Transcript Document

Chapter 16 Carboxylic Acids and
Esters
16.1
Carboxylic Acids
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Carboxylic Acids
A carboxylic acid
 Contains a carboxyl group, which is a carbonyl group
(C=O) attached to a hydroxyl group (—OH).
 Has the carboxyl group on carbon 1.
carbonyl group
O

CH3 — C—OH hydroxyl group or CH3COOH
carboxyl group
2
Models of Carboxylic Acids
 The three-dimensional models show the geometry
of atoms in carboxylic acid molecules.
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3
IUPAC Names
The IUPAC names of carboxylic acids
 Replace the -e in the alkane name with -oic acid.
CH4
methane
HCOOH
CH3—CH3 ethane
methanoic acid
CH3—COOH ethanoic acid
 Number substituents from the carboxyl carbon 1.
CH3
O
|
║
CH3—CH—CH2—C—OH
4
3
2
1
3-methylbutanoic acid
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Common Names
The common names of simple carboxylic acids
 Are formic acid (1C), acetic acid (2C), propionic acid
(3C), and butyric acid (4C).
HCOOH
formic acid
CH3—COOH
acetic acid
 Locate substituents using , , γ for the carbon
atoms adjacent to the carboxyl carbon.
CH3
γ
|

CH3—CH—CH2—COOH
3-methylbutanoic acid (-methylbutryic acid)
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Alpha Hydroxy Acids
Alpha hydroxy acids
(AHAs)
 Occur naturally in
fruit, milk, and
sugarcane.
 Are used in skin
care products.
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Names and Sources of Some
Carboxylic Acids
TABLE 16.1
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Common Carboxylic Acids
Methanoic acid (formic acid)
O
║
H─C─OH
ethanoic acid (acetic acid)
O
║
CH3─C─OH
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Aromatic Carboxylic Acids
Benzoic acid
 Is the aromatic carboxylic acid.
 Locates substituents by assigning 1 to the carbon
attached to the carboxyl group.
 Has common names that assign prefixes ortho,
meta, and para for 2 substituents.
ortho
1, 2 location
meta
1, 3 location
para
1, 4 location
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Aromatic Carboxylic Acids
O
C
OH
O
O
C OH
C OH
Cl
NH2
benzoic acid
3-chlorobenzoic acid
m-chlorobenzoic acid
4-aminobenzoic acid
p-aminobenzoic acid
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Learning Check
Give the IUPAC and common names:
A. CH3—COOH
B.
C.
CH3
|
CH3—CH—COOH
COOH
Br
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Solution
A.
B.
C.
CH3—COOH
CH3
|
CH3—CH—COOH
COOH
Br
ethanoic acid (acetic acid)
2-methylpropanoic acid
(-methylpropionic acid)
2-bromobenzoic acid
(o-bromobenzoic acid)
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Learning Check
Give the IUPAC and common names for the following:
A.
B.
C.
CH3─CH2─COOH
CH3
|
CH3─CH─CH2─COOH
O
C
OH
Br
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Solution
A.
CH3─CH2─COOH
B.
CH3
|
CH3─CH─CH2─COOH
O
C.
C
OH
propanoic acid
(propionic acid)
3-methylbutanoic acid
(β-methylbutyric acid)
3-bromobenzoic acid
(m-bromobenzoic acid)
Br
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Preparation of Carboxylic Acids
 Carboxylic acids can be prepared by oxidizing
primary alcohols or aldehydes.
 The oxidation of ethanol produces ethanoic acid
(acetic acid).
OH
O
|
[O]
||
CH3—CH2
CH3—C—H
ethanol
(ethyl alcohol)
O
[O]
||
CH3—C—OH
ethanal
(acetaldehyde)
ethanoic acid
(acetic acid)
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Learning Check
What alcohol could be used to prepare the following:
1. butanoic acid
2. propanoic acid
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Solution
What alcohol could be used to prepare the following:
[O]
[O]
1. butanol
butanal
butanoic acid
[O]
2. 1-propanol
[O]
propanal
propanoic acid
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Chapter 16 Carboxylic Acids and
Esters
16.2
Properties of Carboxylic Acids
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Polarity of Carboxylic Acids
Carboxylic acids
 Are strongly polar.
 Have two polar groups:
hydroxyl (−OH) and carbonyl (C=O).
δO
║δ+ δ- δ+
CH3CO H
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Boiling Points of Carboxylic Acids
The boiling points of carboxylic acids
 Are higher than alcohols, ketones, and aldehydes of
similar mass.
 Are high because they form dimers in which
hydrogen bonds form between the polar groups in the
two carboxyl groups.
O
H—O
||
|
CH3—C
C—CH3
|
||
O—H
O
A dimer of acetic acid
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Comparison of Boiling Points
Compound
O
║
CH3−CH2−C−H
Molar Mass
Boiling Point
58
49°C
CH3−CH2−CH2−OH
60
97°C
O
║
CH3−C−OH
60
118°C
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Solubility in Water
Carboxylic acids
 Form hydrogen
bonds with many
water molecules.
Water molecules
 With 1-4 carbon
atoms are very
soluble in water.
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Boiling Points and Solubility
TABLE 16.2
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Acidity of Carboxylic Acids
Carboxylic acids
 Are weak acids.
 Ionize in water to produce carboxylate ions
and hydronium ions.
O
O
║
║
CH3−C−OH + H2O
CH3−C−O– + H3O+
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Acid Dissociation Constants
Carboxylic acids
 Have small Ka values.
 Exist mostly as molecules
and a few ions in aqueous
solutions.
TABLE 16.3
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Neutralization of Carboxylic Acids
Carboxylic acid salts
 Are a product of the neutralization of a carboxylic acid
with a strong base.
CH3—COOH + NaOH
CH3—COO– Na+ + H2O
acetic acid
sodium acetate
(carboxylic acid salt)
 Are used as preservatives and flavor enhancers.
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Learning Check
Write the equation for the reaction of propanoic acid with
A. water
B. KOH
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Solution
Write the equation for the reaction of propanoic acid with
A. water
CH3—CH2—COOH + H2O
CH3—CH2—COO– + H3O+
B. KOH
CH3—CH2—COOH + KOH
CH3—CH2—COO– K+ + H2O
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Chapter 16 Carboxylic Acids and
Esters
16.3 Esters
16.4 Naming Esters
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Esters
In an ester,
 The H in the carboxyl group is replaced
with an alkyl group.
O

CH3 — C—O—CH3
ester group
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Esterification
Esterification is
 The reaction of a carboxylic acid and alcohol in the
presence of an acid catalyst to produce an ester.
O

H+
CH3—C—OH + H—O—CH2—CH3
O

CH3—C—O—CH2—CH3 + H2O
ethyl acetate (an ester)
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Learning Check
Write the equation for the reaction of propanoic acid
and methanol in the presence of an acid catalyst.
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Solution
Write the equation for the reaction of propanoic acid
and methanol in the presence of an acid catalyst.
O

H+
CH3—CH2—C—OH + H—O—CH3
propanoic acid
methanol
O

CH3—CH2—C—O—CH3 + H2O
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Naming Esters
The name of an ester contains the names of
 The alkyl group from the alcohol.
 The carbon chain from the acid with –ate ending.
from alcohol
from acid
O
methyl

CH3— O—C —CH3
ethanoate (acetate)
IUPAC: methyl ethanoate
common: methyl acetate
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Ester Products
Aspirin
 Is used to relieve pain and
reduce inflammation.
 Is an ester of salicylic acid
and acetic acid.
Oil of wintergreen
 Is used to soothe sore
muscles.
 Is an ester of salicylic acid
and methanol.
O
C OH
O
O C CH3
O
C O CH3
OH
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Esters in Plants
Esters give
flowers and
fruits their
pleasant
fragrances and
flavors.
TABLE 16.4
36
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Learning Check
Give the IUPAC and common names of the following
compound, which is responsible for the flavor and odor
of pears.
O

CH3—C—O—CH2—CH2—CH3
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Solution
Give the IUPAC and common names of the following
compound, which is responsible for the flavor and odor
of pears.
from 1-propanol
O

CH3—C—O—CH2—CH2—CH3
Propyl ethanoate (IUPAC)
Propyl acetate (common)
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Learning Check
Name the following esters:
O
║
A. CH3—CH2—CH2—C—O—CH3
B.
O

CH3—CH2 —C—O—CH2—CH3
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Solution
A. Methyl butanoate (methyl butyrate)
B. Ethyl propanoate (methyl propionate)
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Learning Check
Write the structure of the following esters:
A. Ethyl pentanoate
B. Propyl butyrate
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Solution
A. Ethyl pentanoate
O
║
CH3—CH2—CH2—CH2—C—O—CH2—CH3
B. Propyl butyrate
O
║
CH3—CH2—CH2—C—O—CH2—CH2—CH3
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Chapter 16 Carboxylic Acids and
Esters
16.5
Properties of Esters
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Acid Hydrolysis of Esters
In acid hydrolysis
 An ester reacts with water to produce a carboxylic
acid and an alcohol.
 An acid catalyst is required.
O

H+
H—C—O—CH2—CH3 + H2O
O

H—C—OH
+ H—O—CH2—CH3
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Base Hydrolysis (Saponification)
Base hydrolysis (also called saponification)
 Is the reaction of an ester with a strong base.
 Produces the salt of the carboxylic acid and an
alcohol.
O
||
CH3—C—O—CH2—CH3 + NaOH
O

CH3—C—O– Na+ + HO—CH2—CH3
salt of carboxylic acid
alcohol
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“Soaps”
The base hydrolysis of long chain fatty acids
produces acid salts called “soaps”.
46
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Cleaning Action of Soap
A soap
 Contains a nonpolar
end that dissolves in
nonpolar fats and
oils, and a polar end
that dissolves in
water.
 Forms groups of
soap molecules
called micelles that
dissolve in water
and are washed
away.
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47
Learning Check
Write the organic products when methyl acetate reacts
with
A. Water and an acid catalyst
B. KOH
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Solution
Write the organic products when methyl acetate reacts
with:
A. Water and an acid catalyst
O

CH3—C—OH + HO—CH3
B. KOH
O

CH3—C—O– K+
+ HO—CH3
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