Oxidation ethers

TRAHANOVSKY Ether oxidation Oxidation of aromatic ethers to carbonyl compounds with cemim ammonium nitrate... 

In the ease of the dextrorotatory pair, einchonine and quinidine, these hydroxydihydro-bases may lose a molecule of water between the two. CHOH. groups at positions 9 and 10 with the formation of ether oxides, represented by formula (C) of which there should be a pair of stereoiso-merides for eaeh alkaloid. This type of compound has not been obtained from the laevorotatory bases, einchonidine and quinine. 

There is also for the quinidine ether oxide group (formula C) an im-expected third isomeride, possibly due to epimerisation about carbon atoms 9 and 10. These quinidine isomerides are no doubt convertible... 

A mixture of sodium peroxide and diethyl ether combusts when water is present. This accident is caused by ether oxidation by hydrogen peroxide, which is formed by the effect of water on alkaline peroxide. 

The mechanism and kinetics of ether oxidation are discussed in monographs [7-10], The valuable information about the chemistry of ether oxidation is given in Ref. [8]. The photo-and radiation-induced oxidation of ethers are described. 

Like hydrocarbons, ethers are oxidized by dioxygen via the chain mechanism. The mechanism of ether oxidation with initiator I includes the following elementary steps [8,9] ... 

The autoxidation of ethers occurs with self-acceleration as autoxidation of hydrocarbons. The kinetics of such reactions was discussed earlier (see Chapter 2). The autoacceleration of ether oxidation occurs by the initiating activity of the formed hydroperoxide. The rate constants of initiation formed by hydroperoxides were estimated from the parabolic kinetic... 

Along with tertiary hydroperoxide of ether, the BDE of the O—H bonds of alkoxy hydroperoxides are higher than that of similar hydrocarbons. Very valuable data were obtained in experiments on ether oxidation (RiH) in the presence of hydroperoxide (RiOOH). Peroxyl radicals of oxidized ether exchange very rapidly to peroxyl radicals of added hydroperoxide ROOH and only R02 reacts with ether (see Chapter 5). The rate constants of alkylperoxyl radicals with several ethers are presented in Table 7.18. The reactivity of ethers in reactions with peroxyl radicals will be analyzed in next section. 

Oxidation of silyl enol ethers. Oxidation of silyl enol ethers to a-hydroxy aldehydes or ketones is usually effected with w-chloroperbenzoic acid (6, 112). This oxidation can also be effected by epoxidation with 2-(phenylsulfonyl)-3-( p-nitrophenyl) oxaziridine in CHC1, at 25-60° followed by rearrangement to a-silyloxy carbonyl compounds, which are hydrolyzed to the a-hydroxy carbonyl compound (BujNF or H,0 + ). Yields are moderate to high. Oxidation with a chiral 2-arene-sulfonyloxaziridine shows only modest enantioselectivity. 

The simplest dialkylchalcogenides R-E-R are the dimethylchalcogenides 105a-108a, with R=Me. The IPs have been calculated from absorption spectra and the expected trend is present, with dimethyltelluride oxidized most readily and dimethyl ether oxidized least readily (Table 12). The electron is removed from a... 

The same basic strategy was applied to the synthesis of the smaller fragment benzyl ester 28 as well (Scheme 4). In this case, aldehyde 22 prepared from (S)-2-hydroxypentanoic acid [9] was allylated with ent-10 and tin(IV) chloride, and the resulting alcohol 23 was converted to epimer 24 via Mitsunobu inversion prior to phenylselenenyl-induced tetrahydrofuran formation. Reductive cleavage of the phenylselanyl group, hydrogenolysis of the benzyl ether, oxidation, carboxylate benzylation, and desilylation then furnished ester 28. 

Ether Oxidations Not Covered Here but Included in Chapter 1... 

Schemes a [CpCONH(CH2)3Si(OEt)3 Mo(CO)3Cl immobilised on MCM-41 by a sUox-ane functionality. Further oxidation into the dioxo analogue is accomplished by TBHP. b [CpCOOMe]Mo(CO)3Cl immobilised on MCM-41/48 by an ether oxide moiety...

Such a mechanism explains why the inhibiting effect of amines decrease as the extent of the surface increases. Such a mechanism is unlikely in the inhibition of ethyl ether oxidation since there is no correlation between the acidity of the surface of the vessel and the ability of amines to inhibit the reaction (28). 

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