Reduction of nitroarenes: practice and mechanism
Metal + acid reduce –NO₂ completely to –NH₂ (aromatic amine) in several steps.
Example
Base metals in acid reduce the nitro group in several steps to the amino group. Nitrobenzene thus becomes aniline, a key route to aromatic amines.
Mechanism step by step
- 1
The metal (Fe, Sn) gives up electrons and the acid supplies protons.
- 2
The nitro group is reduced step by step: –NO₂ → –NO → –NHOH.
- 3
Finally the amino group forms (as –NH₃⁺ in acid; base releases the amine).
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
- A phenol does not form this way: the nitrogen stays on the ring; only the oxygens are removed.
- The nitroso compound is only an intermediate. Fe/HCl reduces all the way to the amine.
Often confused with: Nitration (SEAr)
Frequently asked questions
Why go via nitration?
An NH₂ group cannot be introduced directly. Nitration followed by reduction is the standard route to anilines.
How does the directing effect change?
The strongly meta-directing NO₂ group becomes the strongly activating, o/p-directing NH₂ group.