7.4.3 Friedel-Crafts Acylation

Question 1

Why are arenes stable?

Answer 1

• Delocalisation of π electrons in ring
• Negative charge is spread out over molecule as opposed to being in 1 area (less vulnerable)

Question 2

Difference between substitution reactions and addition reactions in arenes?

Answer 2

• In substitution, the delocalised ring is maintained
• In addition, the delocalised ring is destroyed so aromatic stabilisation is disrupted

Question 3

What are all the reactions arenes undergo?

Answer 3

• Substitution
• Nitration
• Friedel-Crafts alkylation
• Friedel-Crafts Acylation
• Hydrogenation

Question 4

What is special about alkylarenes and halogenation / nitration?

Answer 4

• Alkylarenes undergo halogenation and nitration on 2 or 4 positions
• Because electron-donating alkyl group activates these positions
• In presence of excess halogens multiple substitutions all around the compound occur

Question 5

What is a Friedel Crafts reaction? Why?

Answer 5

• Electrophilic substitution
• Of an alkyl group for a hydrogen
• Arenes are unreactive due to their aromatic stability
• So to use them as starting materials for synthesis of other organic compounds, their structure needs to be changed to make them more reactive

Question 6

What is an acyl group?

Answer 6

Alkyl group containing a carbonyl C=O group

Question 7

What is Friedel-Crafts Acylation?

Answer 7

• Electrophilic substitution
• Of an acyl group for a hydrogen

Question 8

Conditions for Friedel-Crafts Alkylation and Friedel-Crafts Acylation??

Answer 8

Alkylation
- Heat
- AlCl3 catalyst
- Alkyl Chloride + Benzene

Acylation
- Heat
- AlCl3 catalyst
- Acyl Chloride + Benzene

Question 9

Friedel Crafts Acylation mechanism

Answer 9

Question 10

What happens during the hydrogenation of benzene?

Answer 10

• Addition reaction
• Heated with H2 gas
• Nickel / platinum catalyst
• Cyclohexane formed

Question 11

Summary of reactions of Arenes table

Answer 11