Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl group.

1. Chapter 9 Amines and Other
Nitrogen compounds

2. Introduction
 Amines and their derivatives are important
nitrogen compounds.
 They are used as intermediates in organic
reactions, and they are found in many
biological systems.
 They amino acids that make up the proteins,
the purine and pyrimidine bases that make
up DNA and RNA, the molecules of the
genetic code, the mood-controlling drugs
used in the treatment of mental illness.

3. Content:
 Structure and classification
 Nomenclature
 Physical properties
 Familiar reactions
 Visual test
 Conversion of diazonium salts
 Azo compounds
 Biogenic amines

4. 9.1 Structure and classification
 Amines are thought of being derived from
NH3 by replacement of 1, 2 or 3 Hs by alkyl
or aryl groups.
Aliphatic amines
Aromatic amines
Ammonia Aliphatic amines
H H H
H－N－H CH3－N－H CH3－N－CH3

5. Aliphatic amines
Aromatic amines
9.1 Structure and classification
H
CH3－N－CH2－
H H
－N－H －N－CH3

6.  Classification
Primary (10) Secondary (20) Tertiary (30)
9.1 Structure and classification
H H R
R－N－H R－N－R R－N－R
R
R－N－R
R
+
Quaternary
ammonium salt

7.  Difference between classification of
amines and alcohols
9.1 Structure and classification
 Alcohols:
Classified according to the
kind of C atom to which the
OH group is attached.
 Amines
According to the number of
hydrocarbon groups
attached to the N atom.
CH3
CH3－C－CH3
OH
30 alcohol
CH3
CH3－C－CH3
NH2
10 amine

8. 9.2 Nomenclature
 Common names
 Used for simple aliphatic amines
Substituents (alphabetically) + amine
CH3NH2 CH3NHCH2CH3 －CH2NHCH3
Methylamine Ethylmethylamine Benzylmethylamine
CH(CH3)2
CH3NHCH3 CH3CH2NCH2CH3
Dimethylamine Diethylisopropylamine

9.  IUPAC names
the - NH2 is considered as the substituent.
9.2 Nomenclature
NH2 CH3
CH3CH2CHCH2CHCH3 H2NCH2CH2CH2CH2NH2
6 5 4 3 2 1
4-Amino-2-methylhexane 1,4-Diaminobutane
NH2
H2NCH2CH2CH2OH CH3CHCOOH
3-Amino-1-propanol 2-Aminopropanoic acid
Substituent:
-X;
-OR;
-NH2

10.  Amine salts
substituent + ammonium + anion
9.2 Nomenclature
CH3
CH3－N－CH3
CH3
+
Cl -
H
CH3－N－CH2CH3
H
+
Br -
Tetramethylammonium Ethylmethylammonium
chloride bromide

11.  Aromatic amines
named as derivatives of aniline
9.2 Nomenclature
NH2 NH2 NH2 NH2
NO2
OH
CH3
Aniline o-Nitroaniline m-Hydroxyaniline
p-methylaniline
NHCH2CH3
O2N
p-Nitro-N-ethylaniline

12. 9.3 Physical properties
 Low-molecular-weight aliphatic amines
Colorless gases that are soluble in water, and
have unpleasant odors
 Amines containing 4 to 11 C atoms
They are liquids and have unpleasant odors.
 Higher-molecular-weight amines
They are solids.

13.  Hydrogen bonding
10 and 20 amines possess a polar N－H bond,
so they can form intermolecular hydrogen
bonding.
Therefore their B.P. are higher than those of
alkanes of comparable molecular weight, but
lower than those of alcohols of similar m. w.
9.3 Physical properties H H
R－N－H R－N－R
H H
R－N－H ---- N－R
H
R H
R－N－H ---- N－R
R

14.  Hydrogen bonding
Tertiary amines are also polar compounds,
but cannot form intermolecular hydrogen
bonding.
So they have lower B.P. than 10 and 20 amines
of identical molecular weights. But higher
than those of alkanes of similar molecular
weights.
9.3 Physical properties CH3
CH3－N－CH3
30 amine

15. 9.4 Familiar reactions
 Basicity and salt formation
 Alkylation
 Amide formation

16. 9.4.1 Basicity and salt formation
 Amines are bases because N atom has a non-
bonded pair of electrons, which could be
donated to an acid’s proton to form an
ammonium salt.
 The base strength depends on the degree of
availability of the non-bonded electron pair;
the more available the electron pair on N is
to an acid, the stronger the base.
H
RNH2 + HX RNH2 X-
+

17.  Quantitatively, the strength of a base is
expressed by its basicity constant, Kb.
 The large value of Kb, the stronger the base.
Kb < 10-2 weak base
Ammonia NH3 (Kb = 1.8×10-5)
Methylamine CH3NH2 (Kb = 4.4×10-4)
Basicity: CH3NH2 > NH3
9.4.1 Basicity and salt formation

18.  An more convenient method :
pKb = - log Kb
The larger the pKb, the weaker the base.
pKb
Dimethylamine (CH3)2NH 3.29
Methylamine CH3NH2 3.36
Basicity: (CH3)2NH > CH3NH2
9.4.1 Basicity and salt formation

19.  Alkyl groups are electron donors, they can
increase the electron density about the N
atom, so the non-bonded electron pairs are
made more available for reaction with an acid.
Basicity: Aliphatic amines > aromatic amines
(CH3)2NH > CH3NH2 > NH3
> C6H5NH2 > o-Nitroaniline
9.4.1 Basicity and salt formation

20.  Summarize
1. Electron-releasing groups on the N atom of
amines increase the basicity of amines, and
electron-withdrawing groups decrease the
basicity.
2. Resonance effects in aromatic amines lower
their basicity.
3. Electron-withdrawing groups on the
aromatic ring lower the basicity even more.
9.4.1 Basicity and salt formation

21.  Salt formation
Amines + acids ammonium salts
NH4
+ salts are soluble in water but insoluble
in organic solvents(ethyl ether).
Thus it is possible to separate an amine from
non-basic organic compounds.
9.4.1 Basicity and salt formation
RNH2 RNH3Cl RNH3Cl RNH2
RCOR RCOR RCOR
(1)Ether
(2)aq HCl
aq phase
ether
phase
+ －
separate
+ － OH-

22. 9.4.2 Alkylation
 Amines + 10 RX
+ 20 RX
This reaction depend on the electron pair of N.
Alkylated amines
RNH2 + R－X R2NH2 X- R2NH
+ NaOH
R2NH + R－X R3NH X- R3N
+ NaOH
R3N + R－X R4N X-
+
20 Amine
30 Amine
Quaternary
ammonium salt

23.  Two quaternary ammonium salts of
biological significance:
(CH3)3NCH2CH2OHCl－ Choline
O
(CH3)3NCH2CH2OCCH3Cl－ Acetylcholine
9.4.2 Alkylation
+
+

24. 9.4.3 Amide formation
 O O
RC－Cl + H2NR’ RC－NHR’ + HCl
O O
RC－Cl + HNR’2 RC－NR’2 + HCl
O
RC－Cl + NR’3 No reaction
10 amine N-substitued amide
20 amine N,N-Disubstitued amide
30 amine

25.  Sulfonamides
10 or 20 amines + RSO2Cl sulfonamides
9.4.3 Amide formation
O O
R－S－Cl + H2NR’ R－S－NHR’ + HCl
O O
Sulfonyl chloride Sulfonamide

26. 9.5 Visual test for amines
 Differentiate the three classes of amines
NaNO2 + HCl HNO2 + NaCl
Nitrous acid
RNH2 + HNO2 N2 + Mixture of products
10 amine
R2NH + HNO2 R2N－N=O + H2O
20 amine nitrosamine
R3N + NaNO2 R3NH+Cl-
30 amine Ammonium salt
0 ~ 5℃
0 ~ 5℃
cold dil
HCl
No visible sign
of reaction

27. 9.5 Visual test for amines
 Aromatic amines
RNH2 + HNO2 N2 + Mixture of products
10 amine
NH2 + NaNO2 N2
+Cl-
HCl
0℃
Room temp
N2 + mixture of products
A diazonium salt
0 ~ 5℃
10 aromatic amine

28.  Summary:
10 aliphatic amine N2 is produced at 0℃
20 aliphatic amine Oily yellow layer separates from
aqueous layer
30 aliphatic amine No visible reaction
10 aromatic amine N2 is formed at room temperature
9.5 Visual test for amines

29. 9.6 Conversion of diazonium salts
F
OH
Cl
Br
I
CN
H
OCH3
N2
+
H2O
Cu2Br2
H3PO2
KI

30.  Diazonium salt + phenols azo compound
(or aromatic amines)
9.7 Azo compounds
N2
+Cl- + OH N=N OH
N2
+Cl- + NHCH3
N=N NHCH3
An azo compound, yellow
An azo compound, orange

31. 9.8 Biogenic amines
 Many of the drugs used by many Americans
for pleasure more often than for health, such
as benzedrine, methedrine, marijuana, lsd,
barbiturates, and other addictive drugs, are
amines or amine derivatives.
 They affect the nervous system and alter
perception and natural responses to the
environment. Drugs that have the effect of
changing a person’s mental or emotional
state are called psychomimetic drugs.