H2O2 oxidant epoxidation

A major concern in H2O2 oxidation is the alcohol/olefin chemoselectivity (Rao, 1991). This biphasic oxidation was initially developed for olefin epoxidations but with an (aminomethyl)phosphonic acid additive for high selectivity (Rudolph et al., 1997). Now, the removal of this additive has been found to significantly increase the rate and selectivity of alcohol oxidation. 

The catalytic epoxidation proceeds via the formation of peroxytungstic acid. Similarly, other metal catalysts are effective in the H2O2 oxidation. Aqueous conditions are not appropriate for epoxidations since epoxides are prone to undergo acid-catalyzed hydrolysis36. Polymer-anchored catalysts are conveniently separated from the reaction mixture after catalyzed H2O2 epoxidations (equation 8)9. 

Several of the decatungsto anions have been investigated as catalysts for H2O2 oxidations, e.g., alkene epoxidations and oxidation of primary and secondary alco-... 

In the case of the rhenium-catalyzed oxidation of methoxy- and hydroxy-substituted substrates, there is some complementary work concerning the general mechanism of the arene oxidation [10b, 11]. Since the major products in the oxidation of such arenes or phenols are the quinones, the formation of intermediary epoxides seems to be a predominant reaction step. When p-substituted phenols such as 2,6-di( -butyl)-4-methylphenol are treated with the MTO/H2O2 oxidant and acetic acid as solvent, the formation of hydroxydienones is observed. This is also reported for the oxidation using dimethyldioxirane as oxidant [20]. Since an arene oxide intermediate was postulated for the dioxirane oxidation, a similar mechanism is plausible here [11], e. g., for the oxidation of l,2,3-trimethoxy-5-methylbenzene (Scheme 3) or 2,6-di(f-butyl)-4-methyl-phenol. 

OH), or Mn (Me2EBC)(O)2, and is consistent with the earlier conclusion that the Mn(IV) complex is not capable of direct epoxidation of norbomylene. However, a distinct difference exists between the two terminal oxidants for these systems, in that f-BuOOH reacts predominantly via a radical pathway whereas such a reaction path is very clearly minor in the H2O2 oxidation of olefins in the same catalyst system. 

Foucaud, A., and Bakouetila, M., Facile epoxidation of alumina-supported electrophilic alkenes and montmorillonite-supported electrophilic alkenes with sodium hypochlorite. Synthesis, 854, 1987. Duncan, G.D., Li, Z.-M., Khare, A.B., and McKenna, C.E., Oxiranylidene-2,2-Zt/5(phosphonate). Unambiguous synthesis, hydrolysis to l,2-dihydroxyethylidene-l,l-fcA(phosphonate), and identification as the primary product from mild Na2WO4/H2O2 oxidation of ethylidene-l,l-Z7/5(phosphonate), J. Org. Chem., 60, 7080, 1995. 

The in situ generated peroxocomplexes were tested for the catalytic epoxidation of various olefins, such as allyhc alcohols, homoallylic alcohols and non-functionalized olefins. The results of these H2O2 oxidations in an alcohol-water system are summarized in Table 2 for the hydrophilic catalyst A, and in Table 3 for the lipophihc material C. Especially for the more reactive alkenes, the turnover number comes close to the maximum of 300. The epoxide selectivity generally exceeds 90%, with minimal solvolysis. With catalyst A, some substrates gave a lower selectivity. For instance, the product distribution for cyclohexene is 65% epoxide, 27% of allylic oxidation products and only 4% of the diol. The epoxycyclohexane selectivity increases to 91% with the hydrophobic material C. 

The TFE- or HFIP-activated H2O2 oxidant promotes not only epoxidation [34, 47, 48], but also Baeyer-Villiger oxidation [48], oxidation of sulfides to sulfoxide [34, 49], and oxidation of thiols to disulfides [5, 50]. The nature of the weaker nucleophilicity and higher acidity of TFE as compared with ethanol is useful as a solvent for Pd-catalyzed asymmetric hydrogenation of trifluoromethylimines [51]. 

Epoxidation and other oxidation reactions. Regenerative pie-oxidants of the type 156A are derived from a pyranose. They are employed in conjunction with a expendable agent, such as oxone for epoxidation of conjugated cw-enynes, and H2O2 to epoxidize alkenes. ... 

Epoxidation. Hoft and Ganschow report that this reagent converts olefins into epoxides, Schiff bases into oxaziridines, and tertiary amines into N-oxides. Epoxidation can be performed more simply by addition of benzoyl isocyanate to a solution of the alkene in THF containing excess anhydrous H2O2 and a trace of a radical inhibitor. Under these conditions phenanthrene is converted at 25° into biphenyl-2,2 -dicarboxylic acid. 

Benzeneseleninic anhydride converts hydrazones, oximes, and semicarbazones into the parent ketones, and oxidizes phenols to ortho-qmnone derivatives [e.g. (80) gives (81)]. The combination of PhSe(0)0H and H2O2 accomplishes epoxidation... 

The recent development of inorganic crystalline-supported metal catalysts for various liquid-phase oxidation reactions such as alcohol oxidation, epoxidation, Baeyer-Villiger oxidation and oxidation via C H activation using molecular oxygen (O2) or hydrogen peroxide (H2O2) as an oxidant are reviewed in this chapter. 

Inspired by this finding, Katuski further developed a series of structurally tunable di- x-oxo titanium-salan complexes that can be easily prepared and possess amino protons to activate a putative peroxide species. The optimized catalyst (5 mol%) works well for the epoxidation of a variety of unfunctionalized olefins, giving the corresponding epoxides in moderate to good yields with 55-97% ee [262]. The ready availability of the salan ligand and aqueous H2O2 oxidant makes the process very practical for the production of optically active epoxides. 

Safrole can be oxidized to safrole epoxide with H2O2 in a two-phase system, using a quaternary phosphotungstic PTC. The formed safrole epoxide is then isomerized to MDP2P with Lil. 

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

In the organic chemicals industry, H2O2 is used in the production of epoxides, propylene oxide, and caprolactones for PVC stabilizers and polyurethanes, in the manufacture of organic peroxy compounds for use as polymerization initiators and curing agents, and in the synthesis of fine chemicals such as hydroquinone, pharmaceuticals (e.g. cephalosporin) and food products (e.g. tartaric acid). 

Vinylepoxides can be obtained by various strategies, all with their inherent limitations. Racemic epoxidation of olefins is a straightforward route to epoxides, as pure trans- or cis-epoxides can be obtained from ( )- or (Z)-alkenes, respectively. Various oxidants - such as mCPBA and other peracids, H2O2, or VO(acac)2/TBHP - can all be employed in this transformation [1],... 

As an example heme-models have been reported to catalyze the epoxidation of olefins to the corresponding epoxides in good yield [16, 17]. In particular, [Fe TPP)Cl] (TPP = 5,10,15,20-meso-tetraphenylporphyrin) was reported to oxidize naturally occurring propenylbenzenes to the corresponding epoxides up to 98% selectivity (conversion 98%) using H2O2 as oxidant [16]. The major drawback... 

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