8.13: Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozonolysis proceeds through an oxidative cleavage reaction. The first step is the electrophilic addition of ozone across the alkene double bond, forming an unstable molozonide intermediate, which reacts further to form a carbonyl and a carbonyl oxide. These intermediates rearrange to form an ozonide.
The ozonide is treated with a mild reducing agent such as dimethyl sulfide or zinc to yield the carbonyl compounds as the final product.
Ozonolysis with Different Substituted Alkenes
The conversion of ozonide to aldehydes, ketones, or carboxylic acids depends on the structure of the alkene starting material and different reaction conditions.
When a reductive work-up is used, ozonolysis of monosubstituted alkenes such as 1-butene yields a mixture of aldehydes.
Trisubstituted alkenes, such as 2-methyl-2-butene, on the other hand, form an aldehyde and a ketone.
When an oxidative work-up is used, the reaction yields a ketone and an aldehyde that is further oxidized to the corresponding carboxylic acid.