Amines 3

Question 1

define diazonium salts

Answer 1

The diazonium salts have the general formula
–R N X2 where R stands
for an aryl group and X ion may be Cl–
Br–, HSO4–, BF4- , etc.
They are
named by suffixing diazonium to the name of the parent hydrocarbon
from which they are formed, followed by the name of anion such as
chloride, hydrogensulphate, etc.

The N2 - group is called diazonium
group.
For example, –
C H N Cl 6 5 2

is named as benzenediazonium
chloride and C6H5N2
+HSO4
–
is known as benzenediazonium
hydrogensulphate.

Question 2

primary aliphatic diazonium salts

Answer 2

Primary aliphatic amines form highly unstable alkyldiazonium salts. They decompose to form alcohol and quantitative evolution of nitrogen gas.

Question 3

primary aromatic diazonium salts

Answer 3

Primary aromatic amines form arenediazonium
salts which are stable for a short time in solution at low temperatures
(273-278 K).

The stability of arenediazonium ion is explained on the basis of resonance.

Question 4

physical properties of diazonium salts

Answer 4

Benzenediazonium chloride is a colourless crystalline solid. It is readily
soluble in water and is stable in cold but reacts with water when
warmed. It decomposes easily in the dry state.

Benzenediazonium
fluoroborate is water insoluble and stable at room temperature.

Question 5

Reactions involving displacement of nitrogen

Answer 5

Diazonium group being a very good leaving group, is substituted
by other groups such as Cl–
, Br–,I–, CN– and OH–
which displace
nitrogen from the aromatic ring. The nitrogen formed escapes from
the reaction mixture as a gas.

Question 6

uses of benzene diazonium salts

Answer 6

From the above reactions, it is clear that the diazonium salts are very
good intermediates for the introduction of –F, –Cl, –Br, –I, –CN, –OH, –NO2
groups into the aromatic ring.

Aryl fluorides and iodides cannot be prepared by direct halogenation.
The cyano group cannot be introduced by nucleophilic substitution of
chlorine in chlorobenzene but cyanobenzene can be easily obtained
from diazonium salt.

Thus, the replacement of diazo group by other groups is helpful in preparing those substituted aromatic compounds which cannot be
prepared by direct substitution in benzene or substituted benzene.