Clemmensen Reduction & Wolff Kishner Mechanism
TLDRThis video script explores three methods for reducing ketones to alkanes, focusing on the Wolff-Kishner reduction mechanism. It explains the Clementine reduction using zinc, mercury, and HDL under acidic conditions, the Wolff-Kishner reduction with hydrazine and potassium hydroxide under basic conditions, and the Mozingo reduction under neutral conditions. The detailed mechanism of the Wolff-Kishner reduction is presented, highlighting the step-by-step process that leads to the formation of nitrogen gas and alkane, offering insights into the stabilization of intermediates and the driving force behind the reaction.
Takeaways
- 🔍 The video discusses three methods for reducing ketones to alkanes, with a focus on the Wolff-Kishner reduction mechanism.
- 🛠 Clementine reduction is mentioned as a method to convert ketones to alkanes using zinc, mercury, and HDL under acidic conditions.
- 🌟 The Wolff-Kishner reduction involves using hydrazine, H2, and an alkaline solution like potassium hydroxide to reduce ketones to alkanes under basic conditions.
- 🔄 The Mozingo reduction, also known as thio ketone reduction, is a neutral condition method for ketone reduction to alkanes involving the addition of a thio molecule and hydrogen gas with a Raney nickel catalyst.
- 📚 The script explains the step-by-step mechanism of the Wolff-Kishner reduction, detailing the chemical reactions and intermediates formed.
- ⚛ The initial step of the Wolff-Kishner reduction involves the addition of a hydrazine molecule to the carbonyl carbon, forming an intermediate with a negative charge on oxygen.
- 💧 A hydroxide ion acts as a base to abstract a proton from the nitrogen-hydrogen bond, leading to the formation of water and a nitrogen with a positive formal charge.
- 🚫 The oxygen in the intermediate is protonated from water to improve its leaving group ability, facilitating the addition of hydrogen atoms.
- 🔄 A hydroxide ion displaces itself, leading to the formation of a hydrozone intermediate and the release of a hydroxide ion.
- 🔗 Resonance stabilization is key in the formation of the conjugate base, allowing for the reversible transfer of a hydrogen atom to the nitrogen.
- 🌱 The final steps involve the irreversible formation of nitrogen gas and the addition of two hydrogen atoms to the carbon, resulting in the formation of an alkane.
- ♻ An alternative mechanism is proposed to avoid the formation of a carbanion, which is unstable, by directly forming a triple bond between nitrogen and the hydrogen from water.
Q & A
What are the three methods discussed in the video for reducing a ketone to an alkane?
-The three methods discussed are the Clementine reduction, the Wolf-Kishner reduction, and the Mozingo reduction (also known as the thio ketone reduction).
What is the Clementine reduction and what are its conditions?
-The Clementine reduction is a method to reduce a ketone to an alkane using a mixture of zinc, mercury, and HDL under acidic conditions.
How does the Wolf-Kishner reduction differ from the Clementine reduction?
-The Wolf-Kishner reduction uses hydrazine (N2H4) and an alkaline solution like potassium hydroxide, and it occurs under basic conditions, unlike the Clementine reduction which is under acidic conditions.
What is the Mozingo reduction and under which conditions does it occur?
-The Mozingo reduction is a method to reduce a ketone to an alkane under neutral conditions, involving the addition of a thio molecule and subsequent hydrogenation using a Raney nickel catalyst.
What is the role of hydrazine in the Wolf-Kishner reduction?
-In the Wolf-Kishner reduction, hydrazine acts as a reducing agent, donating hydrogen atoms to the ketone to form an alkane.
What is the significance of the hydroxide ion in the Wolf-Kishner reduction mechanism?
-The hydroxide ion acts as a base in the mechanism, facilitating the transfer of hydrogen atoms and the formation of water, which is crucial for the reduction process.
Why is the formation of a carbanion considered a potential issue in the Wolf-Kishner reduction?
-Carbanions are relatively unstable intermediates, and their formation can complicate the reduction process. The video suggests an alternative mechanism to avoid carbanion formation.
What is the final product of the Wolf-Kishner reduction besides the alkane?
-Besides the alkane, the final product of the Wolf-Kishner reduction is nitrogen gas (N2), which is released as a gas.
How does the video script describe the process of transferring a hydrogen atom from one part of the molecule to another in the Wolf-Kishner reduction?
-The script describes the process as involving the solvent (water) and the base (hydroxide ion) to transfer a hydrogen atom, leading to the formation of water and the protonation of the oxygen atom in the intermediate.
What is the driving force behind the irreversible step in the Wolf-Kishner reduction mechanism?
-The driving force is the formation of a very stable nitrogen-nitrogen triple bond, which is the predominant molecule found in the air.
How does the video script suggest avoiding the formation of an unstable carbanion intermediate in the Wolf-Kishner reduction?
-The script suggests an alternative pathway where the electrons from the breaking of the hydrogen-nitrogen bond can go straight to the hydrogen, regenerating the hydroxide ion and avoiding the formation of a carbanion.
Outlines
🧪 Ketone Reduction Methods Overview
This paragraph introduces three methods for reducing ketones to alkanes, with a focus on the mechanism of the Wolff-Kishner reduction. It explains the Clementine reduction using zinc, mercury, and HDL under acidic conditions, the Wolff-Kishner reduction with hydrazine and potassium hydroxide under basic conditions, and the Mozingo reduction, which occurs under neutral conditions. The paragraph sets the stage for a detailed explanation of the Wolff-Kishner reduction mechanism in subsequent sections.
🔍 Detailed Wolff-Kishner Reduction Mechanism
This paragraph delves into the step-by-step mechanism of the Wolff-Kishner reduction, starting with the reaction of acetone with hydrazine. It describes the initial nucleophilic attack by the nitrogen of hydrazine on the carbonyl carbon, leading to the formation of an intermediate. The role of hydroxide as a base is highlighted, as it facilitates the transfer of hydrogen from water to the molecule, resulting in the displacement of oxygen by hydrogen. The paragraph also discusses an alternative pathway to avoid the formation of a carbanion, which is considered unstable, by directly forming a triple bond between nitrogen and hydrogen, leading to the release of nitrogen gas and the formation of the alkane.
🛠 Alternative Mechanism for Ketone Reduction
The final paragraph presents an alternative mechanism for the Wolff-Kishner reduction that circumvents the formation of a carbanion intermediate. It suggests that, after the initial steps, the lone pair on nitrogen can form a triple bond directly with a hydrogen, regenerating the hydroxide ion and avoiding the creation of an unstable carbanion. This alternative mechanism still results in the same final products: nitrogen gas and the reduced alkane. The paragraph emphasizes the stability of the nitrogen-nitrogen triple bond and its significance in the driving force of the reaction.
Mindmap
Keywords
💡Ketone
💡Clementine Reduction
💡Wolff-Kishner Reduction
💡Alkane
💡Thio Ketone Reduction
💡Hydride
💡Catalyst
💡Resonance
💡Carbanion
💡Hydride Transfer
💡Nitrogen Gas
Highlights
The video discusses three methods for reducing ketones into alkanes.
Clementine reduction is introduced as a method using zinc, mercury, and HDL under acidic conditions.
Wolff-Kishner reduction is explained using hydrazine and potassium hydroxide under basic conditions.
The Mozingo reduction is presented as a neutral condition method involving thio compounds and a nickel catalyst.
Cyclohexanol can be reduced to cyclohexane using the Clementine reduction.
Acetone serves as an example ketone for the Wolff-Kishner and Mozingo reductions.
The mechanism of the Wolff-Kishner reduction is detailed, starting with the addition of hydrazine to the carbonyl carbon.
The role of hydroxide as a strong base in the Wolff-Kishner reduction is emphasized.
A step-by-step breakdown of the Wolff-Kishner reduction mechanism is provided.
The formation of an intermediate with a negative charge on oxygen is described.
The transfer of a hydrogen atom from water to the oxygen atom is highlighted.
The displacement of hydroxide by another hydroxide ion is explained in the mechanism.
The formation of a hydro zone intermediate and its subsequent reactions are detailed.
The stabilization of the conjugate base by resonance is discussed.
The reversible nature of the nitrogen-hydrogen bond breaking is noted.
The addition of the first hydrogen to the carbon atom in the reduction process is described.
An alternative mechanism avoiding the formation of a carbanion is proposed.
The formation of a nitrogen-nitrogen triple bond and its stability is highlighted as the driving force of the reaction.
The final step of the reduction process, where the carbon ion grabs a hydrogen from water, is explained.
Transcripts
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