Oxidation aldehydes and ketones

Cerium(IV) is used as an oxidant both in analysis and in preparative chemistry. Dissolved in acetic acid it oxidizes aldehydes and ketones at the or-carbon atom a solution of ammonium hexanitratocerate(IV) will oxidize toluene to benzaldehyde. Aqueous CeIV oxidizes concentrated Cl- to Cl2, but the rate depends strongly on the pH and the presence of a catalyst.40... 

Ceriuin(iv) is used as an oxidant, not only in analysis, but also in organic chemistry where it is commonly used in acetic acid. The solid acetate, which is bright yellow, can be made by ozone oxidation of Ce111 acetate.45 The solutions oxidize aldehydes and ketones at the a-carbon atom, and benzal-dehyde, for example, gives benzoin while ammonium hexanitratocerate will oxidize toluenes to aldehydes. These oxidations appear to proceed by the initial formation of 1 1 complexes the complexes of alcohols are red.46... 

Oxidation. Aldehydes and ketones are produced using the reagent and PhCHO as hydrogen acceptor. 

Besides being prepared by oxidation, aldehydes and ketones can also be prepared by reactions in which the first step includes the addition of water to the triple bond of the alkyne molecule. The first intermediate, the unsaturated alcohol (enol) is unstable and undergoes isomerization to the stable ketone. This type of reaction in which one isomer is transformed to another is called rearrangement. The older name for this molecular rearrangement is taulomerism and this special case is called the keto-enol tautomerism. 

Table 6.1. Some Pyridine and Pyridine X Oxide Aldehydes and Ketones ...

Oxidation if 1° and 2° alcohols to aldehydes and ketones- No over oxidation... 

The final step can involve introduction of the amino group or of the carbonyl group. o-Nitrobenzyl aldehydes and ketones are useful intermediates which undergo cyclization and aromatization upon reduction. The carbonyl group can also be introduced by oxidation of alcohols or alkenes or by ozonolysis. There are also examples of preparing indoles from o-aminophcnyl-acetonitriles by partial reduction of the cyano group. 

Lithiated indoles can be alkylated with primary or allylic halides and they react with aldehydes and ketones by addition to give hydroxyalkyl derivatives. Table 10.1 gives some examples of such reactions. Entry 13 is an example of a reaction with ethylene oxide which introduces a 2-(2-hydroxyethyl) substituent. Entries 14 and 15 illustrate cases of addition to aromatic ketones in which dehydration occurs during the course of the reaction. It is likely that this process occurs through intramolecular transfer of the phenylsulfonyl group. 

The mechanisms by which transition metal oxidizing agents convert alcohols to aldehydes and ketones are complicated with respect to their inorganic chemistry The organic chemistry is clearer and one possible mechanism is outlined m Figure 15 4 The... 

Section 15 11 Oxidation of alcohols to aldehydes and ketones is a common biological reaction Most require a coenzyme such as the oxidized form of nicotin amide adenine dmucleotide (NAD" )... 

Many low molecular weight aldehydes and ketones are important industrial chem icals Formaldehyde a starting material for a number of plastics is prepared by oxida tion of methanol over a silver or iron oxide/molybdenum oxide catalyst at elevated temperature... 

Primary and secondary alcohols are readily oxidi2ed to aldehydes and ketones under alkaline conditions. Aldehydes, both aUphatic and aromatic, are converted into the corresponding carboxyUc acids. Ketones are generally oxidation resistant unless sufficient alkaU is present to effect enolization. The enol can be oxidatively cleaved. 

Dijbner-von Miller Synthesis. A much less violent synthetic pathway, the Dn bner-von Miller, uses hydrochloric acid or 2inc chloride as the catalyst (43). As in the modified Skraup, a,P-unsaturated aldehydes and ketones make the dehydration of glycerol uimecessary, and allow a wider variety of substitution patterns. No added oxidant is required. With excess aniline the reaction proceeds as follows ... 

The aromatic primary and secondary stibines are readily oxidized by air, but they are considerably more stable than their aHphatic counterparts. Diphenylstibine is a powerful reducing agent, reacting with many acids to Hberate hydrogen (79). It has also been used for the selective reduction of aldehydes and ketones to the corresponding alcohols (80). At low temperatures, diphenylstibine undergoes an addition reaction with ketene (81) ... 

V-bromosuccinimide [128-08-5] C H BrNOj 180-183 2.098 brominating olefins, oxidizing alcohols to aldehydes and ketones, converting aldehydes to acid bromides... 

Ethylene oxide reacts with phosphonium haUdes to give yUdes, which are used to synthesize olefins from carbonyl compounds, such as aldehydes and ketones (92). 

Pyridazine aldehydes and ketones with the carbonyl group at the ring or in a side chain react in the usual manner. They form hydrazones, semicarbazides, oximes, etc. Side-chain aldehydes can be easily oxidized to pyridazinecarboxylic acids with silver nitrate and side-chain ketones are oxidized to carboxylic acids by treatment with potassium permanganate or hydrogen peroxide. 

In 1959 Carboni and Lindsay first reported the cycloaddition reaction between 1,2,4,5-tetrazines and alkynes or alkenes (59JA4342) and this reaction type has become a useful synthetic approach to pyridazines. In general, the reaction proceeds between 1,2,4,5-tetrazines with strongly electrophilic substituents at positions 3 and 6 (alkoxycarbonyl, carboxamido, trifluoromethyl, aryl, heteroaryl, etc.) and a variety of alkenes and alkynes, enol ethers, ketene acetals, enol esters, enamines (78HC(33)1073) or even with aldehydes and ketones (79JOC629). With alkenes 1,4-dihydropyridazines (172) are first formed, which in most cases are not isolated but are oxidized further to pyridazines (173). These are obtained directly from alkynes which are, however, less reactive in these cycloaddition reactions. In general, the overall reaction which is presented in Scheme 96 is strongly... 

Reactions with aldehydes and ketones. 4.11 Oxidation Attack at Sulfur... 

Aldehydes and Ketones — These share many chemical properties because they possess the carbonyl (C=0) group as a common feature of their structure. Aldehydes and ketones have lower boiling points and higher vapor pressures than their alcohol counterparts. Aldehydes and ketones through C< are soluble in water and have pronounced odors. Ketones are relatively inert while aldehydes are easily oxidized to their counterpart organic acids. 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

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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