ETHERS

Introduction

The name ether is derived from the Latin word ‘aether’ which means ‘to ignite’. At room temperature under high-pressure ether are flammable.

The organic compounds in which the divalent oxygen atom (-O-) is bonded to two same or different alkyl or aryl groups are called ethers.

Classification & Nomenclature

Examples

Symmetrical ethers: When two alkyl groups or two aryl groups attached with – O – are same, such ethers are termed as symmetrical ethers

Aliphatic ethers can exhibit different types of structural isomerism such as positional isomerism functional isomerism and metamerism, etc. For example Isomers 26 of CHO. Only two isomers are possible among them one is alcohol and the other is ether isomer.

Isomers4 of CH10O

Altogether seven isomers are possible among them four are alcohol isomers and three are ether isomers (metamers).

Method of preparation- Williamson’s Synthesis

Synthesis of Aliphatic ethers:

When alkyl halide (or haloalkane) heated with sodium or potassium alkoxide then ether is obtained. This method is commonly known as Williamson’s synthesis.

This reaction is a nucleophilic substitution reaction in which alkoxide ion (such as methoxide, ethoxide etc.) acts as a nucleophile & attacks the positively charged carbon atom of haloalkane to give ether.

This method is applied for the synthesis of both symmetrical as well as unsymmetrical ethers.

Example:

NOTE:
Secondary and tertiary alkyl halides are not used in Williamson’s ether synthesis because they undergo an elimination reaction to form alkene in presence of alkoxide ion since alkoxide ions are not only nucleophile but also acts as a strong base.

Therefore, for preparation of unsymmetrical ether sodium or potassium salt of secondary or tertiary alcohol and primary alkyl halide is used.

Synthesis of Aromatic ether:

Aromatic ethers can also be synthesized by using same Williamson’s synthesis. When haloalkane reacts with sodium phenoxide (or sodium phenolate) then alkoxy benzene is formed.

NOTE:

But we cannot prepare anisole by reacting with Iodobenzene and sodium methoxide because the Carbon- Iodine bond in Iodobenzene acquires a partial double bond character by resonance which is difficult to break by methoxide nucleophile.

Physical properties of Aliphatic ethers

Solubility:

Lower members of ethers are slightly soluble in water due to their ability to form intermolecular H-bond with water molecules whereas higher members of ethers are insoluble.

Boling point:

Ethers have lower boiling point than its isomeric alcohols because ethers cannot form intermolecular H-bond within them or can only interact through weak dipole-dipole interaction (Van der Waal’s interaction) whereas alcohol can form strong intermolecular H- bond with each other.

Chemical properties of diethyl ether (Ethoxyethane)

1. Reaction with air

When diethyl ether reacts with air in presence of sunlight then diethyl peroxide is formed which is thermally unstable and explode violently on heating. It is very dangerous to distill the old sample of ether. Therefore, ethers are stored in dark colored bottle with iron fillings in it to prevent the formation of diethyl peroxide. If diethyl peroxide is formed by chance it is converted into free ether and iron gets oxidized.

2. Reaction with cold conc. HCl & cold conc H2SO4

In this reaction diethyl ether accepts proton donated form HCl therefore diethyl ether acts as

Bronsted-Lowry base and HCl acts as Bronsted-Lowry acid. The cold conc. H2SO4 when reacts with diethyl ether also give similar result.

3. Reaction with HI

When diethyl ether reacts with HI (or HBr) then C-O bond is broken down.

4. Reaction with H2SO4

1. When diethyl ether is warmed with dil. H2SO4, C-O bond is hydrolyzed then ethanol is produced.

2. When diethyl ether is warmed with conc. H2SO4, C-O bond is broken down & ethanol & ethyl hydrogen sulphate is produced.

5. Reaction with Chlorine

1. When diethyl ether is reacted with limited chlorine in dark condition then α, α- dichloro diethyl ether is formed.

2. When diethyl ether is reacted with excess chlorine in presence of light then perchloro diethyl ether is formed.

Important uses of ether

• Ethers are used as organic solvents in laboratories and industries.

• Lower ethers are used as general anesthetics.
• Ethers are used in various organic reactions like Wurtz reaction, Grignard’s reaction, etc