Epoxides catalysis

All schemes presented are similar and conventional to a great extent. It is characteristic that the epoxidation catalysis also results in the heterolytic decomposition of hydroperoxides (see Section 10.1.4) during which heterolysis of the O—O bond also occurs. Thus, there are no serious doubts that it occurs in the internal coordination sphere of the metal catalyst. However, its specific mechanism and the structure of the unstable catalyst complexes that formed are unclear. The activation energy of epoxidation is lower than that of the catalytic decomposition of hydroperoxides therefore, the yield of oxide per consumed hydroperoxide decreases with the increase in temperature. 

Reactions between alkenes and 07 on MgO also lead to nonselect ive oxidation (21). One would hope to gain insight into the possible role of this ion in epoxidation catalysis, but rapid surface reactions, for example between ethylene oxide and MgO, make it difficult to obtain such information. The principal reaction products, CHi and CO2, are believed to be formed in a manner analogous to reactions 12-15. The initial hydrogen abstraction again is effected by the 07 ion. 

Dioos, B. M. L. Geiutsa W. A. Jacobs, P. A. (2004) Coordination of Crlll(salen) on fimctionalised silica for asymmetric ring opening reactions of epoxides.. Catalysis Lett., 97 125-129. 

Bovine semm albumin (BSA) epoxidation catalysis, 383-4 y-radiation, 614, 691... 

Chiral metal complexes, aUylic alcohol epoxidation catalysis, 394-401 Chiral naphthalene derivatives, singlet oxygen cycloaddition, 271... 

On the other hand, in homogeneous epoxidation catalysis, De Vos et al. [6] have explored the properties of manganese (II) salts in the presence of triazacyclononane derivatives and... 

Active O stoichiometry G(T,P) analysis. Figure 14 plots the free energy of adsorption as a function of temperature for the most stable Ag oxide overlayer at each O coverage.14 The pressure is 15 atmospheres, which is characteristic of the pressure used in industrial epoxidation catalysis [10]. We find that at zero Kelvin the most stable overlayer is the Agt 22O overlayer, i.e. the Ag oxide with an additional O adatom inside each oxide ring... 

However, particularly for the unsaturated acids, the epoxidation catalysis was not heterogeneous. Competitive anion exchange between the (peroxo)-tungstate and the carboxylate possibly causes leakage of W. 

Methyltrioxorhenium(VII) (MTO) absorbance spectroscopy, 130, 132 alkene epoxidation, catalysis with hydrogen peroxide... 

However, these conditions have not been applied to other epoxides. Catalysis by the boron trifluoride -diethyl ether complex is very useful for the ring opening of cyano-substituted epoxides " and glycidic esters see the formation of and Table 14. This is demonstrated by the regioselective opening of the epoxide ring in 2,3-dimethyloxirane-2-carbonitrile to provide 3-fluoro-2-hydroxy-2.3-dimcthylbutanonitrile... 

Having identified Cu as a potential additive to Ag for ethylene epoxidation catalysis, it is useful to examine the properties of Cu in Ag-Cu alloys more closely. The phase diagram of bulk Ag-Cu alloys shows that at almost all compositions, mixtures of Ag and Cu will phase separate into an alloy that is very rich in Ag and an alloy that is very rich in Cu.73 At 200°C, the Ag-rich phase is 99 at.% Ag and the Cu-rich phase contains <1 at.% Ag. This... 

One important component of practical epoxidation catalysis for which many questions remain open is the role of promoters. Industrially, both Cs and Cl are used as promoters.76 Saravanan et al. used cluster DFT calculations to examine the interactions between adsorbed Cs and oxametallacycles on Ag(lll).77 These calculations suggested that both neutral Cs and Cs+ gave similar outcomes and that the promoter atom made the formation of a surface oxametallacycle less energetically favorable than on the bare Ag surface. More recently, Linic and Barteau used plane wave DFT calculations to probe the effect of adsorbed Cs on the transition states controlling the formation of EO and acetaldehyde from oxametallacycles on Ag(lll).78 The role of Cs was... 

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