1. Aromatic amines – forming dyes
L.O: To be able to describe how aromatic amines react to form dyes

2. Benzene diazonium chloride
Formula: C6H5N2+ Cl¯. A diazonium group is attached to the ring.
The aromatic ring helps stabilise the ion
How are they prepared?
reagents Phenylamine, nitrous acid and hydrochloric acid
conditions Keep BELOW 10°C
equation C6H5NH HNO HCl C6H5N2+ Cl¯ H2O
N.B. Nitrous acid is unstable and is made in situ from sodium nitrite
C6H5NH2 + NaNO HCl C6H5N2+ Cl¯ + NaCl H2O
Keeping the solution cold slows down decomposition of the diazonium salt
C6H5N2+ Cl¯ H2O C6H5OH HCl N2

3. Diazonium salts - reactions
Benzene diazonium chloride undergoes two main types of reaction
SUBSTITUTION OF THE DIAZONIUM GROUP (nitrogen expelled)
COUPLING REACTIONS (nitrogen atoms are retained)

4. Diazonium salts - substitution
Substitution by OH
reagents water (HYDROLYSIS)
conditions warm above 10°C
equation C6H5N2+ Cl¯ H2O C6H5OH HCl N2
Where is this used? The only reasonably simple way to substitute OH and forms the last step in the production of phenol.
Phenol is an antiseptic and is used to make polymers.
Substitution by I
reagents potassium iodide solution
conditions warm
equation C6H5N2+ Cl¯ KI C6H5I KCl N2

5. Diazonium salts - coupling
reagents phenol and sodium hydroxide
conditions alkaline solution below 10°C
equation C6H5N2+Cl¯ + C6H5OH + NaOH C6H5-N=N-C6H4OH + NaCl + H2O
(4-hydroxyphenol)azobenzene ORANGE
This type of reaction is used in making azo dyes
AZO GROUP