Oppenauer Oxidation

This article explains about Oppenauer Oxidation oxidizes secondary alcohols to ketones using aluminium alkoxide and ketone acceptors.

Overview of Oppenauer Oxidation:

• Oppenauer oxidation is a mild, selective oxidation method used to convert secondary alcohols into ketones (and sometimes primary alcohols into aldehydes) under non-aqueous, basic conditions.

Reagents:

• Aluminum isopropoxide (Al(O-iPr)₃) – catalyst
• Excess ketone (commonly acetone) – hydrogen acceptor
• Non-aqueous solvent – typically benzene, toluene, or cyclohexane
• Mild heat

General Reaction:

R2CHOH  +  (CH3)2C=O —[Al(O-iPr)3] →  R2C=O  +  (CH3)2CHOH

• The secondary alcohol is oxidized to a ketone.
• Acetone is reduced to isopropanol.

Mechanism:

Step 1: Formation of a coordination complex

• The hydroxyl group of the alcohol and the carbonyl oxygen of acetone both coordinate to Al(O-iPr)₃, forming a six-membered transition state.

Step 2: Hydride transfer

• A hydride (H⁻) is transferred from the alpha-carbon of the alcohol to the carbonyl carbon of acetone.
• The alcohol is oxidized to a ketone.
• Acetone is reduced to isopropanol.

Step 3: Product release

• The product ketone and isopropanol are released.
• The aluminum catalyst is regenerated.

Key Features of Oppenauer Oxidation:

• Mild and selective oxidation
• Ideal for acid-sensitive substrates
• Reverse of the Meerwein–Ponndorf–Verley reduction

Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!