Peroxyacids aldehyde reactions with

Ketones do not react with most of the reagents used to oxidize aldehydes. However, both aldehydes and ketones can be oxidized by a peroxyacid. Aldehydes are oxidized to carboxylic acids and ketones are oxidized to esters. A peroxyacid (also called a per-carboxylic acid or an acyl hydroperoxide) contains one more oxygen than a carboxylic acid, and it is this oxygen that is inserted between the carbonyl carbon and the H of an aldehyde or the R of a ketone. The reaction is called a Baeyer-Villiger oxidation. 

The chain unit in the thermal and photochemical oxidation of aldehydes by molecular dioxygen consists of two consecutive reactions addition of dioxygen to the acyl radical and abstraction reaction of the acylperoxyl radical with aldehyde. Experiments confirmed that the primary product of the oxidation of aldehyde is the corresponding peroxyacid. Thus, in the oxidation of n-heptaldehyde [10,16,17], acetaldehyde [4,18], benzaldehyde [13,14,18], p-tolualdehyde [19], and other aldehydes, up to 90-95% of the corresponding peroxyacid were detected in the initial stages. In the oxidation of acetaldehyde in acetic acid [20], chain propagation includes not only the reactions of RC (0) with 02 and RC(0)00 with RC(0)H, but also the exchange of radicals with solvent molecules (R = CH3). 

Another route to the preparation of a-hydroxy derivatives consists of the transformation of enolates into silyl enolates and their subsequent oxidation. Oxidation of triaLkylsUyl enolates with peroxyacids, most frequently cpba, has been applied for preparation of a-hydroxy- and a-acetoxy aldehydes or ketones. Reactions require mild conditions and generally give good yields of the expected compound . Mechanistic investigations suggest the intermediate formation of epoxides which evolve to the final products via 1,4-sUyl group migration. 

During the induction period propionaldehyde and hydrogen peroxide are the main products, although a little acetaldehyde is also formed. At the end of the induction period the reaction accelerates autocatalytically and formaldehyde, methanol, carbon monoxide, methane and ethane together with acids and peroxides are formed. Hydrogen peroxide is the most abundant peroxidic product, but there are also appreciable amounts of organic peroxides and peroxyacids [17]. These reach concentrations (as does formaldehyde, and to a less marked extent the higher aldehydes) at the time of maximum rate. 

Conjugated dienes can be epoxidized (1,2-addition), although the reaction is slower than for corresponding alkenes, but a,p-unsaturated ketones do not generally give epoxides when treated with peroxyacids.The epoxidation of a,p-unsaturated ketones with hydrogen peroxide under basic conditions is known as the Waits-Schejfer epoxidation, discovered in 1921. This fundamental reaction has been extended to a,()-unsaturated ketones (including quinones), aldehydes, and... 

In these experiments either nitrogen dioxide or ozone was mixed with an organic compound at concentrations of about 1 p.p.t. in air or oxygen and allowed to react with or without artificial sunlight the products were analyzed by means of standard infrared techniques. Alkyl nitrate, alkyl nitrite, aldehyde, and peroxyacid were typical products of the nitrogen dioxide-organic compound reaction. 

The acyl radicals add oxygen to give the peroxyacyl radical, R—C—0—0. This reaction seems probable because, at the concentrations at which compound X is formed, the acyl radical collides with oxygen several thousand times more frequently than with any of the other possible reactants. The likelihood of the reaction is also indicated by the fact that the low temperature oxidation of aldehyde in pure oxygen produces peroxyacids. 

In the cooxidation of olefins with aldehydes, the relative ease of reactions (1) - (3) is utilized for converting the olefin to an epoxide. Both the acylperoxy radical and the peroxyacid may be active reactants in this process. Equations (4) - (7) [2]. 

The aforesaid suggests that a flow graph inherently enables the systematization of intuitive, qualitative and incompletely quantitative knowledge of a researcher and switch over the equation language. Let us illustrate this by the example of liquid-phase oxidation of benzaldehyde by dioxygen, which will be considered in more detail in Chapter 6 [29,56]. Let us suppose that the researcher possesses the following preliminary information about this reaction (i) the peroxyacid is an intermediate product that results in benzoic acid directly or by interaction with the initial aldehyde (ii) the oxidation is autoinitiated by the peroxyacid. 

Liquid-phase oxidation of benzaldehyde belongs to the class of degenerate branching-chain process. In the kinetic model under consideration the degenerate chain branching takes place due to the catalytic decomposition of the formed peroxyacid (step 4). This reaction is also specific, because the nonradical reaction of the formed peroxyacid with the initial benzaldehyde (step 5) is the main channel for the further transformation of the peroxyacid. Here the following reviews should be mentioned [2,5,6] that provide additional information about the mechanism of liquid-phase oxidation of aldehydes. 

Detailed review of studies on the auto- and catalytic-oxidation of unsaturated aldehydes in the liquid phase may be found in [2,9], Here we just note the main specific feature of the unsaturated aldehydes oxidation, briefly cited in Section 5.2. It implies that the free-radical chain process of the aldehyde group oxidation stimulates undesirable reactions, including the copolymerization of aldehyde with oxygen through the aldehyde s double bond, and in some cases also the copolymerization of the reaction products, the unsaturated acids and peroxyacids with oxygen. The oxidation reactions of unsaturated aldehydes are defined as the multicentered chain processes with two types of reaction centers acyl monomeric and polyperoxide free radicals. 

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