Transcript Slide 1

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TYPES OF AMINES
ammonia
1y
H
H
N
amine
2y
R
H
H
H
N
amine
3y
R
R
amine
N
R
N
H
R
CH2CH3
CH2CH3
CH3
H
CH3
N
H
R
R
H
N
4y ammonium
salts
CH3
N
R
N
R
X
CH3
CH3
CH3
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R
N
CH3
CH3
Cl
NOT AMINES
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TYPES OF AMINES
ammonia
1y
H
H
N
amine
2y
R
H
H
H
N
amine
3y
R
R
amine
N
R
N
H
R
CH2CH3
CH2CH3
CH3
H
ethylamine
CH3
R
R
H
N
4y ammonium
salts
CH3
N
N
R
N
R
ethylmethylamine
trimethylamine
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X
CH3
CH3
CH3
H
R
N
CH3
CH3
Cl
tetramethylammonium
chloride
NOT AMINES
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TYPES OF AMINES
• There is some H-bonding between 1y and 2y
amines.
• Quaternary ammonium salts are not amines.
• Aromatic amines have the N joined to the benzene
ring, e.g. phenylamine.
NH2
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BASE STRENGTH OF AMINES
• Amines are weak bases.
• Lone pair on N can accept a proton.
R
H
N
H
+
H2O
H
R
+
N H
+
-
OH
H
• Base strength depends on how well N lone pair
can accept H+.
• The higher the electron density of the N lone pair,
the stronger the base.
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BASE STRENGTH OF AMINES
methylamine + nitric acid
CH3
H
N
CH3
+
HNO3
H
H
N
H
NO3
H
diethylamine + sulphuric acid
CH2CH3
CH2CH3
2
2 CH2CH3
N
+
H2SO4
CH3CH2
H
N
2
H
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SO4
H
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BASE STRENGTH OF AMINES
• Alkyl groups push electrons towards the N better
than H (remember carbocation stability).
H
H
C
H
R
H
C
R
R
H
C
R
R
H
C
R
Stability increases
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BASE STRENGTH OF AMINES
• Alkyl groups push electrons towards the N better
than H (remember carbocation stability).
H
H
N
H
R
H
N
H
R
R
N
R
R
H
N
R
Base strength increases
3y > 2y > 1y > NH3
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BASE STRENGTH OF AMINES
• In aromatic amines, the N lone pair is partially
delocalised into the benzene ring, lowering the
base strength.
3y > 2y > 1y > NH3 > aromatic
BASE STRENGTH OF AMINES
methylamine
diethylamine
CH3
H
CH2CH3
N
CH3CH2
H
N
H
Stronger base = diethylamine
• 2Y compared to 1Y
• Diethylamine has greater electron density on N lone pair
• Diethylamine has greater ability to accept H+
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BASE STRENGTH OF AMINES
propylamine
phenylamine
NH2
CH2CH2CH3
H
N
H
Stronger base = propylamine
• Lone pair on phenylamine N is partially delocalised into benzene
ring
• Propylamine has greater electron density on N lone pair
• Propylamine has greater ability to accept H+
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BASE STRENGTH OF AMINES
ammonia
phenylmethylamine
H
H
CH2
NH2
N
H
Stronger base = phenylmethylamine
• 1Y compared to ammonia
• Phenylmethylamine has greater electron density on N
lone pair
• Phenylmethylamine has greater ability to accept H+
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BASE STRENGTH OF AMINES
ammonia
cyclohexylamine
H
H
NH2
N
H
Stronger base = cyclohexylamine
• 1Y compared to ammonia
• Cyclohexylamine has greater electron density on N lone
pair
• Cyclohexylamine has greater ability to accept H+
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NUCLEOPHILIC SUBSTITUTION
• Met in Module 3 (reaction of haloalkanes + NH3).
• Lone pair on N can attack + C of haloalkane.
C
X
C
+
NH2
X
-
H
NH3
NH3
C
NH2
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NUCLEOPHILIC SUBSTITUTION
• H on N is swapped by R from haloalkane.
• Product also has lone pair on N so product reacts
further.
H
R
RX
H
N
H
R
RX
H
N
H
R
RX
R
N
H
R
RX
R
N
R
R
N
R
R
X
• To get mainly 1y amine use XS NH3.
• To get mainly 4y ammonium salt use XS RX.
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NUCLEOPHILIC SUBSTITUTION
methylamine + chloroethane
CH3
CH3CH2
(products & 1st mechanism)
CH3
N
CH3CH2
H
CH3
N
CH3CH2
N
CH2CH3
CH2CH3 Cl
CH2CH3
H
CH3
C
CH3
H
CH3CH2
Cl
CH3
- Cl
N
CH3CH2
H
N
CH2CH3
H
CH3
CH3CH2
-H
N
CH3
H
CH3CH2
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N
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CH2CH3
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NUCLEOPHILIC SUBSTITUTION
diethylamine + 2-bromopropane
CH2CH3
CH3CH2
CH3
N
CH
CH3
(products)
CH2CH3
CH3CH2
CH3
N
CH
CH
CH3
CH3
Br
CH3
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Soaps, e.g.
O
C
Na
O
long alkyl tail
(hydrophobic)
dissolves grease
ionic head
(hydrophylic)
dissolves in water
Detergents, e.g.
O
O
S
O
Na
O
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4y ammonium salts
• Ones with some long chain alkyl groups can be
used as cationic surfactants.
• Often used in fabric softener as many fabrics have
–ve charge on surface.
N
e.g. (CH3)2N[(CH2)16CH3]2+ Cl-
Cl
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MAKING ALIPHATIC 1y AMINES
1 – Reaction of NH3 with haloalkanes
• Need to separate mixture of products.
2 – Reduction of nitrile compounds
aqueous ethanol
R
R
or
X
C
+
N
KCN
+
R
4 [H]
+
KX
C
N
R
CH2
NH2
R
CH2
NH2
LiAlH4
Ni
R
C
N
+
2 H2
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MAKING ALIPHATIC 1y AMINES
Butylamine
a)
CH3CH2CH2CH2Cl + 2 NH3 → CH3CH2CH2CH2NH2 + NH4Cl
b)
CH3CH2CH2Cl + KCN → CH3CH2CH2CN + KCl
CH3CH2CH2CN + 4 [H] → CH3CH2CH2CH2NH2
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MAKING AROMATIC AMINES
NO2
NH2
Sn & HCl
+
6 [H]
+
2 H2O
followed
by NaOH
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