Amines

Amines

Derivatives of ammonia (NH₃) where one, two, or all three H atoms are replaced by alkyl and/or aryl groups.

Classification of Amines

Amines are classified into primary (1°), secondary (2°), and tertiary (3°) based on the number of alkyl/aryl groups.

Primary amines

Contain one alkyl or aryl group (e.g., CH₃NH₂).

Secondary amines

Contain two alkyl or aryl groups (e.g., (CH₃)₂NH).

Tertiary amines

Contain three alkyl or aryl groups (e.g., (CH₃)₃N).

Amines preparation by ammonolysis

Involves reaction of alkyl halides with ammonia to form 1°, 2°, or 3° amines.

Reactivity of alkyl halides

RI > RBr > RCl in the context of ammonolysis.

Gabriel Phthalimide Synthesis

A method that produces only primary aliphatic amines, not aromatic amines.

Hoffmann Bromamide Degradation

Converts an amide to an amine with one less carbon using Br₂ + KOH.

Solubility of amines in water

1° & 2° amines are soluble due to H-bonding, while 3° amines are insoluble due to lack of N-H bond.

Boiling Point Order of Amines

The boiling point order is 1° > 2° > 3° due to H-bonding.

Lewis bases

Amines act as Lewis bases because of the lone pair of electrons on nitrogen.

Basicity order in gaseous state

3° > 2° > 1° > NH₃.

Basicity in aqueous solution

Depends on +I effect, solvation, and steric hindrance.

Acylation of amines

Involves reaction with acid chlorides or anhydrides in the presence of pyridine.

Carbylamine Test

A reaction where a 1° amine reacts with CHCl₃ and alc. KOH to produce a foul-smelling isocyanide.

Reaction with Nitrous Acid

1° aliphatic amines react to form alcohols, while 1° aromatic amines form stable diazonium salts.

Hinsberg’s Test

Used to differentiate between 1°, 2°, and 3° amines based on their solubility in alkali.

Electrophilic Substitution in Aromatic Amines

The –NH₂ group is ortho/para-directing and strongly activating, requiring protection for monosubstitution.

Nitration of aniline

Aniline gets protonated in acidic medium, leading to meta-directing anilinium ions.

Stable diazonium salts

Primary aromatic amines form stable arenediazonium salts at lower temperatures compared to primary aliphatic amines.