6.2.9: Substitution reactions in aromatic compounds

Question 1

Why do aromatic rings not undergo addition reactions like other unsaturated compounds?

Answer 1

-The delocalisation of electrons offers additional stability to the molecule.

Question 2

How do substitution reactions occur?

Specifically, how do substitution reactions occur in arenes?

Answer 2

• Substitution reactions occur when one or more hydrogen atoms on he aromatic ring are exchanged for another atom or group of atoms.
• For arenes, these reactions occur by electrophilic substitution using a catalyst such as aluminium(III) chloride, AlCl3, or iron(III) chloride, FeCl3.
• A substituted aromatic ring is produced by forming a C-C bond.

Question 3

When do alkylation reactions occur?

Answer 3

-Alkylation reactions occur when hydrocarbon chains are added to an organic compound.

Question 4

What are the reagents for alkylation?

Answer 4

• An aromatic compound
• A haloalkane
• A strong Lewis acid catalyst

Question 5

How could benzene make methylbenzene?

Answer 5

-Benzene can react with chloromethane to make methylbenzene in the presence of FeCl3 catalyst.
-Balanced symbol equation:
C6H6 + CH3Cl → C6H5CH3 + HCl

Question 6

Why can Iron(III) chloride be used as a Friedel-Crafts catalyst?

Answer 6

-It is an electron pair acceptor.

Question 7

When do acylation reactions occur?

Answer 7

-When RCO- is added to an organic compound.

Question 8

What are the reagents for acylation?

Answer 8

• An acyl chloride.

- A strong Lewis acid catalyst.

Question 9

Describe the process of acylation.

Answer 9

-Benzene can be gently heated under reflux with ethanoyl chloride in the presence of anhydrous aluminium(III) chloride to form phenylethanoate.
C6H6 + CH3COCl → C6C5COCH3 + HCl