Chapter 8

Amines

Chemistry 20

Amines:

• Are derivatives of ammonia NH3.

• Contain N attached to one or more alkyl (Aliphatic amine) or aromatic groups (Aromatic amine).

CH3-NH2 CH3-NH-CH3

Amines

-NH2 amino group

CH2CH3 CH3 CH=CH2

TolueneEthylbenzene Styrene

NH2

Amines are classified into three groups:

depending on the number of carbon groups bonded to nitrogen.

CH3 CH3

CH3—NH2 CH3—NH CH3—N—CH3

Amines

Primary 1° Secondary 2° Tertiary 3°

Naming Amines

The same method as we did for alcohols.

- Drop the final “-e” of the parent alkane and replace it by “-amine”.

- Use a number to locate the amino group (-NH2) on the parent chain.

IUPAC name – 1° amines

CH3CHCH3

NH2

NH2

H2N NH2

1,6-HexanediamineCyclohexanamine2-Propanamine

CH3-CH-CH3

NH2

2-propanamine

CH3-CH-CH-CH3

NH2

Cl

3-chloro-2-butanamine 1,6-hexanediamine

123 1 2

3

4

1234

56

Common name

Names of alkyl groups (In alphabetical order) + “amine”

CH3—CH2—NH2 ethylamine

CH3—NH —CH3 dimethylamine

CH3

|

CH3—N—CH2—CH3 ethyldimethylamine

Naming Amines

CH2CH3 CH3 CH=CH2

TolueneEthylbenzene Styrene

CH2CH3 CH3 CH=CH2

TolueneEthylbenzene Styrene

CH2CH3 CH3 CH=CH2

TolueneEthylbenzene Styrene

Aniline (common name)

NO2

CH3 CH3

Aniline

4-Nitroaniline 3-Methylaniline 4-Chloro-3-methylaniline

NH2

NH2NH2 NH2

Cl

1 2

3

4

1 2

3

1 2

34

CH2CH3 CH3 CH=CH2

TolueneEthylbenzene Styrene

Naming Amines

– Take the largest group bonded to nitrogen as the parent amine.

– Name the smaller group(s) bonded to nitrogen, and show their locations on nitrogen by using the prefix “N”.

IUPAC name – 2° and 3° amines

NCH3

CH3

NHCH3

N,N-Dimethyl- cyclopentanamine

N-Methylaniline

NCH3

CH3

NHCH3

N,N-Dimethyl- cyclopentanamine

N-Methylanilineaniline

CH3-N-CH2-CH3

CH3

N,N-Dimethylethanamine

Heterocyclic amines

When N is one of the atoms of a ring.

N

HHCH3

Pyrrolidine Pyridine Nicotine

Physical properties of Amines

1. They have unpleasant odors (rotting fish like ammonia).

2. They are polar compounds.

Difference in electronegativity between N - H (3.0 – 2.1 = 0.9)

3. 1° and 2° amines have hydrogen bonds (N-H).

Weaker than alcohols (O-H).

3° amines do not form hydrogen bonds (no H atom).

4. Boiling points: Hydrocarbons< Amines < Alcohols

5. Almost soluble in water (hydrogen bonding).

Chemical properties of Amines

They are weak bases (like ammonia): react with acids.

N

H

H

CH3 .. + H – O – H....N

H

H

CH3 H+

O – H......

-

Some amines present in our blood and make it approximately basic (pH = 7.4).

(to form water-soluble salts)

Chemical properties of Amines

C6H5NH2

CH3CH2NH2Aliphatic

Ammonia

Aromatic

3.0 - 4.0

4.74

8.5 - 9.5

Class pKb Example Name

Ethanamine

Aniline

Stronger base

Weaker base

Aliphatic amines are weak bases by comparison with inorganic bases

such as NaOH, they are strong bases among organic compounds.

Aliphatic amines are stronger bases than aromatic amines.

(slightly stronger than NH3)

Complete each acid-base reaction and name the salt formed.

(CH3CH2)2NH HCl

NCH3COOH

+(a)

(b) +

Examples

Complete each acid-base reaction and name the salt formed.

Examples

Solutions:

(CH3CH2)2NH HCl

NCH3COOH

NH

(CH3CH2)2NH2+Cl-

CH3COO-

Diethylammoniumchloride

+Pyridinium acetate

+(a)

(b) +