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Oppenauer Oxidation is a gentle process wherein secondary alcohols can be selectively oxidized into ketones. This reaction takes place in the presence of a catalyst called Aluminium isopropoxide [Al(i-Pro)3] in the excess of acetone.
- Oppenauer Oxidation is named after Rupert Viktor Oppenauer.
- The reaction is the opposite of Meerwein-Ponndorf Verley reduction.
- In this reaction, alcohol is oxidized along with aluminium isopropoxide in an excess amount of acetone.
- The reaction is carried out in a controlled atmosphere with the help of selective oxidation.
- This results in shifting the equilibrium toward the product end of the reaction.
- Some real-life applications of Oppenauer Oxidation involve the synthesis of steroids, alkaloids, hormones, and terpenes.
Key Terms: Oppenauer Oxidation, Oxidation Reaction, Alkaloids, Alcohols, Ketones, Acetone, Aluminium Isopropoxide, Hydride, Oxygen, Hydrogen, Electrons, Aldehydes
What is Oppenauer Oxidation?
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Oppenauer Oxidation is the method of conversion of secondary alcohols into ketones through selective oxidation in a reaction catalyzed by Aluminium isopropoxide, provided there is an excess of acetone.
- This reaction is a clever method to oxidise allylic alcohols into α, β – unsaturated ketones.
- The reverse of the Oppenauer Oxidation reaction is called Meerwein-Ponndorf-Verley Reduction.
In this reaction, the Aluminium catalyzed hydride shifts from the α-carbon [of alcohol component] to carbonyl carbon [of second component], which proceeds over a six-membered transition state.
- Oppenauer Oxidation is deployed to oxidize alcohols to carbonyl compounds.
- The method is used for the oxidation of acid-labile substrates.
Example of What is Oppenauer Oxidation?Example: For example, simple ketones like acetone or cyclohexanones are used as hydride acceptor in the presence of aluminium alkoxides like isopropoxide and t-butoxide. |
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| Chapter Related Concepts | ||
|---|---|---|
| Sulphonation | Organic Solvent | Gatterman Reaction |
| Polarity of Bonds | Carbonates | Azo Compound |
What is Oxidation Reaction?
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According to classical concept of chemistry, oxidation reaction can be defined as:
So, oxidation happens in a given substance when reduction happens in its oxidising agent. It means if the oxidising agent has lost the oxygen or gained an electron or lost its oxygen atom when the converse has happened to the given substance, this reaction will be called as oxidation reaction.
Example of Oxidation ReactionExample: For example, CuO + H2 Cu + H2O In this reaction CuO is the oxidising agent which lost its oxygen and Hydrogen gas got oxidised and became water. |
Oppenauer Oxidation Mechanisms
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The Oppenauer Oxidation Mechanisms begins and concludes in following steps:
Step 1
Herein the secondary alcohol taken for the reaction is catalysed by aluminium isopropoxide and this interaction results in formation of a complex.
Step 2
The resultant complex from step 1 will further react to the ketone and six membered transition complexes is formed.
Step 3
In the aluminium catalysed hydride shift the α-carbon of the alcohol will convert into carbonyl carbon.
Step 4
Now the acetone proceeds over a six membered transition state.
Step 5
The desired ketone is now formed as a result of the process of hydride transfer. This reaction involves deprotonation of the alcohol by equilibration with alkoxide followed by hydride transfer.
- The process of equilibrium is achieved by displacing to right, using a large excess of hydride receptor.
Oppenauer Oxidation Mechanisms
Disadvantages of Oppenauer Oxidation
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The Oppenauer Oxidation might be one of the most useful reactions in chemistry, but it has certain demerits attached to it, which are as follows:
- It involves high temperatures usually achieved through the use of large quantities of ketone hydride acceptors.
- This results in the formation of aldol condensation products with the hydride acceptors, making this oxidation less efficient.
- There has been much research to make it more efficient so that these oxidations can be performed under milder conditions.
- Aluminium compounds used as catalysts in these reactions can be basic, which can cause prototrophic shifts within the product.
- Oppenauer Oxidation isn’t very useful when it comes to the production of aldehydes.
- The fundamental medium of this reaction induces a reaction between aldehydes and ketones, like aldol condensation.
Advantages of Oppenauer Oxidation
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The advantages of Oppenauer Oxidation are as follows:
- The reaction uses non-toxic reagents, which are relatively inexpensive.
- The process is unique in comparison to other oxidation reactions like pyridinium chlorochromate.
- It easily converts aldehyde into carboxylic acid.
- Oppenauer Oxidation reaction is quite mild and gentle.
Read More:
| Class 12 Chemistry Related Concepts | ||
|---|---|---|
| Etard reaction | Williamson Ether Synthesis | Uses of Carboxylic Acids |
| Esters | Reimer Tiemann Reaction | Esterification |
Things to Remember
- Oppenauer Oxidation refers to the selective oxidation of secondary alcohols into ketones.
- In this reaction, aluminium causes a hydride shift, which converts the α-carbon of alcohol to convert the carbonyl compound.
- The reaction proceeds to become a six-membered transition state and the desired ketone.
- This reaction can be driven into oxidation or reduction mode using simple alcohols or ketones as donors or acceptors.
- Progesterone is carried out with the help of Oppenauer Oxidation.
Sample Questions
Ques: What is Oxidation? (2 marks)
Ans: Oxidation is a process where an element or a compound gains oxygen i.e., oxygen combines with it and changes its appearance. For example, Rusting is a type of oxidation occurring in nature where atmospheric oxygen reacts with iron and forms a layer of iron oxide which is reddish, and we call it rust.
Ques: What is Oppenauer Oxidation? (2 marks)
Ans: Oppenauer Oxidation is a reaction wherein a metallic aluminium alkoxide catalyses the oxidation of secondary alcohols to corresponding organic compounds. It is mostly employed to convert allylic alcohols in to α, β -unsaturated ketones.
Ques: Why is oxidation of alcohols important? (2 marks)
Ans: Oxidation of alcohols is important because it plays a vital role in human metabolism wherein for degradation of fats it is important that alcohol groups be oxidised into carbonyl groups, such oxidations are part of citric acid cycle.
Ques: What are secondary alcohols? Can they be oxidised? (2 marks)
Ans: Secondary alcohols are those alcohols wherein the alcohol functional called hydroxy (-OH) is attached to a saturated carbon atom with two other carbon atoms. Secondary alcohols can be oxidised and their oxidation results into formation of ketones.
Ques: What are the advantages of Oppenauer Oxidation? (3 marks)
Ans: The advantages of Oppenauer Oxidation are as follows:
- The reaction uses non-toxic reagents, which are relatively inexpensive.
- The process is unique in comparison to other oxidation reactions like pyridinium chlorochromate.
- It easily converts aldehyde into carboxylic acid.
- Oppenauer Oxidation reaction is quite mild and gentle.
Ques: What is the disadvantage associated with Oppenauer Oxidation? (4 marks)
Ans: The disadvantages of Oppenauer Oxidation are as follows:
- Oppenauer High temperatures are needed for oxidation, which is often accomplished by using a lot of ketone hydride acceptors.
- This causes the hydride acceptors to generate aldol condensation products, which reduces the efficiency of this oxidation.
- Many studies have been conducted to increase its efficiency so that these oxidations can be carried out in more temperate environments.
- When aluminum compounds are utilized as catalysts in these processes, the result may undergo prototrophic changes if the catalysts are basic.
Ques: What is the difference between oxidation and reduction reaction? (3 marks)
Ans: The difference between oxidation and reduction reaction are as follows:
| Oxidation Reaction | Reduction Reaction |
|---|---|
| Oxidation reaction is a process of losing electron. | Reduction reaction is a process of gaining electron. |
| It will result in increase in oxidation number. | It will result in decrease in oxidation number. |
| The reaction will release energy. | The reaction will store energy. |
Ques: What is Meerwein-Ponndorf Verley reduction? (3 marks)
Ans: In organic chemistry, the reduction of ketones and aldehydes to their corresponding alcohols using aluminum alkoxide catalysis in the presence of a sacrificial alcohol is known as the Meerwein–Ponndorf–Verley (MPV) reduction.
- The MPV reduction has two advantages: it uses an inexpensive, ecologically benign metal catalyst, and has a high degree of chemoselectivity.
- Due to the introduction of sodium borohydride and similar chemicals, MPV reductions have been referred to be "obsolete".
Ques: How Oppenauer Oxidation works? (4 marks)
Ans: The process of Oppenauer Oxidation are as follows:
- Herein the secondary alcohol taken for the reaction is catalysed by aluminium isopropoxide and this interaction results in formation of a complex.
- The resultant complex from step 1 will further react to the ketone and six membered transition complexes is formed.
- In the Aluminium catalysed hydride shift the α-carbon of the alcohol will convert into carbonyl carbon.
- The acetone proceeds over a six membered transition state.
- The desired ketone is now formed as a result of the process of hydride transfer.
Ques: Give equation involved in Oppenauer Oxidation? (2 marks)
Ans: The equation involved in Oppenauer Oxidation are as follows:
Ques: Give an example of oxidation and reduction reaction? (2 marks)
Ans: The example of oxidation and reduction reaction are as follows:
Oxidation Reaction
- C + O2 → CO2
- Fe + S → FeS
Reduction Reaction
- N2 + 3 H2 → 2NH3
- ZnO + C → Zn + CO
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