Which reagents and conditions are used to nitrate benzene?

Concentrated HNO₃ and concentrated H₂SO₄, at about 50 °C.

Why is the temperature in nitration kept at about 50 °C?

To reduce further substitution, which would form dinitrobenzene.

Write the equation for formation of NO₂⁺.

HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂O

Why is sulfuric acid a catalyst in nitration?

It is regenerated: H⁺ + HSO₄⁻ → H₂SO₄.

Describe the first step of the nitration mechanism.

The delocalised π electrons of benzene attack NO₂⁺, forming a positively charged intermediate.

What happens to the intermediate in an electrophilic substitution?

It loses H⁺, which restores the delocalised ring.

Give two uses of nitration in synthesis.

Making explosives (such as TNT) and forming amines such as phenylamine for dyes.

What reagents are used in Friedel–Crafts acylation of benzene?

An acyl chloride (RCOCl) and anhydrous aluminium chloride, AlCl₃, as catalyst.

Write the equation for forming the electrophile from ethanoyl chloride.

CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻

What is the product of benzene with ethanoyl chloride and AlCl₃?

Phenylethanone, C₆H₅COCH₃ (and HCl).

Why must Friedel–Crafts acylation be carried out under anhydrous conditions?

AlCl₃ reacts with water, which would destroy the catalyst.

How is AlCl₃ regenerated in acylation?

H⁺ + AlCl₄⁻ → AlCl₃ + HCl

Electrophilic substitution of benzeneAQA A-Level Chemistry: Flashcards

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What is the electrophile in the nitration of benzene?

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What is the electrophile in the nitration of benzene?: The nitronium ion, NO₂⁺.
Which reagents and conditions are used to nitrate benzene?: Concentrated HNO₃ and concentrated H₂SO₄, at about 50 °C.
Why is the temperature in nitration kept at about 50 °C?: To reduce further substitution, which would form dinitrobenzene.
Write the equation for formation of NO₂⁺.: HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂O
Why is sulfuric acid a catalyst in nitration?: It is regenerated: H⁺ + HSO₄⁻ → H₂SO₄.
Describe the first step of the nitration mechanism.: The delocalised π electrons of benzene attack NO₂⁺, forming a positively charged intermediate.
What happens to the intermediate in an electrophilic substitution?: It loses H⁺, which restores the delocalised ring.
Give two uses of nitration in synthesis.: Making explosives (such as TNT) and forming amines such as phenylamine for dyes.
What reagents are used in Friedel–Crafts acylation of benzene?: An acyl chloride (RCOCl) and anhydrous aluminium chloride, AlCl₃, as catalyst.
Write the equation for forming the electrophile from ethanoyl chloride.: CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻
What is the product of benzene with ethanoyl chloride and AlCl₃?: Phenylethanone, C₆H₅COCH₃ (and HCl).
Why must Friedel–Crafts acylation be carried out under anhydrous conditions?: AlCl₃ reacts with water, which would destroy the catalyst.
How is AlCl₃ regenerated in acylation?: H⁺ + AlCl₄⁻ → AlCl₃ + HCl

Exam questions on Electrophilic substitution of benzene

In a laboratory preparation of nitrobenzene, a technician adds benzene slowly to a mixture of concentrated nitric acid and concentrated sulfuric acid. The flask is kept in a water bath at about 50 °C and stirred, and the nitrobenzene is later separated from the acids.
Write an equation for the formation of the electrophile in this reaction and state the role of sulfuric acid overall.2 marks
A chemist wants to make phenylethanone, C₆H₅COCH₃, from benzene. The chemist adds ethanoyl chloride, CH₃COCl, to benzene in the presence of anhydrous aluminium chloride, AlCl₃, and warms the mixture. Hydrogen chloride gas is given off.
Write an equation for the formation of the electrophile in this reaction and explain why the reagents and apparatus must be anhydrous.2 marks
A student prepares nitrobenzene, C₆H₅NO₂, from benzene using a mixture of concentrated nitric acid and concentrated sulfuric acid at 50 °C. The student uses 15.6 g of benzene (Mr = 78.0) and obtains 19.7 g of pure nitrobenzene (Mr = 123.0). The reaction is a monosubstitution of the ring.
Calculate the percentage yield of nitrobenzene.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).