Ozonolysis of alkenes is a method in which alkenes are treated with an ozone molecule to form ozonide. This is followed by oxidative cleavage of ozonide using zinc and acetic acid (or dimethyl sulfide ((CH3)2S)) resulting in smaller molecules being formed. This process is generally used when mild oxidation is required.
If strong oxidation is required, potassium permanganate is used. When an unsaturated alkene undergoes Ozonolysis, it results in the formation of aldehyde/ketone. An even stronger oxidation of the unsubstituted alkene in presence of Potassium permanganate directly oxidizes the alkene to Carbon dioxide. The aldehyde is formed as a result of oxidation of monosubstituted alkenes whereas disubstituted alkenes are oxidized to form ketones.
An even stronger of the unsubstituted alkene in presence of Potassium permanganate directly oxidizes the alkene to Carbon dioxide. The aldehyde is formed as a result of oxidation of monosubstituted alkenes whereas disubstituted alkenes are oxidized to form ketones. This method is very useful for finding the position of the double bond in alkenes or other unsaturated compounds. The general ozonolysis reaction of mono- and disubstituted alkenes can be given as follows:
Mechanism of ozonolysis:
Ozonolysis of alkene takes place in three steps:
- 1. Formation of initial ozonide: In this step, the alkene is reacted with ozone and an unstable compound also known as initial ozonide is formed. The initial ozonide then undergoes fragmentation.
- 2. Formation of ozonides: The first step is followed by a sudden and vigorous rearrangement of the fragments of the initial ozonide. The result is a rearranged ozonide which will now get dissociated in the final step.
- 3. Reduction to the desired carbonyl product: Ozonide is a very unstable compound and it has a low molecular weight and explodes violently. Due to this property, they are directly reduced to the carbonyl products using zinc and acetic acid (HOAc) or dimethyl sulfide.
Use of ozonolysis process:
- This process is used in determining the location of the double bond in alkenes or other unsaturated compounds.
- It is used in the preparation of compounds with carbonyl functional group.
This was just a brief layout of one of the chemical reactions of alkene i.e. ozonolysis. To know more about the chemical reactions of alkenes please visit byjus.com.