Chapter 15

Structure & Classification
 Amines are classified as 1 °, 2°, or 3° depending on the number of carbon groups bonded to nitrogen
H
CH
3
-NH
2
Methylamin e
(a 1° amine)
CH
3
-N-CH
3
D imeth ylamine
(a 2° amine)
CH
3
CH
3
-N-CH
3
Trimeth ylamine
(a 3° amine)
NH
2
H
N-CH
3
CH
3
CH
2
-N-CH
3
Anilin e
(a 1° aromatic amine)
N -Methylan iline
(a 2° aromatic amine)
Ben zyldimethylamine
(a 3° aliph atic amin e)

Structure & Classification
 heterocyclic amine: an amine in which the nitrogen atom is part of a ring
N
N
H
Pyrrolidin e
H
Pip eridin e
(h eterocyclic aliph atic amin es)
N N
N
N N N
N N
H
Pyridin e Pyrimidin e Imid azole
(heterocyclic aromatic amines )
H
Purine
N

Nomenclature
 IUPAC names
 Similar to alcohols
 drop the final -e of the parent alkane and replace it by -amine
 use a number to locate the amino group on the parent chain
NH
2
NH
2
CH
3
CHCH
3
2-Propanamine Cyclohexanamine
H
2
N
NH
1,6-Hexan ediamine
2

Nomenclature
 IUPAC names (cont’d)


IUPAC nomenclature retains the common name aniline for C
6
H
5
NH
2
, the simplest aromatic amine use numbers to locate substituents or, alternatively, use the prefixes ortho (o), meta (m), and para (p)
 common names are still widely used
NH
2
NH
2
NH
2
NO
2
A niline 4-N itroaniline
( pN itroan iline)
CH
3
3-Methylaniline
( mTolu idine)

Nomenclature
 IUPAC names (cont’d)
 name unsymmetrical secondary and tertiary amines as N -substituted primary amines
 take the largest group bonded to nitrogen as the parent amine
 smaller group(s) are substituents indicated by using the prefix N
NHCH
3
NMeth ylan ilin e
CH
3
N
CH
3
N,N D im ethyl-
cyclopentan amin e

Nomenclature
 Common names
 for most aliphatic amines, list the groups bonded to nitrogen in alphabetical order in one word ending in the suffix amine
NH
2
Propylamine
NH
2
NH
2
N sec -Butylamin e D ieth ylmethylamin e Cyclohexylamine

Nomenclature
 Amine salts
 when four things are bonded to a nitrogen atom, the nitrogen bears a positive charge
 name the compound as a salt
 replace the ending -amine (or aniline or pyridine or the like) by -ammonium (or anilinium or pyridinium or the like) and add the name of the anion
( CH
3
CH
2
)
3
NH
+
Cl
-
Triethylammonium chloride

Physical Properties
 Like ammonia, low-molecular-weight amines have very sharp, penetrating odors
 trimethylamine, for example, is the pungent principle in the smell of rotting fish
 two other particularly pungent amines are
1,4-butanediamine (putrescine) and 1,5pentanediamine (cadaverine)

Physical Properties
 Amines are polar compounds
 both 1 ° and 2° amines have N-H bonds, and can form hydrogen bonds with one another

Physical Properties
 an N-H---N hydrogen bond is weaker than an O-H---O hydrogen bond
 compare the boiling points of ethane, methanamine, and methanol
MW (amu) bp (°C)
CH
3
CH
3
30.1
-88.6
CH
3
NH
2
31.1
-6.3
CH
3
OH
32.0
65.0

Physical Properties
 all classes of amines form hydrogen bonds with water and are more soluble in water than are hydrocarbons of comparable molecular weight
 most low-molecular-weight amines are completely soluble in water
 higher-molecular-weight amines are only moderately soluble in water or are insoluble

Basicity of Amines
 Like ammonia, amines are weak bases, and aqueous solutions of amines are basic
 the acid-base reaction between an amine and water involves transfer of a proton from water to the amine
H
CH
3
-N :
H
+
Methylam in e
(a bas e)
HO-H CH
3
H
+
-N H
H
-
: O-H
Meth ylam moniu m hydroxide

Basicity of Amines
 The base dissociation constant, K b
, for the reaction of an amine with water has the following form, illustrated for the reaction of methylamine with water to give methylammonium hydroxide
 pK b
K b is defined as the negative logarithm of
K b
=
[CH
3
NH
[ CH
3
3
+
NH
][ OH
-
]
= 4.37 x 10
-4
2
] pK b
= - log 4.37 x 10
-4
= 3.360

Basicity of Amines
 aliphatic amines SS bases than NH
3
 aromatic amines are weaker bases
Clas s
Aliph atic
Ammonia
Aromatic pK b
3.0 - 4.0
4.74
8.5 - 9.5
Example
CH
3
CH
2
NH
2
C
6
H
5
NH
2
N ame
Ethan amin e Stron ger bas e
Anilin e
Weaker base

Basicity of Amines
 We can determine which form of an amine exists in body fluids, pH 7.40
 if an aliphatic amine is dissolved in blood, it is present predominantly as its protonated
(conjugated acid) form
HO NH
2
HO NH
3
+
HO
D opamine
HO
Con jugate acid of d op amine
(the major form p res ent in b lood p lasma)

Reactions of Amines
 The most important chemical property of amines is their basicity
 amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts
HO H
HO NH
2
+
HO
( R )-N orepinep hrin e
(on ly s ligh tly solub le in w ater)
HCl
H
2
O
HO
HO
H
NH
3
+
Cl
-
HO
( R )-N orep ineph rine h yd roch loride
(a w ater-soluble s alt)

Reactions of Amines
 example: complete each acid-base reaction and name the salt formed
(a) ( CH
3
CH
2
)
2
NH + HCl
(b )
N
+ CH
3
COOH

Reactions of Amines
 example: complete each acid-base reaction and name the salt formed
 solution:
(a) (CH
3
CH
2
)
2
NH + HCl (CH
3
CH
2
)
2
NH
2
+
Cl
-
D ieth ylammoniu m chloride
(b)
N
+ CH
3
COOH
N +
H
CH
3
COO
-
Pyridinium acetate

Synthesis of Amines



1) Alkyl halides react with ammonia to make primary amines
This can lead to multiple amination products
 Example on board

2) Alkyl halides may be reacted with cyanide and then hydrogenated to for the primary amine exclusively.
Example on board

Reactions of Amines
 3) Aldehydes and ketones can condense with primary amines and then be hydrogenated to for secondary amines
 Example on the board

Amines