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AMINES
Derivatives of ammonia…
Properties Central N atom - sp3 hybridized
RNR bond angle < 109028’
because of lone pair bond pair
repulsion
Shape of the molecule-pyramidal
Basic in nature , bearing one lone
pair on N. Forms salts with acids
e- donating group
Can form single, double & triple
bond with C
NR
R
R
Classification
NH3 NH2R NHR2 NR3
NHRR' NRR'R''
ammonia 10 - amines 20 - amines 30 - amines
Simple amines
Mixed amines
20 - amines 30 - amines
R = alkyl/ aryl group
Nomenclature Common name IUPAC name
Rule : alkyl + amine = alkylamine Rule : alkane + amines = alkanamines
CH3NH2 Methylamine Methanamine
Isopropylamine Propan-2-amine
NH2-(CH2)6-NH2 Hexamethylenedimine Hexane-1,6-diamine (e –retained)
Trimethylamine N,N-Dimethylmethanamine
N,N-Dimethylethylamine N,N-Dimethylethanamine (one with more number of C atoms is given preference)
Allylamine Prop-2-en-1-amine (not prop-2-ene-1-amine)
Aniline Benzenamine
P-Bromoaniline 4-Bromobenzenamine
H2N
N
N
H2N
NH2
NH2Br
Physical properties
N-H bond is polar, because, electronegativity of N > H
Amines are comparable with alcohols in their physical properties
Since the electronegativity of N < O -----> N-H bond is less polar compared to O-H bond, implying amines are less polar compared to alcohols
So, amines are less effective in forming H-bond than alcohols.
So, boiling point (BP) of amines are less then alcohols
Methylamine Methanol
BP of amines < BP of alcohols
Comparing Between Amines
NR H
H
N RH
H
N
R
H
H N
H
H
R
10 - amines
NR H
R
N
R
R
H N
H
R
R
20 - amines
NR R
R
30 - amines
(no H-bond)
Extent of H-bonding
10 > 20 > 30
Boiling Point
n-butylamine
diethylamine
dimethylethylamine
2-methylbutane butanol
HONNH
H2N
BP
< < < <
Basic character of amines
Basic and nucleophilic because of the presence of lone pair on N
As it is basic, Amines + Acids ------> salts. This property can be used to purify amines
CH3 NH2Separate
NH3 ClCH3
HCl in H2O
soluble in water
insoluble in water
Separating funnel water layer containsamines
NH2
H2OOHR NH3R +
Kb pKb ==NH3R OH
NH2R- log Kb
pKb
strength of base
Structure-Basicity relationship of amines
A. Alkanamines >< ammonia
More basic an amine means,
More easily it denotes the lone pair / formed ammonium ion is more stabilized in the environment
NH2R NH3RH++
ease of donation of stability
N
R
H
H
10 - amines
N
R
H
H
20 - amines
NR H
R
30 - amines
Inductive effect
NH3 < 10 < 20 < 30
Basic character
HaminesH+
R
R
>
>
> >
> >
ingas
phase
N
H
H
HH
ammonia
N
R
H
H
10 - amines
N
R
H
H
20 - amines
NR H
R
30 - amines
Inductive effect
10 < 20 < 30
Basic character
H
amines
H+/H2O
R
R
>
>
> >
>
>
in aqueous phase
OH2
OH2
H2O
OH2
OH2 OH2
Extent of H-bonding
10 > 20 > 30
stability of ammonium ion& basic character
contradicting +steric effect depending on the
size of R, allowing H+ to reach
lone pair
Above three factors together decide the basic character of amines.Whatever dominates, will decide the property of an amine
(C2H5)2NH > (C2H5)3N > C2H5NH2 > NH3(CH3)2NH > CH3NH2 > (CH3)3N > NH3
+
B. Arylamines >< ammonia
H+
NH2 NH2 NH2 NH2 NH2
NH3 NH3
> 5 resonance structures, more stabilized
2 resonance structures, less stabilized
stab
i litydec
reas
es
* So, pKb value for aniline is high
* Means, aniline is less basic
* observed that it is less basic
than ammonia
> lone pair on N is less available becauseof delocalization into the ring
NH2 NH2 NH2 NH2
NO2
OCH3
arrange in the increasingorder of basic character
1 2 3 4
NH2
NO2
NH2 NH2NH2
OCH3
< < <
3. From nitriles
4. From amides
C NR
H+ or OH-
H2Oacid or basehydrolysis
Preparation of Amines
CNH2R
OH2
CNH2R
H2C
NH2H3CC
NH2H3C
O
C NH3COR
10-Amines
nitro compd1. Fromnitro compd
NO2NH2 NO2
H2/Pd (Ni, Pt)
Ethanol
Sn/HCl
Fe/HCl
FeCl2
hydrolysed
Fe(OH)3
or
(Regeneration of catalyst)
10-Amines
5. Gabriel phthalimide synthesis
O
O
N
O
O
NK
O
O
N
O
O
H R
ONa
ONa+R-NH2
KOH RX
NaOH(aq)
10-Amines
phthalimide
6. Hof fmann bromamide degradation reaction
CNH2R
O
RCONH2 + Br2 + 4NaOH RNH2 + Na2CO3 + 2NaBr + 2H2O
Br2 OH-
-Br-
RNH2Na2CO3
CNH
R
O
Br-HBr CNR
O
Br CNR
O
Br-H+
O C N R
H2O+
R'OHCNH
R'
O
R Ex:(CH3CONH2 ------> CH3NH2)
Ex:
10-Amines
2. From alkyl halides
H3N NH3XR X R NaOH NH2R+ + H2O
Cleavage of R-X bond brought about by NH3 -----> Ammonolysis
+ NaX
RNH2 R2NH R3N R4NRX RX RX
10 20 30 ammonium salt
** Excess of NH3 gives 10 - amine as major product
** or else ammonolysis gives mixture of products
** RI > RBr > RCl order of reactivity
LiAlH4 or H2/Ni
1.LiAlH4
2. H2O
From nitriles
CNH2H3C
C NH3C
Hof fmann bromamide degradation
O
NH2H3C
H2
C NH2H3C
(2)
(1)
(2)
(2)
(no. of C atoms)(no. of C atoms)Reactants
(no. of C atoms)
>
>(3)
(2)
(3)
(3)NH2
O
NH2
NH2N
Hof fmann bromamide degradation to reduce the length of amine chain by 1 carbon
Reactions of Amines
benzenesulphonyl chloride/Hinsberg's reagent
with benzoyl chloride(not benzyl chloride)CH3
CH2
N HH CCl
O
S Cl
O
O
R C Cl
O
+ +
+
S
O
O
CH3
H2C
HN C
O
H3CH2C
HN
R C
O
CH3
H2C
HN
Base
N-Ethylbenzenesulphonamide N-Ethylbenzamide
-HCl
-HCl
-HCl
N-Ethylalkanamide
Base
Base
(acidic proton of e-
withdrawing groups)
+
acet
ican
hydr
ide
C CH3
O
C
H3C
OO
H2C CH3
C
H3C
ONH
H3C
COH
O
N-E
thyl
etha
nam
ide
** base used in the above reactions should be stronger than amines
** similarly, secondary amines react
** tertiary amines can not react in this f ashion as it does not have replaceble proton
** both aliphatic and aromatic amines reacts with the above set of reactants
+CH
Cl3
3KOH
+
H3CH2C N C
3H2O
3KCl+
isocyanides orcarbylamines
H+
NH2NH2 NH2 NH2
NH3NH3
ANILINIUM ION
** e--donating to the ring
** ortho, para directing for
the incoming E+
** e-- withdrawing from the ring
** meta directing for the
incoming E+
electrophile - E+
electrophile - E+
NH2
NH3
E
E
NH2
E
NH2
E
EE
(trisubstitution is because of the
high reactivity of NH2 for E+)
OOO
pyridine
HN
electrophile - E+
O
activity
reduction x
acetanilide
HN
O
HN
O
E
NH2
E
Electrophilic substitution on Aniline
Electrophilic substitution on Aniline
NH2HN
O + 3Br2
NH2
BrBr
Br
HN
O
Br
+ H2OBr2CH3CO2H
NH2
Br
H+ or
OH-
HN
O
NO2
H2N
NO2
H+ or
OH-
HNO 3, H 2
SO 4
288K
HNO3 , H
2 SO4288K
NH2
NO2
NH2 NH2
NO2
NO2
+ +
(51%) (47%)(2%)
H2SO4
NH3 HSO4 NH2 NH3
SO3H SO3
Zwitter ion
Friede
l-Cra
ftsre
actio
n
AlC
l 3
X
NH2
AlCl3
Lewis acid + base
Diazonium Salts Ar N N X
N N N N N N N N
diazonium salts formed by aliphatic primary amines are not stable and that of
aromatic primary amines are stable below 50 C because of the resonance structure
NaNO2 HCl+
HNO2
NH2
+
Cl
(0-50C)
Reactions
N N X
CuCl/HCl
CuBr/HBr
CuCN/KCN
PhCl
PhBr
PhCN
+ N2
N2
N2
+
+
Sandmeyer reaction
Gatterman reaction
Cu/HCl
Cu/HBr
PhCl
PhBr
+ N2
N2+
+
+
CuX
CuX
PhI
PhF
+ N2
N2+PhN NBF4-
KI
HBF4
H3PO2 + H2O
CH3CH2OH
PhH + N2 + H3PO3 + HCl
PhH + N2 + CH3CHO + HCl
H2O PhOH + N2 + HCl
NaNO2
Cu,NO2
involving displacement of N2involving retention of diazo group
OH
NH2
OH-
OH-
N N NH2
N N OH
Yellow dye
Orange dye