Carboxylic acid aldehyde oxidation product

Carboxylic acids are the products of the oxidation of aldehydes (see Chapter 6). 

SAMPLE SOLUTION (a) The reactant is a primary alcohol and so can be oxidized either to an aldehyde or to a carboxylic acid. Aldehydes are the major products only when the oxidation is carried out in anhydrous media. Carboxylic acids are formed when water is present. The reaction shown produced 4-chlorobutanoic acid in 56% yield. 

Reduction then proceeds by successive transfers of hydride ion, H e, from aluminum to carbon. The first such transfer reduces the acid salt to the oxidation level of the aldehyde reduction does not stop at this point, however, but continues rapidly to the alcohol. Insufficient information is available to permit very specific structures to be written for the intermediates in the lithium aluminum hydride reduction of carboxylic acids. However, the product is a complex aluminum alkoxide, from which the alcohol is freed by hydrolysis ... 

The direct catalyzed or uncatalyzed oxidation of alkanes with oxygen is an important reaction in the industrial production of carboxylic acids, hydroperoxides (for production of epoxides from alkenes), alcohols, ketones, or aldehydes [60],... 

Double bonds are cleaved by a number of oxidizing agents, converting the olefinic carbons to carboxylic acids, aldehydes, or alcohols. Fatty acids give a monofunctional product from the methyl end and a difunctional product from the carboxyl end (along with low-molecular-weight products from methylene-interrupted systems). 

Just as the oxidation products of aldehydes are carboxylic acids, the reduction products of carboxylic acids are aldehydes. To carry out this reaction, any carboxylic acid with formic acid is passed in gaseous state over a catalyst of Ti02 at 300-350°C. As a result, an aldehyde is obtained and C02 and H20 are given out. 

Oxidation of the aldehyde groups of SVI-IO4 with weakly acidic sodium chlorite " for various times gave products (see 17, SVI-IO4-BH4-CIO2) in which from 16 to 81% of the aldehyde groups had been oxidized, and which showed decreasing precipitation in anti-Pn VI horse and rabbit sera with increasing content of carboxylic acid groups. The product from the con-... 

An exception is norbornene, which after 84% conversion in the presence of PtCl2/SnCl2/(—)-BPPM gives exclusively < .TO-2-formylbicyclo[2.2.1]heptane with 98.7% aldehyde selectivity and 60 % ee12. The product can be converted to the corresponding carboxylic acid upon oxidation without loss of enantiomeric purity. If the hydroformylation reaction is carried out in triethyl orthoformate as solvent, the aldehyde is trapped as the acetal. Thus, higher temperatures with higher conversions and yields can be applied without racemization of the product. 

Akubuiro and Wagner [85,86] proposed ketone oxidation mechanisms at the surface of an activated carbon. Ketones are oxidized to produce peroxides, which are very unstable and decompose with strong exothermic reactions. These by-products give carboxylic acids, aldehydes and/or diketones. An example of the reaction pathways is shown in Fig. 12. 

Reports of the kinetics of ceric oxidation of a variety of different alcohols have been made. The substrate molecules include mono-, di- and trihydroxyalkanes, cyclo-alkanols (cychc alkane alcohols) and phenols (table 3). Hydroxyacids have also been investigated and will be discussed in the section on carboxylic acids. Ceric oxidation of carbohydrates is discussed along with aldehydes and ketones. In those studies with excess substrate, the dominant products (where discussed) are the corresponding aldehydes and ketones. The most remarkable aspect of these investigations is that the resolved values for the stability constants of many of the precursor complexes exceed those observed in analogous Ce(lV)-carboxylic acid oxidations. 

However, if we want to obtain the carboxylic acid as the product, we must leave the aldehyde in contact with the oxidizing agent for a prolonged period of time. In this case the apparatus is set up for reflux (Figure 10.78b), and an excess of the oxidizing agent is used to favour complete oxidation to the carboxylic acid. 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

Chromic acid (H2Cr04) is a good oxidizing agent and is formed when solutions containing chromate (Cr04 ) or dichromate (Cr207 ) are acidified Sometimes it is possible to obtain aldehydes m satisfactory yield before they are further oxidized but m most cases carboxylic acids are the major products isolated on treatment of primary alco hols with chromic acid... 

Oxidative reactions frequently represent a convenient preparative route to synthetic intermediates and end products This chapter includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes and ketones, carboxylic acids, nitrogen compounds, and organophosphorus, -sulfur, -selenium, -iodine, and -boron compounds... 

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