Xylidine is the trivial name of dimethylaniline, (CH3)2C6H3NH2. There are six
structural isomers. The names of six compounds indicate methyl group positions
relative to the amino on the benzene ring. They can be obtained from coal tar as
by-products in the fractional distillation or can be prepared by heating
aniline hydrochloride with methanol at 220 C. Xylidine is an aniline homologue
and has similar properties of aromatic amine. Xylidines are brown liquids at
room temperature except 3,4-Xylidine. They are sparingly soluble in water but
miscible with ethanol and diethyl ether. They are sensitive to air and light and
tend to darken on storage. They are toxic if inhaled, ingested, or absorbed
through the skin. Xylidines and derivatives are widely used as raw materials
to produce imaging chemicals like pigments and dyestuffs. All of these compounds
are also used in the production of antioxidants, agricultural, pharmaceutical,
rubber chemicals and other target organic molecules.
Xylidine
|
CAS
#
|
Melting
point C
|
Boiling
point C
|
Isomer
Mixture
|
1300-73-8
|
|
|
2,3-Xylidine
|
87-59-2 |
2.5
|
222
|
2,4-Xylidine
|
95-68-1 |
16
|
218
|
2,5-Xylidine
|
95-78-3 |
11.5 |
218
|
2,6-Xylidine
|
87-62-7 |
8.4
|
214
|
3,4-Xylidine
|
95-64-7 |
51 |
226
|
3,5-Xylidine
|
108-69-0 |
9.8
|
220 - 221 |
|
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.
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