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Friedel-Crafts reactions

Friedel-Crafts reactions

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Explainer Video

Tutor: Alisha

Summary

Friedel-Crafts reactions

In a nutshell

Benzene rings can be alkylated and acylated via Friedel-Crafts reactions. Friedel-Crafts reactions introduce a new C−CC-C C−C bond. A halogen carrier is required for the reaction to happen. Friedel-Crafts reactions are an example of electrophilic substitution reactions.


Equations

These are general chemical equations. You will need to be able to use these when you write equations for specific substances.


​C6H6 + R−X→refluxhalogen carrierC6H5R + HX C6H6 + RCOCl→dry ether, refluxAlCl3C6H5COR + HClC_6H_6 \ + \ R-X \xrightarrow[reflux]{halogen \ carrier}C_6H_5R \ + \ HX \\ \ \\C_6H_6 \ + \ RCOCl \xrightarrow[dry \ ether, \ reflux]{AlCl_3}C_6H_5COR \ + \ HClC6​H6​ + R−Xhalogen carrierreflux​C6​H5​R + HX C6​H6​ + RCOClAlCl3​dry ether, reflux​C6​H5​COR + HCl​​



Friedel-Crafts reactions

Benzene can be refluxed with a halogenoalkane or acyl chloride in the presence of a halogen carrier to form a new C−CC-CC−C bond.​



Friedel-Crafts alkylation

Friedel-Crafts alkylation adds an alkyl group onto a benzene. A benzene is refluxed with a halogenoalkane in the presence of a halogen carrier.


C6H6 + R−X→refluxhalogen carrierC6H5R + HXC_6H_6 \ + \ R-X \xrightarrow[reflux]{halogen \ carrier}C_6H_5R \ + \ HXC6​H6​ + R−Xhalogen carrierreflux​C6​H5​R + HX​​


General Mechanism


Electrophile formation


​R−X + AlCl3→R+ + AlCl4−R-X \ + \ AlCl_3 \rightarrow R^+ \ + \ AlCl_4^-R−X + AlCl3​→R+ + AlCl4−​​​


Electrophilic substitution


Electrophiles containing an OAlCl3−OAlCl_3^-OAlCl3−​ group can be added to benzene rings to form alcohols.


Example


Chemistry; Organic chemistry III; KS5 Year 12; Friedel-Crafts reactions



Friedel-Crafts acylation

​Friedel-Crafts acylation adds an acyl group onto a benzene. A benzene is refluxed with an acyl chloride in the presence of a halogen carrier. The reaction produces phenylketones or benzaldehydes, depending on the R group. The solvent used must be non-aqueous such as dry ether.


C6H6 + RCOCl→dry ether, refluxAlCl3C6H5COR + HClC_6H_6 \ + \ RCOCl \xrightarrow[dry \ ether, \ reflux]{AlCl_3}C_6H_5COR \ + \ HClC6​H6​ + RCOClAlCl3​dry ether, reflux​C6​H5​COR + HCl​​

​

General Mechanism

Electrophile formation


R−COCl + AlCl3→RCO+ + AlCl4−R-COCl \ + \ AlCl_3 \rightarrow RCO^+ \ + \ AlCl_4^-R−COCl + AlCl3​→RCO+ + AlCl4−​​​


Electrophilic Substitution 

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FAQs - Frequently Asked Questions

What is Friedel-Crafts alkylation?

Friedel-Crafts alkylation adds an alkyl group onto a benzene.

What is Friedel-Crafts acylation ?

Friedel-Crafts acylation adds an acyl group onto a benzene.

What are Friedel-Crafts reactions?

Friedel-Crafts reactions are reactions which introduce a new C-C bond.

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