Friedel Crafts Acylation of Benzene Reaction Mechanism
TLDRThis video delves into the Friedel-Crafts acylation reaction, illustrating the process of converting benzene into acetophenone using acetyl chloride and a Lewis acid catalyst, aluminum chloride. It outlines the mechanism, from the formation of the acylium ion to the aromatic electrophilic substitution, and discusses the subsequent steps to remove the catalyst and obtain the final ketone product. Additionally, the video covers post-reaction reduction methods, such as Clemmensen and Wolff-Kishner reductions, to convert the ketone into an alkane, providing a comprehensive guide to the synthesis and transformation of aromatic compounds.
Takeaways
- 🔬 The video focuses on the Friedel-Crafts acylation reaction, a method to add an acyl group to a benzene ring.
- 📚 Acetyl chloride is used as an example of an acid chloride that reacts with a benzene ring in the presence of a Lewis acid catalyst, aluminum chloride.
- 💧 Water is added in the second step of the reaction to complete the formation of the product, acetophenone, by removing the chloride group.
- 🌀 The mechanism involves the formation of an intermediate complex between the acid chloride and the Lewis acid, leading to the formation of a resonance-stabilized acylium ion.
- ⚛ The acylium ion, stabilized by resonance, does not undergo typical carbocation rearrangements, unlike in Friedel-Crafts alkylation.
- 🔗 The benzene ring attacks the positively charged carbon of the acylium ion, forming a new intermediate that will eventually lead to the ketone product.
- 🔄 A base, such as AlCl4- or chloride ions, is used to abstract a proton and regenerate the aromatic ring, forming the final ketone product.
- 🔑 The presence of excess Lewis acid is crucial for the reaction to proceed effectively, and it must be removed by adding water to obtain the pure ketone.
- 🛠 Post-reaction, the ketone can be further processed through reduction reactions like Clemency reduction or Wolff-Kishner reduction to form alkanes.
- 🌐 The Clemency reduction involves zinc and mercury under acidic conditions, while the Wolff-Kishner reduction uses hydrazine under basic conditions.
- ⚔ Catalytic hydrogenation is another method to reduce the ketone to an alkane, using hydrogen gas and a palladium on carbon catalyst.
Q & A
What is the focus of the video?
-The video focuses on the Friedel-Crafts acylation reaction, its mechanism, and the steps involved in the process.
What is the role of the benzene ring in the Friedel-Crafts acylation reaction?
-The benzene ring acts as the substrate that reacts with an acid chloride to form a ketone, specifically acetophenone in the given example.
Which acid chloride is used as an example in the video?
-Acetyl chloride is used as the example acid chloride in the video.
What is the purpose of using a Lewis acid catalyst in the Friedel-Crafts acylation reaction?
-The Lewis acid catalyst, such as aluminum chloride, is used to activate the acid chloride, facilitating its reaction with the benzene ring.
What is the intermediate formed when the acid chloride reacts with the Lewis acid catalyst?
-An intermediate is formed where the chlorine atom adds to AlCl3, resulting in an aluminum atom with a negative formal charge and a chlorine atom with a positive formal charge.
What is the term for the positively charged carbon intermediate formed during the reaction?
-The positively charged carbon intermediate is called an acylium ion.
How is the acylium ion stabilized in the reaction mechanism?
-The acylium ion is stabilized by resonance, preventing typical carbocation rearrangements.
What is the final product of the Friedel-Crafts acylation reaction described in the video?
-The final product of the described reaction is acetophenone, a ketone.
Why is water added after the acylation reaction in the mechanism?
-Water is added to remove the Lewis acid catalyst from the ketone, preventing the formation of a complex between the ketone and the catalyst.
What are the typical steps taken after the Friedel-Crafts acylation reaction to modify the ketone?
-Typical steps include reduction of the ketone to an alkane using methods such as Clemency reduction, Wolf-Kishner reduction, or catalytic hydrogenation.
What is Clemency reduction, and how is it used after the Friedel-Crafts acylation reaction?
-Clemency reduction is a method where a ketone is reduced to an alkane using an alloy of zinc and mercury under strongly acidic conditions and heat, replacing the oxygen with two hydrogen atoms.
What is the Wolf-Kishner reduction, and how does it differ from Clemency reduction?
-The Wolf-Kishner reduction is a method that uses hydrazine (N2H4) under strongly basic conditions and heat to reduce a ketone to an alkane, differing from Clemency reduction in the reducing agent and reaction conditions.
How can the ketone produced in the Friedel-Crafts acylation reaction be reduced using catalytic hydrogenation?
-Catalytic hydrogenation involves reacting the ketone with hydrogen gas in the presence of a catalyst, such as palladium on carbon, to reduce the ketone to an alkane.
Outlines
🔬 Frito-Crafts Acylation Reaction Mechanism
This paragraph introduces the Frito-Crafts acylation reaction, focusing on the formation of acetophenone from a benzene ring and acetyl chloride. The process involves the use of aluminum chloride as a Lewis acid catalyst and the addition of water to complete the reaction. The mechanism is detailed, starting with the formation of an intermediate complex between the acid chloride and the Lewis acid, followed by the generation of a resonance-stabilized electrophile. The benzene ring then undergoes electrophilic substitution to form the ketone product. The paragraph also notes that the reaction does not lead to carbocation rearrangements, which are typical in Frito-Crafts alkylation reactions.
🧪 Post-Reaction Considerations and Ketone Reduction
After the Frito-Crafts acylation reaction, the presence of the Lewis acid catalyst in the solution is addressed. The catalyst can form a complex with the produced ketone, and it is crucial to use an excess of the catalyst to ensure the reaction's success. To isolate the ketone, water is added to remove the catalyst complex. The paragraph then discusses subsequent reactions that can be performed on the ketone, such as reduction to an alkane through Clemency reduction or Wolf-Kishner reduction, which involve zinc-mercury alloy and hydrazine, respectively, under specific conditions. Catalytic hydrogenation is also mentioned as an alternative reduction method using hydrogen gas and a palladium catalyst.
📚 Frito-Crafts Acylation Applied to Benzene Derivatives
This paragraph extends the discussion to the application of the Frito-Crafts acylation reaction to benzene derivatives, specifically focusing on the synthesis of butylbenzene. It outlines the necessary steps, starting with the preparation of the appropriate acyl chloride with a four-carbon chain. The reaction then requires the presence of aluminum chloride as a Lewis acid catalyst and the addition of water to free the ketone from the catalyst. Finally, the paragraph suggests using the Wolf-Kishner reduction method with hydrazine, hydroxide, and heat to convert the ketone into the desired alkane product, butylbenzene.
Mindmap
Keywords
💡Friedel-Crafts Acylation
💡Benzene Ring
💡Acetyl Chloride
💡Lewis Acid Catalyst
💡Acesolium Ion
💡Aromaticity
💡Electrophile
💡Catalytic Hydrogenation
💡Wolff-Kishner Reduction
💡Clemency Reduction
Highlights
Introduction to the Friedel-Crafts acylation reaction mechanism using acetyl chloride and benzene.
Use of a Lewis acid catalyst, aluminum chloride, to facilitate the reaction.
The formation of acetophenone as the end product of the reaction.
Reaction mechanism begins with the interaction between acid chloride and the Lewis acid catalyst.
Formation of an intermediate with a negative formal charge on aluminum and a positive on chlorine.
Generation of the acylium ion, a resonance-stabilized electrophile.
The acylium ion does not undergo typical carbocation rearrangements due to resonance stabilization.
Benzene ring reacts with the acylium ion to form an intermediate with a positive charge.
Use of a base to regenerate the aromatic ring and form the ketone product.
Complex formation between the ketone product and the Lewis acid catalyst.
Necessity of using water to remove the Lewis acid catalyst and isolate the ketone.
Post-reaction steps including the reduction of the ketone to an alkane.
Clemency reduction as a method for converting the ketone to an alkane.
Wolff-Kishner reduction using hydrazine for ketone to alkane conversion.
Catalytic hydrogenation as an alternative method for reducing ketones to alkanes.
Examples of starting from benzene to produce specific compounds using Friedel-Crafts acylation and reduction reactions.
Detailed explanation of the reagents and steps required for synthesizing ethyl benzene from benzene.
Guidance on using the Friedel-Crafts acylation reaction to create butyl benzene.
Transcripts
Browse More Related Video
5.0 / 5 (0 votes)
Thanks for rating: