1. Diazotization is a reaction where an aryl amine like aniline reacts with nitrous acid to form an unstable diazonium ion intermediate. 2. Coupling reactions involve this diazonium ion reacting with compounds containing activating groups like phenol or aniline to form an azo product by joining the two aryl groups. 3. The coupling reaction is an electrophilic aromatic substitution that proceeds through a two-step mechanism where the diazonium ion attacks the aromatic ring in the first slow step.

1. PRESENTED BY – BUDDHADEV DEY
B.PHARM ,2nd year, 3rd semester
DIAZOTISATION AND
COUPLING REACTION

2. -:Diazotization Reaction:-
Diazo means two nitrogen atoms. When combined with
onium, we have diazonium, which means two nitrogen atoms
and a positive charge (i.e., N2
+). Diazonium ions are produced
when an aryl amine reacts with cold nitrous acid. Nitrous acid is
unstable and is prepared just prior to its use by a reaction
between sodium nitrite and hydrochloric acid.
Reaction:-
NH2
NaNO2 + HCl
N
+
N
+
Cl
0-5'C
Aniline Benzene diazonium chloride

3. H+
H O N
O
H+
H O
N
+
H
O
OH2-
NH2
+
N
+
N O
H
H
H
+
-
N N O
H
N N O HN N O
+
H
H
H
+
OH2-
N N+
N
+
N
CH
+
N
+
N
-
CH
+
N
+
N
-
N O
OH
N+
O
N+
O
Mechanism of reaction:-

4. -:coupling reaction:-
Compounds such as aniline and phenol, which contain
strong electron donating groups (e.g., -OH and –NH2) that
activate the ortho and para positions on a benzene ring, can
undergo coupling reactions with a diazonium ion. A coupling
reaction is one in which two aryl rings are joined by an azo
group. These coupling reactions usually occur at the para
position of the o,p director.
Aniline may serve as the substrate for the formation of a
diazonium ion, and it may serve as the substrate for a coupling
reaction with the diazonium ion.
The reaction is an electrophilic aromatic substitution
reaction; therefore, the mechanism is similar to that for the
nitration of benzene (i.e., it is a two-step reaction in which the
first step is rate determining).

5. N
+
N
Benzene diazonium
chloride
Cl
-
+
OH
H
Phenol
N N
OH
+ ClH
Diazo product
Coupling reaction with phenol
N
+
N Cl
-
Benzene diazonium
chloride
H
NH2
+
N N
NH2
+ ClH
Aniline Diazo product
Coupling reaction with aniline

6. N
+
N
+
OH
H
slow N N
CH
+
H
OH
fast
N N
OH
benzene diazonium
ion
phenol
diazo product
Mechanism of coupling with phenol:-

7. Mechanism of coupling with aniline:-
N
+
N
+
H
NH2
slow N N
CH
+
H
NH2
fast
N N
NH2
benzene diazonium
ion
aniline
diazo product

8. Thank
YOU