MIND MAP CHAPTER 11 AMINES

MIND MAP
AMINES

Prepared by: NFAG, KMPh

PHYSICAL PROPERTIES OF AMINES

BOILING POINT SOLUBILITY

Primary amines vs secondary amines vs tertiary

HOH HOH HOH

R-N-H H R-N-H H R-N-R
O O R

HH 30 amines

HOH RH

10 amines 20 amines 30 amines 10 amines 20 amines

Boiling point of amines increase as:

1) Molecular weight increases • All amines can form hydrogen bond in water.
2) Number of hydrogen bond increases (isomeric amines) •  all amines are soluble in water.

Formation of hydrogen bond: 10 amines > 20 amines, while Two factors that affect the solubility of amines:
30 amines do not form hydrogen bond with its molecules.
1) Number of hydrogen bond with water
Amines vs alcohol, carbonyl compound, haloalkane &
carboxylic acid. • Formation of hydrogen bond with water:
tertiary amine < secondary amine < primary amine.
• Amines, alcohol & carboxylic acid can form strong hydrogen
• Solubility increase as the number of hydrogen bond
bond. with water increase.

• Amines have weaker hydrogen bond compared to alcohol & 2) Size of hydrophobic area

carboxylic acid because nitrogen atom is less electronegative • If the amines form the same number of hydrogen bond
with water, consider size of hydrophobic area.
than oxygen. Amines have lower boiling point compared to
• Solubility of amine decrease as size of hydrophobic area
alcohol & carboxylic acid due to weaker hydrogen bond. increase.

• Carboxylic acid can form stable hydrogen bonded dimers

and the highest boiling point among all.

• Haloalkane & carbonyl compound do not form hydrogen

bond with its molecules. They only have weak van der Waals

forces. OO

R-X R-X R-C-R R-C-R

(Haloalkane) (Carbonyl compound)

Prepared by: NFAG, KMPh

BASICITY OF AMINES

Inductive effect Resonance effect

i) Electron donating group (EDG) • Aromatic amines are less basic than aliphatic amines.

• EDG increase electron density on the nitrogen atom of • The lone pair electrons of nitrogen atom are delocalized into

amine and stabilize alkylammonium ion. the aromatic ring, and less available for bonding to H+.

•  amines are easier to accept proton / H+. • In resonance terms, arylamines are stabilized relative to aryl

• Example: alkyl group ammonium ion because of the four resonance structures.

ii) Electron withdrawing group (EWG)
• EWG reduce electron density on the nitrogen atom
of amine destabilize alkylammonium ion.
•  amines are more difficult to accept proton / H+.
• Example: halogen, NO2

Basicity of Amines Basicity of Amines
(Gaseous Phase) (Aqueous Phase)

(CH3)3N > (CH3)2NH > CH3NH2 > NH3 (CH3)2NH > CH3NH2 > (CH3)3N > NH 3

• 3°amine > 2° amine > 1° amine > ammonia • 2° amine > 1° amine > 3°amine > ammonia
• For 3°amine, there are more alkyl groups attached to the • In water, the ammonium salts of 1° amines & 2° amines

nitrogen atom. undergo solvation effects (due to hydrogen bonding) to a
• Alkyl group act as electron donating group (EDG) much greater degree than ammonium salts of 3°amines (due
• Basicity increase as number of EDG increase. to stearic effect)
• The electron density is greater around the nitrogen atom • These solvation effects increase the electron density on the
amine nitrogen to a greater degree than the inductive effect
making it easier for protonation and stabilize of alkyl groups.
alkylammonium ion. • 2° amine is more basic than 1° amine because it has more
• So the basicity increases. EDG, but 3°amine is less basic than 2° amine & 1° amine
due to steric effect, which hindered the N atom to accept H+

Prepared by: NFAG, KMPh

CHEMICAL PROPERTIES OF AMINES

PREPARATION OF AMINES REACTIONS OF AMINES

1) Reduction of nitro compounds (aromatic amines) 1) Hinsberg’s Test
with Zn / H+ or SnCl2 / H+ or Fe / H+
• To differentiate 10, 20 & 30 amines.
NO2 NH2 • Two steps:

Zn / H+ 1) Reaction with benzene sulphonyl chlorine in excess
aqueous KOH

2) Reaction with acid

2) Reduction of nitriles using LiAlH4 followed by 2) Nitrous acid test
H3O+ or NaBH4 in methanol or H2/catalyst • is unstable and is prepared in-situ by the reaction of dilute
(10 aliphatic amines)
acid (HCl or H2SO4) with sodium nitrite in cold medium.
R- C N LiAlH4/H3O+ R- CH2NH2
NaNO2 (s) + HCl (aq) → NaCl (aq) + HNO2 (aq)

• is used to distinguish between aliphatic amines and aromatic

amines. It can also distinguish 10, 20 & 30 amines

3) Reductions of amides using LiAlH4 followed by 3) Coupling Reaction
H2O (10, 20 and 30 amines) • Diazonium salt (from nitrous acid test) are particularly useful

LiAlH4/H2O R-CH2NH2 in the synthesis of other aromatic compounds because the
diazonium group can be replaced by almost any nucleophile.
R-CONH2
• N2 gas is released when nucleophilic substitution takes place.

4) Hoffmann’s degradation of primary amides 4) Identification Test of Aniline
(10 alkyl and aryl amines)
• The presence of aniline can be identified by using bromine water.
R-CONH2 Br2, NaOH R-NH2 + CO2
H2O Aniline reacts with bromine water to form white precipitate.

• NH2 is ortho-para director (Br will substitute H atom at

position ortho and para)

NH2 NH2

Br Br

+ Br2 H2O

Br

white precipitate

Prepared by: NFAG, KMPh

REACTIONS OF AMINES
1) HINSBERG’S TEST

Amines Primary Secondary Tertiary

Structure R-NH2 R-NH R-N-R
Reaction with benzene R R
sulphonyl chloride in
R-NH2 + O R O R O
excess aq.KOH S-Cl R-NH + R-N-R + S-Cl
O O O
Reaction with HCl aq.KOH
aq.KOH O aq.KOH
S-N-R R
O OR
- R-N-R (no reaction)

S-N-R
O K+

Observation: Observation: Observation:
clear solution Precipitate formed Two layers solution

O Observation: R
- Precipitate remains R-N-R + HCl

S-N-R
O K+

HCl R
R-N+-R
O
S-NH-R Cl-
O
Observation:
Observation: Clear solution formed
Precipitate formed

Prepared by: NFAG, KMPh

REACTIONS OF AMINES

2) NITROUS ACID TEST

Class of Aliphatic Aromatic
amines amines amines

Primary R-NH2 + NaNO2 HCl R-N2+Cl- NH2 N2+
0-50C
diazonium + NaNO2 diazonium salt:
salt:unstable HCl stable
0-50C

R+ + N2
carbocation N2 gas released

-H+ + H20 + Cl- Diazonium salt in aromatic amine is stable, therefore no N2
alkene alcohol haloalkane gas formed. It will undergo coupling reaction

Diazonium salt in aliphatic amine is unstable. It will Observation: no bubbles formed
form carbocation and release N2 gas.

Observation: bubbles formed

Secondary R-NH + NaNO2 HCl R-N-NO -NH + NaNO2 HCl -N-NO
R 0-50C R 0-50C
R R
yellow oil yellow oil

Observation: Yellow oil formed Observation: Yellow oil formed

Tertiary RR R-N-R R-N-R
R-NH+Cl- + R-N+ =OCl + NaNO2
R-N-R + NaNO2 HCl HCl
R 0 - 5 0C RR 0-50C

clear solution formed NO
precipitate

Observation: Clear solution formed Observation: Precipitate formed

Prepared by: NFAG, KMPh

REACTIONS OF AMINES
3) COUPLING REACTION

H2O OH
CuCl
CuBr Cl
Kl
N2+ Br
OH I
Coupling reaction: CH3-N-CH3
Formation of dye N=N OH *Syllabus
N=N orange dye

N-CH3
CH3
yellow dye

Prepared by: NFAG, KMPh

REACTIONS OF PRIMARY AMINES

CH3CH3 Cl2,uv O
CH3CH2Cl CH3CH2CNH2
Nitrous acid test 10 aromatic
amines produce benzene CH3CH2Cl
diazonium salt. It will undergoes
coupling reaction H2O Br2 , NaOH

NH3 NH3

CH3CH2Cl + N2 NaNO2,HCl CH3CH2NH2 NaBH 4 CH3CN
+ 0-5oC CH3OH

CH2=CH2 + CH3CH2OH @ i) LiAlH 4 ii) H3O+ @ H2,Pt
Bubbles of N2 gas formed

*Chemical Test : Nitrous acid test O O CH3Cl
CH3CH
O S Cl HCl
- CH3CH2NHCH3
O
S KN+CH2CH3 KOH
O
Water soluble salt - Clear solution

HCl NHCH2CH3 C H3C H2NH 3+C l -
O CH3CH

S NCH2CH3
H

O
Precipitate formed

*Chemical Test : Hinsberg’s test

Prepared by: NFAG, KMPh

REACTIONS OF SECONDARY AMINES

CH3CH3

Cl2,uv O

CH3CH2CNHCH3

CH3CH2Cl CH3CH2Cl

H2O Br2 , NaOH

NH2CH3 CH3NH2

CH3 NaNO2,HCl CH3CH2NHCH3 NaBH 4
CH3CH2N-N=O 0-5oC CH3OH

Yellow oil formed O @ i) LiAlH 4 ii) H3O+ @ H2,Pt

*Chemical Test : Nitrous acid test S Cl O CH3Cl
HCl
O O CH3CH
S NCH2CH3 CH3CH2NCH3
O CH3 KOH CH3
Precipitate formed

HCl CH3CH2NH 2+Cl -
No reaction CH3

Precipitate remains

*Chemical Test : Hinsberg’s test

Prepared by: NFAG, KMPh

REACTIONS OF TERTIARY AMINES

CH3CH3 Cl2,uv O CH3CH2Cl
CH3CH2Cl CH3CH2CN(CH3)2
Nitrous acid test 30 aromatic
amines. N=O replace with H at H2O Br2 , NaOH
para position & precipitate form

CH3 CH3NHCH3 CH3NHCH3
CH3CH2NH+Cl -
CH3 NaNO2,HCl CH3CH2N(CH3)2 NaBH 4
CH3CH2N+OCl - + CH3 0-5oC CH3OH

CH3

Clear solution formed O @ i) LiAlH 4 ii) H3O+ @ H2,Pt

*Chemical Test : Nitrous acid test S Cl O CH3Cl

No reaction O CH3CH HCl
Two layer solution (insoluble)
KOH

HCl CH3
CH3CH2NH+Cl -
O H+Cl-
S NCH2CH3 CH3
O CH3
Water soluble salt Prepared by: NFAG, KMPh
Clear solution formed

*Chemical Test : Hinsberg’s test

GOOD
LUCK!

Prepared by: NFAG, KMPh