Download Chapter 16, Amines

Chemistry 110
Bettelheim, Brown, Campbell & Farrell
Ninth Edition
Introduction to General,
Organic and Biochemistry
Chapter 16
Amines
Amine Molecules are Weak Bases
Aliphatic & Aromatic Amines
¾Amines are relatives of ammonia, NH3, in which the hydrogen
atoms on nitrogen have been replaced by one or more noncarbonyl substituent groups.
¾ Aliphatic amines in which alkyl groups replace hydrogen are
slightly more basic than ammonia.
¾ Aromatic amines in which one or more of the substituent
groups is an arene, are considerably less basic than ammonia.
¾ Heterocyclic amines have the nitrogen atom within a ring. The
ring may be aliphatic or aromatic.
¾ Heterocyclic aliphatic amines are stronger bases than ammonia.
¾ Heterocyclic aromatic amines are considerably weaker bases
than ammonia. In these rings the nitrogen atom contributes one or
two electrons to the aromatic sextet of electrons .
Aromatic versus Aliphatic Amines
Aliphatic Amines have the amino- group attached by tetrahedral
carbon:
C
C
NH3
NH2
NH
N C
C
C
C
primary, 1E
Ammonia
secondary, 2E
tertiary, 3E
Aromatic amines have the amino- group bonded to a benzene
ring:
NH2
aniline
NHCH3
N-methylaniline
N(CH3)2
N,N-dimethylaniline
Aliphatic amines can have aromatic rings as long as the nitrogen
is attached by tetrahedral carbon.
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Heterocyclic Aliphatic/Aromatic Amines
Heterocyclic aliphatic amines – the nitrogen is incorporated into
a ring and is connected by two tetrahedral carbons.
N
CH3
N-methylpyrrolidine
N
piperidine
2E heterocyclic aliphatic amine
3E heterocyclic aliphatic amine
Heterocyclic aromatic amines – the nitrogen is incorporated
into an aromatic ring – N contributes to the aromatic sextet.
N
N
N
pyramidine
N
pyridine
N
N
H
imidazole
N
N
N
H
purene
Naming of Amines
¾ IUPAC names for aliphatic amines follow that for alcohols.
Drop the final -e of the parent alkane and replace it with
–amine.
¾ Use a number to locate the amino group on the parent chain.
¾ Name unsymmetrical secondary and tertiary amines as
N-substituted primary amines. In this case take the largest
group bonded to nitrogen as the parent amine.
¾ Name the smaller group(s) bonded to nitrogen, and show
that their location is bonded to nitrogen by using the prefix Nbefore the listing of that substituent.
N
CH3
CH3CH2CH2NH2
CH3CH2CH2NHCH3
CH3
propanamine
N,N-dimethylaniline
N-methylpropanamine
Naming of Amines
¾ IUPAC nomenclature retains the common name aniline for
C6H5NH2, the simplest aromatic amine.
¾Name simple derivatives of aniline by using locator numbers
starting with the amino group, or locate substituents by using
the prefixes ortho (o), meta (m), and para (p).
¾Several derivatives of aniline have common names that are
still widely used; among them is toluidine.
¾If another substituent overides with a special name locate the
amine substituent with a locator number starting at the other
substituent.
NH2
NH2
NH2
H3C
aniline
2-methylaniline
o-toluidine
COOH
2-aminobenzoic acid
o-aminobenzoic acid
2
Naming of Amines
Common Names
¾For most aliphatic amines, list the groups bonded to nitrogen
in alphabetical order in one word ending in the suffix –amine.
NH2
N
N
H
isopropylamine
cyclopentyldiethylamine
ethylisopropylamine
¾Because amines are bases they react with strong acids to
form ammonium salts. In these salts nitrogen has four bonds,
has a positive charge and is associated with an anion.
Cl
NH3 Cl
Cl
N
H H
isopropylammonium
chloride
N
H
cyclopentyldiethylammonium
chloride
ethylisopropylammonium
chloride
Properties of Amines
¾Amines are polar, hydrogen bond with water, and 1Eand 2E
with each other, but more weakly than alcohols
¾Amines have lower boiling points than alcohols of similar
molecular weight, they are also soluble in water if the
substituent group part is not too large and non-polar. C1-C7 =
miscible to slightly soluble, C8 and higher are insoluble.
¾Amines are basic in water,
the pH will go to higher
values.
¾Amines readily react with
acid. The resulting
ammonium ion are much
more soluble than the
parent amines.
H
O
O
H
N
H
H
H
H
R
N
H
O
H
H
H
R
H
O
H
H
H
OH
OH
Properties of Amines
¾The N-H---N hydrogen bond is weaker than an O-H---O
hydrogen bond because the difference in electronegativity
between N and H (3.0 - 2.1 = 0.9) is less than that between O
and H (3.5 - 2.1 = 1.4).
¾The effect of hydrogen bonding between molecules of
comparable molecular weight can be seen by comparing the
boiling points of ethane, methanamine, and methanol.
MW (am u)
bp (°C)
CH 3 CH 3
CH3 NH2
CH3 OH
30.1
-88.6
31.1
-6.3
32.0
65.0
¾Like ammonia, low-molecular-weight amines have very sharp,
penetrating odors; for example, rotting fish = trimethylamine.
3
Hydrogen Bonds – Amines in Water
H
O
R
H
H
N
H
H
R
N
H
H
N
H
H
O
R
H
H
H
H
O
O
H
Hydrogen Bonds – Pure Amines – Except 3E
H
R
N
R
H
H
N
H
H
H
N
H
H
N
R
H
R
N
R
H
R
N
H
H
R
N
H
H
Can You Name these Amines?
H3C
NH2
H3C
HC NHCH3
H3C
CH3
HC NH CH
H3C
CH3
Classify them as aromatic, aliphatic,
and as primary, secondary or tertiary.
O
C OH
H3C
H3C
NH2
CH2CH3
C NH CH
H3C
(CH3CH2)3N
CH3
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Amines Are Relatives of Ammonia
Amines are basic: ( Aliphatic amines about as basic as ammonia)
NH3
NH2
C
primary
H
C
C
NH
C
secondary
H
N C
C
tertiary
H
H
H
NH2
C H
NH
C
C
And make ammonium salts in acidic solution.
NH4
C H
N C
C
Note: N has 3 bonds in amines, but 4 bonds in ammonium ions.
Ammonium Ions React with Base
Ammonium salts are weakly acidic:
NH4
C
H
NH2
C H
NH
C
OH
OH
OH
NH3
+
H2O
NH2
C
primary
C H
N C
C
OH
C
C
NH
C
secondary
N C
C
tertiary
And react with hydroxide ion to regenerate the original amine + water
Reaction of Amines with Water
H
H3C
N
H
H
H3C
O
+
H
H
N H +
O
H
H
Reaction of Ammonium Ions with Water
H3C
H
H
N H +
H
O
H
H
H
H3C
N
H
O
+
H
H
5
What is the form of amines in blood plasma?
pH of blood is 7.4, [OH] = 2.5 x 10 -7
Ethylamine: Kb = 4.3 x 10-4 =
+
+
[CH3CH2NH3 ]
Kb
=
[OH ]
[CH3CH2NH2]
-
[CH3CH2NH3 ] [OH ]
[CH3CH2NH2]
=
4.3 x 10-4
2.5 x 10-7
= 1720
An aliphatic amine is mostly in the ammonium form in blood!
+
[C5H5NH ] [OH ]
Pyridine: Kb = 1.5 x 10-9 =
[C5H5N]
+
[C5H5NH ]
Kb
=
[OH ]
[C5H5N]
=
1.5 x 10-9
2.5 x 10-7
= 0.0060
An aromatic amine is mostly in the amine form in blood!
Carboxylic Acids & Amines Give Salts
O
CH3
H NCH2CH3 + CH3C OH
Carboxylic Acid
Acetic Acid
Amine
Ethylmethylamine
100%
O
CH3
H NCH2CH3 + CH3C O
H
Ammonium Ion
Carboxylate Anion
Ethylmethylammonium Acetate
Aminoacids exist in vivo only in their ionized form!
O
O
H2N CH C OH
H3N CH C O
OH
CH2
CH2
Tyrosine
OH
isoelectric form
What Products are Formed?
If No Reaction write – NR
CH3CH2CH2CH2NH3 Cl + NaOH
CH3CH2CH2CH2NH2
+ NaOH
CH3CH2CH2CH2NH3 Cl + HCl
CH3CH2CH2CH2NH2
+
HCl
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