chapter 17 carboxylic acids and esters -...
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1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
17.1 Carboxylic Acids17.2 Physical Properties of Carboxylic
Acids17.3 Acidity of Carboxylic Acids
Chapter 17 Carboxylic Acids And Esters
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The carboxyl group:Is a carbonyl group (C=O) attached to a hydroxyl group (OH).Is found on carbon 1 in carboxylic acids.Is written in different ways.
O||
CH3—C—OH CH3—COOH CH3—CO2H
Carboxyl Group
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Models of Carboxylic AcidsThe 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 acidCH3—CH3 ethane CH3—COOH ethanoic acidNumber substituents from the carboxyl carbon 1.
CH3|
CH3—CH—CH2—COOH4 3 2 1
2-methylbutanoic acid
IUPAC Names
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The common names of simple carboxylic acids:Use formic acid (1C), acetic acid (2C), propionic acid (3C), and butyric acid (4C). HCOOH formic acidCH3—COOH acetic acidLocate substituents by assigning α, β, γ to the carbon atoms adjacent to the carboxyl carbon.
CH3γ β| αCH3—CH—CH2—COOH
β-methylbutryic acid
Common Names
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Names and Sources of Some Carboxylic Acids
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Aromatic Carboxylic AcidsBenzoic 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 locationmeta 1, 3 locationpara 1, 4 location
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Aromatic Carboxylic Acids
Benzoic acid
4-Aminobenzoic acidp-Aminobenzoic acid
3-Chlorobenzoic acid m-Chlorozenoic acid
COOH
NH2
COOH
Cl
COOH
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Alpha Hydroxy Acids Alpha hydroxyacids (AHAs):Occur naturally in fruit, milk, and sugarcane.Are used in skin care products.
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Preparation of Carboxylic Acids
Carboxylic acid can be prepared by oxidizing primary alcohols or aldehydes.The oxidation of ethanol produces ethanoicacid (acetic acid).
OH O O| [O] || [O] ||
CH3—CH2 CH3—C—H CH3—C—OH
Ethanol ethanal ethanoic acidEthyl alcohol acetaldehyde acetic acid
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Give the IUPAC and common names:A. CH3—COOH
CH3|
B. CH3—CH—COOH
C.COOH
Br
Learning Check
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A. CH3—COOH ethanoic acid; acetic acidCH3|
B. CH3—CH—COOH 2-methylpropanoic acid;α-methylpropionic acid
C. 2-bromobenzoic acid;o-bromobenzoic acid
COOH
Br
Solution
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Boiling Points Carboxylic acids:Have higher boiling points than alcohols, ketones, and aldehydes of similar mass.Form dimers in which hydrogen bonds form between two carboxyl groups.
O H—O|| |
CH3 —C C—CH3| ||O—H O
A dimer of acetic acid
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Solubility in WaterCarboxylic acids:
With 1-4 carbon atoms are very soluble in water.Form hydrogen bonds with many water molecules.
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Boiling Points and Solubility
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Acid Dissociation Constants
Carboxylic acids:Are weak acids.CH3—COOH + H2O
CH3—COO– + H3O+
Exist mostly as molecules and a few ions in aqueous solutions.Have small Ka values.
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Salts of Carboxylic Acids
Carboxylic acid salts are:Formed when a carboxylic acid is neutralized by a strong base.CH3—COOH + NaOH CH3—COO- Na+ + H2Oacetic acid sodium acetate
(carboxylic acid salt)
Used as preservatives and flavor enhancers.
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Learning CheckWrite the equation for the reaction of propanoic acid with:A. water
B. KOH
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SolutionWrite the equation for the reaction of propanoic acid with:A. waterCH3—CH2—COOH + H2O
CH3—CH2—COO– + H3O+
B. KOHCH3—CH2—COOH + KOH
CH3—CH2—COO– K+ + H2O
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In amides, an amino group replaces the –OH group of carboxylic acids.
O O|| ||
CH3 — C — OH CH3 — C — NH2
Amides
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Preparation of AmidesAmides are produced by reacting a carboxylic acid with ammonia or an amine (1° or 2°).
O O|| heat ||
CH3—C—OH + NH3 CH3—C—NH2 + H2O
O O|| ||
CH3—C—OH + CH3—NH2 CH3—C—NH—CH3+ H2O
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Amides are named as alkanamides.In the IUPAC and common names, the –oic acid or -ic acid endings are replaced by –amide.
O|| Methanamide (IUPAC)
H—C—NH2 Formamide (common)O|| Propanamide (IUPAC)
CH2—CH2—C —NH2 Propionamide (common)
Naming Amides
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An alkyl group bonded to the N atom is named as N-alkyl in front of the amide name.
O||
CH—C—NH —CH3 N-methylethanamide (IUPAC)N-methylacetamide (common)
O CH3 || |
CH2—CH2—C —N —CH3 N,N-dimethylpropanamideN,N-dimethylpropionamide
Naming Amides with N Groups
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Aromatic AmidesThe amide of benzene is named benzamide.
C
O
NH2
Benzamide
C
O
NH CH3
N methylbenzamide -
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Classification of AmidesAmides are classified according to the number of carbon atoms bonded to the nitrogen atom.
O H|| |
CH3—C—N—H Primary (1°) amide O H|| |
CH3—C—N—CH3 Secondary (2°) amideO CH3|| |
CH3 —C—N—CH3 Tertiary (3°) amide
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Give the common and IUPAC names for the following amides and classify as primary, secondary, or tertiary:
O||
A. CH3—CH2—CH2—C—NH2
O CH3|| |
B. CH3—C—N—CH2—CH3
Learning Check
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O||
A. CH3—CH2—CH2—C—NH2butryamide (common); butanamide (IUPAC) primary(1°) amide
O CH3|| |
CH3—C—N—CH2—CH3N-ethyl-N-methylacetamide (common);N-ethyl-N-methylethanamide (IUPAC)tertiary (3°) amide
Solution
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Draw the condensed structures of A. Pentanamide
B. N-methylbenzamide
Learning Check
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A. PentanamideO||
CH3—CH2—CH2 —CH2—C—NH2
B. N-methylbenzamide
Solution
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Amides in Health and MedicineUrea is the end product of protein metabolism.Saccharin is an artificial sweetener.Some amides such as phenobarbital, Nembutal and Seconal are barbiturates.Acetaminophen is used to reduce fever and pain.
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Amides in Health and Medicine
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Physical Properties of AmidesHydrogen bonds form in primary and secondary amides, but not tertiary amides. The melting points of primary amides are higher than secondary amides, which have higher melting points than tertiary amides. All amides can form hydrogen bonds with water.Amides with 1–5 carbon atoms are soluble in water.
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Hydrogen Bonding of AmidesO ||
CH3—C—N—H |H Hydrogen bonding occurs
between primary amides.
O ||
CH3—C—N—H|H
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Amides undergo:Acid hydrolysis to produce a carboxylic acid and ammonium salt.
Base hydrolysis to produce the salt of a carboxylic acid and an amine or ammonia.
Reactions of Amides
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acid hydrolysis O ||
CH3—C—OH + NH4+Cl-
Hydrolysis Reactions
O ||
CH3—C—NH2
O ||
CH3—C—O-Na+ + NH3
HCl + H2O
NaOH
base hydrolysis
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Write the products of the hydrolysis of N-ethylpropanamide with NaOH.
Learning Check
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Write the products of the hydrolysis of N-ethylpropanamide with NaOH.
O ||
CH3—CH2—C—O-Na+ + CH3 —CH2 —NH2
Solution
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17.4 Esters of Carboxylic Acids17.5 Naming Esters17.6 Properties of Esters
Chapter 17 Carboxylic Acids And Esters
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In an ester, the H in the carboxyl group is replaced by an alkyl group.
O||
CH3—C—O—CH3CH3—COO—CH3
ester group
Esters
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An ester is produced by the reaction of a carboxylic acid and alcohol in the presence of an acid catalyst.
O|| H+
CH3—C—OH + HO—CH2—CH3
O||
CH3—C—O—CH2—CH3 + H2O
Esterification
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Ester ProductsAspirin:
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.
C
O
OH
O C
O
CH3
Acetylsalicylic acid(Aspirin)
C
O
O CH3
OH
Methyl salicylate(Oil of wintergreen)
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Write the equation for the reaction of propionic acid and methyl alcohol in the presence of an acid catalyst.
Learning Check
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Write the equation for the reaction of propionic acid and methyl alcohol in the presence of an acid catalyst.
O|| H+
CH3—CH2—C—OH + HO—CH3
O||
CH3—CH2—C—O—CH3 + H2O
Solution
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Esters are named with the alkyl name of the alcohol followed by the carboxylate name from the acid. from acid from alcohol
O|| methyl
CH3—C—O—CH3
Ethanoate methyl ethanoate (IUPAC)(Acetate) methyl acetate (common)
Naming Esters
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Esters give fruits their pleasant fragrances and flavors.
Some Esters In Nature
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Give the IUPAC and common name of the following compound, which is responsible for the flavor and odor of pears.
O||
CH3—C—O—CH2—CH2—CH3
Learning Check
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Give the IUPAC and common name of the following compound, which is responsible for the flavor and odor of pears.
from 1-propanolO||
CH3—C—O—CH2—CH2—CH3
Propyl ethanoate (IUPAC)Propyl acetate (common)
Solution
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Draw the structure of the following compounds:
A. Butyl acetate
B. Ethyl propionate
Learning Check
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A. Butyl acetateO||
CH3—C—O—CH2 —CH2 —CH2 —CH3
B. Ethyl propionateO||
CH3—CH2—C—O—CH2 —CH3
Solution
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In 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 + H2OO||
H—C—OH + HO—CH2 —CH3
Hydrolysis
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In base hydrolysis or saponification, an ester reacts with a strong base to produce the salt of the carboxylic acid and an alcohol.
O||
CH3—C—O—CH2—CH3 + NaOH
O||
CH3—C—O-Na+ + HO—CH2—CH3salt of carboxylic acid alcohol
Base Hydrolysis (Saponification)
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Base Hydrolysis of Fatty Acids Produces Soaps
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Cleaning Action of SoapA soap:
Contains a nonpolar carbon 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 with:A. 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—CH3B. KOH
O ||
CH3—C—O- K+ + HO—CH3
Solution