levo

Amines

Diazonium salts and coupling

  • 3 things to know
  • Unit A2 2

Overview

Coupling reaction, formed when benzenediazonium chloride couples with phenol and formed when benzenediazonium chloride couples with phenylamine.

What you need to know

Answer each one before you reveal it.

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Process

How is benzenediazonium chloride formed?

Key term

Why must the temperature be kept below about 10 °C when benzenediazonium chloride is made?

Key term

Why is the nitrous acid generated in the reaction mixture rather than added?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is benzenediazonium chloride formed?

    Model answer

    Phenylamine is treated with nitrous acid, made in situ from sodium nitrite and hydrochloric acid, below about 10 °C.

  2. 2

    Why must the temperature be kept below about 10 °C?

    Model answer

    The diazonium salt decomposes above that temperature, giving phenol and nitrogen gas.

  3. 3

    Why is the nitrous acid generated in the reaction mixture rather than added?

    Model answer

    Nitrous acid is unstable and cannot be stored, so it is made as it is needed from sodium nitrite and the acid present.

  4. 4

    Write the formula of the benzenediazonium ion.

    Model answer

    C₆H₅N₂⁺.

  5. 5

    What is a coupling reaction?

    Model answer

    The reaction of a diazonium ion with an activated aromatic compound to form an azo compound joined by a −N=N− group.

  6. 6

    What is formed when benzenediazonium chloride couples with phenol?

    Model answer

    An orange or yellow azo dye, formed under alkaline conditions.

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