Describe the first step of the nitration mechanism.

A curly arrow runs from the delocalised ring to the nitrogen atom of NO₂⁺, forming a carbon–nitrogen bond and giving a positively charged intermediate in which the delocalisation is broken.

Describe the second step of the nitration mechanism.

A curly arrow runs from the C–H bond at the substituted carbon back into the ring, releasing a hydrogen ion and restoring the full delocalised system.

Why is the intermediate formed during nitration unstable?

It carries a positive charge and has lost the stabilisation that comes from a complete delocalised ring.

Why is nitration such an important industrial reaction?

The nitro group can be reduced to an amine, and aromatic amines are the starting point for azo dyes and many other products.

State the reagents and conditions for the sulfonation of benzene.

Benzene is heated under reflux with concentrated sulfuric acid for several hours, or warmed with fuming sulfuric acid.

OCR A-Level Chemistry B H433

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Colour by Design

The nitration mechanism, sulfonation and the Friedel-Crafts reactions

1 thing to know
Components 01, 02 and 03

Overview

Recall questions on the two steps of the nitration mechanism, sulfonation and why a dye manufacturer wants it, and the alkylation and acylation reagents.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Why is the temperature of a nitration kept near 50 °C?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe the first step of the nitration mechanism.
Model answer
A curly arrow runs from the delocalised ring to the nitrogen atom of NO₂⁺, forming a carbon–nitrogen bond and giving a positively charged intermediate in which the delocalisation is broken.
2
Describe the second step of the nitration mechanism.
Model answer
A curly arrow runs from the C–H bond at the substituted carbon back into the ring, releasing a hydrogen ion and restoring the full delocalised system.
3
Why is the intermediate formed during nitration unstable?
Model answer
It carries a positive charge and has lost the stabilisation that comes from a complete delocalised ring.
4
Why is the temperature of a nitration kept near 50 °C?
Model answer
Above about 60 °C a second nitro group is substituted onto the ring, giving dinitrobenzene.
5
Why is nitration such an important industrial reaction?
Model answer
The nitro group can be reduced to an amine, and aromatic amines are the starting point for azo dyes and many other products.
6
State the reagents and conditions for the sulfonation of benzene.
Model answer
Benzene is heated under reflux with concentrated sulfuric acid for several hours, or warmed with fuming sulfuric acid.

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