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Chapter 24
Carboxylic Acid and Esters
Hein * Pattison * Arena * Best
Version 1.0
Jerry Poteat
Science Department
Georgia Perimeter College
1 ©
John Wiley and Sons, Inc.
Chapter Outline
24.1 Carboxylic Acids
24.2 Nomenclature and Sources of Aliphatic
Carboxylic Acids
24.3 Physical Properties of Carboxylic Acids
24.4 Classification of Carboxylic Acids
24.5 Preparation of Carboxylic Acids
24.6 Chemical Properties of Carboxylic Acids
2
Chapter Outline
24.7 Nomenclature of Esters
24.8 Occurrence and Physical Properties of Esters
24.9 Polyesters: Condensation Polymers
24.10 Chemical Properties of Esters
24.11 Glycerol Esters
24.12 Soaps and Synthetic Detergents
24.13 Esters and Anhydrides of Phosphoric Acid
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24.1 Carboxylic Acids
4
Carboxylic acids are organic compounds that contain the
carboxyl functional group as shown here.
These are three different ways to represent the carboxyl
group.
5
Carboxylic acids are either aliphatic or aromatic.
This is the general formula
for an aliphatic carboxylic acid.
acetic acid
( an aliphatic carboxylic acid)
the general formula
benzoic acid
This This
is theisgeneral
formula
benzoic
acid carboxylic acid)
(an aromatic
for an aromatic carboxylic acid.
for an aromatic carboxylic acid.
(an aromatic carboxylic acid)
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24.2 Nomenclature and Sources of
Aliphatic Carboxylic Acids
7
IUPAC Rules for Naming Carboxylic Acids
1. Name the longest continuous carbon chain
containing the –COOH group.
2. The –COOH carbon is numbered carbon one.
8
IUPAC Rules for Naming Carboxylic Acids
3. Drop an –e from the name of the parent alkane and
add the suffix –oic acid as shown below.
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Common Names of Carboxylic Acids
Several carboxylic acids are known by common names as
shown in the table below.
Natural Source
Formula
Name
Reference
HCOOH
formic acid ants
CH3COOH
acetic acid vinegar
CH3(CH2)2COOH butyric acid butterfat
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Naming Substituents of Carboxylic Acids
The substituents of carboxylic acids can also be named using
the Greek alphabet.
.
For example an –OH group on carbon three would be
-hydroxypentanoic acid using the Greek alphabet system
but it would be 3-hydroxypentanoic acid using the IUPAC
system.
11
Naming Substituents of Carboxylic Acids
Compare the IUPAC method with the Greek alphabet method.
Table 24.1 is a list of the common and IUPAC names for
many other carboxylic acids.
12
13
24.3 Physical Properties of
Carboxylic Acids
14
Solubility of Carboxylic Acids
The solubility of carboxylic acids is determined by which
of the two groups (i.e. the nonpolar R group or the polar
–COOH group ) of the molecule is the most dominant
in the chemical structure.
The solubility of RCOOH then is;
(a) carbons 1-4 are water soluble
(b) carbons 5-7 are slightly water soluble
(c) carbons 8 and above are water insoluble
15
Boiling Points of Carboxylic Acids
The relative high boiling points of carboxylic acids are due to
intermolecular attractions resulting from hydrogen bonding.
16
Acid-Base Properties of RCOOH
Carboxylic acids are weak acids that slightly ionize in water
as shown below. A 0.10 M solution of acetic acid (Ka =
1.8 x 10-5) has a percent ionization of 1.3%.
17
Occurrence of Carboxylic Acids
in Biochemistry
Carboxylic acids are released in the blood by the liver in
an excessive amount during ketoacidosis which is a
condition associated with uncontrolled diabetes.
Dopa is a carboxylic acid that is a derivative of dopamine
and is used in the treatment of Parkinson’s disease.
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24.4 Classification of
Carboxylic Acids
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Types of Carboxylic Acids
There are five major types of carboxylic acids in addition
to the saturated monocarboxylic acids like acetic acid
(CH3COOH ).
These acids are summarized and discussed in this section.
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Types of Carboxylic Acids
21
Unsaturated Carboxylic Acids
An unsaturated acid contains one or more C=C bonds.
The C=C bond affects the physical and chemical properties
of the acid.
For example stearic acid (CH3(CH2)16COOH) has no C=C
bonds and melts at 70 C and is a solid at room temperature.
However oleic acid (CH3(CH2)7CH=CH(CH2)7COOH) has
One C=C bond and melts at 16 C and is a liquid at room
temperature.
22
Aromatic Carboxylic Acids
Aromatic acids have a –COOH group bonded to a carbon
in the aromatic ring. Shown here are benzoic acid and the
three isomers of toluic acid.
23
Dicarboxylic Acids
Dicarboxylic acids have two carboxyl (COOH) groups.
These acids undergo a decarboxylation reaction ( i.e.loss of
CO2 ) to form a monocarboxylic acid or an anhydride
as shown below.
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Citric acid is a hydroxytricarboxylic acid. It is 5-8% of
lemon juice and widely distributed in plant and animal
tissues.
It is also an important acid in the citric acid cycle. Examples
of other dicarboxylic acids are listed in Table 24.2.
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26
Hydroxy Acids
Hydroxy acids have the functional groups of an alcohol and
a carboxylic acid. Two important -hydroxy acids are lactic
acid and salicylic acid.
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Hydroxy Acids
Lactic acid is found in sour milk as well as in muscle tissue
as result of exercise.
Salicyclic acid and its derivatives are found in analgesics
like aspirin.
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Hydroxy Acids
Malic acid and tartaric acid are two other common
-hydroxy acids found in apples and grapes respectively.
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Amino Acids
Amino acids have a carboxyl group(– COOH) and an
amino group (– NH2). The –COOH group acts as an acid
while the – NH2 acts as a base.
Most amino acids in nature have the – NH2 in the  position
as shown here.
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Amino Acids
Amino acid units are the building blocks of proteins.
Approximately 20 amino acids are biologically significant.
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24.5 Preparation of Carboxylic
Acids
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Preparation of Carboxylic Acids
Carboxylic acids can be prepared using various reaction
types.
Oxidation and the hydrolysis of nitriles are two reaction
types presented in this section.
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Oxidation of an Alcohol
Primary alcohols are oxidized to carboxylic acids
(general reaction)
34
Oxidation of an Alcohol
Primary alcohols like benzyl alcohol can also be oxidized
to a carboxylic acid.
35
Oxidation of an Aldehyde
Aldehydes are oxidized to carboxylic acids
( general reaction)
36
Oxidation of Alkyl Groups Attached to an
Aromatic Ring
Alkyl benzenes are oxidized in basic solution to the
carboxylate salt and then protonated with acid to form
benzoic acid.
37
Hydrolysis of a Nitrile
Nitriles are prepared by reacting an alkyl halide and a
cyanide salt.
The nitrile is then hydrolyzed to a carboxylic acid.
Acetonitrile is hydrolyzed to acetic acid.
acetonitrile
acetic acid
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24.6 Chemical Properties of
Carboxylic Acids
39
Reactions of Carboxylic Acids
Carboxylic acids undergo two broad classes of reactions
which are acid-base reactions and substitution reactions.
(1) Acid-base reactions occur because the –OH of
the –COOH group can act as a proton donor
(2) The C=O of the –COOH group serves as a site for
substitution reactions.
40
Acid –Base Reactions
Low molar-mass carboxylic acids release H+ ions in
solution and as a result have the following properties
unique to acids in general.
a. Sour taste
b. Blue litmus paper changes to red in an acidic solution
c. Forms solutions with a pH < 7
d. Reacts with bases in neutralization reaction
41
Acid –Base Reactions
The characteristics listed in the previous slide are not true
of higher molar-mass carboxylic acids because the
dominant nonpolar R group makes these higher molarmass carboxylic acids insoluble in water.
However the higher molar-mass carboxylic acids do react
with strong bases like NaOH as shown below. The sodium
and potassium salts are soluble in water.
42
There are four major types of substitution reactions
of carboxylic acids.
1.
2.
3.
4.
Acid Chloride Formation
Acid Anhydride Formation
Ester Formation
Amide Formation
(acid chloride formation)
(anhydride formation)
(ester formation)
(amide formation)
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Acid Chloride Formation
Acid chlorides are prepared by reacting thionyl chloride
(SOCl2) and a carboxylic acid.
44
Reactivity of Acid Chlorides
Acid chlorides are very reactive and will hydrolyze back
to the carboxylic acid if exposed to moisture.
45
Reactivity of Acid Chlorides
Acid chlorides can use to prepare esters like methyl
acetate or amides like acetamide as shown the example
below.
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Acid Anhydride Formation
Acid anhydrides are prepared by reacting two molecules
of a carboxylic acid.
Acid anhydrides are prepared by reacting an acid chloride
with a carboxylate anion.
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Ester Formation
Esters are prepared by a reacting a carboxylic acid and an
alcohol in the presence of a strong acid catalyst.
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24.7 Nomenclature of Esters
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IUPAC Rules for Naming Esters
1. Name the alkoxy alkyl group.
2. Name the carboxylic acid parent and change the -ic
ending to –ate.
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The ester formed by the reaction of propanoic acid
and methanol is methyl propanoate.
Table 24.3 in the next slide lists the IUPAC and common
names of other esters.
51
52
24.8 Occurrence and Physical
Properties of Esters
53
Properties of Low-Molar Mass Esters
Low molar- mass esters are volatile nonpolar liquids at room
temperature. They are good solvents. Ethyl acetate for example is
used in paints and varnishes.
These esters also have a characteristic fragrant or fruity odor compared
to the parent carboxylic acid as shown below.
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Properties of High Molar Mass Esters
High molar mass esters are nonpolar solids at room temperature.
Many of these esters are waxes.
Carnauba wax for example is an ester that can have a 28-carbon fatty
acid chain and a 34-carbon alcohol chain.
High molar mass esters are used in furniture and automobile
wax preparations.
Very high molar mass esters include polyesters such as Dacron.
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24.9 Polyesters: Condensation
Polymers
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Polyesters: Condensation Polymers
A polyester is a polymer formed between an alcohol
monomer and a carboxylic acid monomer.
Polyesters are classified as condensation polymers.
An example of a general polymerization reaction to
produce a polyester is shown here.
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Polyesters: Condensation Polymers
This is a polymerization reaction that produces the
polyethylene terephthalate (PETE) polyester.
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Polyesters: Condensation Polymers
Polyethylene terephthalate is a common polyester found in
Mylar films and the 2-L soft drink bottle.
This is the plastic recycle code
for polethylene terephthalate.
59
Cross-linked Polyesters
If one of the monomers in a polymerization is trifunctional.
then a cross-linked thermosetting polymer will form.
Glycerol is a trifunctional
molecule with three –OH
groups.
o-Phthalic acid would
form a cross-linked polyester
if reacted with glycerol.
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24.10 Chemical Properties of
Esters
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Reactions of Esters
The principal reaction of esters is hydrolysis.
Ester hydrolysis is either acid-catalyzed (i.e. acid hydrolysis)
or base-promoted (i.e. alkaline hydrolysis/saponification).
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Acid Hydrolysis
An ester is hydrolyzed in the presence of an acid catalyst
to an alcohol and a carboxylic acid
(general reaction)
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Specific examples of acid-catalyzed ester hydrolysis
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Alkaline Hydrolysis (Saponification)
An ester is hydrolyzed in the presence of a strong base to
an alcohol and a salt.
The base is consumed in saponification while in acid
hydrolysis the acid is acts a catalyst.
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Alkaline Hydrolysis (Saponification)
The carboxylic acid is formed by reacting the salt with
with a strong acid such as HCl .
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24.11 Glycerol Esters
67
Triacylglycerols
Esters of glycerol (i.e. glycerol esters) are known as
triacylglycerols ( also called triglycerides).
General formula
for a triacylglycerol
This is a triacylglycerol prepared
from glycerol and three different
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fatty acids.
Fats and Oils
Fats and oils are triacylglycerols.
Fats originate from animal sources and are solids at room
temperature because they have a higher percentage of
saturated fatty acid derivatives in their triacylglycerol
structure.
Oils originate from plant sources and are liquids at room
temperature because they have a higher percentage of
unsaturated fatty acid derivatives in their triacylglycerol
structure.
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Fats and Oils
Some common unsaturated fatty acid derivatives found
in oils include the corresponding parent fatty acids oleic
acid, linoleic acid, and linolenic acid as shown here.
Table 24.4 is a list of the types of fatty acids in various
fats and oils by percent composition.
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Reactions of Triacylglycerols
Triacylglycerols undergo two basic types of reactions;
reduction ( to include hydrogenation and hydrogenolysis)
and hydrolysis (acidic or basic).
Hydrogenation of Glycerides
Oils are partially hydrogenated using a metal catalyst
and hydrogen gas to obtain a solid like the shortening
found in a consumer product like Crisco.
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During partial hydrogenation some of the cis bonds change
to trans bonds which is the basis for the term ‘trans fat”.
Research has shown these unnatural fats to be unhealthy
and to increase the risk of heart disease.
Hydrogenolysis
Long chain alcohols are prepared by reducing triacylglycerols
with hydrogen gas and a copper chromite catalyst.
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Hydrolysis
Fatty acids are prepared by hydrolyzing triacylglycerols
with either enzymes or mineral acid catalysts.
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Saponification
Soap ( i.e. carboxylate salts) is prepared by the alkaline
hydrolysis of triacylglycerols.
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24.12 Soaps and Synthetic
Detergents
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Soaps
Soaps are salts of long-chain fatty acids that are prepared by
the general reaction shown here.
For example this is the soap
sodium palmitate. It is the
sodium salt of the fatty acid
palmitic acid.
sodium
palmitate
sodium palmitate
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The Cleansing Action of Soaps
The cleansing action of soaps is determined by the carboxylate
ion.
The hydrocarbon tail of the carboxylate ion is nonpolar
and dissolves the nonpolar grease. The hydrocarbon tail is
said to be hydrophobic (i.e. water-fearing).
The polar head of the carboxylate ion allows it to remain
soluble in water which is also polar . The polar head is
said to be hydrophilic (i.e. water-loving).
Figure 24.1 shows the action of the hydrocarbon tails and the
polar heads of the carboxylate ions.
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Figure 24. 1 The cleansing action of soap.
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The Cleansing Action of Soaps in Hard Water
The cleansing action of soaps in hard water is limited because
hard water contains ions that react with carboxylate ions to
form insoluble salts as shown in the reaction below.
These ions include Ca2+, Fe3+, and Mg2+
(insoluble in water)
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The Cleansing Action of Soaps
in Acidic Solutions
Soaps are also ineffective in acidic solutions because insoluble
fatty acids are formed.
(insoluble in water)
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Synthetic Detergents
Synthetic detergents ( i.e syndets) are synthetic organic
products that act as cleansing agents.
These synthetic detergents are effective in soft water and
hard water.
Chemical structures for
two synthetic detergent
salts.
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Ionic Synthetic Detergents
Synthetic detergents can be ionic ( either anionic or cationic)
or nonionic.
Anionic detergent
Cationic detergent
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Nonionic Synthetic Detergents
A nonionic detergent molecule contains a grease-soluble
component and a water soluble component as shown below.
These detergents have good cleansing action but low
sudsing properties which makes them desirable for use in
automatic washing machines.
Nonionic detergent
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Biodegradability
Biodegradable organic substances are those that can be
readily decomposed by microorganisms in the environment.
For example detergents with straight-chain alkyl benzenes
are biodegradable.
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Biodegradability
However detergents with branched-chain alkyl benzenes
are not biodegradable.
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24.13 Esters and Anhydrides of
Phosphoric Acid
87
Esterification of Phosphoric Acid (H3PO4)
Phosphoric acid and a carboxylic acid have similar structures.
Because of this structural similarity phosphoric acid can form
esters and anhydrides just like a carboxylic acid.
88
Example of a Esterification Reaction with H3PO4
A phosphate ester is formed by the reaction of phosphoric
acid and ethanol in the presence of a strong acid catalyst.
Phosphate esters are biologically important because
they act as “tags” for other biochemicals .
89
Phosphoric Acid Anhydrides
Pyrophosphoric acid is a phosphoric acid anhydride
formed by the reaction of two molecules of phosphoric
acid.
Phosphoric acid anhydrides are biologically important
because they temporarily store metabolic energy in the
form of molecules like ATP.
90
Chapter 24 Summary
Carboxylic acids are organic acids with the general formula
RCOOH.
Classes of RCOOH include saturated monocarboxylic, unsaturated,
dicarboxylic, aromatic, hydroxy acids, and amino acids.
Derivatives of carboxylic acids include acid chlorides, anhydrides,
esters and amides.
Glycerol esters are known as triacylglycerols but they are also
known as triglycerides.
 Both fats and oils are triacylglycerols with the difference being fats
are solids from animal sources while oils are liquids from plant
sources.
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Chapter 24 Summary
Triacylglycerols can be hydrolyzed to form soap in an alkaline
hydrolysis reaction called saponification.
Soaps are salts of long-chain fatty acids.
 The cleansing action of soap is based on the action of the nonpolar
tail and the polar head of the carboxylate ion portion of the
carboxylate salt.
Esters of phosphoric acid act as labels for other biochemicals for
specific metabolic purposes.
Anhydrides of phosphoric acid serve as a temporary storage for
metabolic energy
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