, the epoxide hydrolase responsible for the reaction was isolated and characterized to be a cofactor-independent, soluble monomeric protein of ~35kDa, exhibiting an isoelectric point of 4.7.

Self-emulsifying epoxy curing agent

Abstract: A new epoxy hardener composition is the product of the reaction of (A) a poly(alkylene oxide) monoamine or diamine with a molecular weight (Mn) of about 500 to 3000 and (B) a di- or polyepoxide, in a ratio of epoxide to active amine hydrogens of about 1.1:1 to 6:1 to yield an intermediate (C), which in a second step is reacted with (D) a di- or polyamine, in a ratio of active amine hydrogens to epoxide of greater than about 25 to 1, preferably greater than about 30 to 1. The compositions of the invention are excellent emulsifiers of liquid epoxy resins in aqueous medium without the addition of added surfactants or acidic compounds, and can be used to prepare water resistant water-borne coatings and related products from both liquid and solid epoxy resins, that possess long pot lives and contain relatively small amounts of volatile organic compounds.

Hydroxy-assisted chemo- and stereo-selective epoxidation catalysed by a titanium silicate molecular sieve (TS-1)/H2O2 system

Abstract: The TS-1/H2O2 system efficiently catalyses the hydroxy-assisted chemoselective epoxidation of α-hydroxyalkene in geraniol, and the stereoselective epoxidation of cyclopent-2-en-1-ol/cyclohex-2-en-1-ol producing the epoxide which is cis to OH with high selectivity (90:10 cis: trans).