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Chapter Sixteen
Carboxylic Acids,
Esters, and Other
Acid Derivatives
Carboxylic Acids
Fig. 16.1
The three simplest carboxylic acids: methanoic acid, ethanoic
acid, and propanoic acid.
Chapter 16 | Slide 2 of 39
Carboxylic Acids
→ Fig. 16.2
Benzoic acid molecule
Chapter 16 | Slide 3 of 39
Carboxylic Acids
Carboxylic acids contain the carboxyl group on carbon 1.
• A carboxyl group is a carbonyl attached to a hydroxyl
• Acts differently than an alcohol or a carbonyl compound
O

CH3 — C—OH
=
CH3—COOH
carboxyl group
Chapter 16 | Slide 4 of 39
Naming Carboxylic Acids
Formula
IUPAC
alkan -oic acid
Common
prefix – ic acid
HCOOH
methanoic acid
formic acid
CH3COOH
ethanoic acid
acetic acid
CH3CH2COOH
propanoic acid
propionic acid
CH3CH2CH2COOH
butanoic acid
butyric acid
Chapter 16 | Slide 5 of 39
Naming Rules
• Identify longest chain containing the carboxyl group
• (IUPAC) Number carboxyl carbon as 1
• (Common) Assign , , g to carbon atoms adjacent to
carboxyl carbon
CH3
|
CH3 — CH—CH2 —COOH
IUPAC
3-methylbutanoic acid
Common -methylbutryic acid
Chapter 16 | Slide 6 of 39
Aromatic Carboxylic Acids
• Benzoic Acid is the aromatic carboxylic acid
• Locates substituents by assigning 1 to the carbon with the
carboxyl group
O
OH
C
O
OH
O
C
OH
C
Cl
Benzoic acid
3-chlorobenzoic acid
CH3
4-methylbenzoic acid
Chapter 16 | Slide 7 of 39
Chapter 16 | Slide 8 of 39
Chapter 16 | Slide 9 of 39
Properties of Carboxylic Acids
• Like alcohols, carboxylic acids form strong
intermolecular hydrogen bonds.
• Most carboxylic acids exist as dimers.
– Boiling points higher than alkanes of similar MW.
– Small carboxylic acids (1-4 carbons) are soluble in
water
O
H
O
H3C
CH 3
O
H
O
Chapter 16 | Slide 10 of 39
Chapter 16 | Slide 11 of 39
Synthesis of Carboxylic Acids
• Synthesized from
aromatic rings,
primary alcohols
and aldehydes.
R
Oxidizing agent
R
OH
Carboxylic
Acid
O
R
Chapter 16 | Slide 12 of 39
Oxidation of Aromatic Compounds
• Benzene does not react with KMnO4.
• Alkyl groups on the ring (-R) are readily
oxidized though.
• One product for all reactions.
O
R
OH
+ KMnO4
Chapter 16 | Slide 13 of 39
Oxidation of Aromatic Compounds
with KMnO4
O
OH
Chapter 16 | Slide 14 of 39
• Oxidation of primary alcohols and
aldehydes:
O
OH
CrO3, H3O+
or Na2Cr2O7, H2O, CH3CO2H
R
O
R
R
OH
O
H
AgNO3
NH4OH
R
OH
Chapter 16 | Slide 15 of 39
• Oxidation of alcohols to carboxylic acids.
O
OH
CrO3, H3O+
HO
CrO3, H3O+
OH
OH
O
Chapter 16 | Slide 16 of 39
Properties
• Carboxylic acids are weak acids
– Stronger acids than alcohols
CH3COOH + H2O
• Neutralized by a base
CH3COOH + NaOH
CH3COO– + H3O+
CH3COO– Na+ + H2O
Chapter 16 | Slide 17 of 39
• Carboxylic acids are obviously acidic.
• Stronger acids than alcohols, but weaker than mineral
acids.
• Will react with NaOH to give metal carboxylates.
• There is a large range of acidities depending on the
substituents on a carboxylic acid.
O
O
+ NaOH
R
OH
+ H2O
R
O-Na +
Chapter 16 | Slide 18 of 39
Carboxylate Ions
• The conjugate base of a carboxylic acid
– Formed when a carboxylic acid loses a proton
– Named by dropping the -ic acid ending and replacing it
with –ate
• CH3CH2COO• CH3COO• CH3CH2CH2COO-
Propionate
Ethanoate (Acetate)
Butanoate
Chapter 16 | Slide 19 of 39
Carboxylate Salts
• An ionic compound in which the negative ion is a
carboxylate ion
– Naming: the positive ion is named first, followed by a
separate word giving the name of the negative ion
– Converted back to a carboxylic acid by the addition of a
strong acid
• CH3CH2COO-Na+
• CH3COO-K+
• CH3CH2CH2COO-Li+
Sodium Propionate
Potassium Ethanoate
Lithium Butanoate
Chapter 16 | Slide 20 of 39
Carboxylic Acids
Table 16.3
Chapter 16 | Slide 21 of 39
Esters
← Fig. 16.12
Methyl and ethyl esters
of acetic acid.
Chapter 16 | Slide 22 of 39
Ester
In an ester, the H in the carboxyl group is replaced with an
alkyl group
O

CH3 — C—O —CH3
= CH3—COO —CH3
ester group
Sulfur analogs of esters are called thioesters (sulfur replaces
the hydroxyl oxygen)
Chapter 16 | Slide 23 of 39
Naming Esters
• Name the alkyl from the alcohol –O• Name the acid with the C=O with –ate
acid
alcohol
O

methyl
CH3 — C—O —CH3
Ethanoate
(acetate)
methyl ethanoate (IUPAC)
methyl acetate (common)
Chapter 16 | Slide 24 of 39
Chapter 16 | Slide 25 of 39
Esters
Chapter 16 | Slide 26 of 39
Esterification: Preparation of Esters
• Reaction of a carboxylic acid and alcohol
• Acid catalyst
O

CH3 — C—OH + HO—CH2CH3
H+
O

CH3 — C—O—CH2CH3 + H2O
Chapter 16 | Slide 27 of 39
Hydrolysis: Breaking Up Esters
• Esters react with water and acid catalyst
• Split into carboxylic acid and alcohol
O

H+
H — C—O—CH2CH3 + H2O
O

H — C—OH
+ HO—CH2CH3
Chapter 16 | Slide 28 of 39
Hydrolysis
Chapter 16 | Slide 29 of 39
Saponification
• Esters react with bases
• Produce the salt of the carboxylic acid and alcohol
O

H 2O
CH3C—OCH2CH3 + NaOH
O

CH3C—O– Na+
+
HOCH2CH3
salt of carboxylic acid
• Saponification reactions produce soaps
Chapter 16 | Slide 30 of 39
Soaps
• Carboxylate salts
Chapter 16 | Slide 31 of 39
• The following figure represents soap.
• Which end of the anion is hydrophobic?
Chapter 16 | Slide 32 of 39
• How does soap interact with grease?
Chapter 16 | Slide 33 of 39
Chapter 16 | Slide 34 of 39
Chapter 16 | Slide 35 of 39
Chapter 16 | Slide 36 of 39
Dicarboxylic Acids
Chapter 16 | Slide 37 of 39
The C2 dicarboxylic acid, oxalic acid, contributes to the tart taste of
rhubarb stalks.
Chapter 16 | Slide 38 of 39
Polyfunctional Carboxylic Acids
• Carboxylic acids that contain one or more additional
functional groups
– Unsaturated acids
• Contain a multiple bond
– Hydroxy acids
• Contains an additional hydroxyl group
– Keto acids
• Contains an additional carbonyl group
• Many monoacids and polyfunctional carboxylic acids are
intermediates in metabolic reactions
Chapter 16 | Slide 39 of 39