For B. Sc. & M.Sc. students

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C) Aryl Diazonium Salts:
BDC
Benzene Diazonium Chloride:
Diazotisation:

2. Benzene Diazonium Chloride:
Aryl Diazonium Salts:
Aromatic amines when treated with
nitrous acid in cold mineral acid
solution; to form a compound known as
Aryldiazonium salts or Diazonium salts.
OR
 Aromatic primary amines are reacted with nitrous
acid in cold conditions forming the compounds
known as diazonium salts.
 The reaction is known as diazotization
Q.1) What is diazonium salt? Give the preparation of Benzene diazonium chloride (B.D.C) (W-14, 4 Mark)
Q.2) What is the structural formula of of Benzene diazonium chloride? (W-16, 1 Mark)
Q.3) The process of converting an amine into the diazonoium salt is called as diazotiazetion

3. Diazotisation:
 The process in which there is formation of diazonium
salt by the reaction of primary aromatic amines
dissolved in hydrochloric acid (HCl) with nitrous acid
(HNO2) in ice cold condition is called as diazotization.
 The compounds is characterized by the presence of the functional
group –N+N (diazonium ion) directly bonded to an aryl group, -Ar.
 The aryl diazonium ion Ar–N+N, forms salt with anions such as
Cl-, Br-, NO2
-, HSO4
-, BF4
- ,etc.
 These salts are called Aryldizonium Salts or Diazonium salts.
 The diazonium salts are extremely reactive and give rise to
many important products. 3
Ar N N Ar N N OR ArN2XX
Functional Group
(diazonium ion)
Aryldiazonium ion
Aryldiazonium Salt

4. Structure:
 The electronic structure of diazonium salts (Ar–N+NX-)
is written as..
 Thus the diazonium cation is a resonance stabilized, the
positive charge being distributed over the two N atoms.
 In arenedizonium salt, the C-N bond gets partial double bond characteristics and
is stronger than alkyldiazonium salts.
 The aliphatic diazonium salts are unstable because ‘R’ group is not capable of
participating in resonance.
4
Ar N N XAr N N
..
: :

5. LOGO
Benzene Diazonium Chloride
Preparation of
Benzene diazonium chloride
(B.D.C.)
from Aniline:
Laboratory Preparation of Benzene diazonium chloride (B.D.C.):

6. LOGOLaboratory Preparation of Benzene diazonium chloride
(B.D.C.):
 When aniline (aromatic primary amine) is reacted with nitrous acid (mixture of
NaNO2 & HCl) at about 0-50 C; to form diazonium salts, the compounds
known as benzene diazonium chloride.
 The reaction is known as diazotization.
OR
Ice cold solution of aniline hydrochloride on reaction with ice cold solution of
NaNO2 give benzene diazonium chloride.
 The process of converting an amine into the diazonium salt is called
diazotization. 6
Q.1) Ice cold solution of aniline hydrochloride on reaction with ice cold solution of NaNO2 give
benzene diazonium chloride. (W-12, ½ Mark)
Q.2) Explain the conversion of aniline to benzene diazonium chloride. (W-12, 2 Mark)
Q.3) Give the structural formula of benzene diazonium chloride. (S-13, 1 Mark)
Q.4) How will you convert Aniline to Benzene diazonium chloride (B.D.C)? (S-13, S-14 & W-16, 2 Mark)
Q.5) Give the laboratory preparation of Benzene diazonium chloride (B.D.C). (W-16, 2 Mark)
Q.6) Complete the following reaction: (S-17, 2 Mark)
Q.7) Discuss the diazotization reaction with its any two synthetic applications. (W-17, 4 Mark)
Q.8) How Benzene diazonium chloride (B.D.C) is prepared in laboratory? (S-18, 4 Mark)
Q.9) How will you convert Aniline to Benzene diazonium chloride (B.D.C)? (W-18, 2 Mark)
Q.10) Write short account on diazocoupling reaction of benzene diazonium chloride. (W-19, 4 Mark)
NaNO2 / HCl
NH2
0 - 5 0
C
?

7. LOGOThe process of converting an amine into the diazonium salt is called diazotization
 The nitrous acid is prepared from the mixture of sodium nitrite (NaNO2)
and mineral acid (HCl or H2SO4) in ice cold condition (i.e., at about 0-50 C).
 Mechanism: Following steps are involved-
Step-1) Nitrous acid (NaNO2/HCl) gives nitrosonium ion [N=O]+
7
NaNO2 HCl
N H2
HNO2
N=N .Cl
HNO2
NaCl
+
+
0 - 5 0
C
+
NaNO2/HCl
O=N-OH + H Cl + 2 H2O
Sodium nitrite Nitrous acid
in Ice cold
condition
Nitrous acid
Aniline
(Aromatic 1o
amine)
or 0 - 5 0
C
in Ice cold
condition Benzene diazonium chloride
(B.D.C.)
or Diazonium salt
H2O N O+
nitrosonium ion
H O N O + H+
H O N O
H
nitrous acid
or
HNO2
..
.. ..
[ [
from HCl

8. LOGOThe process of converting an amine into the diazonium salt is called diazotization
 Mechanism: Following steps are involved-
Step-2) Nitrosonium ions combine with aniline; to form nitrosoaniline
 Step-3) Nitrosoaniline undergoes rearrangements followed by;
 Step-4) Dehydration; to form diazonium ion which takes up Cl-
; to form the
diazonium salt as a final product, called as benzene diazonium chloride
8
N O+
nitrosonium ion
..
[ [
C6H5NH2 C6H5 N N O
H
HAniline Nitrosoaniline
Rearrengment
C6H5 N N O
H
H
Nitrosoaniline
C6H5 N N O H
H
H2OC6H5 N NC6H5 N N O H
H
+
Dehydration
Diazonium ion
C6H5 N N ClC6H5 N N
Benzenediazonium chloride
+
Diazonium ion
Cl

9. LOGOThe process of converting an amine into the diazonium salt is called diazotization
 Mechanism: Following steps are involved-
9
- H2O
N O
nitrosonium ion
H O N O + H+
H O N O
H
nitrous acid
or
HNO2
..
.. .. [ [
from HCl
+
..
C6H5NH2
Aniline
Rearrengment
C6H5 N N O
H
H
Nitrosoaniline
- H2O
C6H5 N N C6H5 N N O H
H
Dehydration
Diazonium ion
C6H5 N N Cl
Benzenediazonium chloride
+ Cl
Step-1 Step-2 Step-3
Step-4

10. LOGOBDC

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LOGOBy Dr. P. R. Padole
Synthetic applications of Benzene diazonium chloride:
Or Chemical Reaction of Benzene diazonium chloride:
(A) Reaction in
which –N2
+X- group
is replaced by
another univalent
atom or group,
with the liberation
of
N2 gas:
BDC
Chemical Reactions
(B) Reactions in
Which both N-Atoms
are Retained:
Diazo Coupling Reaction:
(i) Preparation of
p-hydroxy-azobenzene:
&
(ii)Preparation of
p-amino-azobenzene:
N2 Cl
Ar N N XAr N N
..
: :

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LOGO
(A) Reaction in which –N2
+X- group is replaced by
another univalent atom or group, with the liberation of
N2 gas:
BDC
Replacement of -N2Cl by –H
Preparation of Benzene
Replacement of -N2Cl by – NO2:
Preparation of Nitrobenzene
Replacement of -N2Cl
by –OH:
Preparation of Phenol
Replacement of -N2Cl by
–halogen (Cl or Br):
Preparation of Chlorobenzene
or Bromobenzene
Replacement of -N2Cl by
–Fluoro (F) or –Iodo (I):
Preparation of Fluorobenzene
Or Iodobenzene
Replacement of -N2Cl by –CN:
Preparation of Benzonitrile
N2 Cl

13. 13
Benzenediazonium chloride
(BDC)
N2 Cl
Cl
CuCl / HCl
CuCN
Chlorobenzene
+ N2
CuBr / HBr
Br
Bromobenzene
+ N2
CN
Benzonitrile
+ N2
Phosphorous
acid
+ H3PO2 + H2O
+ N2 + H3PO3 + HCl
Benzene
+ H2O /
+ N2 + HCl
Phenol
H+
OH
+ HBF4
Fluoroboric acid
- HCl
N2 BF4
Benzene diazonium
fluoroborate
100o
C
F
Fluorobenzene
+ N2 + BF3
+ KI
+ N2 + KCl
Iodobenzene
I
+ N2 + H-Cl
Nitrobenzene
NO2
+ HNO2
in presence of Cu2O
Nitrous acid
Symmary of Chemical Reaction of Benzene diazonium chloride:
Reaction in which -N2
+
X-
group is replaced by
another univalent atom or group, with the liberation of N2 gas:
Sandmayer
Reaction
(S-13, W -14, W-15, S-16,
W-17 & S-18 2 Mark)
(S-13, S -16, W-16, W-17 ,
W-18 & W-19 2 Mark)
(S -16, S-18, W-18, S-19 &
W-19, 2 Mark)
Reduced by
Schiemann
Reaction
B.D.C. is reduced by hypophosphorous acid

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Reactions in Which both N-Atoms
are Retained:
Diazo Coupling Reaction:
BDC
N
N
Ar N N XAr N N
..
: :

15. LOGO
pramodpadole@gmail.com
Preparation of p-hydroxy-azobenzene:
Or Reaction of BDC with Phenol:
 When benzene diazonium chloride (B.D.C.) is reacted with Phenol
in alkaline solution; to form p-hydroxy-azobenzene.
 These are highly colored derivatives known as Azo Compounds,
Ar-N=N-Ar.
 Such reactions in which the diazonium ion joined or coupled to the ring
of phenol or an aromatic amine are called Diazo Coupling reaction.
Q.1) What happen when Benzene diazonium chloride is treated with Phenol in alkaline medium?
(W-13 & S-15, 2 Mark)
Q.2) How Benzene diazonium chloride(B.D.C.) reacts with Phenol? (S-16, 2 Mark)
Q.3) Write short account on diazocoupling reaction of benzene diazonium chloride. (S-17, 4 Mark)
Q.4) Complete the following reaction and predict the product: (S-19, 2 Mark)
Benzenediazonium chloride
(BDC)
OH OHN N+
Phenol p-Hydroxy azobenzene
(Azo compound)
OH
HN=N .Cl
Diazo Coupling Reaction
+ H-Cl
(from NaOH)
+ HN=N .Cl ?

16. Preparation of p-amino-azobenzene:
Or Reaction of BDC with Aniline:
 When benzene diazonium chloride (B.D.C.) is reacted with
aniline (1o aromatic amine) in mildly alkaline solution
(CH3COONa); to form diazo-amino-benzene, which is on
heating in acidic medium undergoes rearrangement; to form
p-amino-azo-benzene.

Q.1) How will you convert Aniline to p-amino azobenzene? (W-13 & W-15, 2 Mark)
Benzenediazonium chloride
(BDC)
N N+
Aniline Diazo-amino-benzene
OH
H NHN=N .Cl
Diazo Coupling Reaction
+ H-Cl
NH2N N
p-Amino azobenzene
NH
H
Rearrangement
(Acidic medium)
H
(CH3COONa)

17. 17

18. THE END!