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Amine is a group
of basic organic compounds derived by replacement of one (primary amines), two
(secondary amines), or three (tertiary amines) of the hydrogen atoms in ammonia
(NH3) by alkyl or aryl groups. 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
used as a corrosion inhibitor, emulsifying and antiseptic agents. 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 or ester ) to form amides. They react with
halogenoalkanes to form longer chains. 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 fuctional 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
ractions; forming condensation products with aldehydes; forming anilides;
forming alkyl thioureas; yielding isonitriles with alcoholic potash and
chloroform. 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 forms 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. 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. One of the most
important aromatic amines is aniline, a primary aromatic amine replacing one
hydrogen atom of a benzene molecule with an amino group. It is a pale brown
liquid at room temperature; boiling at 184 C, melting at -6 C; slightly soluble
in water and freely soluble in ether and alcohol. It causes serious industrial
poisoning. The substance may have effects on the blood, resulting in formation
of methaemoglobin. Repeated or prolonged exposures may be carcinogenic.
Commercial aniline is obtained from nitrobenzene which is prepared from benzene
with nitric acid by electrophilic substitution reaction or from chlorobenzene by
heating with ammonia in the presence of copper catalyst. It is also obtained as
a by-product of coal tar. In commerce the term of aniline oil blue refers to the
pure one while aniline oil red indicates a mixture of aniline and toluidines with
equimolecular weights.
Considerable quantity of aniline is converted into 4,4กฏ-methylenedianiline (MDA)
by the condensation reaction of formaldehyde with aniline in the presence of
hydrochloric acid. MDA is is used as an epoxy curing agent, a corrosion
inhibitor and molded plastics, and as an intermediate to prepare organic
compounds used for polyurethane, spandex fibers, azo dyes, isocyanates and
poly(amide-imide) resins. Other important aromatic amine compound as the
starting material to produce polyurethane foam production is toluenediamine
(TDA). TDA is the mixture of 2,4-diaminotoluene and 2,6-diaminotoluene, usually
in a ratio of 80:20. Most of TDA is used in the manufacture of toluene
diisocyanate (TDI), which is the predominant diisocyanate in the flexible foams
and elastomers industries. TDI reacts with an alcohol to form urethane linkages.
Other applications of TDA include to produce dyes, polyamides, antioxidants,
hydraulic fluids, and fungicide stabilizers. Aniline is a starting moiety to
prepare plant protecting agents. Examples include fenuron (CAS RN: 101-42-8),
propham (CAS RN: 122-42-9), siduron (CAS RN: 1982-49-6), carboxin (CAS RN:
5234-68-4), fenfuram (CAS RN: 24691-80-3) and propachlor (CAS RN: 1918-16-7).
Aniline is processed to produce a series of compounds being used in the rubber
industry, e.g. diphenylguanidines, phenylenediamines mercaptobenzothiazoles,
aniline ketones and etc. There are three isomers of phenylenediamine: ortho-,
meta-, and para-phenylenediamine. They are low toxic diamines used as components
of plastic composites and engineering polymers. They are used to produce aramid
fibers, dyes including hair dyes, rubber chemicals (vulcanization accelerators
and antioxidants), and pigments.
Aniline is the starting material in the dye
manufacturing industry. It forms aniline colors when combined with other
substances, particularly chlorine or chlorates. Aromatic amines are weaker bases
reacting with strong acids to form amides. Anilide is an amide derived from
aniline by substitution of an acyl group for the hydrogen of NH2. Acetanilide is from acetic acid and aniline. Acetanilide is an odourless,
white flake solid or crystalline powder (pure form);
soluble in hot water alcohol, ether, chloroform,
acetone, glycerol, and benzene;; melting point 114 C and boiling point 304 C;
can undergo self-ignite at 545 C, but is
otherwise stable under most conditions. Acetanilide which can be obtained by
acetylation of aniline
undergoes
nitration at low temperature and yields highly the para-nitro products. Acetyl group can then be removed by acid-catalyzed hydrolysis to yield para-nitroaniline. Although the activating affection
of the
amino group can be reduced, the acetyl derivative remains an
ortho/para-orientation and activating substituent. Aniline is converted into
sulfanilic acid which is the parent compound of the sulfa drugs. Aniline is also
important in the manufacture of rubber-processing chemicals, explosives,
plastics, antioxidants and varnishes. Amines take part in many kinds of chemical
reactions and offer many industrial applications. Chemically modified
amine products take part in many kinds of chemical
reactions and offer many applications in the wide range of industrial fields
include agrochemicals, dyestuffs, pharmaceuticals, and corrosion inhibitors.
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