Reactions of Aldehydes and Ketones—General Considerations

Aldehydes and ketones are also both obtained as products of the oxidative cleavage of alkenes (Section 12.10). 

Problem 21.11 What reagents are needed to convert each compound into butanal (CH3CH2CH2CHO) (a) CH3CH2CH2COOCH3 (b) CH3CH2CH2CH2OH (c) HC = CCH2CH3  

Let s begin our discussion of carbonyl reactions by looking at the two general kinds of reactions that aldehydes and ketones undergo. 

Recall from Chapter 20 that the uncrowded, electrophilic carbonyl carbon makes aldehydes and ketones susceptible to nucleophilic addition reactions. 

Problem 21.14 What alkene would yield 2,2-dimethoxy-1,3-cyclopentanedicarbaldehyde on treatment with O3 

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Preparation of aldehydes and ketones Reactions of aldehydes and ketones—General considerations Nucleophilic addition of H and —A review Nucleophilic addition of "CN... 

This procedure is an adaptation of that described by Emmons for the preparation of oxaziranes from imines using peracetic acid. Other procedures which may be more useful for oxazirane preparation in specific instances are the oxidation of imines with iw-chloroperbenzoic acid and the reaction of aldehydes or ketones with hydroxylamine 0-sulfonic acid in alkaline solution. 2-<-Butyl-3-phenyloxazirane has also been prepared by photolysis of a-phenyl-N-f-butylnitrone (a general reaction of considerable theoretical interest since it represents direct conversion of electromagnetic energy to chemical energy) and in low yields by ozonoly-sis of N-f-butylbenzaldimine. ... 

Sml2 can effectively promote the intermolecular reductive dimerisation of aldehydes or ketones giving rise to symmetrical diols.7 9 Generally, arylalde-hydes and aryl ketones couple within seconds in THF at room temperature. Aliphatic aldehydes and ketones react considerably more slowly several hours are required for the aldehydes, whereas for ketones reaction times of 24 h are usually needed. Nevertheless, these slower couplings can be greatly accelerated by the addition of additives such as HMPA.10... 

In a more general approach, eight examples of the Wolff—Kishner reduction of aromatic aldehydes and ketones are described using 80% hydrazine hydrate in toluene64 (Scheme 4.37). The reaction times are longer than described in the previous paper because less reactive substrates were used. Still, both the formation of the hydrazone and the reduction step are considerably faster than under thermal conditions the reduction proceeds at ambient pressure and in the absence of a solvent. The microwave reduction is compatible with other reducible functional groups such as aromatic OMe, Me, Cl or COOMe, which can otherwise cause problems under conventional reaction conditions64. 

This condensation finds considerable generality, enol silyl ethers of a variety of ketones and both aromatic and aliphatic aldehydes are usable For enol silyl ethers of substituted cyclohexanones the reaction is regio- and stereospecific [id]. 

Wacker (1) A general process for oxidizing aliphatic hydrocarbons to aldehydes or ketones by the use of oxygen, catalyzed by an aqueous solution of mixed palladium and copper chlorides. Ethylene is thus oxidized to acetaldehyde. If the reaction is conducted in acetic acid, the product is vinyl acetate. The process can be operated with the catalyst in solution, or with the catalyst deposited on a support such as activated caibon. There has been a considerable amount of fundamental research on the reaction mechanism, which is believed to proceed by alternate oxidation and reduction of the palladium ... 

Volume 17 covers gas-phase combustion, which includes probably the most complex processes investigated by chemists. Chapter 1, about half the book, deals with the oxidation of hydrogen and carbon monoxide, with extensive consideration of all the individual reactions occurring. In Chapter 2, the combustion of hydrocarbons is discussed, with emphasis on the general mechanisms which have been suggested to account for the numerous products of partial oxidation. In Chapter 3, the oxidation of aldehydes, which are important intermediates in combustion of other compounds, is considered, and in Chapter 4, the oxidation of alcohols, ketones, oxirans, ethers, esters, peroxides, amines and halocarbons. 

In general, carbonyl groups do not function as good initiators in vinylsilane-mediated cyclization reactions and relatively few examples exist. The cyclization of vinylsilanes with ketones or aldehydes as initiators is a highly underdeveloped reaction that holds considerable potential. As reported by Tius and coworkers, treatment of aldehyde (13) with a catalytic amount of p-toluenesulfonic acid gave a mixture of the tetralins (14) and (15) in a combined yield of 53%, with lesser amounts of the enone (16 Scheme 8). The enone system presumably arises from the intramolecular 1,3-hydride transfer of the intermediate a-silyl carbocation (17). Similarly, the vinylsilane (18) undergoes cyclization to produce the disub-stituted benzene derivative (19), although yields are low. 

The reaction of olefins with carbon monoxide and hydrogen in the presence of cobalt carbonyl catalysis affords inter alia aldehydes, ketones, and alcohols. These reactions are of considerable industrial importance. The industrial reactions were originally called the Fischer-Tropsch or Oxo syntheses but now are described under the general title of hydro-formylation reactions 3, 224). 

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