What is Ozonolysis of Alkees
Organic Chemistry Portal
Related reactions:1,3-dipolar cycloaddition, Griesbaum
Organic Chemistry Portal: Ozonolysis
Ozonolysis enables the cleavage of alkenes through the reaction of the C-C double bond with ozone. Depending on the work-up, different end products can be obtained: Reductive work-up gives alcohols or carbonyl compounds; Oxidative work-up leads to carboxylic acids and ketones.
The mechanism was suggested by Criegee (Angew. Chem. Int. Ed., 1975, 87, 745. DOI) and was recently able to use 17O-NMR spectroscopy can be confirmed by the Berger group (Eur. J. Org. Chem., 1998, 1625. DOI).
In the first step, a 1,3-dipolar cycloadditon from the alkene produces the "primary ozonide" (molozonide, 1,2,3-trioxolane or Criegee intermediate), which breaks down to a carbonyl and a carbonyl oxide:
Like ozone, carbon oxides can enter into cycloadditons as 1,3-dipolar compounds. A mixture of three possible "secondary ozonides" (1,2,4-trioxolanes) is obtained by cycloaddition to the carbonyl compounds formed:
These secondary ozonides are more stable than the primary ozonides. But even if the peroxide bridge is shielded by large groups and the ozonides are sufficiently stable, they should never be isolated from unmodified ozonolysis, since highly explosive by-products such as tetroxanes are also formed:
Endoperoxides (compounds with bridging peroxide groups) are of great interest as possible antimalarials. More reliable methods had to be developed for their synthesis (e.g. Griesbaum coozonolysis). Some reactions are described here: V. D.B. Bonifacio, Org. Chem. Highlights2004, October 25. Link
The Criegee mechanism is valid when the reaction occurs in hydrocarbons or the more polar CH2Cl2 is carried out. This is how alcohols react with the carbonyl oxide to form hydroperoxide hemiacetals:
The synthetic value of ozonolysis is determined by the processing options, which result from a complex mixture of different products in a defined composition of end products. The three most important options, including the reagents used, are mentioned above.
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