The mechanism of ozonolysis explains how ozone (O₃) reacts with alkenes (or alkynes) to break their multiple bonds and form smaller carbonyl compounds (like aldehydes, ketones, or carboxylic acids). Here’s the step-by-step process in simple words:
1. Attack of ozone on the double bond
- The double bond in an alkene has high electron density.
- Ozone approaches and reacts with this double bond.
- This forms an unstable, cyclic structure called the molozonide.
2. Rearrangement to ozonide
- The molozonide is unstable and breaks apart into smaller fragments (carbonyl compound fragments and a reactive oxygen species).
- These fragments quickly rearrange and combine to form a more stable ring-like compound called the ozonide.
3. Breakdown of ozonide
- The ozonide itself is unstable.
- Under work-up conditions (either reducing or oxidizing), it breaks down into carbonyl products.
- With a reducing work-up (like zinc + water or dimethyl sulfide), it gives aldehydes and ketones.
- With an oxidizing work-up (like hydrogen peroxide), aldehydes get further oxidized into carboxylic acids.
Key point:
Ozonolysis is very useful in organic chemistry because it can be used to locate the position of double bonds in an unknown compound by analyzing the carbonyl fragments formed.