Benzoic acid,
the simplest aromatic carboxylic acid containing carboxyl group bonded directly
to benzene ring, is a white, crystalline organic compound; melting at 122 C
(starting sublime at 100 C); boiling at 249 C; slightly soluble in water,
soluble in ethanol, very slightly soluble in benzene and acetone. Its aqua
solution is weakly acidic. It occurs naturally in many plants and resins.
Benzoic acid is also detected in animals. The most of commercial benzoic acid is
produced by the reaction of toluene with oxygen at temperatures around 200 C in
the liquid phase and in the presence of cobalt and manganese salts as catalysts.
It can be prepared also by the oxidation of benzene with concentrated sulphuric
acid or carbon dioxide in the presence of catalysts. Other methods are such as
by the oxidation of benzyl alcohol, benzaldehyde, cinnamic acid; by hydrolysis
of benzonitrile, benzoyl chloride. More than 90% of commercial benzoic acid is
converted directly to phenol and caprolactam. Its use in the production of
glycol benzoates for the application of plasticizer in adhesive formulations is
increasing. It is also used in the manufacture of alkyd resins and drilling mud
additive for crude oil recovery applications. It is used as a rubber
polymerization activators and retardants. Benzoic acid is converted to its salts
and esters for the use of preservative application in foods, drugs and personal
products. Sodium benzoate, sodium salt of benzoic acid, is used preferably as
one of the principal anti-microbial preservatives used in foods and beverages
(but it's concentration is limited usually not exceeding 0.1% because it is
poisonous), as it is about 200 times more soluble than benzoic acid. Sodium
Benzoate is also used in medications, anti-fermentation additives and tabletting
lubricant for pharmaceuticals. The industrial applications are as a corrosion
inhibitor, as an additive to automotive engine antifreeze coolants and in other
waterborne systems, as a nucleating agents for polyolefin, as a dye
intermediate, as a stabilizer in photographic processing and as a catalyst. Wide
range of benzoic esters are used as solvents, dying carrier, disinfectant
additive, penetrating agent and pesticides and manufacturing other compounds.
Benzoic acid derivatives substituted by hydroxy
group or ether containing oxygen atom have active bacteriostatic and fragrant
properties. They are typically used in pharmaceutical and perfumery industry.
The destructive metabolic property of oxygen containing benzoic acid
derivatives such as protocatechuic acid (3,4-dihydroxybenzoic acid) and veratric
acid (3,4-dimethoxybenzoic acid) is used in the application for pharmaceuticals.
Protocatechuic acid is a catabolite of epinephrine. Prazosin, a peripheral
vasodilator and antihypertensive, is also an example of the
applicaion of veratric acid. Hydroxy
and ether substituted benzoic
acids feature analogue metabolite
of
aspirin
(acetylsalicylic Acid). They are used as intermediates for
pharmaceuticals (especially for antipyetic anlgesic,
antirheumatism) and other organic synthesis. They are used as matrix for
ionization of peptides, proteins and carbohydrates.
Ether is any of a number of organic compounds characterized by an oxygen atom
joined with single bonds by two carbon atoms that are part of hydrocarbon
groups. The general formula is R-O-R', where R and R' are alkyl or aromatic
groups. Ethers are formed by the condensation of two alcohols by heating with
sulfuric acid; the reaction is one of dehydration. Ethers can be prepared from
alkyl halide reacted with metallic alkoxide (called Williamson synthesis).
Ethers are similar to alcohols but are generally less dense, less soluble in
water, and have lower boiling points. They are relatively unreactive, which
makes them valuable solvents. But ethers will be
cleaved at high temperatures by concentrated hydrogen halides. Ethers have relatively low boiling point
compare to alkanes as they don't form hydrogen bonds each other. Ethers are more
lipophilic than esters [R-C(=O)-O-R']or amides [RCO-NH2]. Ethers are widely used as solvents for various organic reactions because they
are relatively the least reactive among common organic compounds except alkanes
and fluorocarbons. The common reaction of ethers is cleavage of the C–O bond by
strong acids either in linear chain or cyclic structure. Ethers in which oxygen
is bonded to primary and secondary alkyl groups can form peroxide compounds in
the presence of gaseous oxygen due to two unpaired electrons in oxygen. Ethers can act as
Lewis bases in chemical reactions. Commonly, ethers are
named simply in listing the alkyl groups in alphabetical order or alkane order
such as ethyl methyl ether or methyl ethyl ether, which is methoxyethane in
IUPAC nomenclature ( the formula of "alkoxyalkane" ). When ether is a
parts of complex molecule or aromatic derivatives, it is described as an alkoxy
substituent such as methoxybenzene ( trivial name is anisole). The methoxy
prefix indicates the function methyl group joined by single bonds to an oxygen atom,
with the general formula -O-CH3. Cyclic ethers
have ring structure where the oxygen has become part of the ring. The term of
epoxide indicate three membered cyclic ether (also called oxirane) in which an
oxygen atom is joined to each of two carbon atoms that are already bonded to
each other; four
membered cyclic ether is called oxetane; five membered cyclic ether, furan (or
oxolane); six membered cyclic ether, pyran (also called oxane) respectively.
Their unhindered oxygen atom carries two unshared pairs of electrons - a
structure which favors the formation of coordination complexes and the solvation
of cations. Cyclic ethers are used as important solvents, as chemical
intermediate and as monomer for ring-opening polymerization. Crown Ether is a macrocyclic polyether whose structure contains
hydrogen, carbon and oxygen atoms. Each oxygen atoms are confined between two
carbon atoms and exhibits a conformation with a hole (accordingly called
"crown"). Anisole is one of the simplest aromatic compound to
which ether group is linked. But
it is different with aromatic compounds like furan where the oxygen is a part of
the ring. Anisole, C6H5OCH3
(methyl phenyl ether), is a clear liquid that is soluble in ether and
alcohol; insoluble in water; boiling point 155 C. Anisole and its derivatives
are used as solvents and in perfumery. Anisole can be obtained from anise seed.
Anisic acid, p-methoxybenzoic acid, is a part of cresol class antiseptic
compounds. It
is also used as an insect repellent and ovicide.
Anisole, anisic acid, and their derivatives are also widely used in
chemical reaction as intermediates to obtain target materials such as dyes,
pharmaceuticals, perfumes, photoinitiators and agrochemicals. |