Amine is a group
of basic organic compounds derived from ammonia (NH3) by replacement
of one (primary amines), two (secondary amines), or three (tertiary amines)
hydrogen atoms by alkyl, aryl groups or organic radicals. Most
low mole weight aliphatic amines are liquids with characteristic ammonia-like
odor. But methylamines are gases and long chain alkylamines (from C12) or higher
mole weight amines are
solid. The water solubility is decreasing if molecular weight increase. They
are freely soluble in common organic solvents such as methanol, acetone,
toluene, and ether except aliphatic hydrocarbons. Amines, like ammonia,
are weak bases because the unshared electron pair of the nitrogen atom can form
a coordinate bond with a proton. Amines react with acids to give salts and with
acid anhydrides (or ester ) to form amides. They react with halogenoalkanes to
form longer chains.
Many amines
are not only bases but also nucleophiles that form a variety of electrophile
compounds. They are important intermediates for chemical syntheses due to the
basic functionality of the nitrogen atom and electrophilic substitution at
nitrogen. Some examples of compounds obtained by reaction of amines are:
- Amides (by
reaction with acyl halides or ammonium carboxylate salts)
- N-Alkyl amines (by reaction with halogenoalkanes)
- Isocyanates
(by reaction with phosgene)
- Carbamoyl
chlorides or Urea derivatives (by reaction with phosgene)
- Alkoxylated
amines (by reaction alkylene oxide)
- Quaternary
ammonium compounds (by reaction with alkyl halides and dialkyl
sulfates)
- N-Alkylcarbamic acids or N,N'- Dialkyl ureas (by
reaction with carbon dioxide)
- Urea
derivatives (by reaction with isocyanates)
- Schiff bases
(by reaction with aldehydes or ketones)
- Aminopropionitriles (by reaction of 1° and 2° amines
with acrylonitrile)
- N-Alkylamino
acids (by reaction of 1° and 2° amines with monochloroacetic acid or with
unsaturated acids)
- Amine oxides
(by reaction of 3° amines with hydrogen peroxide)
- Sulfonamide
derivatives (by reaction of 1° and 2° amines with benzenesulfonyl
chloride)
Low molecular
amine names are formed by adding '-amine' as a suffix to the name of the parent
compound. In substitutive nomenclature, the prefix 'amino-' is placed before the
name of the parent compound to denote the functional group in high molecular
amines. Synthetic amines are made mostly by reaction of alcohols with ammonia,
catalyzed by metals( nickel or copper) or metal oxide at high temperature. Many
methods have been devised for the synthesis of the amines; reacting ammonia with
an alkyl halide and neutralizing the resulting alkyl ammonium salt with an
alkali, e.g., sodium hydroxide. This procedure yields a mixture of primary,
secondary, and tertiary amines that is easily separated into its three
components by fractional distillation; boiling methyl isocyanate with caustic
potash, heating the alkyl iodides with ammonia; reduction of nitriles with
alcohol and sodium; heating the esters of nitric acid with alcoholic ammonia;
reducing on nitro-paraffms; action of zinc and hydrochloric acid on aldehyde
ammonias; reduction of the phenylhydrazones and oximes of aldehydes and ketones
with sodium amalgam in the presence of alcohol and sodium acetate; action of
dilute hydrochloric acid on the isonitriles; heating the mustard oils with a
mineral acid, by the hydrolysis of the alkyl phthalimides.
Primary amines
contain the functional group -NH2 (called amino group) and are
converted into secondary and tertiary amines if heated with alkyl or aryl
iodides. Primary amines form various oxidation products violently with
concentrated nitric acid. If the amines are acetylated, they form nitro
derivatives with concentrated nitric acid. Primary amines form diazonium salts
with nitrous acid in cold solution in the presence of excess of mineral acid. Or
a diazoamine is obtained in absence of excess of acid. Other reactions are
condensation products with aldehydes; forming anilides; forming alkyl thioureas;
yielding isonitriles with alcoholic potash and chloroform. Tertiary amines
combine with one molecular proportion of an alkyl iodide to form quaternary
ammonium salts in which a central nitrogen atom is joined to four organic
radicals and one acid radical. Quaternary ammonium salts are used as corrosion
inhibitor, emulsifying and antiseptic agents. Aliphatic amines which have the
lowest carbon content are water-soluble gases or liquids of low boiling point
also readily soluble in water in case of the next low carbon content. But
aliphatic amines which have the high carbon content are odourless solids of high
boiling point and are insoluble in water. They are all bases and easily form
salts with the mineral acids and double salts with the halogenoalkanes. Amine
Salts are crystalline substances that are readily soluble in water. Many
insoluble alkaloids (e.g. quinine and atropine) are used medicinally in the form
of soluble salts. If alkali (sodium hydroxide) is added to solutions of such
salts the free amine is liberated. Short chain alkyl amines are used as raw
materials of solvent, alkyl alkanolamines, and ingredients of rocket fuels. They
are used to make other organic chemicals including rubber vulacanization
accelerators, pesticides, quaternary ammonium compounds, photographic chemicals,
corrosion inhibitors, explosives, dyes and pharmaceuticals. They are used in
rayon and nylon industry to improve the tensile strength.
Allylamines are used
as intermediates for ion exchange resins,
pharmaceuticals, water soluble polymers, herbicide softeners, rubber chemicals,
polymerization initiators and cross-linking agents. Amines are used as reducing
agents for the recovery of precious metals. They are versatile intermediates.
They have active applications in organic synthesis for polymerization catalyst,
chain extender in urethane coatings, agrochemicals, pharmaceuticals,
photographic, heat stabilizers, polymerization catalysts, flame-retardants,
blowing agents for plastics, explosives, and colorants. Long chain alkyl amines
are used for the synthesis of organic chemicals and surfactants used as a
corrosion inhibitor, detergent, ore floating agent, fabric softener, anti-static
agent, germicide, insecticide, emulsifier, dispersant, anti-caking agent,
lubricant and water treatment agent. Alkyl tertiary Amines are used as fuel
additives and preservatives. They have similar applications with long chain
alkyl amines. Hexamethylenediamine used in the manufacture of nylon-6,6 is
prepared by catalytic addition of hydrogen to nitriles. Aromatic amines also
exist, such as phenylamine, which are important for the production of diazonium
salts. They dissociate in water (some very weakly). Aromatic amines are much weaker bases than the aliphatics.
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