Chemistry Chapter 16: Amines

Chapter 16: Amines

• Amines are organic compounds containing nitrogen.
• Carbon, hydrogen, and oxygen are the three most common elements in organic compounds.
• Nitrogen is the fourth most common element found in organic compounds.
• Amines are widely distributed in biological systems.
• The most important chemical property of amines is their basicity.
• The functional group of an amine is an amino group (NH₂, RNH₂, R₂NH, or R₃N) – a nitrogen atom bonded to one, two, or three carbon atoms.

Amine Classification

• Primary (1°) amines: Nitrogen bonded to two hydrogens and one carbon group.
• Secondary (2°) amines: Nitrogen bonded to one hydrogen and two carbon groups.
• Tertiary (3°) amines: Nitrogen bonded to three carbon groups.

Aliphatic or Aromatic Amines

• Aliphatic amines: All carbon atoms bonded to nitrogen are derived from alkyl groups.
• Aromatic amines: One or more groups bonded to nitrogen are aryl groups.

Heterocyclic Amines

• Heterocyclic aliphatic amines: Nitrogen atom is part of a saturated ring.
• Heterocyclic aromatic amines: Nitrogen atom is part of an aromatic ring.
• Heterocyclic aromatic amines include pyridine and pyrimidine, where nitrogen atoms replace carbon atoms in a benzene ring.
• Pyrimidine and purine are building blocks for amine bases in DNA and RNA.

Amine Nomenclature

• IUPAC names for aliphatic amines: Derived like alcohols, replacing the -e in the parent alkane with -amine.

• Location of the amino group is indicated with a number.

• Common names for aliphatic amines: List groups bonded to nitrogen in alphabetical order, ending in -amine

• Simplest aromatic amine: Aniline (C₆H₅NH₂).

• Simple derivatives of aniline are named using ortho (o), meta (m), or para (p) to locate substituents.

• Derivatives of aniline: e.g., toluidine (methyl-substituted aniline).

• Unsymmetrical secondary and tertiary amines: Named as N-substituted primary amines.

• The largest group bonded to nitrogen is the parent amine. Smaller groups are prefixed with N.

Physical Properties of Amines

• Low-molecular-weight amines have sharp, penetrating odors.
• Amines are polar compounds.
• Primary and secondary amines associate through intermolecular hydrogen bonding.
• Tertiary amines do not hydrogen bond with each other.
• All classes of amines form hydrogen bonds with water and are more soluble in water than comparable hydrocarbons.
• Most low-molecular-weight amines are completely soluble in water.
• Higher-molecular-weight amines are only moderately soluble or insoluble in water.

Basicity of Amines

• Amines are weak bases like ammonia, forming basic solutions.

• Aliphatic amines are stronger bases than aromatic amines.

• Aliphatic amines are stronger bases than aromatic amines.

• All amines, regardless of solubility, react with strong acids to form water-soluble salts.

Characteristic Reactions of Amines

• Reactions with strong acids form water-soluble salts, aiding in the separation of water-insoluble amines from non-basic compounds.
• Amines accept protons (H+) and form ammonium salts.

Alkaloids

• Alkaloids are amines isolated from plants.
• They often include poisons, drugs, and addictive substances.
  • Examples: Nicotine, strychnine, caffeine, morphine, codeine, heroine, quinine, cocaine, and methadone.