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Amines and Amides
Amines are the organic chemistry equivalents of NH3, alkyl groups take
the place of one, two or three hydrogens…
H-N-H
R-N-H
R-N-H
R-N-R’
H
ammonia
H
1 amine
R’
2 amine
R’’
3 amine
ry
ry
ry
1. Nomenclature:
Lower 1ry’s use suffix “amine” e.g methylamine, ethylamine.
Simple 2ry and 3ry use prefix “di” and “tri” e.g dimethylamine and
triethylamine.
NB: alkyl groups in 2ry and 3ry need not be the same!!
Higher
homologues
use
CH3CH(NH2)CH2CH2CH3
prefix
“amino”
e.g
2-aminopentane,
Some diamines have very derivative names indicating where they are
found e.g putrescine [H2N(CH2)4NH2] and cadaverine [H2N(CH2)5NH2]!
2. Key properties:
If it smells of “fish” or “rotting flesh” chances are you have an
amine!!
Amines behave in a similar way to NH3 but their behaviour is modified by
the alkyl groups.
2.1 Bonding: cf NH3
..
H-N-H
H
Lone pair is responsible for:
Solubility in H2O / base properties /ligand behaviour / nucleophiles props
2.2 Solubility. of Amines
Like NH3 amines can H-bond, because of this small amines are sol. in
water. Large amines disrupt H-bonding in water.
2.3 Amines as bases:
Lone pair on N can take part in dative covalent bonds. When electron
pair is donated to H+, ammonia acts as a proton acceptor i.e a base.
NH3(aq) + H2O(l)
Similarly with amines:
CH3CH2CH2NH2(aq) + H2O(l)
NH4+(aq) + OH-(aq)
Ammonium
ion
CH3CH2CH2NH3+(aq) + OH-(aq)
The presence of the OH-(aq) ion means that aqueous solns of amines are
ALKALINE.
Like NH3 amines react with acids, H3O+ ion is more effective proton
donor than H2O, therefore reaction goes to completion therefore amines
lose their smell (thank goodness!!)
NH2
(aq)
+ H3O+(aq)
NH3
+
(aq)
+ H2O(l)
2.4 Amines as ligands
Lone pair strikes again ! if NH3 is added to a soln of CuSO4 we get the
following complex: [Cu(NH3)4(H2O)2]2+(aq),
If butylamine is added instead we would obtain [Cu(C4H9NH2)4(H2O)2]2+(aq)
2.5 Amines as Nucleophiles:
R-Cl + NH3
R-NH3+Cl
R-NH2 + H+ + Cl-
Product is an amine, but amines are nucleophiles. So amijes undergo
substitution reactions with halogenoalkanes to form 2ry and 3ry amines!
+
H
R’-Cl + R-NH2
R’-N-H
R’-N-H Cl-
+ H+ + Cl-
R
2 amine
R
ry
Similar reaction if use an acyl chloride [RCOCl]
R-C
O
Cl
+ NH3
R-C
O
NH2
primary amide
+ HCl
With a 1ry amine:
R-C
O
Cl
+ R’-NH2
R-C
O
N-R’
+ HCl
H
2 amide
ry
Amides:
Contain functional group
R-C
O
NH2
-C
O
N-
Amide group or “peptide link”
H
1ry amides are formed by reaction of ammonia with an acyl
chloride (see above) named after corresponding
carboxylic acid:
CH3-C
O
CH3-C
OH
O
CH3-C
Cl
NH2
ethanamide
ethanoyl chloride
ethanoic acid
O
Hydrolysis of amides:
This reaction involves breaking the C-N bond at the carbonyl carbon.
a. acid hydrolysis: forms “ammonium” ion and carboxylic acid
b. alkaline hydrolysis: forms carboxylate ion and amine
Condensation Polymers
As we have seen –COOH (and COCl) react with amines to form 2ry amides
R-C
O
OH
+ R’-NH2
R-C
O
+ H2 O
N-R’
H
2 amide
ry
A Condensation reaction is one in which two molecules combine to form a
larger molecule with the elimination of a small molecule.
-C
O
O
H
+ H2 O
-C-N-
N+
OH H
H
2ry amide
If we react a di-acid with a diamine we get condensation polymerisation
with the formation of polyamides or nylons.
O
O
O
O
-C-
-C-NH
-N-CH
-C-NH
-NH