Ethane epoxidation with

The effect of microwave irradiation on the catalytic properties of a silver catalyst (Ag/Al203) in ethane epoxidation was studied by Klimov et al. [91]. It was found that on catalyst previously reduced with hydrogen the rates of both epoxidation and carbon dioxide formation increased considerably on exposure to a microwave field. This effect gradually decreased or even disappeared as the catalyst attained the steady state. It was suggested that this was very likely because of modification of electronic properties of the catalyst exposed to microwave irradiation. 

Chiral metalloporphyrins317,341-343 and salen [/V,/V -bis(salicylideneamino) ethane]344-347 complexes constitute the most enantioselective nonenzymatic olefin epoxidation catalysts, yielding epoxides with 50-80% enantiomeric excess. 

Alkylation of vinyl epoxides. Although Pd(0) catalyzes the rearrangement of vinyl epoxides (9,452-453), alkylation of cyclic or acylic vinyl epoxides with dimethyl malonate under neutral conditions is possible with the same catalyst or with bis[l,2-bis(diphenylphosphino)ethane]palladium. The rearrangement and alkylation proceed with different regio- and stereoselectivity.19... 

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. 

Tetrakis (4-hydroxyphenyl)ethane is prepared by reaction of glyoxal with phenol in the presence of HCl. The tetraglycidyl ether [27043-37-4] (4), mp ca 80°C, possesses a theoretical epoxide functionaUty of four with an epoxy equivalent weight of 185—208 (4). 

Epoxides can also be rearranged to aldehydes or ketones on treatment with certain metallic catalysts.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 1,2-bis(diphenylphosphino)ethane. ... 

The oxidation of propene to propene oxide, a strategic compound in the manufacture of polyurethane and polyols, displays very low selectivity with many catalysts, unlike the epoxidation of ethane, whose selectivity may be as high as 90% when a supported Ag catalyst is used [235]. Lambert et al. recently showed that selectivities of about 50% can be achieved at 0.25% conversion by supported catalysts, although selectivity declines when the conversion increases [236]. 

P-Diketonesfrom %/i-epoxy ketones. 2 In the presence of this Pd(0) complex a,/ -epoxy ketones isomerize to /3-dikelones. An added ligand is usually necessary to avoid precipitation of palladium. The most satisfactory adjunct is l,2-bis(diphenyl-phosphino)ethane (dpe). The reaction is conducted in toluene at 80-140° for 10 100 hours. The isomerization is facile with strained epoxides it is sluggish with epoxides bearing an a-alkyl group. 

However, attempts to develop similar selective catalysts failed in the case of reactions that require one oxygen atom, like the oxidation of methane, ethane and other alkanes to alcohols, aromatic compounds to phenols, alkenes to epoxides, and many others. These mechanistically simple reactions assume one difficult condition the presence of active sites that upon obtaining two atoms from gas-phase 02 can transfer only one of them to the molecule to be oxidized, reserving the second atom for the next catalytic cycle with another molecule. This problem remains a hard challenge for chemical catalysis. 

A large range of different ionic liquids have been screened in the epoxidation of cyclooctene with dioxomolybdenum(VI) complexes and ferf-butyl hydrogenperoxide as oxidant, as shown in Table 5.2.[32] With the diazabutadiene complex, 48, as catalyst, inferior turnover frequencies were observed relative to the reaction in neat substrate or in dichloromethane and the recycling potential of the catalyst turned out to be only limited. Catalyst immobilisation was better with the cationic tris(methylaminomethyl)ethane complex, 49, however at the expense of selectivity. Of the ionic liquids tested, [C4Ciim][Tf2N] gave the best results for both molybdenum complexes. 

Preliminary results for asymmetric epoxidations of ( )-cinnamyl alcohol and geraniol using (15,25)-l,2-di(2-methoxyphenyl)ethane-l,2-diol or (15,25)-l,2-di(4-methoxyphenyl)ethane-l,2-diol as chiral auxiliaries with titanium(IV) isopropoxide and TBHP have been described. High enantioselectivity (95% ee) is observed when the 2-methoxyphenyl compound is used, while somewhat lower enantioselectivity (64% ee) and opposite face selectivity is described for the catalyst comprised of the 4-methoxyphenyl analog.Further elaboration of the scope and generality of these observations will be of interest. 

The reagent is prepared by heating triethyl phosphite with ethyl bromoacetate and is used in the modified Wittig reaction. Sodium hydride abstracts an activated a-hydrogen atom to give an anion salt (2) which functions Hke an ylide in reacting with an aldehyde or ketone to give an a,j3-un aturated ester (3). 1,2-Dimethoxy-ethane is used as solvent. The anion salt (2) reacts with diphenylketene to form the allene (5) and with styrene epoxide to form the cyclopropane (6). 

Other Fe complexes are known to epoxidize olefins with peracetic acid [244]. For example, Jacobson and coworkers report a Fe(mep) complex (mep=N,N -dimethyl-N,N -bis(2-pyridylmethyl)-ethane) (Fig. 1.3c) which self-assembles under reaction conditions to form a /z-oxo, carboxylate-bridged diiron complex similar to that found in the core of the hydroxylase active site of oxidized methane monooxygenase (MMO) [236]. 

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