Introduction to amine s and preparation of amine

1. Aromatic Amines

2. Syllabus
• Preparation and reaction of amine
• Basicity of amines, and effect of substituents
on basicity
• Synthetic uses of aryl diazonium salts.

3. • An amine has the general formula RNH2 ,
R2NH, or R3N, where R is any alkyl or aryl gr
• Amines are classified as primary, secondary, or
tertiary, according to the number of groups
attached to the nitrogen atom.

4. • Aromatic amines those in which nitrogen is
attached directly to an aromatic ring are
generally named as derivatives of the simplest
aromatic amine, aniline.
• An amino toluene is given the special name of
toluidine.

6. Salts of amine
• Aliphatic amines are about as basic as ammonia;
aromatic amines are considerably less basic.
• Although amines are much weaker bases than
hydroxide ion or ethoxide ion, they are much
stronger bases than alcohols, ethers, esters, etc. ;
• They are much stronger bases than water.
• Aqueous mineral acids or carboxylic acids readily
convert amines into their salts; aqueous
hydroxide ion readily converts the salts back into
the free amines.

8. • Amine salts are typical ionic compounds. They
are non-volatile solids, and when heated
generally decompose before the high
temperature required for melting is reached.
• The halides, nitrates, and sulfates are soluble
in water but are insoluble in non-polar
solvents.
• An amine can be separated from non-basic
compounds by its solubility in acid; once
separated, the amine can be regenerated by
making the aqueous solution alkaline.

9. • Amines are simply ammonia in which one or
more hydrogen atoms have been replaced by
organic groups.
• Nitrogen uses SP3 orbitals, which are directed
to the corners of a tetrahedron.
• Three of these orbitals overlap s orbitals of
hydrogen or carbon; the fourth contains an
unshared pair of electrons

10. A molecule in which nitrogen carries three
different groups is not superimposable on its
mirror image; it is chiral and should exist in two
enantiomeric forms (I and 11)

11. • Rapid rotation about carbon-carbon single
bonds prevents isolation of conformational
enantiomers, so rapid inversion about
nitrogen prevents isolation of enantiomers like
I and II.
• Evidently, an unshared pair of electrons of
nitrogen cannot ordinarily serve as a fourth
group to maintain configuration.

12. GENERAL METHOD OF
PREPARATION OF AMINE

13. Reduction of nitrobenzene by the
cheap reagents, iron/tin/zinc and
dilute hydrochloric acid/ dilute
acetic acid

14. Treatment of chlorobenzene & with
ammonia at high temperatures and
high pressures in the presence of a
catalyst.

19. Methylamine, dimethylamine, and
trimethylamine are synthesized on an
industrial scale from methanol and
ammonia.

21. • Nitro compounds reduced catalytically at 200-
400C
• Raney nickel is used as catalyst reduction of
nitro group takes place at room temperature.
• If Raney nickel used to reduce the nitro
compound with thiol group then it takes more
catalyst to give the yield, because sulfur
poisoned the Raney nickel.

22. • Palladised charcoal will be the best choice.
• Nitro compounds may be reduced using
palladium and cyclohexene. If more than one
nitro group is present it will reduce only one.

25. Reductive amination
• Reductive amination (also known as reductive
alkylation) is a form of amination that involves
the conversion of a carbonyl group to
an amine via an intermediate imine. The carbonyl
group is most commonly a ketone or
an aldehyde.
• Typical reagents that meet these criteria
include sodium cyano borohydride (NaBH3CN)
and sodium triacetoxy borohydride
(NaBH(OCOCH3)3)

27. Reductive amination
• Reductive amination, the catalytic or chemical reduction of
aldehydes (RCHO) and ketones (R2CO) in the presence of
ammonia or an amine, accomplishes much the same
purpose as the reaction of halides.
• It too can be used to prepare any class of amine, and has
certain advantages over the halide reaction.
• The formation of mixtures is more readily controlled in
reductive amination than in ammonolysis of halides.
• Reductive amination of ketones yields amines containing a
sec-alkyl group; these amines are difficult to prepare by
ammonolysis because of the tendency of secondary alkyl
halides to undergo elimination rather than substitution.

28. Reduction of nitriles
• The carbon-nitrogen triple bond in a nitrile
can also be reduced by reaction with hydrogen
gas in the presence of a variety of metal
catalysts. Commonly used catalysts
are palladium, platinum or nickel.
• The reaction will take place at a raised
temperature and pressure, but the exact
details vary from catalyst to catalyst.

29. Ethane nitrile can be reduced to
ethylamine by reaction with hydrogen
in the presence of a palladium catalyst.
CH3CN+2H2−→CH3CH2NH2
Pd

30. The Hofmann
rearrangement (Hofmann
degradation)
It is the organic reaction of a primary amide to a
primary amine with one fewer carbon atom.
The reaction involves oxidation of the nitrogen
followed by rearrangement of the carbonyl and
nitrogen to give an isocyanate intermediate.
The reaction can form a wide range of products,
including alkyl and aryl amines.

31. The reaction of bromine with sodium
hydroxide forms sodium hypo bromite in situ, which
transforms the primary amide into an intermediate
isocyanate.
The formation of an intermediate nitrene is not
possible because it implies also the formation of
a hydroxamic acid as a byproduct, which has never
been observed.
The intermediate isocyanate is hydrolyzed to a
primary amine, giving off carbon dioxide.

32. Mechanism of Holfmann degradation

33. Mechanism of Holfmann degradation
• Base abstracts an acidic N-H proton, yielding an anion.
• The anion reacts with bromine in an α-substitution reaction
to give an N-bromoamide.
• Base abstraction of the remaining amide proton gives a
bromoamide anion.
• The bromoamide anion rearranges as the R group attached
to the carbonyl carbon migrates to nitrogen at the same
time the bromide ion leaves, giving an isocyanate.
• The isocyanate adds water in a nucleophilic addition step to
yield a carbamic acid (aka urethane).
• The carbamic acid spontaneously loses CO2, yielding the
amine product.

34. Synthesis of secondary and tertiary
amines
Where ammonia has been used to produce a
primary amine, a primary amine can be used to
produce a secondary amine, or a secondary
amine can be used to produce a tertiary amine.

36. THANK YOU