Oxidative Cleavage of Alkenes with KMno4 and O3

In oxidative cleavage reactions, breaking of C-C bonds occurs forming C-O bonds. In this article, we will specifically focus on the oxidative cleavage of alkenes. This is most commonly achieved with potassium permanganate (KMnO4) and ozonolysis:

So, we have two processes here; first is the oxidation of the carbon atoms since they make bonds with oxygen, and the second is the breaking of C-C bonds, which is what we refer to as “cleavage”.

As a side note, remember that treating alkenes with a cold solution of KMnO4 leads to syn dihydroxylation:

The ozonolysis, on the other hand, can be carried out with an oxidative or reductive work-up. And, most often, what we learn in the ozonolysis of alkenes is the reductive workup of the ozonide cyclic intermediate by dimethyl sulfide (Me2S). This results in the formation of an aldehyde or a ketone depending on the structure of the alkene:

Remember that aldehydes and ketones stand one degree below the carboxylic acids and carbon dioxide in regards the oxidation state of the carbon. Now, if the ozonide ion is treated with hydrogen peroxide instead of DMS, we get an oxidative workup which oxidizes the carbon atoms to the highest degree – that is a ketone forms a secondary carbon, a carboxylic acid and carbon dioxide form a terminal alkene.

The carboxylic acid is formed from an aldehyde which is oxidized by H2O2 in the following mechanism:

The oxidative cleavage by KMnO4 starts with an addition to the π bond forming a cyclic intermediate which eventually breaks down to an aldehyde or a ketone.

The aldehyde is further oxidized to a carboxylic acid by the KMnO4. The mechanism od this transformation is covered in the oxidation of alcohols.

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