12. Ethers
🎯 Learning Outcomes
After the lesson, learners should be able to:
- Describe the nomenclature, classification and isomerism of ethers.
- Show the preparation of aliphatic and aromatic ethers from Williamson’s synthesis.
- State physical properties of ethers.
- Explain the chemical properties of ethoxyethane with HI, Conc. HCl, Conc. H2SO4, air and Cl2
- State important uses of ethers.
Ethers are a class of organic compounds characterised by an oxygen atom bonded to two alkyl or aryl groups. They possess a general structure R–O–R’, where R may be an alkyl or aryl group. E.g.,
(Dimethyl ether)
(Ethyl methyl ether)
These can be considered the derivatives of alkanes with one –H substituted by –OR group.
Classification
Ethers can be classified as simple (symmetrical) and mixed (unsymmetrical) ethers depending upon the nature of the alkyl or aryl groups. If R=R’, it’s called a simple ether, and if R≠R’, it’s called a mixed ether. E.g.,
(Simple ether)
(Mixed ether)
Ethers can also be classified as aliphatic and aromatic ethers depending upon the R. e.g.,
Aromatic ethers
| Formula | IUPAC name | Common name |
|---|---|---|
 | Methoxybenzene | Methyl phenyl ether or Anisole |
 | Ethoxybenzene | Ethyl phenyl ether or Phenetole |
 | Phenoxybenzene | Diphenyl ether |
Nomenclature
The IUPAC names of the ethers are written by general rules of IUPAC, which take the general form Alkoxy alkane.
The common names of simple and mixed ethers take the general form Dialkyl ether and Alkyl alkyl ether (listed in alphabetical order), respectively.
| Structure ⇅ | IUPAC name ⇅ | Common name ⇅ |
|---|---|---|
| CH₃-O-CH₃ | Methoxymethane | Dimethyl ether |
| CH₃CH₂-O-CH₃ | Methoxyethane | Ethyl methyl ether |
| CH₃CH₂-O-CH₂CH₃ | Ethoxyethane | Diethyl ether |
| CH₃-O-CH₂CH₂CH₃ | 1-methoxypropane | Methyl n-propyl ether |
| CH₃-CH(CH₃)-O-CH₃ | 2-methoxypropane | Isopropyl methyl ether |
Isomerism
Chain isomerism
Isomers that differ only in chain are called chain isomers. E.g., C₅H₁₂O
Functional isomerism
Ethers show functional isomerism with alcohols.
Metamerism
Like ketones and secondary amines, ethers also show metamerism. Isomers that differ in the distribution of carbon atoms (alkyl groups) on either side of the functional group are called metamers.
Examples
Preparations ⚗️
- From Haloalkanes (Williamson’s etherification process) — (studied in properties of Haloalkanes already)
- Preparation of Methoxybenzene (Anisole) By Williamson’s synthesis
This method is generally used for the preparation of aromatic ethers. Alkyl aryl ethers are prepared by reacting sodium phenoxide with an alkyl halide.
Physical Properties
- Dimethyl ether and ethyl methyl ether are gases, but others are colourless, volatile liquids with a pleasant odour.
- Boiling points of ethers are lower than alcohols and carboxylic acids with comparable molecular masses.
- They are generally highly inflammable.
- They are sparingly soluble in water but more soluble in alcohol and other organic solvents.
[A] Reaction due to ethereal oxygen
1. Action with cold conc. HCl and H₂SO₄ (formation of oxonium salt)
Since ethers can behave as weak Lewis bases, they dissolve in cold and conc. Mineral acids to form oxonium salt.
The salt is stable at low temperatures in a strongly acidic solution. On dilution with water, the oxonium salt decomposes back to ether and acid.
2. Action with Conc. H₂SO₄
When heated with hot and conc. H₂SO₄, alcohol and alkyl hydrogen sulphate are formed.
[B] Reaction involving cleavage of C–O bond
3. Action with HI
When ethers are heated with conc. Halogen acids (especially HI and HBr), the C–O bond is cleaved, and we get alcohol and alkyl halide.
If hydroiodic acid is in excess, the alcohol produced also gets converted into an Iodoalkane.
When anisole is heated with HI, the products are always phenol and methyl iodide, NOT methanol and iodobenzene.
[C] Reactions involving alkyl group
3. Action with Air
When exposed to air for a long time in light, the oxygen of air slowly reacts with the ether to form peroxides.
⚠️ Explosion Hazard & Prevention
Ether peroxides are thermally unstable and explosive! Distilling old samples of ethers containing accumulated peroxides can cause severe explosions.
Prevention: Keeping iron wire or ferrous salts in the bottle prevents peroxide formation because atmospheric oxygen combines preferentially with iron:
4. Action with Cl₂
When ether is chlorinated in the absence of sunlight, substitution by halogen preferably takes place at the α position.
But if the reaction is carried out in the presence of sunlight and excess chlorine, all the hydrogen atoms are substituted.
1-(1,1,2,2,2-pentachloroethoxy)-1,1,2,2,2-pentachloroethane
📝 Worked Example
1. How is Ethoxyethane converted to Methoxymethane?
Uses of Ethoxyethane
- As solvent (for oils, resins, petroleum, etc.)
- Solvent for the extraction of compounds in labs and industries
- As a reaction medium, e.g., in preparation of Grignard’s reagent, Wurtz reaction, etc.
- As an anaesthetic (historical use)
- As a coolant.
Uses of Anisole
- For making perfumes
- In pharmaceuticals.
- Starting material for organic synthesis.
📌 Quick Revision Summary
- Definition & Formula: Ethers possess the general formula R–O–R’. They are functional isomers of monohydric alcohols (CₙH₂ₙ₊₂O).
- Classification: Divided into symmetrical (R=R’) and unsymmetrical (R≠R’) as well as aliphatic and aromatic ethers.
- Nomenclature: Systematically named as Alkoxyalkanes (smaller group = alkoxy, larger group = alkane).
- Preparation: Williamson’s synthesis (R–X + R’–ONa → R–O–R’ + NaX) is the standard method for preparing simple, mixed, and aromatic ethers (like Anisole).
- Physical Properties: Lower boiling points than alcohols due to absence of hydrogen bonding. Highly volatile and inflammable.
- Chemical Reactions:
- Oxygen lone pairs form oxonium salts with cold conc. acids.
- C–O bond cleavage occurs with HI (hot) to form alkyl iodides.
- Anisole + HI produces Phenol and Methyl Iodide.
- Prolonged exposure to air forms explosive peroxides (prevented with iron wire).
- Chlorination yields substituted halo-ethers depending on dark vs. light conditions.