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1
Carboxylic Acids
2
A poem by Ogden Nash
The ant has made himself illustrious
Through constant industry industrious
So what?
Would you be calm and placid
If you were full of formic acid?
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• The functional group of the
carboxylic acid is called a
carboxyl group and is represented
in the following ways:
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Nomenclature and
Sources of
Aliphatic
Carboxylic Acids
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IUPAC Rules for Naming Carboxylic Acids
1. To establish the parent name, identify the
longest carbon chain that includes the carboxyl
group.
2. Drop the final –e from the corresponding
hydrocarbon name.
3. Add the suffix –oic acid.
HCOOH, methanoic acid
CH3COOH ethanoic acid
CH3CH2COOH propanoic acid
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Naming Carboxylic Acids
• Other groups bonded to the parent chain are
numbered and named as we have done
previously.
5 4 3 2 1
CH3CH2CHCH2COOH
CH3
3-methylpentanoic acid
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Common Names for Acids
•
•
•
•
•
•
HCOOH
CH3COOH
CH3CH2COOH
CH3(CH2)2COOH
CH3(CH2)3COOH
CH3(CH2)4COOH
Formic
Acetic
Propionic
Butyric
Valeric
Caproic
Formica (ant)
Acetum (sour)
Pro (first) + Pion (fat)
Butyrum (butter)
Valere (strong)
Caper (goat)
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Common Names for Acids
•
•
•
•
•
•
CH3(CH2)6COOH
CH3(CH2)8COOH
CH3(CH2)10COOH
CH3(CH2)12COOH
CH3(CH2)14COOH
CH3(CH2)16COOH
Caprylic
Capric
Lauric
Myristic
Palmitic
Stearic
Caper (goat)
Caper (goat)
Laurel
Muron (perfume)
Palm Oil
Stear (solid fat)
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Nomenclature of Carboxylic Acids
• Use of Greek letters:
5 4 3 2 1
CH3CH2CH2CH2COOH
  
CH3CH2CHCOOH
OH
-hydroxybutyric acid
2-hydroxybutanoic acid
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Physical Properties of
Carboxylic Acids
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Physical Properties of Carboxylic Acids
• Each aliphatic carboxylic acid molecule
is polar and consists of a carboxylic acid
group and a hydrocarbon group (-R).
– Carbons 1-4 = water soluble
– Carbons 5-8 = slightly water soluble
– Carbons 8 and above = virtually insoluble in water
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Physical Properties of Carboxylic Acids
• The comparatively high boiling points for
carboxylic acids are due to intermolecular
attractions resulting from hydrogen
bonding.
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Physical Properties of Carboxylic Acids
• Carboxylic acids are generally weak acids;
that is, they are only slightly ionized in
water.
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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
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Unsaturated Carboxylic Acids
• An unsaturated acid contains one or more C=C.
– Acrylic acid, CH2=CHCOOH, also called propenoic
acid.
• Even one C=C bond exerts an influence on the
physical and chemical properties of the acid.
Ex: stearic acid CH3(CH2)16COOH, mp = 70 ºC vs.
oleic acid CH3(CH2)7CH=CH(CH2)7COOH, mp = 16 ºC
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Aromatic Carboxylic Acids
• In an aromatic carboxylic acid, the carbon
of the carboxyl group (-COOH) is bonded
directly to a carbon in an aromatic ring.
COOH
COOH
CH3
benzoic acid
o-toluic acid
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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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Hydroxy Acids
• Hydroxy acids have the functional group
of an alcohol and a carboxylic acid.
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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
• Each amino acid molecule has a carboxyl
group that acts as an acid and an amino
group that acts as a base.
• About 20 biologically important amino
acids, each with a different group
represented by R, are found in nature.
NH2CHCOOH
The R group does not
necessarily represent an
alkyl group in amino acids.
R
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Preparation of
Carboxylic Acids
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Preparation of Carboxylic Acids
• oxidation of an aldehyde or primary
alcohol
• oxidation of alkyl groups attached to
aromatic rings
• hydrolysis of nitriles
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Oxidation of an Aldehyde or a
Primary Alcohol
H
R
C
O
OH
H
primary (1o)
[O]
R
C
O
H + H2O
[O]
R
C
OH
[O] = Cr2O72-
alcohol
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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.
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Hydrolysis of Nitriles
H+
• RCN + 2 H2O  RCOOH + NH4+
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Chemical Properties of
Carboxylic Acids
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Chemical Properties of
Carboxylic Acids
1. Acid-Base reactions
2. Substitution reactions
•
•
•
•
acid chlorides
acid anhydrides
esters
amides
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Acid-Base Reactions
•
Because of their ability to form hydrogen
ions in solution, acids in general have the
following properties:
1. Sour taste
2. Change blue litmus to red and affect other
suitable indicators.
3. Form water solutions with pH values less
than 7.
4. Undergo neutralization reactions with bases
for form water and a salt.
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Acidity of Carboxylic Acids
O
O
C
C
OH + H2O
H3C
H3C
-
H3C
O
O
O
C
C
OH + NaOH
H3C
+ H3O+
O-Na +
+ H2O
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Substitution Reactions
• acid chlorides
• acid anhydrides
• esters
• amides
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Acid Chloride Formation
Acid chlorides are prepared by reacting thionyl chloride
(SOCl2) and a carboxylic acid.
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Reactivity of Acid Chlorides
Acid chlorides are very reactive and will hydrolyze back
to the carboxylic acid if exposed to moisture.
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Acid Anhydride Formation
•An organic anhydride is formed by the
elimination of water from two molecules of
carboxylic acid.
O
+
C
R
OH
HO
O
O
O
C
C
C
R'
R
O
+ H2O
R'
anhydride
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Ester Formation
• An ester is formed by the reaction of an
acid with an alcohol or a phenol; water is
also produced in the reaction:
O
O
+
C
R
OH
carboxylic
acid
R'
HO
alcohol
H+
C
R
R'
+ H2O
O
ester
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Nomenclature of
Esters
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Nomenclature of Esters
• The alcohol part is named first, followed
by the name of the acid modified to end in
–ate.
O
O
C
R
acid
R'
O
alcohol
C
H3C
ethanoate
or
acetate
CH3
O
methyl
methyl ethanoate or
methyl acetate
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Occurrence and
Physical Properties
of Esters
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Properties of Esters
• Simple esters derived from monocarboxylic
acids and monohydroxy alcohols are
colorless, generally nonpolar liquids or
solids.
• Low- and intermediate-molar-mass esters
(both acids and alcohols up to about 10
carbons) are liquid with characteristic
(usually fragrant or fruity) odors.
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Occurrence and Properties of Esters
• High-molar-mass esters (formed from acids
or alcohols of 16 or more carbons) are
waxes and are obtained from various plants.
– They are used in furniture wax and automobile
wax preparations.
– Carnauba wax contains esters of 24-and 28carbon fatty acids and 32- and 34-carbon
alcohols.
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Chemical
Properties of Esters
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Hydrolysis
• The most important reaction of esters is
hydrolysis – the splitting of molecules
through the addition of water.
• A catalyst is often required.
– An acid or base
– In living systems, enzymes act as catalysts.
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Acid Hydrolysis
• The hydrolysis of an ester involves the
reaction with water to form a carboxylic
acid and an alcohol.
O
O
R'
C
O
ester
H+
+ H2O
or enzyme
R
+
R'
OH
alcohol
C
HO
R
carboxylic
acid
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Alkaline Hydrolysis (Saponification)
• Saponification is the hydrolysis of an ester by a
strong base (NaOH or KOH) to produce an
alcohol and a salt (or soap if the salt formed is
from a high-molar-mass acid).
• Notice that in saponification, the base is a
reactant and not a catalyst.
O
O
R'
+ NaOH
C
O
R
ester
H2O
+
R'
OH
alcohol
C
-
O Na+
R
salt
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Glycerol Esters
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Fats and Oils
• Fats and oils are esters of glycerol
and predominantly long-chain fatty
acids.
• Fats and oils are also called
triacylglycerols or triglycerides,
since each molecule is derived from
one molecule of glycerol and three
molecules of fatty acid:
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H
glycerol
portion
O
H
C
O
C
O
R
H
C
O
C
O
R'
C
O
C
H
R"
H
General formula for a
triacylglycerol
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Triacylglycerol
The structural formulas of triacylglycerol
molecules differ because:
1. The length of the fatty acid chain varies
from 4 to 20 carbons, but the number of
carbon atoms in the chain is nearly always
even.
2. Each fatty acid may be saturated or
unsaturated and may contain one, two, or
three C=C.
3. A triacylglycerol may, and frequently
does, contain three different fatty acids.
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• The most abundant unsaturated
acids in fats and oils contain 18
carbon atoms.
• In all of these naturally occurring
unsaturated acids, the
configuration about C=C is cis.
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Physical Differences Between Fats & Oils
• Fats are solid; oils are liquid at room
temperature
• Fats contain a larger portion of saturated
fatty acids whereas oils contain greater
amounts of unsaturated fatty acids.
– Polyunsaturated means that each molecule of
fat contains several C=C.
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Comparison of Fats & Oils
• Fats come from animal sources:
–Lard from hogs, tallow from
cattle and sheep
• Oils come from vegetable sources:
–Olives, corn, peanut, soybean,
canola
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Hydrogenation of Glycerides
• Hydrogen adds to the C=C of oil to
saturate it and form fats:
Ni
• H2 + -CH=CH-  -CH2-CH2• In practice, only some of the C=C are
allowed to become saturated.
– Partial hydrogenation
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Hydrogenolysis
• Triacylglycerols can be split and reduced
in a reaction called hydrogenolysis
(splitting by hydrogen).
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Hydrolysis
• Triacylglycerols can be hydrolyzed,
yielding fatty acids and glycerol.
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Saponification
• The saponification of a fat or oil
involves the alkaline hydrolysis of a
triester.
• The products formed are glycerol and
the alkali metal salts of fatty acids,
which are called soaps.
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Soaps and Synthetic
Detergents
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Soaps and Synthetic Detergents
• In the broadest sense possible, a
detergent is simply a cleansing agent.
• A soap is distinguished from a synthetic
detergent (syndet) on the basis of
chemical composition and not on the
basis of function or usage.
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Soaps
• Salts of long-chained fatty acids are
called soaps.
• Fat or oil + NaOH  Soap + Glycerol
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Cleansing action of soap.
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Synthetic Detergents - Anionic
The one great advantage these synthetic detergents have
over soap is that their Ca+2, Mg+2, and Fe+3 salts, as well as
their Na+1 salts, are soluble in water. Therefore, they are
nearly as effective in hard water as in soft water.
sodium lauryl sulfate
OSO3-Na+
nonpolar hydrophobic end,
grease soluble
polar hydrophilic end,
water soluble
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Synthetic Detergents – Nonionic
• The molecule of a nonionic detergent contains a
grease-soluble component and a water soluble
component.
• Some of these substances are especially useful in
automatic washing machines because they have
good detergent, but low sudsing, properties.
CH3(CH2)10CH2-O-(CH2CH2O)7-CH2CH2OH
grease soluble,
hydrophobic
water soluble, hydrophilic
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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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