Preparation of Aldehydes and Ketones from Hydrocarbons
Aldehydes and ketones are formed by the ozonolysis of alkenes, and ketones (and acetaldehyde) by the hydration of alkynes.
What is Preparation of Aldehydes and Ketones from Hydrocarbons?
A reaction where ozone (O3) cleaves a carbon-carbon double bond (alkene) or triple bond (alkyne), typically followed by a reductive or oxidative workup to form carbonyl compounds.
Key formula / rule: Ozonolysis of Alkene (General)
Key points
- Explain the ozonolysis reaction for alkene cleavage.
- Predict the products of ozonolysis for various alkenes.
- Describe the hydration of alkynes to form carbonyl compounds.
- Identify the specific conditions and catalysts required for these reactions.
Common exam trap
Confusing reductive and oxidative ozonolysis products.
Definitions
- Term
Ozonolysis
- Meaning
A reaction where ozone (O3) cleaves a carbon-carbon double bond (alkene) or triple bond (alkyne), typically followed by a reductive or oxidative workup to form carbonyl compounds.
- Term
Hydration of Alkynes
- Meaning
The addition of water across the triple bond of an alkyne, catalyzed by mercuric sulfate and dilute sulfuric acid, leading to the formation of aldehydes or ketones via an enol intermediate.
- Term
Enol
- Meaning
An unsaturated alcohol containing a hydroxyl group attached to a carbon atom that is part of a carbon-carbon double bond (C=C-OH).
Learning objectives
Explain the ozonolysis reaction for alkene cleavage.
Predict the products of ozonolysis for various alkenes.
Describe the hydration of alkynes to form carbonyl compounds.
Identify the specific conditions and catalysts required for these reactions.
Relate hydrocarbon structure to the resulting aldehyde or ketone.
Formulae
- Name
Ozonolysis of Alkene (General)
- Note
Products are aldehydes and/or ketones.
- Expression
R1R2C=CR3R4 + O3 → Ozonide Intermediate Ozonide Intermediate + Reductive Workup (e.g., Zn/H2O) → R1R2C=O + R3R4C=O
- Name
Hydration of Alkyne (General)
- Note
Applies to terminal alkynes, yielding methyl ketones. Exception: Ethyne yields ethanal.
- Expression
RC≡CH + H2O (HgSO4/H2SO4) → [RC(OH)=CH2] (Enol) → RCOCH3 (Ketone)
- Name
Hydration of Internal Alkyne
- Note
Yields two different ketones if R ≠ R'.
- Expression
RC≡CR' + H2O (HgSO4/H2SO4) → Mixture of Ketones
Prerequisites
Nomenclature of Alkenes and Alkynes
Structure and Reactivity of Alkenes and Alkynes
Basic understanding of functional groups (aldehydes, ketones)
Common mistakes
Confusing reductive and oxidative ozonolysis products.
Incorrectly predicting the products from unsymmetrical alkenes.
Forgetting the specific catalysts (HgSO4, H2SO4) for alkyne hydration.
Assuming all terminal alkynes yield ketones other than acetaldehyde.
Misinterpreting the structure of the carbonyl compound formed from a given hydrocarbon.
Keywords
Ozonolysis
Alkene
Aldehyde
Ketone
Hydration
Alkyne
Ozone
Mercuric Sulfate
Sulfuric Acid
Reductive Workup
Enol
Practice preview
Which of the following methods can be used for the preparation of aldehydes from alkenes?…
easy
Consider the reaction: R-C≡C-R' + H₂O (HgSO₄/H₂SO₄) → Product. The product formed is:…
medium
Ozonolysis of 2,3-dimethylbut-2-ene followed by reductive workup yields:…
medium