matriculation chemistry ( amines ) part 1
TRANSCRIPT
Amines are organic derivatives of ammonia, NH3
Introduction
Classification of Amines
Primary amines
Secondary amines
Tertiary amines
H N R'
R
H N H
R
R'' N R'
R
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.1
Classify the following amines:CH3CH2CH2NH2i.
CH3CH2 N H
CH3
ii.
CH3CH2 N CH3
CH3
iii.
N CH3
H
iv.
NH2v.
N CH3
CH2CH3
vi.
1°
2°
3°
2°
1°
3°
Aliphatic amines
Aromatic amines
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.1
IUPAC Nomenclature
In primary amines, the suffix ‘amine’ replaces the ‘e’ in the name of the parent alkane
CH3CH2CH2NH2i.3 2 1
Secondary and tertiary amines are named as N-substituted derivatives of primary amines
CH3CH2 N H
CH3
ii.2 1
2°
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.2
propaneaminee
N-methylethaneeamine
StructureStructure IUPAC NameIUPAC Name
MethanMethanamineamine
2-propan2-propanamineamine
CyclopentanCyclopentanamineamine
NN-methylpentan-methylpentanamineamine
N-ethyl-N-methyl N-ethyl-N-methyl ethanethanamineamine
CH3NH2
Examples:
CH3CH(NH2)CH3
NH2
CHCH2CH3
NHCH3
CH3CH2
N CH2CH3CH3CH2
CH3
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.2
When multiple functional groups are present and the –NH2 group does not take priority, it is named as an “amino” substituent
Examples:
NH2CH2COOH
IUPAC Nomenclature
2 1
OH
NH2
H2N 1
23
4
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.2
ethanoic acid2-amino
phenol2,4-diamino
IUPAC Nomenclature
Aromatic amines are named as derivatives of aniline
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.2
N-ethyl-N-methylanilineN-ethyl-N-methylaniline
Most primary amines are named as alkylamines
Common Name
CH3NH2
CH3CH2NH2
CH3CH2CH2NH2
StructureStructure IUPAC NameIUPAC Name
methylmethylamineamine
ethylethylamineamine
propylpropylamineamine
dimethyldimethylamineamine
methylethylmethylethylamineamineCH3NHCH2CH3
CH3NHCH3
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.2
(i) Boiling Point
Both primary and secondary amines can form intermolecular hydrogen bonds.
Tertiary amines cannot form hydrogen bonds to each other.
1° amines
CH3 N H
H
H
N CH3
H
hydrogen bonds
CH3 N H
CH3
H
N CH3
CH3
hydrogen bonds
2° amines
CH3 N CH3
CH3
CH3
N CH3
CH3
no hydrogen bond
3° amines
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
The table below compares the boiling points of isomeric amines.
AminesAmines ClassClass Relative Relative molecular molecular
massmass
Boliling Boliling points/points/oo
CC
CHCH33CHCH22CHCH22NHNH22 1°1° 5959 4949
CHCH33CHCH22--NHNH--
CHCH33
2°2° 5959 3737
CHCH33
|| CHCH33--NN-CH-CH33
3°3° 5959 44
Examples:
Boiling Point : CH3CH2CH2NH2 > CH3CH2NH(CH3) > (CH3)3N
(i) Boiling Point
Amines have higher boiling points than alkanes or haloalkanes of similar relative molecular mass due to
Amines have lower boiling points than alcohols or carboxylic acids of comparable molecular weight because
intermolecular intermolecular hydrogen bondinghydrogen bonding
(Nitrogen is less electronegative than the (Nitrogen is less electronegative than the Oxygen)Oxygen)
H- bond in RNHH- bond in RNH22 is weaker than the is weaker than the
H- bond in ROH and RCOOHH- bond in ROH and RCOOH
Example
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
The table below compares the boiling points of organic compounds of comparable relative molecular mass.
Amines Type Relative molecular
mass
Boliling points/oC
CH3CH2CH2CH3
butane
CH3CH2Cl
chloroethane
CH3CH2CH2NH2 1-propanamine
Examples:
58
64.5
59
-0.5
12.5
48.6
Alkane
Haloalkane
Amine
(i) Boiling Point
Amines have higher boiling points than alkanes or haloalkanes of similar relative molecular mass due to
Amines have lower boiling points than alcohols or carboxylic acids of comparable molecular weight because
intermolecular intermolecular hydrogen bondinghydrogen bonding
(Nitrogen is less electronegative than the (Nitrogen is less electronegative than the Oxygen)Oxygen)
H- bond in RNHH- bond in RNH22 is weaker than the is weaker than the
H- bond in ROH and RCOOHH- bond in ROH and RCOOH
Example
Example
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
The table below compares the boiling points of organic compounds of comparable relative molecular mass.
Amines Type Relative molecular
mass
Boiling points/oC
CH3CH2CH2CH3
butane
CH3CH2Cl
chloroethane
CH3CH2CH2NH2 1-propanamine
Examples:
Boiling Point : Carboxylic acid > Alcohol > Amine > Haloalkane > Alkane
58
64.5
59
60
60
-0.5
12.5
48.6
97.2
118
Alkane
Haloalkane
Amine
Alcohol
Carboxylic acid
CH3CH2CH2OH1-propanol
CH3COOHethanoic acid
CH3CH2CH2NH2
1-propanamine
(ii) Solubility
All amines including tertiary amines, are capable of forming hydrogen bonds with water molecules. Thus simple amines (amines of fewer than 5 carbons) are generally water soluble and dissolve to form basic aqueous solutions
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
Comparison the solubility between 1°,2° and 3°amine
R N H
H
O H
H
O H
H
O H
H
H
R N H
R
R N H
R
R N R
1o 2o 3o
R N H
R
O H
H
O H
H
R N R
R
O H
H
: hydrogen bonds
3 hydrogen bonds per a 1° amine
molecule
2 hydrogen bonds per a 2° amine
molecule
1 hydrogen bond per a 3° amine
molecule
The solubility : 3° < 2 ° < 1 °
Increasing solubility
Basicity An amine is a nucleophilenucleophile (a Lewis baseLewis base)
because its lone pair of non-bonding electrons on nitrogen
Ammonium ion Ammonia
+H N
H
H
H OH+
H N H
H
H
+ OH-
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
An alkyl group is electron donating group, and it stabilises the alkylammonium ion by dispersing its positive charge
Basicity – (i) Inductive effect
alkylammonium ion 1° Amine
Stabilised by the alkyl group Stronger base
+R N
H
H
H OH+
R N H
H
H
+ OH-
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
alkylammonium ion 1° Amine
+R N
H
H
H OH+
R N H
H
H
+ OH-
+R N
R
H
H OH+
OHR N H
R
H
+
alkylammonium ion 2° Amine
Strength as a base : Methyl, 1°, 2°
Increasing
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
Basicity – (ii) Resonance effect Aromatic amines (e.g., aniline) are
weaker bases than the corresponding aliphatic and cyclic amines
NH2NH2
Example:
Cyclohexylamine Aniline pKb = 3.36 pKb = 9.42
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
Aromatic amines are less basicBasicity – (ii) Resonance effect
The lone pair electrons of nitrogen atom are delocalised and overlapped with the aromatic ring π electrons system make it less available for bonding to H+
NH2 NH2 NH2 NH2
arylamines are stabilised due to the 4 resonanceresonance structures
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.3
Boiling pointBoiling point
Solubility Solubility
BasicityBasicity
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of nitro compounds
Aromatic amines can be prepared by reduction of nitro compounds using Zn/H+ or SnCl2/H+
Zn/H+ or
SnCl2/H+NO2 NH2
nitrobenzene anline
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
Aniline
Reduction of nitriles
Nitriles are reduced to primary amines by H2 / catalyst, LiAlH4 / H+ or NaBH4 / H+.
R C NH2
catalyst (Pt, Ni, Pd)RCH2NH2
Example :
OH
CH2NH2
OH
CN
1. LiAlH4
2. H+
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
Reduction of amides
Reduction of an amide using LiAlH4 / H+ or NaBH4 / H+ can yield a primary, secondary, or tertiary amine depending on the type of amide used
1. LiAlH4
2. H+R C NH2
O
R C NH2
H
H
+ H2O
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
Example :
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
1. LiAlH4
2. H+CH3 C NH2
O
Ethanamide (2o amide)
i.
CH3 C NH2
H
H
+ H2O
Ethanamine (1o amine)
1. NaBH4
2. H+
CH3 C NH
O
N-methylethanamide (2o amide)
ii.CH3
CH3 C NH
H
H
+ H2O
CH3
N-methylethanamine (2o amine)
Hoffmann’s degradation of amides
On warming a primary amide with bromine in solution of NaOH, a primary amine is formed.
This reaction is used to synthesise primary alkyl and aryl amines.
+ CO3
2-Br2 , NaOH
H2OR C NH2
O
amide amine
RNH2
The elimination of carbonyl group is shorteningshortening the length of carbon chain by one carbon atomone carbon atom.
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
Example :
CONH2 NH2
+ CO32-
Br2, OH-
H2O
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.4
Reduction of Reduction of nitro compoundnitro compound
Reduction of Reduction of nitrilesnitriles
Reduction of Reduction of amidesamides
Hoffmann’s Hoffmann’s degradation of degradation of
amidesamides
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Reaction with acyl chlorides
1° and 2° amines are acylated to form N-substituted amides
3° amines are not acylated because they do not have a H atom attached to N atom.
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
Formation of dye
+
1o amine
R N H
H
Cl C CH3
O
2 RNH3 Cl+R N C CH3
H O
2o amide
+ -
+
2o amine
R N H
R
Cl C CH3
O
2R2NH2 Cl+
R N C CH3
R O
3o amide
+ -
Reaction with acid anhydride
1° and 2° amines are acylated to form N-substituted amides
3° amines are not acylated because they do not have a H atom attached to N atom.
R N C CH3
OH
2o amide
+
1o amine
R N H
H
CH3 C O C CH 3
O O
acid anhydride
+ CH3COOH
+
2o amine
R N H
R
CH3 C O C CH 3
O O
acid anhydride
R N C CH3
OR
3o amide
+ CH3COOH
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Reaction with benzenesulphonyl chloride
Hinsberg’s test
This reaction is used to differentiate between 1°, 2° and 3° amines.
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Benzenesulphonyl chloride reacts with a 1° amine to form a white precipitate (N-substituted sulphonamides)
1°1° amineaminess
(-HCl)
Acidic hydrogen
NaOH
N-substituted sulphonamides have an acidic hydrogen, N-H.
Therefore, it dissolve in aqueous NaOH.
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
R-N-H
H
+ Cl-S-
O
O
OH-
1 amineo
O
O
-S-R-N
H
(precipitate)
N-substituted
benzenesulphonamides
O
O
-S-R-N
Na
water soluble salt(clear solution)
N,N-disubstituted sulphonamides do not have an acidic hydrogen, N-H.
2°2° amineaminess
(-HCl)
Therefore, it dissolve in aqueous NaOH.
Benzenesulphonyl chloride reacts with a 2° amines to form a white precipitate (N,N-disubstituted sulphonamide)
NaOHNo reaction
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
R-N-H
R'
+ Cl-S-
O
O
OH-
2 amineo
O
O
-S-R-N
R'
(precipitate)
N,N-disubstituted
benzenesulphonamides
3°3° amineaminess
3° amine do not gives visible reaction with benzenesulphonyl chloride
1° amines white precipitate clear solution
NaOH
Summary of Hinsberg’s test:
2° amines white precipitate do not dissolved
NaOH
3° amines do not give any visible change
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Reaction with nitrous acid (NaNO2 + HCl)
Nitrous acid (HNO2) is a weak and unstable acid.
It is always prepared in situ, by treating cold sodium nitrite (NaNO2) with an aqueous solution of a cold dilute hydrochloride acid (-5°C).
Nitrous acid reacts with all classes of amines
Nitrous acid test can be used to distinguish:• 1° aliphatic and 1° aromatic amines• 1° and 2° aliphatic amines
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Primary aliphatic amines react with nitrous acid to yield highly unstable aliphatic diazonium salts
1°1° amineamines (Aliphatic)s (Aliphatic)
C=C + ROH + RX
Observation :
Formation of gas bubbles (N2)
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
R-N-H
H
1 amineo
NaNO2, HX
-5 to 0 Co[ R-N NX ]
+
aliphaticdiazonium salt
(unstable)
-N2R+
+ X-
carbocation
Primary arylamines react with nitrous acid to give arenediazonium salts
1°1° amineamines (Aromatic)s (Aromatic)
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
NH2N2
+Cl
+NaNO2, HCl
coldNaCl H2O+
arenediazonium salt
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
Primary aliphatic amines
Form a mixture of alkenes, alcohols, alkyl halides and nitrogen gas.
Secondary aliphatic amines
Form secondary N-nitrosamines as yellow oil, which is stable under the reaction conditions.
1° aliphatic amines and 2° aliphatic amines 19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
Reaction with bromine water
Aniline reacts with aqueous bromine to yield white precipitatesNH2 group is an activating and ortho-para directors group
+
NH2 NH2
Br
Br
Br3Br2(aq)
room temperature 3HBr
(2,4,6-tribromoaniline)
Observation: White precipitate formed
Identification test
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
Formation of dye
Primary arylamines react with nitrous acid to give arenediazonium salts which are stable at 0 C
Arenediazonium salts also undergo coupling reaction with aromatic compounds with strong electron donating group, such as –OH and –NR2 at the para position to yield azo compounds
Azo compounds are usually intensely coloured and relatively inexpensive compounds, they are used as dyes
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye
Chapter 19 : Amines
19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties
19.1 : Introduction 19.2 : Nomenclature
N N X: -+
OH
N=N
N
(orange)
OH
CH3
CH3
N=N
(yellow)
N
CH3
CH3
19.5
Reaction with :Reaction with :
Acyl chlorideAcyl chloride
Acid anhydrideAcid anhydride
Benzenesulphonyl Benzenesulphonyl chloridechloride
Nitrous acidNitrous acid
Bromine waterBromine water
Formation of dye