Transcript (a) (CH 3 CH 2 )

Chapter 36
Nitrogen Compounds
36.1
36.2
36.3
36.4
36.5
36.6
36.7
1
Introduction
Nomenclature of Amines
Physical Properties of Amines
Preparation of Amines
Reactions of Amines
Uses of Amines and their Derivatives
Amino Acids
New Way Chemistry for Hong Kong A-Level Book 3B
36.1 Introduction (SB p.67)
Organic nitrogen compounds:
• amines, amino acids, amides and nitro compounds
• According to the number of organic groups (both
alkyl or aryl groups) directly bonded to the nitrogen
atom, amines are classified as:
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36.1 Introduction (SB p.67)
Examples of 1° amines:
Examples of 2° amines:
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36.1 Introduction (SB p.68)
Examples of 3° amines:
Addition of the fourth
organic group to tertiary
amine yields a quaternary
ammonium ion
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36.1 Introduction (SB p.68)
Aromatic amines are formed when one or more
hydrogen atoms in the ammonia are replaced by phenyl
or substituted phenyl groups
e.g.
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36.1 Introduction (SB p.67)
Check Point 36-1
Classify the following amines as primary, secondary or
tertiary amines.
I is a primary amine.
II is a tertiary amine.
III is a secondary amine.
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Answer
36.2 Nomenclature of Amines (SB p.69)
1° amines are named as alkylamines
e.g.
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36.2 Nomenclature of Amines (SB p.69)
• 2° and 3° amines are named in the same general way
• If the organic groups attached to the nitrogen are
the same, use the prefixes ‘di-’ or ‘tri’
• If they are not the same, use the prefixes ‘N-’ or
‘N,N-’ to designate the substituents
e.g.
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36.2 Nomenclature of Amines (SB p.70)
Check Point 36-2
Complete the following table by filling in the structural
formulae or IUPAC names of the amines.
IUPAC name
(a)
Structural formula
(a) 1-Methylpropylamine
(b)
(b)
2-Aminophenol
(c)
(c) Diethylamine
Answer
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36.3 Physical Properties of Amines (SB p.70)
•
Lower members of amines are gases and have a characteristic
‘ammonia’ odour.
•
The higher members are liquids with a distinctive ‘fishy’
odour
Amine
Formula
Primary amines:
Methylamine
Ethylamine
Propylamine
Butylamine
Pentylamine
Hexylamine
Phenylmethylamine
Phenylamine
10
CH3NH2
CH3CH2NH2
CH3(CH2)2NH2
CH3(CH2)3NH2
CH3(CH2)4NH2
CH3(CH2)5NH2
C6H5CH2NH2
C6H5NH2
Boiling Melting
Density at
point (°C) point (°C) 20°C (g cm–3)
–6.3
16.6
48.6
77.8
103
130
185
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–92.5
–84
–83
–50.5
–55
–19
10
–6.2
—
—
0.719
0.741
0.761
0.768
0.981
1.022
36.3 Physical Properties of Amines (SB p.70)
Amine
Formula
Boiling Melting
Density at
point (°C) point (°C) 20°C (g cm–3)
Secondary amines:
Dimethylamine
Diethylamine
N-Methylphenylamine
Diphenylamine
(CH3)2NH2
(CH3CH2)2NH2
C6H5NHCH3
(C6H5)2NH
7.4
56.3
196
302
–96
–48
–57
52.8
—
0.707
0.989
—
Tertiary amines:
Trimethylamine
Triethylamine
N,N-Dimethylphenylamine
Triphenylamine
(CH3)3NH2
(CH3CH2)3NH2
C6H5N(CH3)2
(C6H5)3N
3.5
89.4
194
365
–117
–115
2.5
126
—
0.728
0.956
—
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36.3 Physical Properties of Amines (SB p.71)
Boiling Point and Melting Point
1° or 2° amines can
form strong
hydrogen bonds with
each other
 the b.p. is higher than those of alkanes but lower than those
of alcohols of comparable molecular masses
∵ O – H bond is more polar than N – H bond as oxygen is
more electronegative  stronger hydrogen bonds are formed
between alcohol molecules
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36.3 Physical Properties of Amines (SB p.71)
• 3° amines have lower b.p. and m.p. than 1° and 2°
∵
all hydrogen in 3° amines are replaced by organic
groups
 no hydrogen bond can be formed
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36.3 Physical Properties of Amines (SB p.71)
Density
Molecular mass of amines 
 densities 
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36.3 Physical Properties of Amines (SB p.72)
Solubility
15
•
The solubility of amines in water:
1° amines > 2° amines > 3° amines
∵
The intermolecular hydrogen bonds formed between
2° or 3° amines and water molecules decrease
•
Amines are soluble in common organic solvents, e.g.
hexane, ethanol and propanone
New Way Chemistry for Hong Kong A-Level Book 3B
36.3 Physical Properties of Amines (SB p.72)
Example 36-1
Solution:
Match the boiling points 65°C, –6°C and –88°C with the
Compounds
Boiling
Point (°C)
compounds CH3CH
3, CH3NH2 and CH3OH. Explain your
CH
–88
answer
briefly.
3CH3
Answer
CH3NH2
–6
CH3OH
65
Ethane (CH3CH3) is a non-polar compound. In pure liquid form, ethane
molecules are held together by weak van der Waals’ forces. However,
both methylamine (CH3NH2) and methanol (CH3OH) are polar
substances. In pure liquid form, their molecules are held together by
intermolecular hydrogen bonds. As van der Waals’ forces are much
weaker than hydrogen bonds, ethane has the lowest boiling point among the
three. Besides, as the O – H bond in alcohols is more polar than the
N – H bond in amines, the hydrogen bonds formed between
methylamine molecules are weaker than those formed between
methanol molecules. Thus methylamine has a lower boiling point than
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methanol.
36.4 Preparation of Amines (SB p.72)
Reduction of Nitriles
Reaction with Hydrogen
Hydrogen reduces a nitrile to a 1° amine in the presence of
nickel catalyst
Example:
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36.4 Preparation of Amines (SB p.73)
Reaction with Lithium Tetrahydridoaluminate
Nitriles are reduced to 1° amines by LiAlH4 in dry ether
Example:
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36.4 Preparation of Amines (SB p.73)
Reduction of Amides
Reaction with Lithium Tetrahydridoaluminate
Amides can be reduced by LiAlH4 to give 1°, 2° or 3° amines
• The product is 1° amine if R’ and R’’ = H
• The product is 2° amine if R’ or R’’ = H
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36.4 Preparation of Amines (SB p.73)
Examples:
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36.4 Preparation of Amines (SB p.74)
Hofmann Degradation
• Amides with no substituent on the nitrogen react with Br2 in
NaOH (or Cl2 in NaOH) to give amines
• The amines formed have one carbon less than the parent
amides
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36.4 Preparation of Amines (SB p.74)
Reduction of Ammonia with Haloalkanes
1°, 2°, 3° and quaternary
ammonium salts can be
prepared by heating
haloalkanes with
ammonia under pressure
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36.4 Preparation of Amines (SB p.75)
Examples:
CH3CH2Br + NH3  CH3CH2NH2 + HBr
CH3CH2Br + CH3CH2NH2  (CH3CH2)2NH + HBr
CH3CH2Br + (CH3CH2)2NH  (CH3CH2)3N + HBr
CH3CH2Br + (CH3CH2)3N  (CH3CH2)4N+Br–
• This method always give a mixture of products
• Successive alkylations always occur because
aliphatic amines are more reactive than ammonia
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36.4 Preparation of Amines (SB p.75)
Preparation of Phenylamine through Reduction of Nitrobenzene
The reduction of the nitro group can be carried out by
• Catalytic hydrogenation
•
24
Treatment of the nitro compound with an acid (e.g.
HCl) and Fe, Zn or Sn or a metal salt such as SnCl2
New Way Chemistry for Hong Kong A-Level Book 3B
36.4 Preparation of Amines (SB p.75)
Check Point 36-3
(a) Show how the following conversions can be achieved:
(a) (i)
1. NaCN
CH CH Br  CH CH CN
3
2
3
2
2.CH
HCl3CH2CH
(i) CH3CH2Br

2NH2
(ii)
1. LiAlH4 / dry ether

CH3CH
2CH
2NH2
CH3CH
COOH  CH
CH
NH
2. 2water
3
2
2
(ii)
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Answer
36.4 Preparation of Amines (SB p.75)
Check Point 36-3
(b) Draw the structural formulae for the major organic
products, A to C, in the following reactions:
(b) A:
B:
C:
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Answer
36.5 Reactions of Amines (SB p.76)
Basicity of Amines
• Amines are far weaker bases than hydroxide ions
and alkoxide ions but are stronger bases than water
• The lone pair electrons on nitrogen atom can accept
a proton from a water molecule
 amines are basic
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36.5 Reactions of Amines (SB p.76)
Amines dissolve in mineral acids such as HCl to form salts
e.g.
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36.5 Reactions of Amines (SB p.76)
Methylamine will partially dissociate into ions
The basic strength of amines is shown by the value of base
dissociation constant (Kb)
[CH 3 NH 3 ][OH  ]
Kb 
[CH 3 NH 2 ]
pKb is used for convenience as Kb is small for weak bases
pKb = –log Kb , the smaller the pKb value, the stronger is the
base
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36.5 Reactions of Amines (SB p.77)
Name
Formula
pKb
Ammonia
NH3
4.75
Primary aliphatic amines:
Methylamine
Ethylamine
Propylamine
Butylamine
CH3NH2
CH3CH2NH2
CH3(CH2)2NH2
CH3(CH2)3NH2
3.36
3.27
3.16
3.39
Aromatic amines:
Phenylamine
C6H5NH2
9.38
The basicity of amines is
governed by the availability
of the lone pair electrons
on the nitrogen atom
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36.5 Reactions of Amines (SB p.77)
• Primary aliphatic amines are the most basic
∵
electron-releasing alkyl groups enhance the
availability of the lone pair electrons on the
nitrogen atom while ammonia does not
• Aromatic amines are weaker bases than ammonia
∵
31
the lone pair electrons on the nitrogen atom
are delocalized over the benzene ring making
it less available to a proton
New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.78)
Check Point 36-4
CH3CH2NHCOCH3 is much less basic than (CH3CH2)2NH
because of
presence
of the electron-withdrawing
group
Compare
thethebasic
strength
of (CH3CH2)2NHacyl
and
the compound.
The acyl group withdraws electrons away from
CHin3CH
2NHCOCH3.
the –NH group by both the inductive and resonance effects.
Two
Answer
resonance structures can be drawn for the amide compound as shown
below:
As shown in structure II, the lone pair electrons of the nitrogen
atom delocalize to form a  bond with the acyl carbon atom.
Thus, the availability of the lone pair electrons on the nitrogen
atom is much reduced. As a result, the amide is much less
basic than the amine.
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36.5 Reactions of Amines (SB p.78)
Reactions with Ethanoyl Chloride and Benzoyl Chloride
• 1° and 2° amines react readily in cold with ethanoyl
chloride to form N-substituted amides
Examples:
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36.5 Reactions of Amines (SB p.78)
• 1° and 2° amines react with benzoyl chloride in the
presence of alkalis to form N-substituted amides
Examples:
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.78)
• The reaction between ethanoyl chloride and benzoyl
chloride and amines would not give a mixture of amides
∵
resulting amide is less nucleophilic than original
amine due to the electron-withdrawing carbonyl
group make the lone pair electrons on nitrogen
atom less available
• 3° amines do not react since they do not possess a
hydrogen atom
• Amines are susceptible to oxidations, conversion of
amine to amide can ‘protect’ against oxidation
• Free amines can be regenerated by acid hydrolysis
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.79)
Reactions of Primary Amines with Nitric(III) Acid
• All amines react with nitric(III) acid
• As nitric(III) acid is a weak and unstable acid, it is
prepared by treating NaNO3 with an aqueous solution of a
strong acid
NaNO2(aq) + HCl(aq)  HNO2(aq) + NaCl(aq)
2NaNO2(aq) + H2SO4(aq)  2HNO2(aq) + Na2SO4(aq)
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.79)
Reaction of Primary Aliphatic Amines with Nitric(III) Acid
• 1° aliphatic amines react with HNO2 to yield aliphatic
diazonium salts
• Diazonium salts, even at low temperatures, are highly
unstable, they decompose spontaneously by losing
nitrogen to form carbocations
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36.5 Reactions of Amines (SB p.80)
Reaction of Primary Aromatic Amines with Nitric(III) Acid
• 1° aromatic amines react with HNO2 to yield
benzenediazonium salts
• Benzenediazonium salts are unstable, but they do not
decompose when the temperature of the reaction mixture
is kept below 5°C
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36.5 Reactions of Amines (SB p.80)
• The greater stability of benzenediazonium salts is due to the
delocalization of the positive charge of the diazonium group
+
(–N  N) over the benzene ring
• The benzenediazonium salts are important in synthesis
because the diazonium group can be replaced by a
variety of functional groups to give a a range of organic
products
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.80)
Replacement of the Diazonium Group by –Cl, –Br or –CN
The diazonium group of benzenediazonium ions can be
replaced by –Cl, –Br and –CN by treating with CuCl,
CuBr and CuCN respectively
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.81)
Replacement of the Diazonium Group by –I
The diazonium group of benzenediazonium ions can be
replaced by –I on reacting with KI
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36.5 Reactions of Amines (SB p.81)
Replacement of the Diazonium Group by –F
The diazonium group of benzenediazonium ions can be
replaced by –F on reacting with KBF4
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36.5 Reactions of Amines (SB p.81)
Replacement of the Diazonium Group by –OH
The diazonium group of benzenediazonium ions can be
replaced by –OH by adding Cu2O to a dilute solution of
the benzenediazonium salt containing a large excess of
CuNO3
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36.5 Reactions of Amines (SB p.81)
Coupling Reactions of Benzenediazonium Ions
• Benzenediazonium ions react with highly reactive
aromatic compounds in an alkaline medium to give azo
compounds
Example:
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36.5 Reactions of Amines (SB p.81)
• This reaction is used to identify 1° aromatic amines
• Azo compounds are usually intensely coloured
∵
– N = N – link brings the two aromatic rings into
conjugation, and the  electrons are delocalized
over the entire structure
• Azo compounds are used as dyes due to intense colours
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.82)
Example 36-2
Draw the structural formulae of the major products
formed in the following reaction:
Solution:
(a) (CH3CH2)2NH + HCl 
(b)
(a) (CH3CH2)2NH2+Cl–
(b)
(c)
(c)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
36.5 Reactions of Amines (SB p.82)
Check Point 36-5
Suggest a series of reactions for the following
conversion:
(a)
(a)
Answer
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36.5 Reactions of Amines (SB p.82)
Check Point 36-5
Suggest a series
(b) of reactions for the following
conversion:
(b)
Answer
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36.5 Reactions of Amines (SB p.82)
Check Point 36-5
Suggest a series of reactions for the following
conversion:
(c) CH3CH2NH2  CH3CH2NHCH3
Answer
(c)
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36.5 Reactions of Amines (SB p.82)
Check Point 36-5
Suggest(d)a series of reactions for the following
conversion:
(d)
Answer
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36.6 Uses of Amines and their Derivatives (SB p.83)
As Dyes
• 1° aromatic amines are used as a starting material for
the manufacture of azo dyes
Note:
G is an electron-releasing substituent like –OH or –NH2
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36.6 Uses of Amines and their Derivatives (SB p.83)
• Azo compounds are highly coloured and can be
synthesized from relatively inexpensive compounds
 widely used in dyeing industry
Azo compounds are
used as dyes in
garments and food
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New Way Chemistry for Hong Kong A-Level Book 3B
36.6 Uses of Amines and their Derivatives (SB p.83)
Examples:
1. Methyl orange (an orange dye for fabrics)
2. Sunset Yellow FCF (an orange-yellow dye for food products)
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36.6 Uses of Amines and their Derivatives (SB p.83)
3. Direct Brown 138 (a brown dye for fabrics)
4. Ponceau (a red dye for food products)
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36.6 Uses of Amines and their Derivatives (SB p.84)
As Drugs
Amine derivatives are commonly used as drugs such as
painkillers (analgesics), transquillizers and antihistamines
1. Acetaminophen (also known as paracetamol)
• used to relieve pains
• less harmful to the stomach compared with aspirin
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36.6 Uses of Amines and their Derivatives (SB p.84)
2. Chlorpheniramine
• helps to relieve allergic disorders caused by cold, insect
bites and stings
• present in some over the counter drugs such as Coricidin,
Coltaline, Piriton and Dristan
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36.6 Uses of Amines and their Derivatives (SB p.84)
3. Chlorpromazine
• sedative effect without inducing sleep
• used to relieve anxiety, excitement, restlessness and
even metal disorders
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36.7 Amino Acids (SB p.85)
• Amino acids are compound containing both the basic
amino group (–NH2) and the acidic carboxyl group
(–COOH)
• Amino acids found in nature as the constituents of natural
proteins are mostly -amino acids
• 22 -amino acids can be obtained from proteins
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36.7 Amino Acids (SB p.85)
• According to the structures, they are classified into 3
groups: neutral amino acids, acidic amino acids
and basic amino acids
Name
Formula
Neutral amino acids:
Glycine
Alanine
NH2CH2COOH
Valine
Leucine
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36.7 Amino Acids (SB p.85)
Name
Formula
Acidic amino acids:
Aspartic acid
Glutamic acid
Basic amino acids:
Lysine
Arginine
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36.7 Amino Acids (SB p.86)
• All naturally occurring amino acids are optically
active except glycine
 contain an asymmetric carbon atom(*)
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36.7 Amino Acids (SB p.86)
Amino Acids as Dipolar Ions
• Amino acids are bifunctional compounds
∵
contain a basic amino group and an acidic
carboxyl group
• Amino acids are neither strong bases nor strong acids
• As dipolar ion (also called zwitterions) in aqueous solution
by transferring the acidic proton to the amino group
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36.7 Amino Acids (SB p.87)
• The predominant form of an amino acid present in
a solution depends on the pH of the solution
• The concentration of the zwitterion is at maximum when the
solution is at an intermediate pH called the isoelectric point
 concentration of the anions and cations are equal
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36.7 Amino Acids (SB p.87)
Due to the formation of dipolar ions, amino acids exhibits
many abnormal properties:
• low volatility
• high melting point
• low solubility in organic solvents
• high dipole moment
• abnormal acid and base dissociation constants
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36.7 Amino Acids (SB p.87)
Check Point 36-6
All amino acids are solids at room temperature.
Explain why that should be the case.
Answer
Ionic compounds are solids at room temperature. As amino
acids in the form of zwitterions are ionic compounds, they
exist as solids at room temperature.
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36.7 Amino Acids (SB p.87)
Dipeptides and Polypeptides
Dipeptide: dimers of amino acids
Two amino acid molecules join together with the
elimination of a water molecule to form a dipeptide
 condensation reaction
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36.7 Amino Acids (SB p.88)
Peptide linkage: the
linkage formed between
amino acids
Polypeptide: polymer of amino acids formed by
condensation polymerization reaction of a
large number of amino acids
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36.7 Amino Acids (SB p.88)
• The polypeptide can
be hydrolyzed and
broken down into
their constituent
amino acids
• The hydrolysis can
be carried out in an
acidic or alkaline
medium
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36.7 Amino Acids (SB p.89)
Check Point 36-7
(a), (b) After complete hydrolysis of the polypeptide, three
In a polypeptide,
amino acids are joined together by peptide
amino acids are formed. Their structures are shown
linkages which as
arefollows:
amide groups. The peptide linkages have
the same chemistry as the amides. Polypeptides are readily
hydrolyzed by acids or bases. A polypeptide has the
following structure:
(a) Draw the structures of the amino acids formed after
complete hydrolysis of the polypeptide shown above.
* indicates the asymmetric carbon atom
(b) Indicate the asymmetric carbon of the amino acids, if
there are any.
Answer
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The END
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