AMINE

AMINE

Introduction:

Amines and amides are abundant in nature. They are a major component of proteins and enzymes, nucleic acids, alkaloid drugs, etc. (Alkaloids are N containing, weakly basic organic compounds; thousands of these substances are known.) Amines are organic derivatives of ammonia (NH₃), in which one or more of the three H’s is replaced by a carbon group. Amines are classified as primary (1°), secondary (2°), and tertiary (3°), depending on how many carbon groups are connected to the nitrogen atom, for example:

Nomenclature of Amines:

Primary, secondary and tertiary amines: common names are obtained by alphabetically arranging the names of the alkyl substituents on the nitrogen and adding the suffix -amine (e.g., ethylmethylamine).

Amines in the IUPAC system: the “e” ending of the alkane name for the longest chain is replaced with –amine. The amine group is located by the position number. Groups that are attached to the nitrogen atom are located using “N” as the position number. More complex primary amines are named with —NH₂ as the amino substituent.

Physical properties of Amines:

1) Phases: Lower aliphatic amines (Liquid phase):

For example: (a) CH₃NH₂ (Methylamine)

(b) CH₃CH₂NH₂ (Ethylamine)

• If the amines having more than three hydrocarbon alkyl chain amines which are liquid in nature because of increases the Van der Waals force.

• If the amines having 8 to 10 carbon atoms alkyl chain amines which are solid in nature.

2) Colour: In case of aniline, it is colour less, but when it will come into contact in atmosphere oxygen and convert into coloured form.

3) Solubility in water: Water is a polar molecule and amines having nitrogen groups in its molecular structure, so nitrogen is electronegative in nature.

Electronegativity order: F > O > N

• Lower amines are soluble in water due to formation of the hydrogen bonding.

• And higher carbon containing amines decreases the solubility in the water.

• And amines are not soluble in the water due to increases the hydrophobicity of the amines.

1) Boiling point:

CH₃ CH₂ CH₂NH₂(Primary amine): It can form two-hydrogen bond form.

CH₃CH₂NH CH₃(Secondary amine): It can form one-hydrogen bond form.

CH₃)₃N (Tertiary amine): It cannot form any hydrogen bond form.

In Case, When the molecular formula will same then the boiling point is follows as:

1°>2°> > 3° Boiling point order

ROH > RNH₂> R₂NH > R₃N > R-H Boiling point oder

v Primary and secondary amines can hydrogen bond to each other:

v Intramolecular hydrogen bond possible in primary and secondary amines.

• Tertiary amines cannot hydrogen bond to each other:

v Water Solubility: Primary (1°), secondary (2°), and tertiary (3°) amines can all form hydrogen bonds with water. Low-molecular weight amines are generally water soluble.

v Odour: Low molecular weight amines tend to have sharp, penetrating odours similar to ammonia.

v Higher molecular weight amines often smell like rotting fish, and are often found in decaying animal tissues.

Basicity of amines:

NOTE : Amines show strong basicity as compared to the ammonia.

Order of the basicity of the amines primary (1°), secondary (2°), and tertiary (3°) amines

1) +I Effect: +I Effect increases then basicity of amines decreases, basic compounds are easily donate the electrons pair.

Note: In the tertiary (3°) amines the three R groups donate the electron than in this situation the electron density on nitrogen is increased and easily donate the electron pair.

Tertiary amine > Secondary amine > Primary amine: Basicity order of amine

Note: Tertiary amine > Secondary amine > Primary amine: Basicity order of amine in the gas phase

2) Solvation theory (Applicable only for aqueous phase):

· Compound having lower energy means it more stable according to the law of thermodynamic.

v It means the three water molecules increases the stability as well as decreases the energy of the molecules. So, the stability order follows as: primary (1°) >Secondary (2°) >Tertiary (3°).

3) Steric hindrance:

a) R = CH₃CH₂-

Note: Primary, secondary and tertiary amines show different chemical reaction with the same reagent.

1) Reactivity of amines:

v Due to acidic hydrogen and lone pair of amines at the nitrogen atom. Because of the lone pair they act as a base and nucleophile. Basic character of amines show due to lone pair of electron.