Download Lecture 6_Carboxylic Acids and Esters

Lecture 6: Carboxylic Acids and
Esters
Carboxylic Acids
A carboxylic acid
ƒ Contains a carboxyl group, which is a carbonyl group
(C=O) attached to a hydroxyl group (—OH).
ƒ Has the carboxyl group on carbon 1.
carbonyl group
O
||
CH3 — C—OH hydroxyl group or CH3COOH
carboxyl group
16.1
Carboxylic Acids
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Publishing as Benjamin Cummings
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Models of Carboxylic Acids
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IUPAC Names
The IUPAC names of carboxylic acids
ƒ The three-dimensional models show the geometry
of atoms in carboxylic acid molecules.
ƒ Replace the -e in the alkane name with -oic acid.
methane
CH4
HCOOH
CH3—CH3 ethane
methanoic acid
CH3—COOH ethanoic acid
ƒ Number substituents from the carboxyl carbon 1.
O
CH3
|
║
CH3—CH—CH2—C—OH
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2
1
3-methylbutanoic acid
3
4
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Common Names
Alpha Hydroxy Acids
The common names of simple carboxylic acids
ƒ Are formic acid (1C), acetic acid (2C), propionic acid
(3C), and butyric acid (4C).
HCOOH
formic acid
acetic acid
CH3—COOH
ƒ Locate substituents using α, β, γ for the carbon
atoms adjacent to the carboxyl carbon.
CH3
γ
β|
α
CH3—CH—CH2—COOH
3-methylbutanoic acid (β-methylbutryic acid)
Alpha hydroxy acids
(AHAs)
ƒ Occur naturally in
fruit, milk, and
sugarcane.
ƒ Are used in skin
care products.
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5
Names and Sources of Some
Carboxylic Acids
6
Common Carboxylic Acids
TABLE 16.1
Methanoic acid (formic acid)
O
║
H─C─OH
ethanoic acid (acetic acid)
O
║
CH3─C─OH
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Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Aromatic Carboxylic Acids
Aromatic Carboxylic Acids
O
Benzoic acid
ƒ Is the aromatic carboxylic acid.
C
OH
ƒ Locates substituents by assigning 1 to the carbon
attached to the carboxyl group.
O
O
C OH
C OH
ƒ 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
Cl
benzoic acid
3-chlorobenzoic acid
m-chlorobenzoic acid
NH2
4-aminobenzoic acid
p-aminobenzoic acid
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Learning Check
Learning Check
Give the IUPAC and common names for the following:
A. CH3─CH2─COOH
CH3
|
B. CH3─CH─CH2─COOH
C.
O
Give the IUPAC and common names:
A. CH3—COOH
B.
10
CH3
|
CH3—CH—COOH
C
C.
OH
COOH
Br
11
Br
12
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Preparation of Carboxylic Acids
Learning Check
What alcohol could be used to prepare the following:
ƒ Carboxylic acids can be prepared by oxidizing
primary alcohols or aldehydes.
ƒ The oxidation of ethanol produces ethanoic acid
(acetic acid).
OH
O
|
[O]
||
CH3—CH2
CH3—C—H
ethanol
(ethyl alcohol)
1. butanoic acid
2. propanoic acid
O
[O]
||
CH3—C—OH
ethanal
(acetaldehyde)
ethanoic acid
(acetic acid)
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Lecture 6: Carboxylic Acids and
Esters
Polarity of Carboxylic Acids
16.2
Properties of Carboxylic Acids
Carboxylic acids
ƒ Are strongly polar.
ƒ Have two polar groups:
hydroxyl (−OH) and carbonyl (C=O).
δO
║δ+ δ- δ+
CH3⎯C⎯O⎯ H
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16
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Boiling Points of Carboxylic Acids
Comparison of Boiling Points
The boiling points of carboxylic acids
ƒ Are higher than alcohols, ketones, and aldehydes of similar
mass.
Compound
O
║
CH3−CH2−C−H
ƒ Are high because they form dimers in which hydrogen bonds
form between the polar groups in the two carboxyl groups.
O
H—O
||
|
C—CH3
CH3—C
|
||
O—H
O
A dimer of acetic acid
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
ƒ Form hydrogen
bonds with many
water molecules.
18
Boiling Points and Solubility
Water molecules
TABLE 16.2
ƒ With 1-4 carbon
atoms are very
soluble in water.
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Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Acidity of Carboxylic Acids
Acid Dissociation Constants
Carboxylic acids
ƒ Are weak acids.
ƒ Ionize in water to produce carboxylate ions
and hydronium ions.
O
O
║
║
CH3−C−OH + H2O
CH3−C−O– + H3O+
Carboxylic acids
ƒ Have small Ka values.
ƒ Exist mostly as molecules
and a few ions in aqueous
solutions.
TABLE 16.3
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21
Neutralization of Carboxylic Acids
Learning Check
Carboxylic acid salts
ƒ 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)
ƒ Are used as preservatives and flavor enhancers.
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22
23
Write the equation for the reaction of propanoic acid with
A. water
B. KOH
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6
Lecture 6: Carboxylic Acids and
Esters
Esters
In an ester,
ƒ The H in the carboxyl group is replaced
with an alkyl group.
16.3 Esters
16.4 Naming Esters
O
||
CH3 — C—O—CH3
ester group
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Publishing as Benjamin Cummings
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Esterification
Learning Check
Esterification is
ƒ 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
Write the equation for the reaction of propanoic acid
and methanol in the presence of an acid catalyst.
O
||
CH3—C—O—CH2—CH3 + H2O
ethyl acetate (an ester)
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Naming Esters
Ester Products
The name of an ester contains the names of
ƒ The alkyl group from the alcohol.
ƒ 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
Aspirin
ƒ Is used to relieve pain and
reduce inflammation.
ƒ Is an ester of salicylic acid
and acetic acid.
Oil of wintergreen
ƒ Is used to soothe sore
muscles.
ƒ 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.
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Learning Check
TABLE 16.4
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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8
Learning Check
Learning Check
Name the following esters:
O
║
A. CH3—CH2—CH2—C—O—CH3
Write the structure of the following esters:
B.
A. Ethyl pentanoate
B. Propyl butyrate
O
||
CH3—CH2 —C—O—CH2—CH3
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Lecture 6: Carboxylic Acids and
Esters
Solution
16.5
Properties of Esters
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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Acid Hydrolysis of Esters
Base Hydrolysis (Saponification)
Base hydrolysis (also called saponification)
ƒ Is the reaction of an ester with a strong base.
ƒ 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
In acid hydrolysis
ƒ An ester reacts with water to produce a carboxylic
acid and an alcohol.
ƒ An acid catalyst is required.
O
||
H+
H—C—O—CH2—CH3 + H2O
O
||
H—C—OH
+ H—O—CH2—CH3
salt of carboxylic acid
alcohol
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“Soaps”
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Cleaning Action of Soap
A soap
ƒ Contains a nonpolar end
that dissolves in
nonpolar fats and oils,
and a polar end that
dissolves in water.
ƒ Forms groups of soap
molecules called
micelles that dissolve in
water and are washed
away.
The base hydrolysis of long chain fatty acids
produces acid salts called “soaps”.
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Publishing as Benjamin Cummings
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Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Learning Check
Solution
Write the organic products when methyl acetate reacts with:
A. Water and an acid catalyst
O
||
CH3—C—OH + HO—CH3
Write the organic products when methyl acetate reacts
with
A. Water and an acid catalyst
B. KOH
B. KOH
O
||
CH3—C—O– K+
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+ HO—CH3
42
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