Oxidation of Methylidene Groups to Carbonyl Groups
Oxidation of Methylidene Groups to Carbonyl Groups: Introduction
The direct conversion of alkenes to carbonyl compounds is exemplified by the Wacker process. However, alternative methods exist that oxidize an alkene in two or three intermediate steps (for example via alcohols, esters, etc.).
- Catalysts (aqueous solutions of palladium(II)- and copper(II)-salts)
An oxygen atom is added to the β position of the olefin. In the first step, a π-complex of the olefin and the transition metal is formed. This is followed by nucleophilic addition of an external water molecule to the coordinated olefin, resulting in an alcohol which rearranges to an enol. Transformation of the π-complex of the coordinated enol yields a hydroxypalladium-σ-complex which breaks up into the carbonyl compound and metallic palladium. The latter is reoxidized with oxygen in the presence of the cooxidant copper(II) chloride to palladium(II), reusable again for olefin oxidation.
Preparation of acetone and acetaldehyde from olefins using the Wacker process.