What is Oppenauer Oxidation?
Oppenauer Oxidation is the process of conversion of secondary alcohols to ketones by selective oxidation. This reaction is named after Rupert Viktor Oppenauer. Oxidation reaction takes place in the presence of [Al(i-Pro)3] in excess of acetone.
It is an aluminium alkoxide catalyzed the oxidation of a secondary alcohol to the corresponding ketone. This is reverse of the Meerwein Ponndorf Verley reduction. It is a very good method to oxidise allylic alcohols to α, β- unsaturated ketones.
Oppenauer Oxidation
Oppenauer Oxidation Mechanism
- In the first step, alcohol coordinates with aluminium isopropoxide to form a complex
- This complex reacts with ketone to form a six-membered transition complex
- The alpha-carbon of the alcohol is converted to the carbonyl carbon from the aluminium-catalyzed hydride shift.
- The acetone proceeds over a six-membered transition state.
- The desired ketone is formed after the hydride transfer
Oppenauer Oxidation Mechanism
This reaction is used to oxidize alcohols to carbonyl compounds. For example, simple ketone acetone or cyclohexanones is used as the hydride acceptor in the presence of aluminium alkoxide usually isopropoxide or t-butoxide. The oxidation is the exact reverse of Meerwein-Ponndorf-Verley reduction and involves deprotonation of the alcohol by equilibration with the alkoxide followed by hydride transfer. This equilibrium is generally displaced to the right by using a large excess of the hydride acceptor.