Epoxides solvolysis products

The rate of catalyst deactivation is a function of the TS-1 crystal size [12a, 13a] with larger crystals, the slow diffusion of the epoxide solvolysis products (especially with more hindered products) makes the blockage of pores more likely. In propene epoxidation, polyethers are mainly responsible for this phenomenon, when the catalyst is used in consecutive reaction cycles. The activity of the catalyst can be restored by washing it with a solvent or by calcining it at temperatures higher than 500 °C. 

S = selectivity, X = (mmol substrate converted)/(mmol substrate initially present) and E = efficiency of oxidant use, measured as (meq O in oxidation products / mmol H2O2 consumed). Control experiments prove the truly heterogeneous character of the catalysis. Maximally 0.3% of the total W was found in solution, which is by far insufficient to account for the observed activity. H2O2 was analyzed via cerimetry. TON = mmol (epoxide + solvolysis products) / mmol W. Maximum TON value is 300. in 4.5 ml MeOH. 

The oxidahon of olefins with aqueous hydrogen peroxide in methanol can produce several products, by different reachon paths double bond epoxidation, allylic H-abstraction, epoxide solvolysis, alcohol and glycol oxidation (Scheme 18.6). Normally, oxide catalysts of Group IV-Vl metals are poorly selechve, because of their acidic properhes, the inhibition they are subject to in aqueous media and homo-lytic side reachons with hydrogen peroxide. The only excephon concerns the epoxidahon of a,(3-unsaturated alcohols and acids, which are able to bind on the... 

Scheme I shows a simplified block diagram illustrating the four main stq>s of a new route to propylene oxide production. In die first step, an alkylanthrahydroquinone, propylene and air react through a series of reactors producing propylene oxide, a minor amount of solvolysis products and water. Propylene oxide is separated by distillation and recovered. In die next step, methanol, propylene glycol and its methyl ether derivatives are extracted widi water and purified. The remaining organic phase passes to the alkylanthraquinone purification/hydrogenation step and finally is fed widi methanol, back to the epoxidation reactors. The regeneration and purification of the working solution are not shown in Scheme I.

Epoxidation of the olefin, 36, affords 40. Solvolysis of the latter in dry formic acid gives a mixture of the desired product, 42 (both a and 3 hydroxyl at 15), as well as a mixture of the glycols (41). Solvolytic recycling of the mixture in the same medium affords eventually about a 45% yield of the product. 

In a variation on this scheme, the 15 acetate is first saponified and the resulting alcohol converted to the methanesul-fonate (49). Solvolysis in acetone results in what in essence is an SNi displacement and thus affords a 1 1 mixture of 15a and 153 isomers. The former is isolated to afford the desired product with the mammalian configuration at 15 (SO). Application of the epoxidation scheme mentioned above (44 to 46) leads to dinopros-tone (8). ... 

Scheme 12.15 gives some examples of both acid-catalyzed and nucleophilic ring openings of epoxides. Entries 1 and 2 are cases in which epoxidation and solvolysis are carried out without isolation of the epoxide. Both cases also illustrate the preference for anti stereochemistry. The regioselectivity in Entry 3 is indicative of dominant bond cleavage in the TS. The reaction in Entry 4 was studied in a number of solvents. The product results from net syn addition as a result of phenonium ion participation. The ds-epoxide also gives mainly the syn product, presumably via isomerization to the... 

There are major differences that distinguish Ti,Al-P, Ti-P and Ti-MWW. The first concerns the activity and selectivity, which, under optimum conditions for each catalyst, are considerably lower than for TS-1. The activity in methanol decreases in the order, TS-1 > Ti-P >Ti,Al-P> Ti-MWW, in a parallel trend with the decrease of the hydrophobicity. Actually, the density of surface Si—OH species increases in the reverse order TS-1 < Ti-P < Ti,Al-P < Ti-MWW. The selectivity, in turn, drops owing to a greater incidence of solvolysis and hydrogen peroxide decomposition. Even in the absence of framework A1 sites, as in Ti-P, the solvolysis can significantly reduce epoxide yields. Ion exchange with basic compounds or just their addition in the reaction medium is an effective tool to limit the losses of product [84]. 

In general, K-region arene oxides behave rather like aliphatic epoxides and thus readily undergo hydration reactions, whereas benzene oxides and non-K-region arene oxides form dihydrodiols much more reluctantly. Kinetic studies of the mechanism of solvolysis of phenanthrene 9,10-oxide 2 have been carried out in several laboratories.Below pH 7 the hydrolysis reaction was acid-catalyzed and the products included the trans- and c/s-9,10-dihydrodiols along with a preponderance of 9-phenanthrol, while above pH 7 the reaction proceeded via the spontaneous mechanism ( o) mainly the frans-dihydrodiol. 

Data obtained in the catalytic epoxidation of 1-hexene over Ox-Ti-P and other samples are summarized in Table 2. Catalytic properties of Ti-P zeolites were studied by Corma et al. [4,10] and Davis et al. [11,12]. Despite some discrepancies, it is agreed that these catalysts are active in the epoxidation of olefins. Our results also indicate that all of our Ox-Ti-P and Ti-P samples are active in the epoxidation of 1-hexene. The selectivity toward epoxide was very low. The major products were ethers, obtained from solvolysis of glycol by methanol which is catalyzed by the zeolite acid sites. It was found that over Ox-Ti-P samples, the reaction takes place slowly, while the hydrogen peroxide is utilized efficiently. Over Ti-P, the reaction takes place very rapidly and is usually finished in less than 1 hour. It was also found that the parent aluminosilicate P (sample 1) was completely inactive in this reaction. Davis et al. [12] demonstrated that framework Ti is the active site in epoxidation reactions, particularly in aqueous media. It is inferred that our catalysis data provide a strong evidence that Ti(IV) species in our Ox-Ti-P samples are present as isolated framework cations. 

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. 

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