Download File

Carboxylic Acids, Esters, Amines,
and Amides
Carboxylic acids and esters are two families of
organic molecules that contain a carbonyl group
(C=O) singly bonded to an oxygen atom.
• A carboxylic acid contains a carboxyl group (COOH).
• An ester contains an alkoxy group (OR) bonded to
the carbonyl carbon.
1
Carboxylic Acids, Esters, Amines,
and Amides
Amines and amides are nitrogen-containing organic
molecules.
• An amine is an organic nitrogen compound
formed by replacing one or more hydrogen atoms
of ammonia (NH3) with alkyl groups.
• An amide is a carbonyl compound that contains a
nitrogen atom bonded to the carbonyl carbon.
2
Nomenclature
Naming a Carboxylic Acid (RCOOH)
To name a carboxylic acid using the IUPAC system:
• Find the longest chain containing the COOH
group, and change the “-e” ending of the parent
alkane to “-oic acid.”
• Number the chain to put the COOH group at C1, but
omit “1” from the name. Apply all other
nomenclature rules.
CH3
O
CH3CHCHCH2CH2C OH
5 4
CH3
1
hexane  hexanoic acid
Answer:
4,5-dimethylhexanoic acid
3
Nomenclature
Naming a Carboxylic Acid (RCOOH)
• Many simple carboxylic acids are referred to by
their common names. A common name uses the
suffix -ic acid.
formic acid
acetic acid
benzoic acid
4
Nomenclature
Naming an Ester (RCOOR’)
To name an ester using the IUPAC system:
• Name the R' group bonded to the oxygen atom as
an alkyl group.
• Name the RCO– group by changing the “-ic acid”
ending of the parent carboxylic acid to the
suffix “-ate.”
5
Nomenclature
Naming an Ester (RCOOR′)
Sample Problem 13.2
Give the IUPAC name for the following ester:
O
CH3CH2CH2 C
OCH3
Step [1] Name the R’ group bonded to the O atom as
an alkyl group.
O
CH3CH2CH2 C
OCH3
methyl group
6
Nomenclature
Naming an Ester (RCOOR′)
Sample Problem 13.2
Step [2] Name the acyl group (RCO-) by:
• Changing the “-ic acid” ending of the
parent carboxylic acid to “-ate.”
• This becomes the second part of the name.
O
CH3CH2CH2 C
OCH3
Answer:
methyl butanoate
derived from
butanoic acid  butanoate
7
Physical Properties of Carboxylic Acids
and Esters
• Carboxylic acids and esters are polar compounds.
• Only carboxylic acids can undergo intermolecular
hydrogen bonding.
8
Physical Properties
Carboxylic acids also have higher boiling points
than esters because esters are incapable of
intermolecular hydrogen bonding.
methyl acetate
propanoic acid
Increasing boiling point
9
Physical Properties
Carboxylic acids have higher boiling points than
similar alcohols because there are more hydrogen
bonding interactions possible than alcohols.
Increasing boiling point
10
Interesting Carboxylic Acids
• Simple carboxylic acids have foul or biting odors.
• Formic acid (HCO2H) is responsible for the sting
of some types of ants.
• Acetic acid (CH3CO2H) is the sour-tasting
component of vinegar; it can be made by air
oxidation of ethanol when wine “goes bad.”
11
Focus On Health & Medicine
Skin Care Products
• Several skin care products purported to smooth
fine lines contain a-hydroxy acids.
• General structure of an a-hydroxy acid:
• These acids work by removing the outer, older layer
of skin cells, revealing the healthier looking, new
cells underneath.
12
Focus On Health & Medicine
Aspirin and Anti-Inflammatory Agents
• Common pain relievers that are also antiinflammatory agents contain a carboxyl group:
aspirin
ibuprofen
13
Interesting Carboxylic Acids
Aspirin and Anti-Inflammatory Agents
• Pain relievers work because they block the
synthesis of prostaglandins, compounds
responsible for pain responses in the body.
14
The Acidity of Carboxylic Acids
• Carboxylic acids are proton (H+) donors:
• They are weak acids compared to inorganic acids
like HCl or H2SO4.
• Only a small percentage of a carboxylic acid is
ionized in aqueous solution.
15
The Acidity of Carboxylic Acids
Reaction with Bases
• Carboxylic acids react with bases such as NaOH
to form water-soluble salts.
• A proton is removed from acetic acid to form its
conjugate base, the acetate anion, which is present
in solution as its sodium salt, sodium acetate.
• Hydroxide (OH−) gains a proton to form neutral H2O.
16
The Acidity of Carboxylic Acids
Carboxylate Anions—Salts of Carboxylic Acids
• The salts of carboxylic acids formed by acid-base
reactions are water-soluble ionic solids.
• Thus, the reaction will turn a water-insoluble
carboxylic acid into a water-soluble carboxylic
acid salt.
O
CH3(CH2)6—C—O—H
octanoic acid
Water-insoluble
O
+ Na+ −OH
base
CH3(CH2)6—C—O− Na+ + H—O—H
sodium octanoate
Water-soluble
17
The Acidity of Carboxylic Acids
How Does Soap Clean Away Dirt?
• Soap has been used by humankind for ~2000 years.
• Soaps are salts of carboxylic acids that have
many C atoms in a long hydrocarbon chain.
• A soap molecule has two parts:
1. The ionic end is called the polar head.
2. The carbon chain of nonpolar C—C and C—H
bonds is called the nonpolar tail.
18
The Acidity of Carboxylic Acids
How Does Soap Clean Away Dirt?
• Structure of a soap molecule:
polar head
ionic end
nonpolar tail
nonpolar end
19
The Acidity of Carboxylic Acids
How Does Soap Clean Away Dirt?
• In water, soap forms micelles, spherical droplets
with the ionic heads on the surface and the nonpolar
tails packed together in the interior.
20
The Acidity of Carboxylic Acids
How Does Soap Clean Away Dirt?
• Nonpolar hydrocarbon tails trap nonpolar material
like grease and oil.
• The polar head remains on the surface, sealing
off the grease and oil, and washing away in
the presence of water.
21
Reactions Involving Carboxylic Acids
and Esters
• Carboxylic acids and esters undergo a common
type of reaction—substitution.
22
Reactions Involving Carboxylic Acids
and Esters
Ester Formation
• Carboxylic acids react with alcohols to form
esters.
• Here, the OR′ group replaces the OH group.
23
Reactions Involving Carboxylic Acids
and Esters
Ester Formation
• Formation of an ester is done by the Fisher
esterification:
24
Reactions Involving Carboxylic Acids
and Esters
Ester Hydrolysis
• Treatment of an ester (RCOOR') with water in the
presence of an acid catalyst forms a carboxylic
acid (RCOOH) and a molecule of alcohol (R'OH).
• Here, the OH group replaces the OR′ group.
25
Reactions Involving Carboxylic Acids
and Esters
Ester Hydrolysis
• This reaction is a hydrolysis, since bonds are
cleaved by reaction with water.
26
Focus on Health & Medicine
Olestra, a Synthetic Fat
• Triacylglycerols, common naturally occurring
esters, contain three ester groups, each with a long
C chain.
• They are lipids, water-insoluble organic
compounds, present in fats and oils.
27
Focus on Health & Medicine
Olestra, a Synthetic Fat
• Animals store energy in the form of triacylglycerols.
• Using enzymes called lipases, the three ester
bonds are hydrolyzed when the triacylglycerol is
metabolized.
• Diets high in fat lead to obesity, so the “fake fat”
olestra (Olean) was invented to replace some
triacylglycerols in snack foods.
• The lipase enzymes cannot hydrolyze the olestra,
so it passes through the body unmetabolized,
providing no calories to the consumer.
28
Focus on Health & Medicine
Olestra, a Synthetic Fat
• Hydrolysis of a triacylglycerol by lipase:
O
O
CH2O
CH O
C R
O
C
R’
C
+
HO
C R
O
CH OH
+
HO
C
lipase
O
CH2O
H2O
CH2OH
R’’
O
CH2OH
glycerol
The 3 bonds
that break are
drawn in red.
R’
+
HO
C
R’’
3 long-chain
carboxylic acids
29
Focus on Health & Medicine
Structure of Olestra
30
Amines
Structure and Classification
• Amines are organic nitrogen compounds, formed by
replacing one or more hydrogen atoms of ammonia
(NH3) with alkyl groups.
• Amines are classified by the number of alkyl groups
bonded to the N atom.
• A primary (1o) amine contains
1 C—N bond, and has the
general structure RNH2.
31
Amines
Structure and Classification
• A secondary (2o) amine
contains 2 C—N bonds, and
has the general structure R2NH.
• A tertiary (3o) amine has
3 C—N bonds, and has the
general structure R3N.
• The 1o, 2o, and 3o amine N atom has a lone pair of
e−, which is omitted in condensed structures.
32
Amines
Structure and Classification
• The amine N has a trigonal pyramidal shape,
with bond angles of ~109.5o.
33
Amines
Structure and Classification
• The amine N atom can also be part of a ring.
• Morphine and atropine each contains a nitrogen
atom in a ring.
• They are alkaloids—naturally occurring amines
derived from plant sources.
34
Nomenclature
Amines
• To name a primary (1o) amine, name the alkyl group
bonded to the nitrogen atom and add the
suffix “-amine.”
• For 2o and 3o amines with different alkyl groups,
alphabetize the names of the alkyl groups.
• 2o and 3o amines with identical alkyl groups are
named using the prefix “di-” or “tri-”:
35
Nomenclature
Amines
Sample Problem 13.8
Name each amine.
a.
For a 1°amine, name the
alkyl group and add the
suffix -amine.
Answer:
pentylamine
36
Nomenclature
Secondary and Tertiary Amines
Sample Problem 13.8
b.
For a 2°amine, name each
alkyl group, alphabetize the
names, and add the suffix
-amine.
Answer:
ethylmethylamine
37
Nomenclature
Aromatic Amines
• Amines with the N directly bonded to a benzene
ring are named as derivatives of aniline.
• Use the prefix N- before any alkyl group bonded
to the amine nitrogen.
38
Physical Properties
• Many low molecular weight amines have very foul
odors like rotting fish, urine, and bad breath.
• Amines are polar molecules, containing either
polar C—N or polar H—N bonds.
• 1o and 2o amines can have intermolecular
hydrogen bonding:
39
Physical Properties
• 1o and 2o amines have higher boiling points than
compounds that do not have intermolecular
hydrogen bonding.
CH3CH2OCH2CH3
diethyl ether
CH3CH2CH2CH2NH2
butylamine
bp = 38 oC
bp = 78 oC
Increasing boiling point
40
Physical Properties
• 1o and 2o amines have lower boiling points than
alcohols, as alcohols have stronger intermolecular
hydrogen bonds.
CH3CH2CH2CH2NH2
butylamine
CH3CH2CH2CH2OH
1-butanol
bp = 78 oC
bp = 117 oC
Increasing boiling point
41
Physical Properties
• 3o amines have lower boiling points than 1o or
2o amines of comparable size because they have no
N—H bonds.
Increasing boiling point
42
Amines as Bases
• Amines are bases; they are proton (H+) acceptors.
• This acid–base reaction occurs with 1º, 2º, and
3º amines.
• Amines are weak bases compared to inorganic
bases like NaOH.
43
Amines as Bases
Reactions of Amines with Acids
• Amines react with acids (HCl) to form watersoluble salts.
base
acid
conjugate conjugate
acid
base
44
Amines as Bases
Ammonium Salts
• When an amine reacts with an acid, the product is an
ammonium salt.
• The amine forms a positively charged ammonium
ion and the acid forms an anion.
45
Amines as Bases
Ammonium Salts
To name an ammonium salt:
• Change the suffix “-amine” of the parent
amine to the suffix “-ammonium.”
• Add the name of the anion.
Answer:
triethylammonium
acetate
46
Amines as Bases
Ammonium Salts
• A water-insoluble amine is converted to a watersoluble ammonium salt by treatment with acid.
water-insoluble
water-soluble
47
Focus on Health & Medicine
Ammonium Salts as Useful Salts
• Many amines with medicinal properties are sold
as their ammonium salts, which are transported
through the aqueous bloodstream.
• The antihistimine Benadryl is sold as the salt
diphenhydramine hydrochloride.
48
Amides
Amides contain a carbonyl
group bonded to a N atom.
Amides are classified based on the number of C
atoms bonded to the N atom.
• A primary (1o) amide contains
1 C—N bond.
• It is abbreviated as RCONH2.
49
Amides
• A secondary (2o) amide
contains two C—N bonds,
and is abbreviated RCONHR′.
• A tertiary (3o) amide
contains three C—N bonds,
and is abbreviated RCONHR′2.
50
Nomenclature
Naming an Amide
• All 1o amides are named by replacing the “-oic acid”
ending of the parent carboxylic acid with “-amide.”
O
O
CH3 C
C
NH2
derived from
acetic acid  acetamide
NH2
derived from
benzoic acid  benzamide
51
Nomenclature
Naming an Amide
To name a 2º or 3º amide:
• Name the alkyl group (or groups) bonded to
the N atom of the amide. Use the prefix “N-”
preceding the name of each alkyl group.
• Name the RCO– group with the suffix “-amide.”
52
Nomenclature
Naming an Amide
Sample Problem 13.12
Name the following amide:
HCONHCH2CH3
Step [1]
Name the alkyl group on the N atom, and
precede its name with N-.
O
H
C
NHCH2CH3
Name: N-ethyl
ethyl group
53
Nomenclature
Naming an Amide
Sample Problem 13.12
Step [2] Name the acyl group with “-amide.”
O
H
C
NHCH2CH3
derived from
formic acid  formamide
Answer: N-ethylformamide
54
Physical Properties
1o and 2o amides have higher boiling points than
3o amides and esters because of intermolecular
hydrogen bonding.
Increasing boiling point
55
Hydrolysis of Esters and Amides
Amide Hydrolysis
• Treatment of an amide with water in the presence
of an acid catalyst (HCl) forms a carboxylic acid
and an ammonium salt.
56
Hydrolysis of Esters and Amides
Amide Hydrolysis
• Amides are also hydrolyzed in aqueous base to
form carboxylate anions and a molecule of ammonia
(NH3) or amine.
57
Interesting Amines and Amides
Caffeine and Nicotine
• Caffeine and nicotine are widely used stimulants
of the central nervous system that contain
nitrogen atoms in rings.
• They are alkaloids—naturally occurring amines
derived from plants.
58
Focus on the Human Body
Epinephrine and Related Compounds
• A hormone is a compound produced by an
endocrine gland, which travels through the bloodstream to a target tissue or organ.
• Epinephrine (adrenaline) is a hormone made from
norepinephrine, the neurotransmitter.
59
Focus on the Human Body
Epinephrine and Related Compounds
• Danger or emotional stress causes the formation
of epinephrine.
• The body will metabolize stored carbohydrates
to form glucose, which is further metabolized to
provide an energy boost.
• The heart rate increases and lung passages are
dilated.
• This effect is known as a “rush of adrenaline” or
“fight-or-flight” response.
60
Focus on Health & Medicine
Penicillin
• The antibiotic properties of penicillin were first
discovered in 1928 by Sir Alexander Fleming.
• Penicillin interferes with the enzyme that
synthesizes bacterial cell walls, killing the
bacterium.
• All penicillins contain a β-lactam:
61
Focus on Health & Medicine
Common Penicillin Used Today
62