2. INTRODUCTION
Amines are similar to ammonia (base) with one or more
alkyl groups bonded to the nitrogen atom.
H
The classification:
N
H Ammonia
H
1o, 2o, or
3o corresponding to the number of hydrogen atoms
or alkyl replaced.
General structure:
R
N
H
H
R
N
R'
R''
R
N
R'
H
2
5. NOMENCLATURE OF
AMINES
Count the carbons in the longest chain containing the amine
Drop the –e ending for the parent name and add –amine
For a secondary amine an N prefixes the compound giving the
shorter carbon chain its side chain prefix name
For a tertiary amine an N,N prefixes the compound giving the
two shorter carbon chains their side chain prefix names
Structural
Formula
H
H C N H
H H
H H
H C C N CH3
H H H
H H
H C C N CH3
H H CH3
Condensed
Structural
Formula
CH3NH2
CH3CH2NHCH3
CH3CH2N(CH3)2
CA format
methanamine
N-methylethanamine
5
N,N-dimethylethanamine
6. NOMENCLATURE OF
AMINES
Aromatic amines belong to specific families, which act as
parent molecules.
For example, an amino group (—NH ) attached to benzene
2
produces the parent compound aniline.
phenylamine
6
7. NOMENCLATURE OF
AMINES
The prefix ‘amino’ is used to indicate the presence of an
–NH2 group in a molecule containing more than one
functional group.
1
1
7
8. NOMENCLATURE OF
AMINES
Compounds with two –NH2 groups are named by adding
the suffix ‘diamine’ to the name of the corresponding alkane
or aromatic compounds.
H2N
(CH2)6 NH2
hexane-1,6-diamine
(1,6-hexanediamine)
H 2N
NH2
benzene-1,4-diamine
(1,4-benzenediamine)
8
10. PREPARATION OF
AMINES
1.
Reduction of nitro compounds – gives 1o amines
Aromatic amines are normally prepared by reduction of the
corresponding aromatic nitro compound.
Aniline is prepared from nitrobenzene.
Reducing agents: Fe/H+, Sn/H+ or catalytic hydrogenation (example,
H2/Pd or Pt or Ni).
10
12. PREPARATION OF
AMINES
2.
Reduction of halides with ammonia
The reaction of ammonia with an alkyl halide leads to the
formation of a primary amine.
The primary amine that is formed can also react with the alkyl
halide, which leads to a disubstituted amine.(2o amine)
12
14. PREPARATION OF
AMINES
3.
Reduction of amides
Amides yield primary amines on reduction by lithium aluminum hydride,
LiAlH4.
The oxygen atom is replaced by two hydrogen atoms.
2o and 3o amides produce 2o and 3o amines, respectively.
Reaction occurs via nucleophilic acyl substitution then nucleophilic addition.
14
15. PREPARATION OF
AMINES
4.
Reduction of nitriles
Nitriles can be reduced by strong reducing agent like H2 with
catalyst (example Ni) or LiAlH4 to yield primary amines via
nucleophilic addition reaction.
Example:
2H2, catalyst
R CN
R CH NH
or LiAlH4, ether
2
2
15
20. REACTION OF AMINES
Formation of amides
1.
a.
From acid anhydride
O
R C O
C R
acid anhydride
O
R C O
O
O
2RNH2
R
O
2R2NH
R C O RNH3
+
amide
amine
O
C R
C NHR
O
R
C NR2
O
+
R C O R2NH2
20
21. REACTION OF AMINES
Formation of amides
1.
From ester
Esters reacts with ammonia, primary and secondary
amines to produce amides and alcohols.
a.
O
R
C O R
ester
C O R
ester
R
H N R
C NH
primary amine
secondary amide
R
R OH
O R
O
R
O R
H
R
H N R
secondary amine
C N R
R OH
tertiary amide
EXAMPLE
O
H3C
C O CH2CH3
H
H N H
O
O
0-5 C
H3C
C NH2
CH3CH2 OH 21
22. REACTION OF AMINES
2.
Amine alkylation: formation of quarternary salts
Reaction
of amines and acid will give amine salt (an ammonium ion).
CH3CH2NH2 + HCl CH3CH2NH3+ + Cl -
CH3CH2CH2 NH2
HCl
n-propylammonium chloride
n-propylamine
(CH3CH2)3 N
triethylamine
CH3CH2CH2 NH3Cl
HCl
(CH3CH2)3 NH Cl
22
triethylammonium chloride
24. REACTION OF AMINES
3.
With nitrous acid
Nitrous
acid is unstable and must be prepared in the reaction solution by
mixing sodium nitrite with acid.
Primary
amines react with nitrous acid to yield a diazonium salt, which is
highly unstable and degradates into a carbocation that is capable of
reaction with any nucleophile in solution. Therefore, reacting primary
amines with nitrous acid leads to a mixture of alcohol, alkenes, and alkyl
halides.
24
25. REACTION OF AMINES
With nitrous acid
Primary
aromatic amines form stable diazonium salts at zero
degrees.
25
26. REACTION OF AMINES
With nitrous acid
Secondary
aliphatic and aromatic amines form nitrosoamine (yellow
oils) with nitrous acid.
26
27. REACTION OF AMINES
With nitrous acid
Tertiary
amines react with nitrous acid to form N-nitrosoammonium
compounds (ammonium salts).
27
28. REACTION OF AMINES
Reaction of nitrous acid with aliphatic amines in cold acidic solution
can be used to distinguish between primary, secondary and tertiary
amines.
RNH2 + HNO2 → N2 gas evolution from a clear solution.
(1° amines)
R2NH + HNO2 → An insoluble yellow oil formed (N-nitrosoamine)
(2° amines)
R3N + HNO2 → A clear solution (ammonium salt formation)
(3° amines)
28
29. REACTION OF AMINES
Isocyanides (nitrile compound)
4.
Primary amines heated with trichloromethane (CHCl3) and
alcoholic KOH solution will produce a foul odor of isocyanide,
RNC.
• Isocyanide:
- an organic compound with functional group R N C
- The CN functionality is connected to the organic
fragment via the nitrogen atom, not via carbon atom.
- a zwitterion (nitrogen atom carries positive charge,
carbon atom carries negative charge).
•
29
31. REACTION OF AMINES
5.
Benzenediazonium salts
1. Preparation of Benzenediazonium chloride
Structure
• has the formula C6H5N2+Cl¯
• a diazonium group is attached to the benzene ring
• the aromatic ring helps stabilise the ion
31
32. REACTION OF AMINES
5.
Benzenediazonium salts
1. Preparation of Benzenediazonium chloride
From phenylamine (which can be made by reduction of
nitrobenzene)
Reagents: nitrous acid and hydrochloric acid
Conditions: keep below 10°C
Equation:
C6H5NH2 + HNO2 + HCl C6H5N2 + Cl¯+ 2H2O
32
33. REACTION OF AMINES
5.
Benzenediazonium salts
2. Reaction of Benzenediazonium chloride
Diazonium salts of aromatic amines are very useful as
intermediates to other compounds.
Aromatic diazonium salts are only stable at very low
temperatures (zero degrees and below), warming these
salts initiates decomposition into highly reactive cations.
These cations can react with any anion present in
solution to form a variety of compounds. Figure
illustrates the diversity of the reactions.
33
