Carboxylic acids & esters

1
Chapter 16 Carboxylic Acids and
Esters
16.1
Carboxylic Acids
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
2
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
Carboxylic Acids
3
Models of Carboxylic Acids

The three-dimensional models show the geometry of atoms in
carboxylic acid molecules.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
4
The IUPAC names of carboxylic acids


Replace the -e in the alkane name with -oic acid.
CH4 methane HCOOH methanoic acid
CH3—CH3 ethane 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
IUPAC Names
5
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 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)
Common Names
6
Alpha Hydroxy Acids
Alpha hydroxy acids
(AHAs)


Occur naturally in
fruit, milk, and
sugarcane.

Are used in skin care
products.
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Publishing as Benjamin Cummings
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Names and Sources of Some
Carboxylic Acids

TABLE 16.1
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Publishing as Benjamin Cummings
8
Common Carboxylic Acids
Methanoic acid (formic acid)
O
║
H─C─OH
ethanoic acid (acetic acid)
O
║
CH3─C─OH
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Publishing as Benjamin Cummings
9
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
OHC
O
OHC
O
OHC
O
Cl
NH
2
benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid
m-chlorobenzoic acid p-aminobenzoic acid
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Give the IUPAC and common names:
A. CH3—COOH
CH3
|

B. CH3—CH—COOH
C.
Learning Check
COOH
Br


12
A. CH3—COOH ethanoic acid (acetic acid)
CH3
|
B. CH3—CH—COOH 2-methylpropanoic acid
(α-methylpropionic acid)
C. 2-bromobenzoic acid
(o-bromobenzoic acid)
Solution
COOH
Br


13
Learning Check
Give the IUPAC and common names for the following:
A. CH3─CH2─COOH
CH3
|
B. CH3─CH─CH2─COOH
C.
OHC
O

Br
14
Solution
A. CH3─CH2─COOH propanoic acid
(propionic acid)
CH3
|
B. CH3─CH─CH2─COOH 3-methylbutanoic acid
(β-methylbutyric acid)
C. 3-bromobenzoic acid
(m-bromobenzoic acid)

OHC
O
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
| [O] || [O] ||
CH3—CH2 CH3—C—H CH3—C—OH
ethanol ethanal ethanoic acid
(ethyl alcohol) (acetaldehyde) (acetic acid)
16
Learning Check
What alcohol could be used to prepare the following:

1. butanoic acid
2. propanoic acid
17
Solution
What alcohol could be used to prepare the following:
[O] [O]
1. butanol butanal butanoic acid
[O] [O]
2. 1-propanol propanal propanoic acid
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16.2
Properties of Carboxylic Acids
Chapter 16 Carboxylic Acids and
Esters
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Publishing as Benjamin Cummings
19
Polarity of Carboxylic Acids
Carboxylic acids

Are strongly polar.

Have two polar groups:
hydroxyl (−OH) and carbonyl (C=O).
δ
-
O
║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 Molar Mass Boiling Point
O
║
CH3−CH2−C−H 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.

With 1-4 carbon atoms
are very soluble in water.
Water molecules
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Publishing as Benjamin Cummings
23
Boiling Points and Solubility

TABLE 16.2
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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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
+
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
25
Acid Dissociation Constants
Carboxylic acids

Have small Ka values.

Exist mostly as molecules and
a few ions in aqueous
solutions.
TABLE 16.3