Transcript Carboxylic Acids

Chapter 35
Carboxylic Acids
and their Derivatives
35.1
35.2
35.3
35.4
35.5
35.6
35.7
1
Introduction
Nomenclature of Carboxylic Acids and their
Derivatives
Physical Properties of Carboxylic Acids
Preparation of Carboxylic Acids
Reactions of Carboxylic Acids
Reactions of the Derivatives of Carboxylic Acids
Uses of Carboxylic Acids and their Derivatives
New Way Chemistry for Hong Kong A-Level Book 3B
35.1 Introduction (SB p.29)
Carboxylic acids refer to the class of organic compounds
with the carboxyl group
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35.1 Introduction (SB p.29)
General formula of carboxylic acid: RCOOH
Examples:
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35.1 Introduction (SB p.30)
Carboxylic acid derivatives
Name
Structure
Acyl
chlorides
Acid
anhydrides
Amides
Esters
4
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.30)
Carboxylic Acids
Carboxylic acids are named by replacing the final “-e” of
the name of the corresponding alkane with “-oic acid”
When other substituents are present, the carboxyl carbon is
assigned position 1
Examples:
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.31)
Acyl Chlorides
Acyl chlorides are named by replacing the final “-ic acid”
of the name of the parent carboxylic acid with “-yl
chloride”
Examples:
6
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.31)
Acid Anhydrides
Acid anhydrides are named by dropping the word “acid”
from the name of the parent carboxylic acid and then
adding the word “anhydride”
Examples:
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.31)
Amides
• Amides that have no substituents on the nitrogen atom are named
by replacing “-oic acid” from the parent carboxylic acid with
“amide”
• Substituents on the nitrogen atom of amides are named and the
named substituent is preceded by N-, or N,N-
Examples:
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.31)
Esters
• The names of esters are derived from the names of the
alcohol (with the ending “-yl”) and the carboxylic acid (with
the ending “-oate”)
• The portion of the name derived from the alcohol comes first
Examples:
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.32)
Example 35-1
Give the IUPAC names of the following compounds:
(a)
Solution:
(b)
(a) 3-Methylbutanoic acid
(b) N-methylethanamide
(c)
(c) Ethyl benzoate
(d) Benzoic anhydride
(d)
Answer
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.33)
Example 35-2
An ester is formed by reacting an alcohol with a carboxylic
acid. Draw the structural formula of the following ester
molecule and give the name of the alcohol and the
carboxylic acid that form the ester.
(a) Methyl ethanoate
Solution:
Answer
(a) The structural formula of methyl ethanoate is:
It is formed from the reaction of ethanoic acid and
methanol.
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.33)
Example 35-2
An ester is formed by reacting an alcohol with a
carboxylic acid. Draw the structural formula of the
following ester molecule and give the name of the alcohol
and the carboxylic acid that form the ester.
(b) Ethyl methanoate
Answer
Solution:
(b) The structural formula of ethyl methanoate is:
It is formed from the reaction of methanoic acid
and ethanol.
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35.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.33)
Check Point 35-1
Complete the following table by filling in the molecular
formulae, structural
formulae or IUPAC names of the
(a)
carboxylic acids.
Molecular formula Structural formula
IUPAC name
(a)
C3H7COOH(b) Butanoic
acid
(c)
(c)(b)
CH3CH(CH3)CH2COOH
(d) 3-Methylbutanoic acid(d)
(e) C6H4ClCOOH
(f) 2-Chlorobenzoic acid
(g) CCl3COOH
(h)
(e)
(f)
Answer
(g)
13
(h)
Trichloroethanoic acid
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35.3 Physical Properties of Carboxylic Acids (SB p.34)
• Carboxylic acids are colourless liquids at room conditions
• They have characteristic pungent smell and sour taste
Carboxylic acid
Methanoic acid
Ethanoic acid
Propanoic acid
Butanoic acid
Pentanoic acid
Hexanoic acid
Benzoic acid
Phenylethanoic acid
2-Methylpropanoic acid
Chloroethanoic acid
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Formula
HCO2H
CH3CO2H
CH3CH2CO2H
CH3(CH2)2CO2H
CH3 (CH2)3CO2H
CH3 (CH2)4CO2H
C6H5CO2H
C6H5CH2CO2H
(CH3)2CHCO2H
CH2ClCO2H
Boiling Melting
Density at
point (°C) point (°C) 20°C (g cm–3)
101
118
141
164
186
205
249
266
154
189
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8.4
16.6
–20.8
–6.5
–34.5
–1.5
122
76
–47
63
1.220
1.049
0.992
0.964
0.939
0.927
—
—
0.950
—
35.3 Physical Properties of Carboxylic Acids (SB p.34)
Carboxylic acid
Dichloroethanoic acid
Trichloroethanoic acid
Hydroxyethanoic acid
2-Hydroxypropanoic acid
Cis-Butenedioic acid
Trans-Butenedioic acid
Ethanedioic acid
Propandioic acid
Butanedioic acid
Benzene-1,2-dicarboxylic
acid
15
Formula
Density
Boiling
Melting
at 20°C
point (°C) point (°C)
(g cm–3)
CHCl2CO2H
194
CCl3CO2H
198
HOCH2CO2H
dec.
CH3CHOHCO2H
dec.
HO2CCH = CHCO2H
dec.
HO2CCH = CHCO2H
dec.
HO2CCO2H
—
HO2CCH2CO2H
dec.
HO2C(CH2)2CO2H
235 (dec.)
C6H4(CO2H)2
dec.
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10.8
57.7
79
16.8
130 – 131
268 (dec.)
190 (dec.)
136 (dec.)
182
206 (dec.)
1.566
—
—
1.249
1.590
1.635
—
—
—
—
35.3 Physical Properties of Carboxylic Acids (SB p.35)
Boiling Point and Melting Point
Due to formation of
intermolecular hydrogen bonds
 high b.p. and m.p.
The hydrogen bonds are more
extensive than those in alcohols
 higher b.p. and m.p. than
alcohols
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35.3 Physical Properties of Carboxylic Acids (SB p.36)
Density
• The densities of carboxylic acids decrease with
increasing relative molecular masses
• Only methanoic acid and ethanoic acid are denser
than water at 20°C
∵
closer packing of the smaller molecules in
the liquid phase
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35.3 Physical Properties of Carboxylic Acids (SB p.36)
Solubility
• Carboxylic acids of low molecular masses show
appreciable solubilities in water
∵
carboxylic acids are polar and can form strong
hydrogen bonds with water molecules
• First four carboxylic acids are miscible with water
• The length of the hydrocarbon portion  
solubilities in water 
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35.3 Physical Properties of Carboxylic Acids (SB p.36)
Example 35-3
(a) Propanoic acid has a boiling point of 141°C which is
considerably higher than that of butan-1-ol (117°C),
although they have the same molecular mass.
Explain why.
Answer
Solution:
(a) Each propanoic acid molecule forms two
intermolecular hydrogen bonds with another
propanoic acid molecule. However, two butan-1-ol
molecules form only one hydrogen bond. As
molecules of propanoic acid form more extensive
intermolecular hydrogen bonds than those of butan-1-ol,
the boiling point of propanoic acid is higher than that of
butan-1-ol.
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35.3 Physical Properties of Carboxylic Acids (SB p.36)
Example 35-3
(b) Rank the following compounds in decreasing order
of solubility in water:
CH3CH2CH2COOH, CH3CH2COOCH3, CH3COOH
Answer
Solution:
(b) The solubility of the compounds in water decreases in
the order:
CH3COOH > CH3CH2CH2COOH > CH3CH2COOCH3
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35.3 Physical Properties of Carboxylic Acids (SB p.36)
Example 35-3
(c) Propanedioic acid forms intramolecular hydrogen
bonds. Draw its structural formula showing clearly
the formation of intramolecular hydrogen bonds.
Solution:
(c)
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Answer
35.4 Preparation of Carboxylic Acids (SB p.37)
Hydrolysis of Nitriles
• 2-hydroxyalkanenitriles is formed by nucleophilic addition
reaction of aldehydes or ketones with hydrogen cyanide
• Acid hydrolysis or alkaline hydrolysis of 2-hydroxyalkanenitriles
produce carboxylic acids or carboxylate ions respectively
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35.4 Preparation of Carboxylic Acids (SB p.37)
Nitriles can be formed by nucleophilic substitution
reaction of haloalkanes with sodium cyanide
Acid hydrolysis of the nitrile produces a carboxylic acid
with one more carbon atom
e.g.
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35.4 Preparation of Carboxylic Acids (SB p.38)
Hydrolysis of Esters
• Hydrolysis of esters give parent carboxylic acids and alcohols
by boiling under reflux with the dilute HCl or dilute H2SO4
• Acyl chlorides, acid anhydrides, esters and amides can be
hydrolyzed to give the corresponding carboxylic acids
• Reactive derivatives react vigorously with water, e.g. acyl chlorides
• Less reactive derivatives require more severe conditions to bring
about the reaction
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35.4 Preparation of Carboxylic Acids (SB p.38)
Oxidation of Alcohols and Aldehydes
Aldehydes and 1° alcohols can be oxidized to carboxylic
acids by KMnO4/H+
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35.4 Preparation of Carboxylic Acids (SB p.38)
Examples:
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35.4 Preparation of Carboxylic Acids (SB p.39)
Oxidation of Alkybenzenes
1° and 2° alkyl groups (but not 3°) directly attached to a
benzene ring are oxidized by hot KMnO4/OH– to carboxyl group
e.g.
This oxidation takes place initially at the benzylic carbon
 alkyl groups longer than methyl group are ultimately
degraded to benzoic acid
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35.4 Preparation of Carboxylic Acids (SB p.39)
Check Point 35-2
Write the equations for the acid-catalyzed and basecatalyzed hydrolyses of each of the following substances:
(a)
(a) Ethyl butanoate
Answer
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35.4 Preparation of Carboxylic Acids (SB p.39)
Check Point 35-2
Write the equations for the acid-catalyzed and basecatalyzed hydrolyses of each of the following substances:
(b) Propanamide
(b)
29
Answer
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35.4 Preparation of Carboxylic Acids (SB p.39)
Check Point 35-2
Write the equations for the acid-catalyzed and basecatalyzed hydrolyses of each of the following substances:
(c) Benzoyl
chloride
(c)
Answer
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35.5 Reactions of Carboxylic Acids (SB p.39)
Acidity of Carboxylic Acids
• Carboxylic acids are weak acids
• Their acidic properties are due to the presence of
ionizable hydrogen atom
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35.5 Reactions of Carboxylic Acids (SB p.39)
e.g. ethanoic acid
The acid strength of ethanoic acid is shown by the value of its
acid dissociation constant (Ka)
[CH 3COO- ][H 3O  ]
Ka 
[CH 3COOH ]
pKa is used for convenience as Ka is small for weak acids
pKa = –log Ka , the smaller the pKa value, the stronger is the acid
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35.5 Reactions of Carboxylic Acids (SB p.40)
• Unsubstituted carboxylic acids have pKa values in the
range of 3 to 5
• Alcohols have pKa values in 15 to 18
 carboxylic acids are much more acidic than alcohols
Name
33
Formula
pKa
Methanoic acid HCOOH
3.75
Ethanoic acid
CH3COOH
4.76
Propanoic acid
CH3CH2COOH
4.87
Butanoic acid
CH3CH2CH2COOH
4.82
Benzoic acid
C6H5COOH
4.20
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35.5 Reactions of Carboxylic Acids (SB p.40)
Resonance Effect
The greater stability of carboxylic acids is attributed to
resonance stabilization of the carboxylate ions
Example:
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35.5 Reactions of Carboxylic Acids (SB p.41)
• By the resonance effect, the ethanoate ion can be stabilized
by spreading the negative charge over two oxygen
atoms
• No stabilizing resonance structures for alkoxide ions
e.g.
• Carboxylic acids are much acidic than alcohols
∵ formation of more stable conjugate base
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35.5 Reactions of Carboxylic Acids (SB p.41)
Inductive Effect
• Both compounds contain the highly polarized O – H
bond due to the difference in electronegativity
• The greater acidity of ethanoic acid is due to the
presence of the powerful electron-withdrawing carbonyl
group
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35.5 Reactions of Carboxylic Acids (SB p.41)
Two resonance structures for the carbonyl group:
• The carbonyl atom of ethanoic acid bears a large
partial positive charge and exerts a powerful electronwithdrawing inductive effect to hydroxyl oxygen atom,
making the hydroxyl hydrogen atom much more
positive
 proton dissociate more readily
• The electron-withdrawing inductive effect of the
carbonyl group stabilizes the carboxylate ion
 carboxylic acids are stronger acid than alcohols
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35.5 Reactions of Carboxylic Acids (SB p.42)
Inductive Effects of Other Groups
1. Electron-withdrawing Groups
• The presence of electron-withdrawing groups increase
the acidity of a carboxylic acid
e.g.
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35.5 Reactions of Carboxylic Acids (SB p.42)
• The chlorine atom withdraws electron from the carbonyl
group and oxygen making the hydroxyl hydrogen more
positive than that of ethanoic acid
• The chlorine atom also stabilizes the chloroethanoate ion
to greater extent
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35.5 Reactions of Carboxylic Acids (SB p.41)
Effect of electron-withdrawing substituents on the acidity of carboxylic acids
Acidity CH3COOH <
Ethanoic
Chloroethanoic
acid
acid
pKa
4.76
2.86
Acidity CH3COOH <
<
pKa
<
<
Dichloroethanoic
acid
1.29
<
CCl3COOH
Trichloroethanoic
acid
0.65
<
Ethanoic Iodoethanoic Bromoethanoic ChloroethanoicFluoroethanoic
acid
acid
acid
acid
acid
4.76
3.17
2.90
2.86
2.66
• The greater the number of electron-withdrawing groups, the
stronger is the acid
40
• The more electronegative of halogen substituents (F > Cl >
Br > I), the stronger is the acid
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35.5 Reactions of Carboxylic Acids (SB p.43)
• The further away of the substituents from the carboxyl
group, the weaker is the acid
Acidity
<
pKa
41
4-Chlorobutanoic
acid
4.52
<
3-Chlorobutanoic
acid
4.06
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2-Chlorobutanoic
acid
2.84
35.5 Reactions of Carboxylic Acids (SB p.43)
2. Electron-releasing Groups
• The presence of electron-releasing groups reduce the
acidity of a carboxylic acid
e.g.
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35.5 Reactions of Carboxylic Acids (SB p.43)
• Electron-releasing alkyl groups release electrons towards the
electron-deficient carbonyl carbon, thus reducing its charge
• Reduce the positive character of the hydroxyl
hydrogen atom
 dissociate less readily
• Intensify the negative charge on the carboxyl group
 destablizes the ethanoate ion
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35.5 Reactions of Carboxylic Acids (SB p.44)
Check Point 35-3
(a) Match the Ka values: 2.19  10–3 M and 1.26  10–3 M,
to the carboxylic acids: CH2FCOOH and
CH2BrCOOH. Explain your answer briefly.
(a) The greater the Ka value, the stronger is the acid.Answer
CH2FCOOH is a stronger acid than CH2BrCOOH.
This –F substituent exerts a stronger inductive effect
than the –Br substituent, as fluorine is more
electronegative than bromine. The –F substituent
stabilizes the conjugate base (i.e. CH2FCOOH–) to a
greater extent than the –Br substituent. Therefore,
CH2FCOOH has a Ka value of 2.19  10–3 M, and
CH2BrCOOH has a Ka value of 1.26  10–3 M.
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35.5 Reactions of Carboxylic Acids (SB p.44)
Check Point 35-3
(b) Arrange the following acids in ascending order of acidity:
CHCl2COOH, CCl3COOH, CH2ClCOOH, CH3COOH
Explain the order briefly.
Answer
(b) CH3COOH < CH2ClCOOH < CHCl2COOH
< CCl3COOH
The –Cl substituent is an electron-withdrawing
group. An increasing number of the –Cl substituent
brings about a greater negative inductive effect.
Thus, the conjugate base will be stabilized more,
and the acidity of the acid increases.
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35.5 Reactions of Carboxylic Acids (SB p.44)
Check Point 35-3
(c) Arrange the following aryl carboxylic acids in descending
order of acidity:
Explain the order briefly.
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35.5 Reactions of Carboxylic Acids (SB p.44)
(c)
is more acidic than
,because
contains
the –Cl substituent which is an electron-withdrawing group. Thus, it
exerts a negative inductive effect to the conjugate base, and hence
stabilizes the carboxylate ion formed.
is less acidic than
, because
contains
a methyl group which is an electron-releasing group. Thus, it exerts a
positive inductive effect to the conjugate base, and hence destabilizes
the carboxylate ion formed.
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35.5 Reactions of Carboxylic Acids (SB p.44)
Check Point 35-3
(d) Which is a stronger acid, CH2ClCOOH or
CH3CHClCOOH? Explain your answer briefly.
Answer
(d) CH2ClCOOH is a stronger acid as CH3CHClCOOH
contains a methyl group which is an electron-releasing
group. It exhibits a positive inductive effect and thus
destabilizes the conjugate base of the acid. Therefore,
CH3CHClCOOH is less acidic.
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35.5 Reactions of Carboxylic Acids (SB p.44)
Formation of Salts
Reaction with Active Metals
• Carboxylic acids react with reactive metals such as Na
or Mg to give the corresponding metal carboxylates and
hydrogen gas
49
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Example:
50
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35.5 Reactions of Carboxylic Acids (SB p.45)
Reaction with Bases
Carboxylic acids react with strong alkalis such as NaOH to
form sodium carboxylates and water
Examples:
51
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35.5 Reactions of Carboxylic Acids (SB p.45)
Carboxylic acids also react weak alkalis such as Na2CO3 or
NaHCO3 to form sodium carboxylates, carbon dioxide and
water
52
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35.5 Reactions of Carboxylic Acids (SB p.45)
Examples:
• This reaction serves as a test to distinguish carboxylic acids
and other acidic organic compounds
53
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35.5 Reactions of Carboxylic Acids (SB p.46)
NaOH and
Na2CO3 can be
used to separate a
mixture of
alcohols, phenols
and carboxylic
acids
54
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35.5 Reactions of Carboxylic Acids (SB p.46)
Check Point 35-4
(a) Describe how to separate a mixture of benzoic acid
and phenol in the laboratory.
Answer
(a) Sodium hydrogencarbonate, water and diethyl ether are
added to the mixture. Benzoic acid reacts with sodium
hydrogencarbonate to form a water-soluble salt which
dissolves in the aqueous layer. After separation by the use
of a separating funnel, phenol can be recovered by distilling
off the ether. To the aqueous layer, hydrochloric acid is
added to generate the benzoic acid which can be extracted
by diethyl ether. After separation from the aqueous
layer, benzoic acid is obtained by distilling off the
ether.
55
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35.5 Reactions of Carboxylic Acids (SB p.46)
Check Point 35-4
(b) Outline how a mixture of butanone and ethanoic
acid can be separated in the laboratory.
Answer
56
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35.5 Reactions of Carboxylic Acids (SB p.46)
(b)
57
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35.5 Reactions of Carboxylic Acids (SB p.47)
Formation of Acyl Chlorides
• Acyl chlorides are the most reactive amongst the
carboxylic acid derivatives
• They can be prepared by the use of SOCl2, PCl3 or
PCl5 in good yields
58
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35.5 Reactions of Carboxylic Acids (SB p.47)
• Acyl chlorides can be used to prepare aldehydes, ketones,
esters, amides and acid anhydrides in organic synthesis
• Acyl chlorides are extremely sensitive to moisture,
therefore, it must be stored in anhydrous conditions
∵ hydrolyze rapidly to form carboxylic acids
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35.5 Reactions of Carboxylic Acids (SB p.47)
Formation of Acid Anhydrides
• Acid anhydrides can be prepared by reacting acyl
chlorides with carboxylic acids in the presence of
pyridine
• This can be used to prepare mixed anhydrides (R  R´)
or simple anhydrides (R = R´)
60
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35.5 Reactions of Carboxylic Acids (SB p.47)
• Acyl chlorides react with sodium salts of carboxylic
acids to give acid anhydrides
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35.5 Reactions of Carboxylic Acids (SB p.48)
Formation of Amides
• Ammonia reacts with carboxylic acids to form ammonium
salts. The dry salts are heated to dehydrate to give amide
• The better way to prepare amides is reacting
ammonia or amines with acyl chlorides
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35.5 Reactions of Carboxylic Acids (SB p.48)
Formation of Esters
• Carboxylic acids react with alcohols to form esters
through condensation reactions
• Esterification reactions are acid-catalyzed and reversible
63
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35.5 Reactions of Carboxylic Acids (SB p.48)
Reduction with Lithium Tetrahydridoaluminate
LiAlH4 is a powerful reducing agent which reduces
carboxylic acids to primary alcohols in good yields
Example:
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35.5 Reactions of Carboxylic Acids (SB p.49)
Example 35-4
(a) Complete and balance the following acid-base
Solution:
equations:
(a) (i)(i)
(ii)
(ii)
Answer
65
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35.5 Reactions of Carboxylic Acids (SB p.49)
Example 35-4
(b) Draw the structural formulae for the products formed
from the following compounds when they are reduced
with lithium tetrahydridoaluminate.
(i)
(ii)
Solution:
(b) (i)
Answer
(ii) HOCH2CH2CH2CH2OH
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35.5 Reactions of Carboxylic Acids (SB p.49)
Example 35-4
Solution:the following equations:
(c) Complete
(i)
(c) (i)
(ii) (ii)
(iii) (iii)
Answer
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.50)
Reactions of Acyl Chlorides
• Both chlorine and oxygen atoms are electronwithdrawing groups, thus making the acyl carbon much
electron-deficient
 acyl carbon is a good nucleophilic site
• Chloride ion is a good leaving group which is
substituted by other atoms or groups easily
 acyl chlorides are very reactive
68
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.50)
• Benzoyl chloride is much less reactive than aliphatic acyl
chlorides
∵ reduction of electron-deficiency on the acyl carbon
due to delocalization of electrons (resonance effect)
69
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.51)
Reaction with Water
Acyl chlorides are hydrolyzed by water to form the parent
carboxylic acids and hydrogen chloride
Examples:
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.51)
Reaction with Alcohols
Acyl chlorides react with alcohols to give esters and HCl
Examples:
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.51)
Acyl chlorides react with phenols to give esters in the
presence of base as catalyst
∵
an alkaline medium converts phenol to a powerful
nucleophile, phenoxide ion
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.52)
Reaction with Ammonia and Amines
Acyl chlorides react with ammonia to form amides rapidly
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.52)
Acyl chlorides react rapidly with 1° and 2° amines to form
N-, N,N- substituted amides respectively
• The reaction takes place at room temperature and produces
amides in high yield
• This method is widely used in laboratory for amides synthesis
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.52)
Check Point 35-5
Explain why ethanoyl chloride must be protected from
atmospheric moisture during storage.
Answer
This is because ethanoyl chloride reacts readily
with water (from atmospheric moisture) to form
ethanoic acid.
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.53)
Reactions of Acid Anhydrides
Reaction with Water
Acid anhydrides undergo hydrolysis to form carboxylic acids
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.53)
Reaction with Alcohols
Acid anhydrides react with alcohols to form esters in the
presence of acid catalyst
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.54)
Reaction with Ammonia and Amines
Acid anhydrides react with ammonia and with 1° and 2°
amines in the ways similar to those of acyl chlorides
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.54)
Examples:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.53)
Reactions of Amides
Amides are the least reactive among the carboxylic acid
derivatives towards nucleophilic substitution reactions
∵
NH2–, NHR– or NR2– are strong bases and thus
poor leaving groups
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.55)
Reaction with Water
Amide undergo acid and alkaline hydrolyses to form
carboxylic acids and carboxylates respectively
Acid hydrolysis:
Alkaline hydrolysis:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.55)
Dehydration
Amides are dehydrated by heating with P4O10 to form nitriles
• Useful synthetic method for preparing nitriles that are
not available by nucleophilic substitution reactions
between haloalkanes and cyanide ions
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.55)
Hofmann Degradation
• Amides react with a solution of Br2 in NaOH or a solution of
Cl2 in NaOH to give amines through a reaction called Hofmann
degradation
• The resulted amines have one carbon less than original amides
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.56)
Reduction with Lithium Tetrahydridoaluminate
Amides are reduced by LiAlH4 in dry ether to
give 1° amines
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.56)
Reactions of Esters
Acid-catalyzed Hydrolysis
Acid-catalyzed hydrolysis of esters is the reverse reaction
of esterification
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.56)
Alkali-catalyzed Hydrolysis
• When esters are refluxed with an alkali such as NaOH, the
corresponding alcohol and sodium salt of the carboxylic
acid are produced
• Alkali-catalyzed hydrolysis are irreversible
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.57)
• Soap is made by the alkaline hydrolysis of fats or oils (i.e.
triesters) to produce sodium carboxylates (i.e. soap)
• The reaction is called saponification
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35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.57)
Reduction with Lithium Tetrahydridoaluminate
Esters are reduced to alcohols by LiAlH4
Example:
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.57)
Example 35-5
Draw the structural formulae of the missing compounds A to
Solution:
M:
(a)
(a)
(b)
(b)
(c)
(c)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.58)
Example 35-5
Draw theSolution:
structural formulae of the missing compounds A to
M:
(d)
(d)
(e)
(e)
(f)
(f)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
35.6 Reactions of the Derivatives of Carboxylic Acids (SB p.58)
Example 35-5
Draw the structural formulae of the missing compounds A to
M:
Solution:
(g)
(h)
(i)
(g)
(h)
(i)
Answer
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.59)
As Food Preservatives
• Benzoic acid and its sodium salt used as food
preservatives
• Prevent the microbial growth and spoilage
• Used in oyster sauce, fish
sauce, ketchup, non-alcoholic
beverages, fruit juices,
margarine, salad dressings,
jams and pickled products
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.59)
As Raw materials for Making Polymers
• Nylon-6,6,
condensation polymer
,is a
• It is a polyamide made by adding NaOH containing
hexanedioyl dichloride and hexane-1,6-diamine to CH3CCl3
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
Advantages of Nylon-6,6
• Drip dry easily
• Not attack by insects easily
• Resist creasing (no ironing required
after washing)
• Used for making ropes, thread, cords,
and various kinds of clothing from
stockings to jackets
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
Terylene,
, is a polyester
made from acid-catalyzed condensation polymerization
of benzene-1,4-dicarboxylic acid and ethane-1,2-diol
Terylene is used to make washand-wear garments
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
As Solvents
Liquid esters are widely used as solvents for all-purpose
adhesives, thinners for paints and nail varnish removers
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
As Flavourings
•
Volatile esters often have characteristic sweet and
fruity smells
•
They are used as artificial flavourings
in food-processing industry
An artificial flavouring
made of esters
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
Some esters and their characteristic flavours
Structure of ester
Characteristic flavour
Banana
Apple
Apricot
Pineapple
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New Way Chemistry for Hong Kong A-Level Book 3B
35.7 Uses of Carboxylic Acids and their Derivatives (SB p.60)
Some esters and their characteristic flavours (cont’d)
Structure of ester
Characteristic flavour
Rum
Grape
Wintergreen
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The END
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New Way Chemistry for Hong Kong A-Level Book 3B