25.2 - Electrophilic Substitution of Benzene

Question 1

Do benzene molecules react with all electrophiles?

Answer 1

No, only ones with full +ve charge, partially positive is not enough

Catalysts are used to generate electrophiles

Question 2

What are the reagents and conditions for benzene nitration and the mechanism

Answer 2

Reagents: Conc. HNO₃; conc. catalyst H₂SO₄

Conditions: 50^oC, if the temp. is more than this, further substitution occurs. making dinitrobenzene (impure product)

Electrophile Generation:

HNO₃ + H₂SO₄ → NO₂⁺ (electrophile) + HSO₄^- + H₂O

Catalyst Regeneration:

H⁺+HSO₄^- → H₂SO₄

LEARN MECHANISM

Question 3

What are the reagents, conditions and mechanisms for benzene halogenation?

Answer 3

• Requires halogen carrier (carries halogen ion throughout reaction until the halide ion is released to form a hydrogen halide (catalysts)

Reagents: Chlorination: Cl₂; Catalyst AlCl₃/FeCl₃ (for bromination replace the Cl with Br)

RTP

Electrophile Generation:

Cl₂ + AlCl₃ → Cl⁺ (electrophile) + AlCl₄^-

Catalyst Regeneration:

AlCl₄^- + H⁺ > AlCl₃ + HCl

Question 4

What are the reagents, conditions and mechanisms for benzene alkylation?

Answer 4

Reagents: CH₃Cl (haloalkane bonded to alkyl chain); AlCl₃

Electrophile Generation:

CH₃Cl + AlCl₃ → CH₃⁺ (electrophile) + AlCl₄^-

Catalyst Regeneration:

AlCl₄^- + H⁺ → AlCl₃ + HCl

Question 5

What are the reagents and conditions for benzene acylation?

Answer 5

benzene + acyl chloride (+AlCl₃ catalyst) > aromatic ketone

Reagents: CH₃COCl (ethanoyl chloride, 1^st member of acyl chloride homologous series; +AlCl₃ catalyst

Electrophile Generation:

CH₃COCl +AlCl₃ → CH₃C⁺O + AlCl₄^-

Catalyst Regeneration:

AlCl₄^- + H⁺ → AlCl₃ + HCl