Oxidation of Aldehydes Having Other Functionalities

Oxidations of unsaturated aldehydes, as long as the oxidation affected only the aldehyde group, have been discussed with the oxidations of saturated and aromatic aldehydes. In this section, only such oxidations that affect the double bonds are described. 

Because of the easy oxidizability of the aldehydes to carboxylic acids, any oxidation at the double bond is a delicate operation. Only a few oxidants are suitable to produce aldehyde epoxides, if used under controlled conditions. 

Whereas hydrogen peroxide in acids [125] and peroxysulfuric acid [200] convert methacrolein into methacrylic acid, hydrogen peroxide in an alkaline medium (best at pH 8-8.5) forms the epoxy aldehydes (equation 364) [146]. 

The procedure just mentioned fails with cinnamaldehyde. The epox-idation of cinnamaldehyde is accomplished by tert-butyl hydroperoxide in aqueous methanolic sodium hydroxide (equation 365) [219]. 

Oxidation of hydroxy aldehydes may affect only the aldehyde group or both the aldehyde and alcoholic groups. Both types are especially common in sugar chemistry for example, aldoses may be converted into aldonic acids or aldaric acids. 

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