Ozonolysis of alkenes to ketones and aldehydes (reductive workup)
Description: Ozone will cleave carbon-carbon double bonds to give carbonyl compounds such as aldehydes or ketones, after treatment with a reducing agent such as zinc or dimethyl sulfide (“reductive workup”)
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What is the preferred acid and is Me2S the aprotic form for this please?
Why must this reaction occur in acid again?
Just the work-up. Breaking the O-O bond makes O- , which is not the greatest leaving group. If acid is around to protonate it to O-OH, then the O-O bond is easier to break.
The conjugate acid is a better leaving group.
What is the purpose of acid here?
Won’t Zinc react with acid to Zinc ion then there is no zinc metal in the system to perform as a catalyst?
The purpose of acid is to protonate the O-O bond, making it easier to reduce. Essentially once the O-O bond is protonated the oxygen is a much better leaving group.
For both ozonolysis mechanisms, the starting material has had at least 1 hydrogen attatched to the alkene carbons, is it possible to do this with 4 alkyl groups?
Oh yes. Absolutely. The C-H bonds where there to show the effect of oxidative vs reductive workup, but ozonolysis works fine for tetrasubstituted alkenes.