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Phthalic Acid,
also called Benzenedicarboxylic Acid with formula
C6H4(COOH)2, is the name of any of three
isomers. The ortho form (1,2-benzenecarboxylic acid) is called simply phthalic
acid. It is a white crystals decomposing at 191°C and slightly soluble in water
and ether. This compound is mainly produced and marketed in the form of its
anhydride produced by the oxidation of orthoxylene and naphthalene. Its wide
application is based on the ortho related carboxylic acid groups as their
dehydration is highly reactive with broad processing conditions to produce
various downstream products. It is used to make simple esters widely used as
plasticizers. It is used as in making unsaturated polyester resins, alkyd
resins, polyester polyols, dyes and pigments, halogenated anhydrides,
polyetherimide resins, isatoic anhydride and insect repellents. The meta form is
isophthalic acid (1,3-benzenecarboxylic acid). It is a white crystals subliming
at 345°C slightly soluble in water, alcohol and acetic acid (insoluble in
benzene). It is obtained by oxidizing meta-xylene with chromic acid, or by
fusing potassium meta-sulphobenzoate, or meta-brombenzoate with potassium
formate. IPA has excellent performance characteristics in coatings including
excellent hardness, corrosion and stain resistance, hydrolytic stability of
coatings and gel coats, excellent thermal stability and low resin color. It is a
key ingredient in FRP markets for such products as marine, automotive, and
corrosion resistant pipes and tanks. Polyesters containing isophthalic acid are
also used extensively in industrial coatings applications for home appliances,
automobiles, aluminum siding, and metal office furniture. It used as an
intermediate for polyesters, polyurethane resins, plasticizers. The para form,
known as terephthalic acid (1,4-benzenecarboxylic acid) is a combustible white
powder insoluble in water, alcohol and ether; (soluble in alkalies), sublimes at
300°C. It can be produced by oxidizing caraway oil, a mixture of cymene and
cuminol or by oxidizing para-diderivatives of benzene with chromic acid. TPA has
been used mainly as a raw material of polyester fiber but lately it has been
exploited for various uses such as non-fiber field, PET-bottle, PET-film and
engineering plastics and as poultry feed additives. Phthalic acid derivatives
are also widely used to make dyes, medicine, and synthetic perfumes, pesticides,
and other chemical compounds.
Aldehydes are
organic compounds containing -CHO radical, in which a carbon atom forms a solid
bond with an oxygen atom and is also bonded to a hydrogen atom and another group
denoted by R, which can be a second hydrogen atom, an alkyl group, or an aryl
group. The most important and the simplest examples are methanal (formaldehyde),
HCOH, and ethanal (acetaldehyde), CH3CHO.( In systematic chemical
nomenclature, aldehyde names end with the suffix -al). Formaldehyde is used to
make synthetic resins by reaction with phenols, urea, and melamine, as a
chemical intermediate, as an embalming fluid, and as a disinfectant.
Acetaldehyde is used chiefly to manufacture acetic acid. They are
unpleasant-smelling liquids widely used in the chemical industry, whereas
aromatic aldehydes frequently have pleasant smells and are used widely as
flavourings and perfumes. An example is benzaldehyde (benzenecarbaldehyde,
C6H5CHO), a derivative of benzene with an aldehyde group
attached to the ring. It is a colourless oil smelling of almonds offer
applications to both in perfumes and flavourings. Aldehydes are formed by
oxidation of primary alcohols; further oxidation yields carboxylic acids.
Aldehydes have certain characteristic addition and condensation reactions.
Aldehydes can be reduced to primary alcohols (ketones to secondary alcohols).
Aldehydes form cyanohydrins with hydrogen cyanide, acetals with alcohol,
yellow-orange solid derivatives with DNP ( 2,4-dinitrophenylhydrazones) and
undergo condensation reactions to yield oximes (compounds containing the group
C:NOH), hydrazones (organic compounds containing the group =C:NNH2),
and semicarbazones (organic compounds containing the unsaturated group
=C:N.NH.CO.NH2). Terephthalaldehyde
is used as an intermediate for manufacturing
dyes and fluorescent whitening agents. |
