Definition

Ozonolysis is reaction where the double bonds of alkenes are cleaved with ozone (O3). Alkanes form organic compounds in which the multiple carbon-carbon bonds have been replaced by a carbonyl group. The outcome of the reaction depends on the type of multiple bonds being oxidized and the work-up conditions. Reductive work-up conditions are far more commonly used than oxidative conditions.

Structural reaction scheme for Ozonolysis (Reductive workup), diagram 1 of 5
Figure 1. Ozonolysis (Reductive workup)

Explanation

Ozonolysis is the specific reaction in which cleavage occurs and π and σ bond. In this reaction, ozone is mainly used. In order to understand how this reaction occurs, we must first explore the structure of ozone. Ozone is a compound with the following resonance structures:


The gas mixture is passed through a solution of the alkene in methanol or dichloromethane. The first isolable intermediate is a species called an ozonide (or molozonide). The molozonide is unstable and undergoes rearrangement to produce a more stable ozonide:

Structural reaction scheme for Ozonolysis (Reductive workup), diagram 2 of 5
Figure 2. Ozonolysis (Reductive workup)
Structural reaction scheme for Ozonolysis (Reductive workup), diagram 3 of 5
Figure 3. Ozonolysis (Reductive workup)

When treated with a mild reducing agent, the ozonide is converted into products:

Structural reaction scheme for Ozonolysis (Reductive workup), diagram 4 of 5
Figure 4. Ozonolysis (Reductive workup)


Common examples of reducing agents include dimethyl sulfide (DMS) or Zn/H2O:

Structural reaction scheme for Ozonolysis (Reductive workup), diagram 5 of 5
Figure 5. Ozonolysis (Reductive workup)