Aromatic amines

Aromatic Amines
Prepared by Mr. N. M. Jangade

Aromatic Amines
• Aromatic amines are derivatives of aromatic hydrocarbons
in which a hydrogen of the benzene ring has been replaced
by an amino group (-NH2).
• All such compounds in which an amino or substituted
amino group is bonded directly to an aromatic ring are
termed as Aromatic amines.
• e.g.

• The derivatives of Arenes in which -NH2 is bonded to a
side chain are to be regarded as aryl substituted
aliphatic amines.

IUPAC Nomenclature
1. C6H5NH2, is the simplest form of the aromatic amine.
2. Its simplest derivatives are named using the prefixes –o, -m
and –p or numbers to locate substituent’s.

3. Several derivatives of Aniline have common names
that are still widely used.

4. Prefixes placed like N- or N,N- depending on
Substituent’s present on the nitrogen atom.

Classification
1. Primary aromatic amines:
2. Secondary aromatic amines:
3. Tertiary aromatic amines:

Methods of Preparation
1. Reduction of Nitro compounds:
The reduction is carried out with
A. Hydrogen in presence of Ni, Pd or Pt as a catalyst.

B. Sn or Fe and HCl:

C. By using Lithium Aluminium Hydride (LiAlH4):

2. Aminolysis of Aryl chlorides:
Chlorobenzene on reaction with Ammonia in the presence
of Copper salts at high temperature and pressure forms
Aniline.

3. Hofmann Rearrangement:
Aryl amide on reaction with Bromine or Chlorine in an
alkaline solution yields Primary amine.

4. Reduction of Azo compounds:
Azo compounds when reduced with hydrogen in
presence of Nickel as a catalyst, gives Arylamines.

Physical properties
1. Aromatic amines in general are colourless liquids / Solids,
having characteristic odour (Not Pleasant).
2. They turn brown in air owing to oxidation.
3. Hydrogen bonding leads to increase Melting and Boiling
point.
4. They are soluble in water but more in organic solvents.
5. They are steam volatile so they can be purified by steam
distillation. Prepared by Mr. N. M. Jangade

Chemical reactions of Aniline
• Salt formation:
• Aromatic amines on reaction with mineral acids such
as HCl or H2SO4 forms Aryl ammonium salt.

• Alkylation / Reaction with Alkyl halide:
Aromatic amines on reaction with alkyl halide they form 20
or 30 amines which on further reaction with Hydrogen
halide (HX) to form salt. These salts on reaction with aq.
NaOH to give free 20 or 30 amines.

• Acylation:
Aromatic amines on reaction with acid halides/
anhydrides forms N-aryl amides.

• Reaction with Aldehydes:
Aromatic amines on reaction with Aldehydes forms
Imines.

• Reaction with Nitrous acid:
10 Aromatic amine on diazotiazation with Sodium
Nitrite and Hydrochloric acid at 0-50C to give Diazonium
salt.

Coupling reaction:
Aniline reacts with Benzene diazonium chloride to give
p-aminoazobenzene.

Halogenation:
Bromine water with the Aniline at room temperature
reacts vigorously to form a white precipitate of 2,4,6-
Tribromoaniline.

• Sulfonation:
Aniline on sulfonation with fuming sulfuric acid forms
p-Aminobenzene sulfonic acid.

• Nitration:
Aniline on reaction with a mixture of Conc. HNO3 and
Conc. H2SO4 to give m-Nitroaniline.

Why meta Product?

Two effect for –NH2:
•Electron donating by resonance
•Electron withdrawing by inductive effect
One effect for –NH3:
•Electron withdrawing by inductive effect
•( No resonance effect)

• Oxidation:
Aromatic amine on oxidation with Potassium dichromate
and sulfuric acid gives p-benzoquinone.

Basicity of Aromatic Amines

• Nitrogen in aniline have lone pair of electrons which
are available to accept protons.
• But in Aniline lone pair of electrons can delocalize
over Benzene ring this decreases the electron
density on Nitrogen and makes it weak basic in
nature.

1. Nitrogen in Aniline and Ethylamine have lone pair of
electrons which are available to accept protons.
2. But if we compare basicity of Aniline and Ethylamine then
in Aniline lone pair of electrons can delocalize over
Benzene ring this decreases the electron density on
Nitrogen and makes it weak basic in nature, while in
Ethylamine lone pair of electrons localize over Nitrogen
atom (As no resonance possible in Ethylamine) this
increases the electron density on Nitrogen and makes it
more basic in nature than Aniline

Effect of the substituent’s on the basicity of Aromatic
amines
Anything that withdraws
electron density from
nitrogen atom decreases
basicity.

Anything that donates
electron density to nitrogen
atom increases basicity.

Uses of Aniline
1. Preparation of dye and dye intermediates.
2. Manufacturing of Antioxidants.
3. Vulcanization accelerator in rubber industry.
4. Synthesis of drugs notably Sulfa drugs.
5. For making Isocynates required for Polyurethane
plastics used for insulation.

Aryl diazonium ion

Aryl diazonium salt

• Aryldiazonium salt is an important class of
compound having (diazonium ion)
bonded to an aryl group.
• This (diazonium ion) forms salt with
anions such as Cl-, Br-, HSO4-, BF4- etc these salts
are called Aryldiazonium salt.

Preparation of Arenediazonium salt
Diazotiazation:
The process of converting an amine into the diazonium salt is
called diazotization.
Benzene diazonium chloride is prepared by treating a
solution of Aniline in dil. HCl with Sodium nitrite
solution at 0-50C.

Physical Properties of Aryldiazonium salt
• Colourless, crystalline and solid which turn
brown on exposure to air.
• Unstable, explode on warming.
• Soluble in water, sparingly soluble in ethanol
and glacial Acetic acid.
• Insoluble in Ether.

Reactions of Arenediazonium salt
• Two types of reactions
1. Reactions in which N2+X- is replaced
2. Reactions in which N-atoms are retained.

Reactions in which N2+X- is replaced
Reduction to Arene’s / Replacement of N2+X- by H
A diazonium salt on reduction with Hypophosperous acid
to give the respective Arene.

• Synthesis of Phenols/ Replacement of N2+X-
by OH
Aqueous solution Benzenediazonium salt is acidified
and heated to form Phenol.

• Synthesis of Aryl Bromide, Aryl Chloride or Aryl
nitrile (Replacement of N2+X- by Br, Cl and CN) :
• When cold diazonium salt solution is treated with cuprous
bromide, cuprous chloride or Cuprous cyanide results in
the formation of Aryl bromide, Aryl chloride or Aryl
cyanide. This reaction is known as Sandmayer’s reaction.

Synthesis of Aryl fluoride
(Replacement of N2+X- by F) :
The diazonium salt is treated with Fluoroboric acid (HBF4)
forms precipitates of diazonium fluoroborate. This is isolated,
dried and heated to give aryl fluoride. This reaction is called
as Schiemann reaction.

Synthesis of Aryl Iodide
(Replacement of N2+X- by I) :
• Aqueous solution of diazonium salt on heating with
excess of Potassium iodide results in formation of Aryl
iodide.

Synthesis of Thiophenols
(Replacement of N2+X- by SH) :
• diazonium salt on reaction with Potassium
hydrosulfide results in formation of
Thiophenols.

Synthesis of Nitro compounds
(Replacement of N2+X- by NO2) :
• diazonium salt on reaction with Sodium nitrite in
presence of Cu powder results in formation of
Nitrobenzene.

Reactions in which N-atoms are retained
• Reduction to Arylhydrazine:
Aryldiazonium salt on reduction with Sodium bisulfite
(NaHSO3) or Stannous chloride yields Arylhydrazines.

• Azo Coupling:
Diazonium salt on reaction with aromatic compound
that contains a strong electron donating group, the two
ring joins together to form an azo compound, a
compound with nitrogen nitrogen double bond.

Application
• Diazonium group can be replaced by OH, I, SH,
Cl, I, Br, CN, F, NO2, H and Ar.
• Diazonium compounds used for the synthesis
of aromatic compounds.
• Example:

Problems
• How to Synthesize 3,5-dichlorophenol from
Benzene?

Problems
• How to Synthesize m-Bromoiodobenzene from
Benzene?

Problems
• How to Synthesize 1,3,5-tribromobenzene
from Benzene?

Problems
• How to Synthesize m-Cyanobenzoic acid from
Toluene?

Problems
• How to Synthesize m-hydroxybenzoic acid
from Toluene?

Problems
• How to Synthesize o-dinitrobenzene from
Benzene?

Problems
• How to Synthesize p-fluoroaniline from
Nitroenzene?

Problems
• How to Synthesize m-Nitroaniline from
Toluene?

Effect of same substituent on different
positions (o, m, p) on the basicity of Aromatic
amines.

Hyperconjugation effect:

Ortho effect
It refers mainly to the set of steric effects and some bonding interactions
along with polar effects which are altering its chemical properties and
physical properties.
Ortho effect in substituted aniline
Ortho-substituted anilines are weaker bases than their meta and para
isomers, regardless of the nature of the substituent

Aromatic amines

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