Reaction of Ether with Hydrogen Iodide (HI)

Chemical properties of Ethers (With HI)

On heating with concentrated Hydrogen iodide (HI) the C-O bond in ethers breaks forming alcohol and alkyl iodide. For example,

C₂H₅ -O-C₂H₅ + HI ------------> C₂H₅ - I + C₂H₅OH

On boiling with excess of concentrated Hydrogen iodide (HI), Alkyl iodide is formed.


C₂H₅ -O-C₂H₅ + 2HI ------------> 2C₂H₅I + H₂O

In the case of mixed ethers with two different alkyl groups, the site of cleavage and hence the alcohol and alkyl iodide that form depend on the nature of the alkyl groups.

When one group is methyl and the other is primary or secondary alkyl group, it is the lower alkyl group that forms alkyl iodide due to steric factors.
For Example,









When one group is methyl and the other alkyl group is a tertiary group, the halide formed is a tertiary group, the halide formed is a tertiary halide.
For Example,






It is because the attack by I- takes place at that carbon of alkyl group, which has a greater electron pushing inductive effect and a lower electron density.

Phenolic ethers react with HI to form phenol and alkyl iodide. This can be attributed to the resonance and steric effects of the benzene ring.


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Ether forming Peroxides (Auto oxidation)

Reaction of ethers with atmospheric Oxygen

Ethers form peroxides by the action of atmospheric oxygen or ozonised oxygen due to co-ordination of one lone pair of the ethereal oxygen with another oxygen atom

For example,

C₂H₅O₂H₅ + O ------------> (C₂H₅)₂O (diethyl ether Peroxide)---> O


These peroxides are unstable compounds and decomposes violently on heating. Hence, ethers should never be evaporated to dryness. it is essential to remove the peroxides by washing before distilling the ether. This can be done by washing the ether with a solution of ferrous sulphate.


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Reaction of Ether with Sulphuric Acid

Chemical Properties of Ethers (with H₂SO₄)

On heating with dilute sulfuric acid under pressure, ethers are hydrolysed to alcohols.
For example,

C₂H₅OC₂H₅ + H₂O ----(dil.H2so4,high pressure)-----> 2C₂H₅OH

Mixed ethers under similar conditions give a mixture of alcohols.

CH₃OC₂H₅ + H₂O ------(dil.H2so4,high pressure)------>C₂H₅OH + CH₃OH

But if concentrated sulfuric acid is used, then the products are alcohol and alkyl hydrogen sulphate.

C₂H₅OC₂H₅ (Diethyl ether) -----(heat, conc. H2SO4)-----> C₂H₅OH (ethanol)+ C₂H₅OSO₂OH (ethyl hydrogen sulphate)


Ethers containing secondary and tertiary alkyl groups form alkenes with conc. sulphuric acid.
For example




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Chemical Properties of Ether

The functional group in ethers (-O-) is comparatively inert with respect to the -OH functional group in alcohols and phenols even though the oxygen atom in each of the groups has two lone pairs of electrones. Therefore, ethers are not easily attacked by alkalies, dilute mineral acids, PCl₅, metallic sodium etc. under ordinary conditions. But they undergo chemical reactions under specific conditions.

1. Cleavage of C-O bond in ethers

The cleavage of C-O bond in ethers takes palce under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules.

R-O-R + 2HX -------------> 2RX + H₂O

Alkyl aryl ethers are cleaved at the alkyl-oxygen bond. The reaction yields phenol and alkyl halide.

Ethers with two different alkyl groups are also cleaved in the same manner.

R-O-R' + H-X ------------> R-X + R'-OH

The order of reactivity of hydrogen halides is as follows: HI > HBr > HCl.

1. Reaction with HI

2. Reaction with H₂SO₄

3. Formation of Peroxides

Physical Properties Of Ethers

Lower members of ethers are gases while higher members are volatile with pleasant smell. The C-O bond in ethers are polar. They are nonlinear (angular) molecules with C-O-C bond angle of about 110⁰. Therefore, ethers are polar compounds and have a net dipole moment. For example, dipole moment of dimethyl ether is 1.3D.

Ethers are isomeric with alcohols. But they do not show hydrogen bonding and association because of their low polarity. The weak polarity of ethers do not appreciably affect their boiling points which are comparable to those of alkanes of comparable molecular mass but are much lower than the boiling points of isomeric alcohols.

Ethers containing upto 3 carbon atoms are soluble in water due to their hydrogen bond formation with water molecules.
The increase in the size of the alkyl group decreases the polar nature of C-O bond and hence it decreases the hydrogen bonding with water. As a result solubility of ethers decreases with increase in the number of carbon atoms. Ethers are soluble in hydrocarbons and other non-polar solvents like benzene.

Williamson's synthesis of Ethers

Preparation of ethers using sodium alkoxide

This is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. In this method, ethers are prepared by heating an alkyl halide with sodium alkoxide.

Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by this method. The reaction involves a nucleophilic substitution of halide ion by an alkoxide ion.

Thus, good results are obtained if the alkyl halide is primary. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. For example, the reaction of CH3CONa with (CH3)3 C-Br gives exclusively 2 -methyl propene.

It is because alkoxides are not only nucleophiles but also strong bases. They react with alkyl halides leading to elimination reactions.

Since halogen attached to the benzene ring is not reactive, in order to prepare an alkyl aryl ether, a mixture of alkyl halide and sodium phenoxide must be heated.


For example, ethyl phenyl ether is obtained by heating a mixture of ethyl iodide and sodium phenoxide.

Preparation of Ethers

Preparation of Ethers by Dehydration of Alcohols

When excess of a primary alcohol is heated with protonic acids like conc.H₂SO₄ or H₃PO₄ at 413 K , it undergoes dehydration to form an ether.

2R - OH (Alcohol) -----(conc.H₂SO₄, 413K)-----> R-O-R (Ether) + H₂O

2C₂H₅ OH (Ethanol)-----(conc.H₂SO₄, 413K)-----> C₂H₅-O-C₂H₅ (Diethyl ether) + H₂O



But this reaction cannot be used for the preparation of unsymmetrical ethers.

The formation of reaction product depends on the reaction conditions. At high temperature, if excess of acid is used dehydration occurs in a different way to form an alkene. For example, ethanol when heated with conc.H₂SO₄ at 440K undergoes dehydration to give ethylene.

CH₃ CH₂ OH -----(conc.H₂SO₄, 413K)-----> CH₂ = CH₂ + H₂O

The dehydration of secondary and tertiary alcohols to the corresponding ethers is unsuccessful as alkenes are formed easily in these reactions.

The dehydration of alcohols can also be brought about by passing the vapours of the alcohol under pressure over a heated catalyst like alumina or thoria at 523 K.



2C₂H₅ OH (Ethanol) -----(conc.H₂SO₄, 523K)-----> C₂H₅-O-C₂H₅ (Diethyl ether) + H₂O


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