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Common Carboxylic Acids
Methanoic acid (formic acid)
O
║
H─C─OH
ethanoic acid (acetic acid)
O
║
CH3─C─OH
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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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
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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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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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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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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.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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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
12
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.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
13
Esters
In an ester,
 The H in the carboxyl group is replaced
with an alkyl group.
O

CH3 — C—O—CH3
ester group
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
14
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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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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Esters in Plants
Esters give
flowers and
fruits their
pleasant
fragrances and
flavors.
TABLE 16.4
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Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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”.
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Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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