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8.13: Oxidative Cleavage of Alkenes: Ozonolysis
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Organic Chemistry

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Oxidative Cleavage of Alkenes: Ozonolysis
 
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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.

Figure1

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.

Figure2

The ozonide is treated with a mild reducing agent such as dimethyl sulfide or zinc to yield the carbonyl compounds as the final product.

Figure3

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.

Figure4

Trisubstituted alkenes, such as 2-methyl-2-butene, on the other hand, form an aldehyde and a ketone.

Figure5

When an oxidative work-up is used, the reaction yields a ketone and an aldehyde that is further oxidized to the corresponding carboxylic acid.

Figure6

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