Oxidative Cleavage of Alkynes with Ozone (O3)
Description: Alkynes treated with ozone (O3) will be cleaved at the triple bond to form carboxylic acids. Terminal alkynes will give carbon dioxide (CO2)
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Notes: The exact same reaction can be performed by KMnO4
Examples:
Notes: For terminal alkynes (examples 1 and 4) the byproduct is carbon dioxide (CO2)
Mechanism: For the purposes of Org 1 / Org 2 the detailed mechanism is generally not considered to be “important”. However the mechanistic pathway is similar to that for the ozonolysis of alkenes.
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{ 8 comments… read them below or add one }
Can ozonolysis be used to cleave a double bond dividing a Bicyclic compound?
Sure thing! Imagine two six membered rings fused together. Now if at the ring fusion you had a double bond, ozonolyzis would cleave the double bond to give a 10 membered ring with two C=O groups.
So ozonlysis of alkenes however with O3 produces not carboxylic acids but rather aldehydes or ketones. Why do not carboxylic acids form?
Ozonolysis of alkYNES gives carboxylic acids, always.
Ozonolysis of alkENES will give aldehydes /ketones if using a “reductive workup” e.g. Zn, Me2S
Ozonolysis of alkenes will give carboxylic acids instead of aldehydes if using an “oxidative workup” e.g. H2O2
I am guessing the mechanism is not as simple as with the alkenes
you are saying that alkynes would always give carboxylic acids on ozonolysis but
there is also a chance of formation of alkane with two keto or an acid anhydride….
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The one exception is that with terminal alkynes, formic acid is created, which is then oxidized to give carbon dioxide.
Carbonic acid does this, so formic acid does too?