Oxidation of alcohols to aldehydes or ketones

DESS - MARTIN Oxidizing Reagent Oxidation of alcohols to aldehydes or ketones by means of penodinanes. 

Catalytic oxidant.1 In combination with N-methylmorpholine N-oxide (7,244) as the stoichiometric oxidant, this ruthenium compound can be used as a catalytic oxidant for oxidation of alcohols to aldehydes or ketones in high yield in CH2C12 at 25°. Addition of 4A molecular sieves is generally beneficial. Racemization is not a problem in oxidation of alcohols with an adjacent chiral center. Tetrabutylammonium perruthenate can also be used as a catalytic oxidant, but the preparation is less convenient. 

Oxidation of alcohols to aldehydes or ketones is accomplished with chromate bound to an anion-exhange resin (XXXIX with A = HC1O4 ) [Frechet et al., 1981 Taylor, 1986]. Other oxidants include polymers functionalized with CIO-, CICr04, and RuOj [Kirschning et al.,... 

The functions of flavoprotein enzymes are numerous and diversified.151-1533 A few of them are shown in Table 15-2 and are classified there as follows (A) oxidation of hemiacetals to lactones, (B) oxidation of alcohols to aldehydes or ketones, (C) oxidation of amines to imines, (D) oxidation of carbonyl compounds or carboxylic acids to a,(3-unsaturated compounds,... 

Normally, the oxidation of alcohols to aldehydes or ketones is carried out using a suspension of PDC in CH2CI2 at room temperature. Other organic solvents, such as EtOAc, MeCN, benzene or CHCI3, are occasionally used. 

The Dess-Martin Periodinane (DMP), a hypervalent iodine compound, offers selective and very mild oxidation of alcohols to aldehydes or ketones. 

The oxidation of alcohols to aldehydes or ketones by periodane has several advantages over chromium and DMSO-based oxidants because of its shorter reaction times, higher yields and simplified work up. There is very little overoxidation to the carboxylic acid. It is a practical reagent for the facile and efficient oxidation of benzylic and allylic alcohols. Saturated alcohols are slow in their reactions with it. It oxidizes alcohols in the presence of non-hydroxylic functional groups such as sulfides, enols, ethers, furans and 2°-amides. An example of the DMP oxidation is the oxidation of 3,4,5-trimethoxybenzyl alcohol (7.17) with 7.16 in CH2CI2 to give 94% yield of 3,4,5-trimethoxybenzaldehyde (7.18). 

In a typical experiment, trityl benzyl ether (5.0 mmole) is added to a stirred solution of the trityl salt (0.50 mmole) in acetonitrile. After4 hr., water is added and the products isolated, fienzaldehyde and triphenylmethane are obtained in quantitative yields. The reaction thus provides a method for oxidation of alcohols to aldehydes or ketones. 

Benzeneseleninic anhydride, C5HjSe(0)0(0)SeC5Hs, which is prepared in situ from diphenyldiselenide and tert-hniyX hydroperoxide, is used for the oxidation of alcohols to aldehydes or ketones [525]. This reagent is a suitable dehydrogenating agent for the introduction of double bonds a to carbonyl groups [526] and the regeneration of ketones from their oximes, semicarbazones, and phenylhydrazones [527]. 

Carbonyl compounds act as hydrogen acceptors in the Oppenauer oxidation of alcohols to aldehydes or ketones. The reaction is based on hydride transfer from the alkoxide ion of the starting alcohol prepared in situ from anhydrous bases, aluminum isopropoxide, or, better still, tert-butoxide (equation 256). 

One example is Swern oxidation, which uses oxalyl chloride and DMSO and is particularly suitable for the selective oxidation of alcohols to aldehydes or ketones. The disadvantages of this oxidation method are the need for low temperatures, the smell of the dimethyl sulfide formed and the possible oxidation of other heteroatoms. Dess-Martin periodinane (DMP, 5) or iodoxybenzoic acid (IBX, 6) are also common oxidizing agents. The main advantage of these two methods is the short reaction time at room temperature. However, typical problems are the low solubility of IBX and the formation of byproducts. In this context, Finney et al. have reported an interesting procedure avoiding these problems by a variation of the temperature IBX is sufficiently soluble in solvents such as ethyl acetate or dichloromethane at elevated temperatures, whereas it is insoluble in these solvents at room temperature. Because of this, the remaining IBX as well as the IBX-derived byproducts can be separated from the reaction mixture by simple filtration. These reisolated IBX byproducts can then be reoxidized and reused. 

Friedrich, H. B. The oxidation of alcohols to aldehydes or ketones high oxidation state ruthenium compounds as catalysts. Platinum Metals Rev/ew 1999, 43, 94-102. 

Oxidation of alcohols to aldehydes or ketones has always been considered as a difficult reaction by organic chemists, they generally prefer to avoid the use of oxidation reaction during a synthesis. Most of the common reactions involve stoicheiometric,... 

The oxidation of alcohols to aldehydes or ketones can be performed using the very toxic potassium dichromate. The oxidizing agent in these reactions is a solution of Na2Cr207 or K2Cr207, acidified with sulfuric add (Equation 4.8). If the oxidation takes place, the orange dichromate(VI) ions in the solution are reduced to green Cr(III) ions (Equation 4.9). 

Oxidation of alcohols to aldehydes or ketone by DMSO activated with DCC (Pfitzner-Moffat), Ac2Q, (COCI)2, TFA, (Swem), P205l or pyridine-S03 (see 1sted). 

The methylotropic yeast Candida boidinii SA051 showed excellent ability for oxidation of alcohols to aldehydes or ketones. In the production of isovaleraldehyde, the generated aldehyde was up to 50 grams/L. Also this oxidation showed reaction selectivities. It was an example of chemoselectivity that the yeasts preferred (E)-2-hexenol among various C6 alcohols and oxidized it selectively to the desired (E)-2-... 

Oxidation catalyst. The oxidation of alcohols to aldehydes or ketones by iodo-sylbenzene is catalyzed by this salt. Other lanthanide(III) nitrates are also effective, but LnCl. are inferior. 

Oxammonium salts such as 81 are new and powerful oxidizing agents for the selective oxidation of alcohols to aldehydes or ketones. 28 Such salts can be generated catalytically from small amounts of a nitro-xide in the presence of a secondary oxidation procedure, either chemical or electrochemical,. 29 or with two equivalents of acid and 2 equivalents of a nitroxide. When 81 was mixed with acetylenic alcohol 82 in dichloromethane, aldehyde 83 was isolated in 93% yield. The reaction can be monitored as the initial yellow slurry changes to a white slurry and the presence of unreacted oxidant can be checked with starch. 3l It is not necessary to use anhydrous conditions, and it was discovered that the rate of reaction was enhanced by the presence of silica gel. This reagent is compatible for the mild oxidation of many alcohols, including aliphatic primary and secondary as well as allylic and benzylic alcohols. 

One the most popular of all oxidations of alcohols to aldehydes or ketones involves the formation of intermediate alkoxysulfonium salts. A number of methods are available for the formation of the alkoxysulfonium salts, which are treated with a base to give the aldehyde or ketone. The conditions of the reaction are mild, the reactions proceed rapidly and high yields of carbonyl compounds are generally obtained. 

Many methods for the oxidation of alcohols to aldehydes or ketones have been described above. Using a primary alcohol substrate, care must be taken to avoid oxidation to the carboxylic acid if the aldehyde is the desired product. Aldehydes are readily oxidized by a number of reagents, including chromic acid, permanganate salts, silver oxide or even by molecular oxygen. If the carboxylic acid is desired. 

The oxidation of alcohols to aldehydes or ketones assmnes new importance with long term attention to biomass based economics. Acetaldehyde, the product of ethanol oxidation, is of special interest since it can be utilized in the synthesis of other basic chemikals such as acetic acid, butanol, etc. [6]. The following Equations 9-23 and 9-24 can be formulated ... 

---