1 carboxylic acids and esters carboxylic acids copyright © 2007 by pearson education, inc....
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Carboxylic Acids and Esters
Carboxylic Acids
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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
Carboxylic Acids
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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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The IUPAC names of carboxylic acids
Replace the -e in the alkane name with -oic acid.
CH4 methane HCOOH methanoic acid
CH3—CH3 ethane 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
IUPAC Names
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The common names of simple carboxylic acids Are formic acid (1C), acetic acid (2C), propionic acid
(3C), and butyric acid (4C). HCOOH formic acidCH3—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)
Common Names
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Alpha Hydroxy Acids
Alpha hydroxy acids
(AHAs) Occur naturally in
fruit, milk, and sugarcane.
Are used in skin care products.
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Names and Sources of Some Carboxylic Acids
TABLE 16.1
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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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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
OHC
O
OHC
O
OHC
O
ClNH2
benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid m-chlorobenzoic acid p-aminobenzoic acid
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Give the IUPAC and common names:
A. CH3—COOH
CH3
|B. CH3—CH—COOH
C.
Learning Check
COOH
Br
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Learning Check
Give the IUPAC and common names for the following:
A. CH3─CH2─COOH
CH3
|B. CH3─CH─CH2─COOHC.
OHC
O
Br
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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 ethanoic acid(ethyl alcohol) (acetaldehyde) (acetic acid)
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Learning Check
What alcohol could be used to prepare the following:
1. butanoic acid
2. propanoic acid
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16.2 Properties of Carboxylic Acids
Lecture 6: Carboxylic Acids and Esters
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Polarity of Carboxylic Acids
Carboxylic acids Are strongly polar. Have two polar groups:
hydroxyl (−OH) and carbonyl (C=O).
δ-
O ║δ+ δ- δ+
CH3CO 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 Molar Mass Boiling Point
O
║
CH3−CH2−C−H 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.
With 1-4 carbon atoms are very soluble in water.
Water molecules
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Boiling Points and Solubility
TABLE 16.2
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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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Acid Dissociation Constants
Carboxylic acids Have small Ka values. Exist mostly as molecules
and a few ions in aqueous solutions.
TABLE 16.3
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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.
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Learning Check
Write the equation for the reaction of propanoic acid with
A. water
B. KOH
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Lecture 6: Carboxylic Acids and Esters
16.3 Esters
16.4 Naming Esters
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Esters
In an ester, The H in the carboxyl group is replaced
with an alkyl group.
O
CH3 — C—O—CH3
ester group
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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)
Esterification
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Write the equation for the reaction of propanoic acid and methanol in the presence of an acid catalyst.
Learning Check
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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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Ester Products
Aspirin Is used to relieve pain and
reduce inflammation. Is an ester of salicylic acid
and acetic acid.
Oil of wintergreen Is used to soothe sore
muscles. Is an ester of salicylic acid
and methanol.
CH3
O
CO
OH
O
C
OH
CH3O
O
C
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Esters in Plants
Esters give flowers andfruits theirpleasant fragrances and flavors.
TABLE 16.4
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Learning Check
Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears.
O
CH3—C—O—CH2—CH2—CH3
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Learning Check
Name the following esters: O ║A. CH3—CH2—CH2—C—O—CH3
O
B. CH3—CH2 —C—O—CH2—CH3
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Learning Check
Write the structure of the following esters:
A. Ethyl pentanoate
B. Propyl butyrate
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Solution
A. Ethyl pentanoate O ║
CH3—CH2—CH2—CH2—C—O—CH2—CH3
B. Propyl butyrate
O ║
CH3—CH2—CH2—C—O—CH2—CH2—CH3
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Lecture 6: Carboxylic Acids and Esters
16.5
Properties of Esters
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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
Acid Hydrolysis of Esters
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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
Base Hydrolysis (Saponification)
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“Soaps”
The base hydrolysis of long chain fatty acids produces acid salts called “soaps”.
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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.
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Write the organic products when methyl acetate reacts withA. Water and an acid catalyst
B. KOH
Learning Check
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Write the organic products when methyl acetate reacts with:A. Water and an acid catalyst
O CH3—C—OH + HO—CH3
B. KOH O
CH3—C—O– K+ + HO—CH3
Solution