Criegee Ozonolysis

Theory and Defination :

The reaction between olefins and ozone to form aldehydes, ketones, carboxylic acids, etc., is known as the Criegee ozonolysis. This reaction occurs in three steps: formation of primary ozonides, splitting of primary ozonides, and formation of secondary ozonides. The study finds that the electron-donating groups accelerate the reaction, and the electron-withdrawing groups decrease the reaction rate. This reaction has application for structure determination as well as synthetic purposes and it is found that the ozonolysis of olefins is one of the major methods of forming aerosol.

General Reaction :

Mechanism :

First step is a 1,3-dipolar cycloaddition of ozone to the alkene leading to the primary ozonide (molozonide, 1,2,3-trioxolane, or Criegee intermediate) which decomposes to give a carbonyl oxide and a carbonyl compound:

The carbonyl oxides are similar to ozone in being 1,3-dipolar compounds, and undergo 1,3-dipolar cycloaddition to the carbonyl compounds with the reverse regiochemistry, leading to a mixture of three possible secondary ozonides (1,2,4-trioxolanes):

These secondary ozonides are more stable than primary ozonides. Even if the peroxy bridge is shielded by steric demanding groups leading to isolable products, they should not be isolated from an unmodified ozonolysis, because still more explosive side products (tetroxanes) may have been formed:

As endoperoxides are investigated as antimalarial compounds, more selective methods have been developed for their preparation .
The Criegee mechanism is valid for reactions in hydrocarbons, CH2Cl2, or other non-interactive solvents. Alcohols react with the carbonyl oxide to give hydroperoxy hemiacetals:

The synthetic value lies in the way the complex mixtures of intermediates can be worked up to give a defined composition of products and a clean conversion of all peroxide species. The three main possibilities are given above, along with examples for the reagents used.