Oxidation of Alcohols and Aldehydes

The main problem of catalyzed processes based on platinum or palladium nanoparticles for such a needed target as the oxidation of alcohols and polyols is the scarce selectivity achieved with a complex substrate. 

A recent contribution reported by Aoshima and Tsukuda showed the aerobic oxidation of alcohols such as benzyl alcohol catalyzed by gold nanoclusters. These stable and durable clusters of less than 4 nm were prepared using thermosensitive vinyl ether star polymers previously obtained by living cationic polymerization. 

One advantage of this method is that the clusters can be easily separated from the reaction mixture due to their thermosensitive nature, allowing for repeated reuse [234]. 

OxidatiOTis of primary and secondary alcohols catalyzed by dehydrogenases to furnish aldehydes and ketones, respectively, are common chemical reactions that rarely present insurmotmtable problems to the synthetic organic chemist. In contrast to the corresponding reductimi reactions, oxidation reactions using isolated dehydrogenase enzymes have been rather scarcely reported [1023]. The reasons for this situation are as follows. 

Substrate polyol Product keto-alcohol Reference 

The major difficulty in the resolutitMi of alcohols via selective oxidation of one enantiomer using isolated horse liver alcohol dehydrogenase (HLADH) is the regeneratiOTi of NAD. Besides the highly efficient enzymatic systems described 

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The standard redox potentials of inorganic oxidants used in organic synthesis are generally around or above + 1.0 V. Organic substrates do not have such high potentials. The values for the CH4/CH3OH and CjHj/CjHjOH couples are at +0,59 V and 0.52 V, respectively. The oxidation of alcohols and aldehydes corresponds to values around 0.0 V (W.M. 

M. Besson, and P. Gallezot, Selective oxidation of alcohols and aldehydes on metal catalysts, Catal. Today 57(1-2), 127-141 (2000). 

The [Con(bipy)2 ]2+ species has also been reported to activate hydrogen peroxide and ter -butyl hydroperoxide for the selective ketonization of methylenic carbons, the oxidation of alcohols and aldehydes, and the dioxygenation of aryl olefins and acetylenes (36). Later reports (37), however, while confirming that the cobalt complexes did indeed cata-... 

Precolumn derivatization with a solid-phase derivatizing precolumn has also been reported. Xie et al. (43) applied polymeric permanganate oxidations of alcohols and aldehydes for the production of UV-absorb-ing species. 

It was also shown that the ratio of oxidized alcohol to oxidized Fe2+ could be greater then one. Baxendale and Wilson (1957) showed that hydroxyl radical initiating the chain polymerization of olefins by hydrogen peroxide was the same process as the rapid oxidation of glycolic acid. Merz and Waters (1947) confirmed that simple water-soluble alcohols are oxidized rapidly by Fenton s reagent. The primary alcohols are oxidized to aldehydes, which are further oxidized at comparable rates by exactly the same mechanism. Merz and Waters proposed a mechanism of chain oxidation of alcohols and aldehydes by sodium persulfate, hydrogen peroxide, and an excess of ferrous salt as follows ... 

We have already encountered three methods for preparing carboxylic acids (1) oxidation of alcohols and aldehydes, (2) oxidative cleavage of alkenes and alkynes, and (3) severe side-chain oxidation of alkylbenzenes. 

Carbonyl reductases and alcohol and aldehyde dehydrogenases are cytosolic enzymes being involved in the oxidation of alcohols and aldehydes and in the reduction of aldehydes and ketones (Lang and Kalgutkar 2003). 

Oxidation of alcohols and aldehydes. Primary alcohols and aldehydes are oxidized to the corresponding acids in good yield by this reagent, which can be used in catalytic amounts in the presence of excess oxidant for regeneration. Secondary alcohols afford ketones alkenes and tertiary alcohols do not react. ... 

Introduction. Acids may be prepared by several general methods. The oxidation of alcohols and aldehydes, and the hydrolysis of nitriles and trihalogen derivatives give carboxylic acids. The present experiment illustrates the first general method. 

Table 4-6 Activation of HOOH and t-BuOOH by Co (bpy)2 for the Oxygenation of Hydrocarbons, the Oxidation of Alcohols and Aldehydes, and the Dioxygenation of Arylolefins and Acetylenes in 4 1 MeCN/py"... 

When is NAD, rather than FAD, used in a particular oxidation-reduction reaction It depends on the chemical properties of the electron donor and the enzyme catalyzing the reaction. In oxidation reactions, NAD accepts two electrons as a hydride ion to form NADH, and a proton (H ) is released into the medium (Fig 19.9). It is generally nsed for metabolic reactions involving oxidation of alcohols and aldehydes. In contrast,... 

The best catalysts for the liquid phase oxidation of alcohols and aldehydes with molecular oxygen contain Pd and/or Pt and are developed industrially. In general, elements like Bi or Pb substantially increase the overall catalytic performances (activity, sometimes selectivity) and/or the lifetime of the Pd/C and Pt/C catalysts. In the selective oxidation of glucose to gluconic add, the presence of Bi as promoter of Pd/C catalysts is known to increase significantly the catalytic activity and to cancel the deactivation occurring during the first minutes... 

As in the case of CO oxidation [14], the liquid phase oxidation of alcohols and aldehydes is quite sensitive to the size of the gold particles and this behavior was observed since the early tests [9]. A great contribution to this study was the discovery of the catalytic activity of unsupported gold particles. Starting from experimental evidence, it became possible to derive the simple model discussed in Section 13.3.2,... 

Show how to synthesize carboxylic acids from oxidation of alcohols and aldehydes, car-boxylation of Grignard reagents, hydrolysis of nitriles, and oxidation of alkylbenzenes. 

Foreign compounds may be metabolized by non-microsomal enzyme systems. These reactions include deamination of amines, oxidation of alcohols and aldehydes, reduction of aldehydes and ketones, hydrolysis of some esters and amides and may occur in the mitochondria, or the cell supernatant fraction, or in the circulating plasma. A thorough discussion of these non-microsomal mechanisms has been presented by Parke [20], These reactions are confined to Phase I oxidations, reductions, and hydrolyses (see Fig. 1). 

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