Tertiary Amine

Amines are derived from ammonia. Alkyl or aryl groups replace one or more hydrogen atoms in ammonia. The –NH2 group is known as an amino group. Amides have a nitrogen atom attached to the carbonyl group. Amines are further divided into three categories: aliphatic amines, aromatic amines, and heterocyclic amines. When an alkyl group is attached to the nitrogen, it is an aliphatic amine. When an aryl group is attached to nitrogen, it is an aromatic amine. When nitrogen of an amine is a part of a cyclic ring, it is a heterocyclic amine. Amines are basic in nature. Tertiary amines can also be cyclic in nature and be aliphatic and aromatic.

Classification of amines on the basis of structure

Amines can be classified into three categories on the basis of the number of hydrogen atoms replaced in the ammonia molecule:

• Primary amine: 1 hydrogen molecule of ammonia molecule replaced by an alkyl or aryl group.
• Secondary amine: 2 hydrogen molecules of ammonia replaced by an alkyl or aryl group.
• Tertiary amine: 3 hydrogen molecules of ammonia replaced by an alkyl or aryl group.

Nomenclature of tertiary amines

According to IUPAC nomenclature, carbon compounds with a double bond have a suffix as -ene, and those with triple bonds have suffix as yne.

The substituent of –NH in primary amines is known as an amino group, for secondary and tertiary amines is complex as it involves all the names of the alkyl groups.

-amine suffix is added to the parent alkyl name, and for secondary and tertiary amines, the extra substituents of nitrogen is named with prefix N-.

Preparation of tertiary amines

• Tris(2-Cyanoethyl)amine undergoes selective oxidation to form intermediate hydroxylamine followed by benzoylation and cobalt catalysed electrophilic amination to yield tertiary amines.
• Tertiary amines can also be prepared by SN2 reaction of the secondary alkyl halide known as alkylation.
• Aldehydes and ketones, through reductive amination, can form tertiary amines.
• Tertiary amines can also be prepared by reductive alkylation of aldehydes with secondary amines in the presence of catalysts.
• N-alkylation of amines or nitro amines with alkyl halides or alcohols yield tertiary amines.
• Amination of aryl halides also yields tertiary amines.

Physical properties of tertiary amines

• Hydrogen bonding between tertiary amines is negligible.
• Their boiling point is low.
• Tertiary amines can form hydrogen bonds with water using the non-bonded electron pair present on the nitrogen atom.
• Tertiary amines show chirality, but due to nitrogen inversion, they are present as a racemic mixture.

Chemical properties of tertiary amines

• Tertiary amines are basic in nature and react with acids to form a salt.
• In the gaseous phase, tertiary amines have the highest basicity than secondary and primary amines.
• Tertiary amines do not show a positive isocyanide test. Isocyanide test is also known as carbylamine reaction where amines react with chloroform and ethanolic potassium hydroxide to form isocyanide.
• Tertiary amines do not react with benzene sulphonyl chloride.
• Tertiary amines react with nitrous oxide in a different way compared to a secondary amine.
• Hinsberg test is used to distinguish tertiary amine from primary and secondary amine. In this test, benzene sulphonyl chloride is used. Primary amines react with this to form sulfonamide, which is soluble in alkali, while secondary and tertiary amines also form sulfonamides but are not soluble in alkali. This distinguishes between primary and tertiary amine. 
• The precipitate tertiary amine can be dissolved in hydrochloric acid, but that of secondary amine does not dissolve in hydrochloric acid, due to which we can distinguish between secondary and tertiary amines.

• Tertiary amines in the presence of platinum react with oxygen to form amides.

Applications of Tertiary Amines

• Tertiary amines have great importance in chemical industries.
• Tertiary amine derivatives are used in water treatments, oil fields, personal care, etc.
• 6 to 20 carbon-containing linear tertiary amine is used in manufacturing surfactants.
• Tertiary amines containing iso-alkyl groups are hard to produce but are greatly used as a non-nucleophilic base and a stabiliser for polymers.
• Under certain conditions, tertiary amines are used to produce lactams which are chemical compounds.

Conclusion

Amines are organic compounds derived from ammonia. Ammonia is an inorganic compound with a central nitrogen atom bonded to 3 hydrogen atoms. The valency of nitrogen being 5 in the structure of ammonia or amines, it has a lone pair of electrons on it. When the hydrogen atoms of ammonia are replaced by either an aryl group, alkyl group or a cyclic structure, it is termed as an amine. The structure of amine is classified into three categories on the basis of the number of hydrogen atoms bonded to the central nitrogen atom. If two hydrogen atoms are bonded to the central nitrogen atom, it is known as primary amine. If a single hydrogen atom is bonded to the central nitrogen atom, it is known as secondary amine. If no hydrogen atom is bonded to the central nitrogen atom, it is a tertiary amine. Tertiary amines can also be cyclic in nature and be aliphatic and aromatic.