Types of amines – primary, secondary, tertiary, quarternary amines

An amine is a derivative of ammonia (NH3) in which one or more of the hydrogen atoms are replaced with a substituent groups such as an alkyl or aryl groups.

Amine structure

Amines are classified as:

  • primary (1°) if one alkyl group is attached to the nitrogen atom (R-NH2),
  • secondary (2°) if two alkyl groups are present (R2-NH),
  • tertiary (3°) if all three hydrogen atoms in ammonia have been replaced by alkyl groups (R3-N),
  • quarternary (4°) has four alkyl groups bonded to the nitrogen and the nitrogen bears a positive charge (R4-N+).

Amines are further divided into aliphatic, aromatic, and heterocyclic amines:

  • Aliphatic amine: a nitrogen is bonded only to alkyl groups.
  • Aromatic amine: a nitrogen is bonded to one or more aryl groups (an aryl group - a functional group derived from an aromatic ring).
  • Heterocyclic amine: an amine in which nitrogen is one of the atoms of a ring.

Accordingly, an amine general formula can be represented as a nitrogen atom bonded with one or more functional groups.

Naming Amines

Using the IUPAC (International Union of Pure and Applied Chemistry) naming system, a primary amine would be named by adding the -amine suffix to the name of the chain or ring to which it is attached. The -e is removed from this name.

 Common primary, secondary, tertiary amines

The IUPAC name for an aromatic amine consisting of an amine group attached to a benzene ring is aniline, rather than benzamine.

To name secondary and tertiary amines, begin with an amine name based on the name of the longest alkyl group. Use the locator, N, to indicate the attachment of additional chains to the nitrogen atom.

For example, an amine with an ethyl group, a propyl group, and a butyl group, each bonded to the nitrogen atom at carbon number 1, is named N-ethyl-N-propylbutan-1-amine.

N-ethyl-N-propylbutan-1-amine - tertiary amine


Properties of Amines

Small amines are soluble in water. Since nitrogen is more electronegative than either carbon or hydrogen, the N2C bonds and any N2H bonds are polar.

The mono-, di-, and tri- methylamines and ethylamine are gases at room temperature and have odors similar to ammonia. Most other amines are liquids, and a lot of them have odors resembling that of raw fish. A few amines (such as diamines) have strong, disagreeable odors.

The bacterial decomposition of protein from dead fish and decaying flesh releases amines with the foul odor. Two of these compounds are the diamines - putrescine and cadaverine.

The simpler amines are irritating to the skin, eyes, and mucous membranes and are toxic by ingestion. Aromatic amines are generally toxic. Many are readily absorbed through the skin and affect both the blood and the nervous system.

Amine reactions

An amine can generally be synthesized from an alkyl halide and ammonia.

Preparing amines - alkylation of ammonia

Amines, like ammonia, are weak bases.

 NH3  +            H2O ⇌             NH4+  +              OH-
 Ammonia    Ammonium ion  Hydroxide ion

Amines behave similarly

CH3-NH2  +            H2O ⇌     CH3-NH3+  +              OH-
Methylamine   Methylammonium ion  Hydroxide ion

The lone pair of electrons on nitrogen makes amines basic and nucleophilic. Thus, they react with electrophiles.

Amine salt

Amines react with acids to form acid-base salts.

When an amine (a weak base) is neutralized by an acid, an alkylammonium salt is produced.

Amine salt - alkylammonium salt

An amine salt is an ionic compound in which the positive ion is a mono-, di-, or trisubstituted ammonium ion (RNH3°, R2NH2°, or R3NH°) and the negative ion comes from an acid.

Amine salts can be obtained in crystalline form (odorless, white crystals) by evaporating the water from the acidic solutions in which amine salts are prepared.

The process of forming amine salts with acids is an easily reversed process. Treating an amine salt with a strong base such as NaOH regenerates the "parent" amine.

What are biogenic amines?

Biogenic amines are a large group of compounds that have an animal or vegetable origin.

Some of biochemically important amines are:

  • Norepinephrine
  • Epinephrine
  • Dopamine
  • Serotonin

Norepinephrine (also called noradrenaline) is an organic chemical that functions in the brain and body as a hormone and neurotransmitter.

Epinephrine (also known as adrenaline) has some neurotransmitter functions but is more important as a central nervous system stimulant.

Epinephrine and Norepinephrine are the same except that epinephrine has a methyl group attached to its nitrogen in place of a hydrogen atom.

Dopamine plays several important roles in the brain and body as a neurotransmitter and a local chemical messenger.

Serotonin is a monoamine neurotransmitter.

Norepinephrine, Dopamine, Serotonine molecular structures - biogenic amines

Also many heterocyclic amines are biologically important, or biologically active.

  • DNA, RNA, myoglobin, chlorophyll, histamine
  • LSD, strychnine

The heterocyclic amine histamine is responsible for the unpleasant effects felt by individuals susceptible to hay fever and various pollen allergies.

LSD (lysergic acid diethylamide) is one of the most powerful hallucinogenic drugs known. Its psychological effects may include altered awareness of the surroundings, perceptions, and feelings.

The alkaloids are an important group of biologically aclive amines. They generally synthesized by plants to protect them from being eaten by insects and other animals.

  • Cocaine in coca leaves
  • Nicotine in tobacco
  • Caffeine in coffee beans
  • Theobromine in cacao plant
  • Mescaline in peyote cactus
  • Morphine in opium poppies

Many drugs of addiction are classified as alkaloids.

Theobromine, Caffeine structure - Heteroamines

Caffeine (1,3,7-Trimethylxanthine) stimulates central nervous system. The most well known source of caffeine is the coffee beans.

Theobromine (3,7-Dimethylxanthine) is a bitter alkaloid of the cacao plant.

Theobromine and caffeine compounds influence in a positive way our moods and our state of alertness.

Like caffeine, theobromine can keep you more alert and awake.

Comparing with theobromine caffeine has an extra methyl group.

Cocaine – a tropane alkaloid - is a strong addictive stimulant made from the leaves of the coca plant native to South America.

Nicotine is an alkaloid in cigarettes that naturally occurs in tobacco. It is a powerful parasympathomimetic stimulant.

Strychnine is a highly toxic, colorless, indole alkaloid used as a pesticide in poison baits for rodents.

Some compounds that contain quaternary ammonium ions are important part of biochemical systems.

Two important quaternary ammonium ions present in the human body are choline and acetylcholine.

  1. Choline has important roles in both fat transport and growth regulation.
  2. Acetylcholine is involved in the transmission of nerve impulses.