Epoxidation catalyst

With cationic catalysts, epoxides become so reactive that polyesterethers are formed instead of polyesters256. ... 

Catalyst Epoxidation of Allyl Alcohol (AA)a Phenol hydroxylationb,c ... 

The key factor is the action of the metal on the peroxo group making one oxygen atom electrophilic. Whether or not the metal is bonded to carbon in the intermediate is not known, but also considered unlikely naturally this will depend on the particular substrate and catalyst. Epoxidation will be discussed in Chapter 14, with special emphasis on asymmetric epoxidation with chiral metal catalysts. 

In conclusion we find that on both catalysts epoxidation proceeds similarly via a non-concerted process. Concerted mechanisms in which O adds across the C=C bond, directly producing epoxide, have been ruled out. In both pathways a C-Ag bond is formed and further broken. The key implications are that both surfaces are active for epoxidation. This partial oxidation reaction is hence shown to take place over a wide O coverage regime characterizing two types of oxygen species. 

To obtain a heat and water resistant crosslinked polymer, Cu naphthenate and an alcohol (e.g. benzyl alcohol) were added to BPA/DC as a catalyst epoxide resins (cf. Sect. 6) can be used as well [19]. The use of Zn acetate together with dicumyl peroxide was also mentioned [20],... 

C imlBr Iron-porphyrin complex H202 CH2C12 as co-solvent product isolated by decantation catalyst recycled 4 times, slow decrease in activity excess oxidant leads to degradation of the catalyst epoxide-selectivity is substrate-dependent. [36]... 

Boron-containing catalysts have also found application, with a relatively lower stereoselectivity. Cyclohexene oxides can be obtained with a selectivity of 97.5% in the H2O2-AS2O3 system. Arsonated polystyrenes have also been employed as catalysts. Epoxidation of olefins may be attained with hydroperoxide bound on an aluminium oxide surface. ... 

A good way to prepare p-diketones consists of heating a,p-epoxy ketones at 80-140°C in toluene with small amounts of (Ph3P)4Pd and l,2-bis(diphenyl-phosphino)ethane. ° Epoxides are converted to 1,2-diketones with Bi, DMSO, O2, and a catalytic amounts of Cu(OTf)2 at 100°C. a,p-Epoxy ketones are also converted to 1,2-diketones with a ruthenium catalyst or an iron catalyst. Epoxides with an a-hydroxyalkyl substituent give a pinacol rearrangement product in the presence of a ZnBr2 " or Tb(OTf)3 catalyst to give a y-hydroxy ketone. 

Epoxide opening. With Eu(dpm)3 as catalyst epoxides give P-chlorohydrin esters... 

Figure 10. Various modes of catalyst transformation via catalyst-epoxide Intermediate by the attack of an epoxide molecule.

Catalyst Epoxide Yield in mmoles 2-cyclohexen-1 -ol 2-cyclohexenone ... 

Acid catalysis of the epoxide-alcohol reaction is no more selective than base catalysis. The ratio of alcohols formed and the amount of polyether obtained vary with the type and amount of catalyst, epoxide-to-alcohol ratio, solvent, and reaction temperature. 

Carbonates and carbamates. In the presence of phosphine-CBr4 and base, alcohols combine with CO2 to afford carbonates. Mixed carbonates are obtained under different conditions, and with a Mg—A1 mixed oxide as catalyst, epoxides formed cyclic carbonates. The preparation of dimethyl carbonate from acetone dimethyl acetal and supercritical carbon dioxide in the presence of a metal catalyst (e.g., dibutyltin methoxide) is successfully carried out. ... 

Olefin epoxidation has many features in common with biological monooxygenation. This reaction requires heterolysis of the peroxide bond. The presence of carbonyl groups facilitates heterolysis in peracids. Epoxidation occurs through electrophilic attack, so di- and tri-substituted double bonds are more easily epoxidized. In the presence of metal complex catalysts, epoxidation proceeds under mild conditions because in the transition state the 0-0 bond is more easily heterolyzed (Eq. 12-29). 

In order to observe rapid rates and high epoxide selectivity, the conditions under which reaction (226) is run must be within fairly restricted limits. In most instances, an excess of olefin over hydroperoxide will result in more efficient use of hydroperoxide and thus in greater selectivity [370]. In general, the lower the temperature, the less radical decomposition of hydroperoxide and the higher the selectivity. The maximum temperature at which each metal complex may be run without a large amount of radical decomposition varies with the metal center. For molybdenum catalysts epoxide selectivities of 98% can be achieved at 100 °C but fall to 75-80% at 130°C. For vanadium complexes the maximum temperature for selective operation is 80 °C and for chromium it is below 60 [370]. 

Bisphenol A Epoxy Novolacs. Bisphenol A novolacs are produced by reacting bisphenol A and formaldehyde with acid catalysts. Epoxidation of the bisphenol A novolacs gives bisphenol A epoxy novolac (BPAN) with improved thermal properties such asTg, Td of the epoxy-based electrical laminates. 

The reaction of ethylene oxide with n-butanol gives 2-butoxyethanol (527,578) in very high yield over MgAl- and CuCr-LDO catalysts. Epoxides, such as propylene oxide and styrene oxide, can also react with CO2 to form cyclic carbonates with MgAl-oxide catalysts (579). On the industrial scale, ethylene oxide and propylene oxide can be polymerized into water-soluble polyols over an MgAl-COs-LDO catalyst (580-583). 

A similar protocol has been applied by Wicha and co-workers in efforts toward the synthesis of a cyclopenta[8]annulene ring precursor to ophiobolin metabolites. Using BF3 OEt2 as a Lewis acid catalyst, epoxide ring opening of 87 resulted in the suprafacial 1,2-methyl shift followed by two consecutive hydride migrations to form ketone 88 in moderate yield. 

A catalytic cycle starting from the formation of a catalyst-epoxide complex that further reacts with the thione tautomer of the thiobenzoic add 17 (Scheme 3.7) was computed. Full molecule of the catalyst was used in the PCM-M06-2X/6-31H-G V/M06-2X/6-31G computations. 

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