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*Revision Materials* 1 Atomic Structure 2 Atoms, molecules and stoichiometry 3 Chemical Bonding 4 States of matter 5 Chemical energetics 6 Electrochemistry 7 Equilibria 8 Reaction kinetics 9 The Periodic Table, chemical periodicity 10 Group 2 11 Group 17 12 Nitrogen and sulfur 13 Organic 14 Hydrocarbons 15 Halogen compounds 16 Hydroxy compounds 17 Carbonyl compounds 18 Carboxylic acids and derivatives 19 Nitrogen compounds 20 Polymerisation 21 Organic synthesis 22 Analytical techniques 23 Chemical energetics 24 Electrochemistry 25 Equilibria 26 Reaction kinetics 27 Group 2 28 Chemistry of transition elements 29 Organic 30 Hydrocarbons 31 Halogen compounds 32 Hydroxy compounds 33 Carboxylic acids and derivatives 34 Nitrogen compounds 35 Polymerisation 36 Organic synthesis 37 Analytical techniques

34 Nitrogen compounds

34.1 Primary and secondary amines 34.2 Phenylamine and azo compounds 34.3 Amides 34.4 Amino acids

Phenylamine and Azo Compounds

Specification Reference Organic Chemistry, Amines 34.2

Quick Notes

  • Phenylamine can be prepared from benzene in two steps:
    • Benzene to nitrobenzene (via HNO3/H2SO4)
    • Then reduction using Sn/HCl + NaOH
  • Phenylamine reactions:
    • Reacts with Br2(aq) to form a tribromo derivative.
    • Reacts with NaNO2 + HCl (<10 °C) to form benzenediazonium salt.
      • Warming the diazonium salt forms phenol.
  • Basicity: Ethylamine > ammonia > phenylamine, due to availability of the nitrogen lone pair.
  • Azo compounds:
    • Formed by coupling a diazonium salt with a phenol or aromatic amine.
    • The azo group is –N=N–.
    • Azo compounds are widely used as dyes due to their extended conjugation and vivid colours.

Full Notes

Preparation of Phenylamine

Phenylamine can be formed from benzene in a series of steps.

CIE A-Level Chemistry diagram showing the preparation of phenylamine from benzene.

Step 1: Nitration of Benzene

CIE A-Level Chemistry nitration of benzene to form nitrobenzene.

Step 2: Reduction of Nitrobenzene to Phenylamine

CIE A-Level Chemistry reduction of nitrobenzene to phenylamine.

Reactions of Phenylamine

The following are reactions of phenylamine you need to know.

Reaction with Bromine Water

CIE A-Level Chemistry reaction of phenylamine with bromine water forming tribromo derivative.

This is an example of electrophilic substitution. The –NH2 group activates the benzene ring, making it more reactive towards substitution, especially at the 2, 4, and 6 positions.

Forming Diazonium Salt and Formation of Phenol

CIE A-Level Chemistry formation of diazonium salt from phenylamine.

Warming the diazonium salt with water:

Relative Basicity of Ammonia, Ethylamine and Phenylamine

Basicity depends on how available the nitrogen's lone pair is for accepting a proton (H+).

Order of basicity: Ethylamine > ammonia > phenylamine

CIE A-Level Chemistry comparison of basicity of ammonia, ethylamine and phenylamine.

Azo Compounds

Azo compounds are formed in coupling reactions and contain the –N=N– functional group.

CIE A-Level Chemistry azo functional group.

The Azo functional group joins two aromatic rings and extends the conjugation (delocalised pi-bonding system), allowing absorption of visible light.

Coupling Reaction

CIE A-Level Chemistry coupling reaction of diazonium salt with phenol forming azo dye.

Use in Dyes

Azo compounds are widely used in textile dyes, indicators, and pigments. Their colour varies depending on the groups attached to the benzene rings. Other azo dyes can be formed by similar reactions using different phenols or amines, yielding a wide range of coloured dyes.

Summary