Aldehydes primary alcohol oxidations

Primary alcohols oxidize to aldehydes, which, in turn, oxidize to carboxylic acids. Secondary alcohols oxidize to ketones. In each case, the reverse process is called re- duction... 

R—CH2 primary alcohol [oxidizing agent] —Tit R—C—H aldehyde [over-oxidation] [O] R—C—OH carboxylic acid... 

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. ... 

By the three preceding reactions and by the formation of carbohydrates by the oxidation of poly-hydroxy alcohols, carbohydrates are poly-hydroxy alcohols in which one alcohol group is oxidized to aldehyde (primary alcohol group at the end of the chain), or to ketone (secondary alcohol group). 

Among the aliphatic alcohols, oxidation of methanol has been studied most extensively [122-125]. At a platinum anode in acidic aqueous solutions, methanol oxidizes completely to CO2. Higher primary alcohols oxidize to aldehydes and acids under these conditions, though detailed mechanistic studies are lacking [126,127]. Anodic oxidation of secondary alcohols in aqueous acid leads to the corresponding ketones in high yield, but the reaction has received little attention over the years [126,128]. Indirect oxidation methods employing mediators are of considerable interest in this area and are treated elsewhere. 

Primary alcohols oxidize rapidly and efficiently to aldehydes. Aldehydes (from whatever source) oxidize very rapidly indeed to produce acids (eq. (22)), the likely final product ... 

Reaction of the C-0 and O-H Bonds Primary alcohols oxidize to carboxylic acids secondary alcohols oxidize to ketones with chromium trioxide or sodium dichromate. Tertiary alcohols do not oxidize under mild conditions. With pyridinium chlorochromate (PCC) the oxidation of primary alcohols can be stopped at aldehydes. 

With some primary alcohols, it is possible to establish an equilibrium between the initially formed aldehyde and the precursor alcohol in which unreacted alcohol is converted to an hemiacetal (17), which can be further oxidized to an ester. This often accompanies the oxidation of lower molecular weight primary alcohols. Oxidation of 1-butanol to butyl butyrate with Cr(VI), for example, is an Organic Syntheses preparation. ... 

The most characteristic reactions of alcohols are their oxidation to aldehydes and ketones, which may undergo further oxidation, producing carboxylic acids. While primary alcohols oxidize to aldehyde, secondary alcohols produce ketones ... 

Aldehydes. Primary alcohols (in CH2CI2) can be oxidized to aldehydes with potassium dichromate in 9 A/ sulfuric acid in the presence of tetra-n-butylr ammonium bisulfate as a phase-transfer catalyst. It is generally advantageous to use a slight excess of oxidant. The oxidation is complete in a few seconds at room temperature. Yields are generally high except for water-soluble aliphatic alcohols and ,/3-unsaturated alcohols (the double bonds appear to be oxidized). Of course, secondary alcohols can also be oxidized to ketones in the same way. ... 

Aldehydes can be prepared by the oxidation of primary alcohols. Oxidizing agents such as pyridinium chlorochromate (PCC) or pyridinium dichromate (PDC) can be used for such conversions. 

Aristeromycin 5 -aldehyde has been prepared, and was shown to be a potent inhibitor of SAH hydrolase this study indicated that the fluoromethylene compounds (Vol. 26, p. 247), which are also inhibitors, do not act as precursors of the aldehyde. 2-Halo-derivatives 39 (X=F, Cl) of neplanocin A have been prepared, as have the equivalent structures lacking the CH2OH group and the analogue 40. Neplanocin analogues with the primary alcohol oxidized to the carboxylic acid level have also been made by oxidation, and aristeromycin and its cytosine analogue (carbodine) have been incorporated into a hammerhead ribozyme domain. ... 

With primary alcohols, oxidation can be stopped at the aldehyde stage by special reagents, such as pyridinium chlorochromate (PCC), shown in eq. 7.38. ... 

In the synthesis of methyl-2,3-0-isopropylidene-4-0-(methoxymethyl)-6-methylene-a-D-mannopyranoside (13), the hydroxyl groups of methyl-a-o-mannopyranosides are selectively protected 6-hydroxyl group as silyl ether 2,3-hydroxyl groups as acetonides and 4-hydroxyl group as methoxymethyle-ther. The silyl group at the C-6 position is then selectively cleaved to get primary alcohol. Oxidation of the alcohol to aldehyde followed by Wittig methylenation yields the desired olefin (13, Scheme 31.13). 

Primary alcohols afforded the corresjjonding carboxylic adds via further oxidation of the aldehyde intermediate for example, 1-hexanol afforded 1-hexanoic acid in 95% yield. It is important to note, however, thatthis was achieved without the requirement of one equivalent of base to neutralize the carboxylic acid product (which is the case with supported noble metal catalysts [5]). In contrast, when lmol% TEMPO (4 equivalents per Pd) was added the aldehyde was obtained in high yield for example, 1 -hexanol afforded 1 -hexanal in 97% yield. Some representative examples of primary alcohol oxidations using this system are shown in Table 5.9. The TEMPO was previously shown to suppress the autoxidation of aldehydes to the carboxyhc adds (see earlier). 

Aldehydes can be formed by oxidizing a primary alcohol oxidation of a secondary alcohol gives a ketone. What happens when we try to oxidize a tertiary alcohol The answer is simple Nothing happens. 

Waxes are synthesised by reduction of fatty acids to primary alcohols via aldehydes. Primary alcohols react with acyl-CoAs to form esters, aldehydes eliminate carbon monoxide (by decarbonylation) giving rise to hydrocarbons (alkanes). Oxidation of alkanes yields secondary alcohols, and oxidation of secondary alcohols gives rise to ketones. 

Primary alcohols oxidize to aldehydes, which in turn may readily oxidize further to the corresponding carboxylic acids. 

When chlorine is passed into boiling ethanol, both chlorination of the methyl group and oxidation of the primary alcohol group to an aldehyde occur, giving trichloro-acetaldehyde or chloral ... 

By the controlled oxidation of primary alcohols with a solution of potassium or sodium dichromate in dilute sulphuric acid. To avoid the further oxidation to the corresponding acid, the aldehyde is removed as rapidly as possible by distillation through a fractionating column, for example ... 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

The slow oxidation of primary alcohols, particularly MeOH, is utilized for the oxidation of allylic or secondary alcohols with allyl methyl carbonate without forming carbonates of the alcohols to be oxidized. Allyl methyl carbonate (564) forms 7r-allylpalladium methoxide, then exchange of the methoxide with a secondary or allylic alcohol 563 present in the reaction medium takes place to form the 7r-allylpalladium alkoxide 565, which undergoes elimination of j3-hydrogen to give the ketone or aldehyde 566. The lactol 567 was oxidized selectively with diallyl carbonate to the lactone 568 without attacking the secondary alcohol in the synthesis of echinosporin[360]. 

Primary alcohols may be oxidized either to an aldehyde or to a carboxylic acid... 

Conditions that do permit the easy isolation of aldehydes in good yield by oxida tion of primary alcohols employ various Cr(VI) species as the oxidant in anhydrous media Two such reagents are pyndmium chlorochromate (PCC), CsHsNH ClCr03 ... 

To the synthetic chemist the most important of the reactions m Table 17 1 are the last two the oxidation of primary alcohols to aldehydes and secondary alcohols to ketones Indeed when combined with reactions that yield alcohols the oxidation methods are so versatile that it will not be necessary to introduce any new methods for preparing aide hydes and ketones in this chapter A few examples will illustrate this point... 

Oxidation of primary alcohols to aide hydes (Section 15 10) Pyridinium di chromate (PDC) or pyridinium chloro chromate (PCC) in anhydrous media such as dichloromethane oxidizes primary al cohols to aldehydes while avoiding over oxidation to carboxylic acids... 

Oxidation of primary alcohols (Section 15 10) Potassi um permanganate and chromic acid convert primary al cohols to carboxylic acids by way of the corresponding aldehyde... 

The reaction of aldoses with nitric acid leads to the formation of aldaric acids by oxidation of both the aldehyde and the terminal primary alcohol function to carboxylic acid groups Aldaric acids are also known as saccharic acids and are named by substi tutmg aric acid for the ose ending of the corresponding carbohydrate... 

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