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.
• Amines are widely distributed in biological systems.
• Amines are basic.
• The functional group of an amine is the amino group (NH₂, RNH₂, R₂NH, or R₃N). Here, nitrogen bonds to one, two, or three carbon atoms.

Amine Types

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

Aliphatic or Aromatic Amines

• Aliphatic amines: All carbon atoms bonded to nitrogen are derived from alkyl groups. Examples include propylamine and sec-butylamine.
• Aromatic amines: One or more of the groups bonded to nitrogen are aryl groups. Examples include aniline and toluidine.

Heterocyclic Amines

• Heterocyclic amines: Nitrogen is part of a ring.
• Heterocyclic aliphatic amines: The ring is saturated.
• Heterocyclic aromatic amines: Nitrogen is part of an aromatic ring. Examples include pyridine, pyrimidine, and purine. These are building blocks for DNA and RNA.

Nomenclature of Amines

• IUPAC names for aliphatic amines are similar to alcohols, replacing the final -e with -amine and indicating the position if the amino group on the parent chain with a number. Examples include 2-propanamine, cyclohexanamine and 1,6-hexanediamine. Common names use alphabetical order for groups bonded to nitrogen, followed by -amine.
• The simplest aromatic amine is aniline (C₆H₅NH₂). Derivatives are named using numbers or ortho (o), meta (m), and para (p) locators. Example: 4-nitroaniline (p-nitroaniline) and 3-methylaniline (m-toluidine).
• Unsymmetrical secondary and tertiary amines are named as N-substituted primary amines. The largest group bonded to nitrogen is the parent amine. The smaller groups are indicated by the prefix N.

Physical Properties of Amines

• Low molecular weight amines have sharp, penetrating odors (like ammonia). Trimethylamine smells like rotting fish.
• Amines are polar compounds.
• Primary and secondary amines associate through intermolecular hydrogen bonding.
• Tertiary amines do not have hydrogen bonding capability.
• All classes of amines form hydrogen bonds with water. Low molecular weight amines are completely soluble in water, while higher molecular weight amines are only moderately soluble or insoluble in water.

Basicity of Amines

• Amines are weak bases, like ammonia (NH₃).
• Aqueous solutions of amines are basic.
• Aliphatic amines are stronger bases than aromatic amines.
• Heterocyclic aromatic amines are weaker bases compared to aliphatic amines.

Characteristic Reactions of Amines

• Amines react with strong acids to form water-soluble salts.
• This property allows separation of water-insoluble amines from other non-basic water-insoluble compounds.
• Amines accept protons, forming ammonium salts.

Alkaloids

• Amines found in plants are called alkaloids, which can include poisons, drugs, and addictive substances. Examples include nicotine, strychnine, caffeine, morphine, codeine, heroin, quinine, cocaine, and methadone.