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Carboxylic Acids
CnH2nO2
Carboxylic acids are organic acids characterized by The O
presence of a carboxyl group, which has the formula - C(=O)OH,
usually written –COOH or –CO2H.
carboxylic C
acids are Bronsted acids they are proton donors. Salts R OH
and anions of carboxylic acids they are called carboxylates.
The simplest series of carboxylic acids are the alkanoic acids, RCOOH,
where R is a hydrogen or an alkyl group.
carbonyl group
O

CH3 — C—OH hydroxyl group or CH3COOH
carboxyl group
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Models of Carboxylic Acids
• The three-dimensional models show the
geometry of atoms in carboxylic acid
molecules.
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Common Carboxylic Acids
Methanoic acid (formic
acid)
O
║
H─C─OH
ethanoic acid (acetic acid)
O
║
CH3─C─OH
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IUPAC Names
• Nomenclature and examples
• The carboxylate anion R-COO- is usually
named with the suffix –ate, so acetic acid, for
example, becomes acetate ion. In IUPAC
nomenclature,
• carboxylic acids have an –oic acid suffix (e.g.
octadecanoic acid).
• In common nomenclature, the suffix is usually
–ic acid(e.g. stearic acid).
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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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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
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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Learning Check
Give the IUPAC and common names:
A. CH3—COOH
CH3
|
B. CH3—CH—COOH
COOH
C.
Br
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Learning Check
Give the IUPAC and common names for the
following:
A. CH3─CH2─COOH
CH3
O
|
B. CH3─CH─CH2─COOH
C OH
C.
Br
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Some representative carboxylic acids include:
1. Short chain saturated monocarboxylic acids
 Formic acid(methanoic acid) –HCOOH, found in
insect stings
(formic from the Latin word meaning ant)
 Acetic acid (ethanoic acid) –CH3COOH, the
principal component of vinegar
 Propionic acid (propanoic acid) –CH3CH2COOH
2. Medium chain saturated monocarboxylic acids
 Valeric acid (pentanoic acid) –C4H9COOH
 Enanthic acid (heptanoic acid) – C6H13COOH
 Pelargonic acid(nonanoic acid) -C9H17COOH
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• 3. Short chain unsaturated monocarboxylic acids
•  Acrylic acid(2-propenoic acid) –CH2=CHCOOH, used in
polymer
• synthesis
• 4. Fatty acids-medium to long chain saturated and
unsaturated
• monocarboxylic acids, with even number of carbons
•  Butyric acid (butanoic acid) –CH3CH2CH2COOH, found
in rancid butter
•  Lauric acid (dodecanoic acid) –
CH3(CH2)10COOH,found in coconut oil
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• 5. Amino acids – the building blocks of proteins
• 6. Keto acid – acids of biochemical significance
that contain a ketone group
•  Pyruvic acid
•  Acetoacetic acid
• 7. Aromatic carboxylic acids
•  Benzoic acid –C6H5COOH.sodium benzoate, the
sodium salt of benzoic acid used as a food
preservative
•  Salicylic acid – found in many skin care
products
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•
•
•
•
•
•
•
•
•
•
•
8. Dicarboxylic acids – containing two carboxyl groups
 Aldaric acid – a family of sugar acids
 Oxalic acid – found in many foods
 Malonic acid
 Malic acid – found in apples
 Succinic acid – a component of the citric cycle
 Glutaric acid
9. Tricarboxylic acid – containing a hydroxy groups
 Citric acid – found in citrus fruits
10.Alpha hydroxyl acids – containing a hydroxyl group
 Lactic acid (2-hydroxypropanoic acid) – found in sour
milk
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Properties of
Carboxylic Acids
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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
(ethyl alcohol) (acetaldehyde)
ethanoic acid
(acetic acid)
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• Physical properties
• Carboxylic acids are polar, and form
hydrogen bonds with each other.
• Lower carboxylic acids (1 to 4 carbons ) are
miscible with water, while higher carboxylic
acids are very much less soluble due to the
increasing hydrophobic nature of the alkyl
chain. They tend to be rather soluble in less
polar solvents such as ethers and alcohols
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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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Solubility in Water
Carboxylic acids
• Form hydrogen
bonds with many
water molecules.
Water molecules
• With 1-4 carbon
atoms are very
soluble in water.
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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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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 typically weak acids, meaning they
only partially dissociate into H+ cations and RCOOanions in aqueous solution. For example, at room
temperature, only 0.02%of all acetic acid molecules are
dissociated in water. Since the carboxylic acids are weak
acids, in water, both forms exist in an equilibrium:
RCOOH
―‣ RCOO- + H+
• The acidity of carboxylic acids can be explained either
by the stability of acids, or the stability of the conjugate
base using inductive effects or resonance effects.
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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+
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