Chapter 7 Amines and Amides

Chapter 7
Amines and Amides
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.
Prepared by:
GIZEL R. SANTIAGO

3
Chapter 7 Topics
• Bonding Characteristics of Nitrogen Atoms in Organic
Compounds
• Structure and Classiﬁcation of Amines
• Nomenclature for Amines
• Isomerism for Amines
• Physical Properties of Amines
• Basicity of Amines
• Amine Salts
• Preparation of Amines and Quaternary Ammonium
Salts

4
Chapter 7 Topics
• Heterocyclic Amines
• Selected Biochemically Important Amines
• Alkaloids
• Structure of and Classiﬁcation of Amides
• Nomenclature for Amides
• Selected Amides and Their Uses
• Physical Properties of Amides
• Preparation of Amides
• Hydrolysis of Amides
• Polyamides and Polyurethanes

5
Bonding Characteristics of Nitrogen Atoms in
Organic Compounds

6
Structure and Classifications of Amines
An amine is an organic derivative of
ammonia (NH3) in which one or more alkyl,
cycloalkyl, or aryl groups are attached to the
nitrogen atom. Amines are classiﬁed as
primary (10), secondary (20), or tertiary (30)
on the basis of how many hydrocarbon
groups are bonded to the ammonia nitrogen
atom.

7
A primary amine is an amine in which the
nitrogen atom is bonded to one hydrocarbon
group and two hydrogen atoms. The generalized
formula for a primary amine is RNH2. A secondary
amine is an amine in which the nitrogen atom is
bonded to two hydrocarbon groups and one
hydrogen atom. The generalized formula for a
secondary amine is R2NH.

8
A tertiary amine is an amine in
which the nitrogen atom is
bonded to three hydrocarbon
groups and no hydrogen atoms.
The generalized formula for a
tertiary amine is R3N.

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The basis for the amine primary-secondary-
tertiary classiﬁcation system differs from that
for alcohols.
1.For alcohols we look at how many R groups
are on a carbon atom, the hydroxyl bearing
carbon atom.
2.For amines we look at how many R groups
are on the nitrogen atom.

10
Tert-butyl alcohol is a tertiary alcohol,
whereas tert-butylamine is a primary
amine.

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The functional group present in a
primary amine, the —NH2 group, is
called an amino group. An amino
group is the —NH2 functional group.
Secondary and tertiary amines
possess substituted amino groups.

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Nomenclature for Amines
Both common and IUPAC names are
extensively used for amines. In the common
system of nomenclature, amines are named by
listing the alkyl group or groups attached to
the nitrogen atom in alphabetical order and
adding the sufﬁx -amine; all of this appears as
one word. Preﬁxes such as di- and tri- are
added when identical groups are bonded to
the nitrogen atom.

18
The IUPAC rules for naming amines are similar
to those for alcohols. Alcohols are named as
alkanols and amines are named as alkanamines.
IUPAC rules for naming primary amines are as
follows:
Rule 1: Select as the parent carbon chain the
longest chain to which the nitrogen atom is
attached.

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Rule 2: Name the parent chain by changing the
-e ending of the corresponding alkane name to
-amine.
Rule 3: Number the parent chain from the end
nearest the nitrogen atom.
Rule 4: The position of attachment of the
nitrogen atom is indicated by a number in front
of the parent chain name.

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Rule 5: The identity and location of any
substituents are appended to the front of the
parent chain name.

21
In diamines, the ﬁnal -e of the carbon chain
name is retained for ease of pronunciation.
Thus the base name for a four-carbon chain
bearing two amino groups is butanediamine.

22
Secondary and tertiary amines are named as N-
substituted primary amines. The largest carbon
group bonded to the nitrogen is used as the parent
amine name. The names of the other groups
attached to the nitrogen are appended to the front
of the base name, and N- or N,N- preﬁxes are used
to indicate that these groups are attached to the
nitrogen atom rather than to the base carbon chain.

29
Isomerism for Amines
Constitutional isomerism in amines can arise
from several causes. Different carbon atom
arrangements produce isomers.

30
Different positioning of the nitrogen atom on a
carbon chain is another cause for isomerism,
illustrated in the following compounds.

31
For secondary and tertiary amines,
different partitioning of carbon atoms
among the carbon chains present produces
constitutional isomers. There are three C4
secondary amines; carbon atom
partitioning can be two ethyl groups, a
propyl group and a methyl group, or an
isopropyl group and a methyl group.

33
Physical Properties for Amines
The methylamines (mono-, di-, and tri-)
and ethylamine are gases at room
temperature and have ammonia-like
odors. Most other amines are liquids, and
many have odors resembling that of raw
ﬁsh. A few amines, particularly diamines,
have strong, disagreeable odors.

34
The foul odor arising from dead ﬁsh
and decaying ﬂesh is due to amines
released by the bacterial
decomposition of protein. Two of
these “odoriferous” compounds are
the diamines putrescine and
cadaverine.

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The simpler amines are irritating to the
skin, eyes, and mucous membranes and
are toxic by ingestion. Aromatic amines are
generally toxic. Many are readily absorbed
through the skin and affect both the blood
and the nervous system.

37
The boiling points of amines are intermediate
between those of alkanes and alcohols of
similar molecular mass. They are higher than
alkane boiling points, because hydrogen
bonding is possible between amine molecules
but not between alkane molecules.
Intermolecular hydrogen bonding of amines
involves the hydrogen atoms and nitrogen
atoms of the amino groups.

38
Amines with fewer than six carbon atoms are
inﬁnitely soluble in water. This solubility results
from hydrogen bonding between the amines
and water. Even tertiary amines are water-
soluble, because the amine nitrogen atom has
a nonbonding electron pair that can form a
hydrogen bond with a hydrogen atom of water.

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Basicity of Amines
Amines, like ammonia, are weak bases.

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Basicity of Amines
The result of the interaction of an amine with
water is a basic solution containing substituted
ammonium ions and hydroxide ions. A
substituted ammonium ion is an ammonium
ion in which one or more alkyl, cycloalkyl, or
aryl groups have been substituted for
hydrogen atoms.

41
Basicity of Amines
Two important generalizations apply to substituted
ammonium ions.
1. Substituted ammonium ions are charged species
rather than neutral molecules.
2. The nitrogen atom in an ammonium ion or a
substituted ammonium ion participates in four
bonds. In a neutral compound, nitrogen atoms form
only three bonds. Four bonds about a nitrogen atom
are possible, however, when the species is a positive
ion because the fourth bond is a coordinate covalent
bond.

42
Basicity of Amines
Naming the positive ion that results
from the interaction of an amine with
water is based on the following two
rules:
Rule 1: For alkylamines, the ending of
the name of the amine is changed
from amine to ammonium ion.

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Basicity of Amines
Rule 2: For aromatic amines, the ﬁnal -e of
the name of the amine is replaced by -ium
ion.

47
Amine Salts
The reaction of an acid with a base
(neutralization) produces a salt. Because
amines are bases, their reaction with an acid
produces a salt, an amine salt.

48
Amine Salts
Aromatic amines react with acids in a similar
manner.

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Amine Salts
An amine salt is an ionic compound in which
the positive ion is a mono-, di-, or trisubstituted
ammonium ion (RNH30, R2NH20, or R3NH0) and
the negative ion comes from an acid. Amine
salts can be obtained in crystalline form
(odorless, white crystals) by evaporating the
water from the acidic solutions in which amine
salts are prepared.

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Amine Salts
Amine salts are named using standard
nomenclature procedures for ionic compounds.
The name of the positive ion, the substituted
ammonium or anilinium ion, is given ﬁ rst and is
followed by a separate word for the name of
the negative ion.

51
Amine Salts
An older naming system for amine salts, still
used in the pharmaceutical industry, treats
amine salts as amine–acid complexes rather
than as ionic compounds. In this system, the
amine salt made from dimethylamine and
hydrochloric acid is named and represented as

52
Amine Salts
The process of forming amine salts with acids is
an easily reversed process. Treating an amine
salt with a strong base such as NaOH
regenerates the “parent” amine.

53
Amine Salts
The “opposite nature” of the processes of
amine salt formation from an amine and the
regeneration of the amine from its amine salt
can be diagrammed as follows:

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Amine Salts
Because amines and their salts are so
easily interconverted, the amine itself is
often designated as the free amine or free
base or as the deprotonated form of the
amine, to distinguish it from the
protonated form of the amine, which is
present in the amine salt.

58
Preparation of Amines and Quaternary
Ammonium SaltsGeneralized equations for the alkylation process are:

59
Ammonium SaltsAlkylation under basic conditions is actually a two-
step process. In the ﬁ rst step, using a primary amine
preparation as an example, an amine salt is
produced.

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Ammonium SaltsThe second step, which involves the base present
(NaOH), converts the amine salt to free amine.

61
Ammonium SaltsA speciﬁc example of the production of a primary
amine from ammonia is the reaction of ethyl
bromide with ammonia to produce ethylamine. The
chemical equation (with both steps combined) is

62
Ammonium Salts
If the newly formed primary amine
produced in an ammonia alkylation
reaction is not quickly removed from the
reaction mixture, the nitrogen atom of the
amine may react with further alkyl halide
molecules, giving, in succession, secondary
and tertiary amines.

63
Ammonium Salts

64
Ammonium Salts

65
Ammonium SaltsTertiary amines react with alkyl halides in
the presence of a strong base to produce
a quaternary ammonium salt. A
quaternary ammonium salt is an
ammonium salt in which all four groups
attached to the nitrogen atom of the
ammonium ion are hydrocarbon groups.

66
Ammonium Salts

67
Ammonium Salts
Compounds that contain quaternary
ammonium ions are important in biochemical
systems. Choline and acetylcholine are two
important quaternary ammonium ions
present in the human body. Choline has
important roles in both fat transport and
growth regulation. Acetylcholine is involved in
the transmission of nerve impulses.

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Ammonium Salts

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Heterocyclic Amines
A heterocyclic amine is an organic
compound in which nitrogen atoms of
amine groups are part of either an
aromatic or a nonaromatic ring
system. Heterocyclic amines are the
most common type of heterocyclic
organic compound.

70
Heterocyclic Amines
Heterocyclic amine structures shows
that (1) ring systems may be
saturated, unsaturated, or aromatic,
(2) more than one nitrogen atom may
be present in a given ring, and (3)
fused ring systems often occur.

74
Selected Biochemically Important Amines
Neurotransmitters
A neurotransmitter is a chemical substance
that is released at the end of a nerve,
travels across the synaptic gap between
the nerve and another nerve, and then
bonds to a receptor site on the other
nerve, triggering a nerve impulse.

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Neurotransmitters
The most important
neurotransmitters in the human body
are acetylcholine and the amines
norepinephrine, dopamine, and
serotonin.

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Epinephrine
Epinephrine, also known as adrenaline, has
some neurotransmitter functions but is more
important as a central nervous system
stimulant.

80
Histamine
The heterocyclic amine
histamine is responsible
for the unpleasant effects
felt by individuals
susceptible to hay fever
and various pollen
allergies.

81
Alkaloids
An alkaloid is a nitrogen-containing organic
compound extracted from plant material.

82
Alkaloids
These
three
compounds
have
similar
chemical
structures.

84
Structure and Classification of Amides
An amide is a carboxylic acid derivative in
which the carboxyl —OH group has been
replaced with an amino or a substituted amino
group.

85
Amides, like amines, can be classiﬁed as
primary (10), secondary (20), or tertiary (30),
depending on how many hydrogen atoms are
attached to the nitrogen atom.

86
A primary amide is an amide in which two
hydrogen atoms are bonded to the amide
nitrogen atom. Such amides are also called
unsubstituted amides. A secondary amide is an
amide in which an alkyl (or aryl) group and a
hydrogen atom are bonded to the amide
nitrogen atom. Monosubstituted amide is
another name for this type of amide.

87
A tertiary amide is an amide in
which two alkyl (or aryl) groups
and no hydrogen atoms are
bonded to the amide nitrogen
atom. Such amides are
disubstituted amides.

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89
The simplest amide
has a hydrogen
atom attached to an
unsubstituted
amide functional
group.

90
Next in complexity are amides in which a methyl
group is present. There are two of them, one with
the methyl group attached to the carbon atom and
the other with the methyl group attached to the
nitrogen atom.

91
The ﬁrst of these structures
is a 10 amide, and the second
structure is a 20 amide. The
structure of the simplest
aromatic amide involves a
benzene ring to which an
unsubstituted amide
functional group is attached.

92
Cyclic amide structures are possible. Examples
of such structures include

93
Cyclic amides are called lactams, a term that
parallels the use of the term lactones for cyclic
esters

94
A lactam is a cyclic amide. The ring size in a
lactam is indicated using a Greek letter. A
lactam with a four-membered ring is a b-
lactam because the b carbon from the
carbonyl group is bonded to the
heteroatom. A lactam with a ﬁve-
membered ring is a g-lactam.

95
The members of the penicillin family of
antibiotics have structures that contain a b-
lactam ring.

96
Nomenclature for Amides
Rule 1: T he ending of the name of the
carboxylic acid is changed from -ic acid
(common) or -oic acid (IUPAC) to -amide. For
example, benzoic acid becomes benzamide.
Rule 2: T he names of groups attached to the
nitrogen (20 and 30 amides) are appended to
the front of the base name, using an N- preﬁ x
as a locator.

98
Nomenclature for secondary and tertiary amides,
amides with substituted amino groups, involves use
of the preﬁx N-, a practice we previously
encountered with amine nomenclature

99
The simplest aromatic amide, a benzene ring bearing
an unsubstituted amide group, is called benzamide.
Other aromatic amides are named as benzamide
derivatives.

102
Selected Amides and their Uses
The simplest naturally occurring amide is urea,
a water-soluble white solid produced in the
human body from carbon dioxide and ammonia
through a complex series of metabolic
reactions.

103
Urea is a one-carbon diamide. Its molecular
structure is

104
Melatonin is a polyfunctional amide; amine
and ether groups are also present.

105
Barbiturates, which are cyclic amide
compounds, are a heavily used group of
prescription drugs that cause relaxation
(tranquilizers), sleep (sedatives), and death
(overdoses). All barbiturates are derivatives
of barbituric acid, a cyclic amide that was ﬁrst
synthesized from urea and malonic acid.

106

107
Physical Properties of Amides
Amides do not exhibit basic properties in
solution as amines do.
Methanamide and its N-methyl and N,N-
dimethyl derivatives (the simplest 10, 20, and 30
amides, respectively), are all liquids at room
temperature. All unbranched primary amides,
except methanamide, are solids at room
temperature, as are most other amides.

108
Physical Properties of Amides
In many cases, the
amide melting point is
even higher than that of
the corresponding
carboxylic acid. Amides
of low molecular mass,
up to ﬁve or six carbon
atoms, are soluble in
water.

111
Preparation of Amides
An amidification reaction is the reaction of
a carboxylic acid with an amine (or
ammonia) to produce an amide. In
amidification, an —OH group is lost from
the carboxylic acid, a —H atom is lost from
the ammonia or amine, and water is
formed as a by-product. Amidification
reactions are thus condensation reactions.

117
Hydrolysis of Amides
In amide hydrolysis, the bond between
the carbonyl carbon atom and the
nitrogen is broken, and free acid and
free amine are produced. Amide
hydrolysis is catalyzed by acids, bases,
or certain enzymes; sustained heating
is also often required.

119
Hydrolysis of Amides
Acidic or basic hydrolysis conditions
have an effect on the products. Acidic
conditions convert the product amine
to an amine salt. Basic conditions
convert the product carboxylic acid to
a carboxylic acid salt.

124
Polyamides and Polyurethanes
Amide polymers—polyamides—are
synthesized by combining diamines and
dicarboxylic acids in a condensation
polymerization reaction. A polyamide is a
condensation polymer in which the
monomers are joined through amide
linkages.

125
The most important synthetic polyamide is nylon.
Nylon is used in clothing and hosiery, as well as in
carpets, tire cord, rope, and parachutes. It also has
nonfiber uses; for example, it is used in paint
brushes, electrical parts, valves, and fasteners. It is a
tough, strong, nontoxic, nonflammable material that
is resistant to chemicals. Surgical suture is made of
nylon because it is such a strong fiber.

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A urethane is a hydrocarbon
derivative that contains a carbonyl
group bonded to both an —OR group
and a —NHR (or –NR2) group. Such
compounds are prepared by reaction
of an alcohol with an isocyanate
(R-N=C-O).

133

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A polyurethane is a polymer
formed from the reaction of
dialcohol and diisocyanate
monomers. The monomers
benzene diisocyanate and
ethylene glycol are the reactants.

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End of Chapter 7
Amines and Amides
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.
Prepared by:
GIZEL R. SANTIAGO

Chapter 7 Amines and Amides

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