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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. 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.
Guaiacol is the methyl ether of pyrocatechol. It is a main constituent of
creosote obtained from wood tar (mainly beech) by distillation mostly between
203 and 220 C. It is synthesized from anisole also. The dimethyl ether of pyrocatechol is called veratrol. They and
their derivatives are used as an external antiseptic, expectorant, gastric
sedative, deodorant, and as a parasiticide. Methoxyphenols
are used in manufacturing stabilizers and antioxidants for plastics and rubbers.
They are also used in analgesics, local anesthetic,
flavorings, biocides, antiseptics. 2-Methoxyphenol is
used in manufacturing vanillin and other flavorings.
Dimethoxyanilines
are used as an intermediate for dyes, pigments
and pharmaceuticals.
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