Ether is an organic compound containing an oxygen atom bonded to two same or different alkyl or aryl groups. The general formula for ethers can be R-O-R, R-O-Ar or Ar-O-Ar, where R represents an alkyl group and Ar represents an aryl group. They are generally classified into two categories on the basis of substituent groups attached: symmetrical ether (when two identical groups are attached to the oxygen atom) and asymmetrical ether (when two different groups are attached to the oxygen atom). Ethers exhibit a wide range of physical and chemical properties. Some of the physical and chemical properties of ethers are discussed below:
Physical Properties of Ethers:
- An ether molecule has a net dipole moment due to the polarity of C-O bonds.
- The boiling point of ethers is comparable to the alkanes but much lower than that of alcohols of comparable molecular mass despite the polarity of the C-O bond. The miscibility of ethers with water resembles those of alcohols.
- Ether molecules are miscible in water. This is attributed to the fact that like alcohols, the oxygen atom of ether can also form hydrogen bonds with a water molecule.
Chemical Properties of Ethers:
Ethers generally undergo chemical reactions in two ways:
- Cleavage of C-O bond: Ethers are generally very unreactive in nature. When an excess of hydrogen halide is added to the ether, cleavage of C-O bond takes place leading to the formation of alkyl halides. The order of reactivity is given as HI>HBr>HCl
R-O-R + HX → RX + R-OH
- Electrophilic substitution: The alkoxy group in ether activates the aromatic ring at ortho and para positions for electrophilic substitution. Common electrophilic substitution reactions are halogenation, Friedel Craft’s reaction etc.
- Halogenation of ethers: Aromatic ethers undergo halogenation, for example, bromination, upon the addition halogen in the presence or absence of a catalyst.
- Friedel Craft’s reaction of ethers: Aromatic ethers undergo Friedel Craft’s reaction for example addition of alkyl or acyl group upon the reaction with alkyl or acyl halide in the presence of a Lewis acid as catalyst.
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