Alcohols, secondary, oxidation with oxygen

The palladium(II) complex of sulfonated bathophenanthroline was used in a highly effective aqueous biphasic aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes or carboxylic acids and ketones respectively (Fig. 7.15) [52, 53]. No organic solvent was necessary, unless the substrate was a solid, and turnover frequencies of the order of 100 h-1 were observed. The catalyst could be recovered and recycled by simple phase separation (the aqueous phase is the bottom layer and can be left in the reactor for the next batch). The method constitutes an excellent example of a green catalytic oxidation with oxygen (air) as the oxidant, no organic solvent and a stable recyclable catalyst. 

The platinum-catalyzed oxidation with oxygen can also be applied for selective oxidation of secondary alcohols if no primary alcohol is present [73]. Like the tin-bromine method, axial secondary hydroxy groups will undergo preferential oxidation over equatorial hydroxy groups. However, as described above large amounts of platinum metal are required for these oxidations. Some improvement in catalyst activity has been achieved by promotion of platinum with bismuth or lead [76]. This also causes a change in selectivity and makes it possible in... 

T he experiments showed that allyl alcohol as well as primary and secondary aliphatic alcohols are oxidized by oxygen under conditions mentioned in Table 3. The oxidation proceeds quickly (at 3-5 min). For all studied reactions only the initial alcohol and corresponding carbonyl compound were detected in the reaction mixture by GLC. The yields of carbonyl compounds are in agreement with the expended quantities of oxygen, determined by the gas... 

Oxidation with oxygen gas can be carried out in aqueous biphasic systems. Primary and secondary alcohols have been oxidized to the corresponding aldehydes or ketones, respectively, using a palladium(I I) complex (Equation 4.11) [18]. No organic solvents were used, except the substrate is a solid, and the catalyst could be easily recycled and reused by simple phase separation, because the aqueous phase is the lower layer and so can be recycled. The only disadvantage of water as a solvent for oxidations with oxygen/air is the low solubility of oxygens in water. 

Anastreptene (37), an extremely air sensitive sesquiterpene hydrocarbon, is widely distributed in the Jungermanniales species. The stereochemistry of (37) was based on chemical correlation with (—)-myliol (44) and the degradation shown in Scheme 4 (6). Hydroboration of (37) gave a secondary alcohol, whose oxidation with H2Cr04 afforded dihydromylione A (43), the latter was easily converted into its stable isomer, whose spectral data were in agreement with those of the oxygenated product (83) of the dihydro derivative prepared from (44). 

Alcohols are oxidized slowly with PdCh. Oxidation of secondary alcohols to ketones is carried out with a catalytic amount of PdCh under an oxygen atmo-sphere[73.74]. Also, selective oxidation of the allylic alcohol 571 without attacking saturated alcohols is possible with a stoichiometric amount of PdfOAc) in aqueous DMF (1% H OifSll],... 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

A secondary alcohol is oxidized to a ketone. All the carbon bonding sites are now occupied with bonds to carbon and oxygen, so no further oxidation is possible. 

A Co(II) Schiff-base complex converts 1- and 2-alkenes into methyl ketones and the corresponding secondary alcohols in the presence of oxygen or H2O2 in primary alcohol solvent.543 A radical oxidation with cobalt hydroperoxide through the formation and subsequent decomposition of alkyl hydroperoxide was suggested.543 An efficient conversion of alkenylarenes to ketones was achieved by the use of molecular oxygen and EtjSiH in the presence of a catalytic amount of Co(II) porphyrin in 2-propanol.544... 

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