Chemical Reactions of Ethers

Are you aware of the chemical reactions of ethers? We have looked at the chemical properties of ethers, but are they all similar to their chemical reactions? If we ask you about the chemical reactions of ether, would you be able to identify those for us? Well, in this chapter, we will look at the different chemical reactions of ether and understand the behaviour of ethers better.

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Reactions of Ether

Ethers are relatively unreactive compounds. The ether linkage is quite stable towards bases, oxidizing agents, and reducing agents. Therefore, we must remember that with respect to the ether linkage, ethers undergo just one kind of reaction. It is cleavage by acids :

R-O-R’  +  HX   →   R-X  +  R’-OH R’ ¾X

Reactivity of HX : HI > HBr > HCl

Cleavage takes place only under quite extreme conditions, like in concentrated acids (usually HI or HBr) and high temperatures. A dialkyl ether produces, initially, an alkyl halide and an alcohol. This alcohol may react further and form a second mole of alkyl halide. For example :

The oxygen of an ether is basic, similar to the oxygen of an alcohol. The initial reaction between an ether and an acid is no doubt, the formation of the protonated ether. Cleavage, then, involves the nucleophilic attack by a halide ion on this protonated ether, with the displacement of the weakly basic alcohol molecule.

Such a reaction usually occurs much more readily as compared to the displacement of the strongly basic alkoxide ion from the neutral ether.

Browse more Topics under Alcohols Phenols And Ethers

• Chemical Reactions of Alcohols, Phenols & Ethers
• Introduction and Classification of Alcohols, Phenols & Ethers
• Nomenclature
• Physical Properties of Alcohols, Phenols and Ethers
• Preparation of Alcohols
• Physical Properties of Ethers
• Preparation of Ethers
• Preparation of Phenols
• Some Commercially Important Alcohols

1) Reactions of Ether Due to an Alkyl Group

• Combustion: Ethers are highly inflammable and they form extremely explosive mixtures with air giving CO₂ and water.

C₂H₅O C₂H₅ + 6O₂   →   4CO₂ + 5H₂O

• Halogenation: The alkyl group undergoes substitution reaction with chlorine or bromine. The resultant product is halogenated ether in absence of sunlight. However, in presence of sunlight, it substitutes all the hydrogen atoms of ethers.

CH₃CH₂OCH₂CH₃           CH₃CHCIOCHCICH₃ (α α’-dichloro diethyl ether)

CH₃CH₂OCH₂CH₃               C₂CI₂OC₂CI₅ (Perchloro diethyl ether)

2) Reaction of Ether Due to Ethereal Oxygen

Ethers behave as Lewis bases because of the presence of two lone pairs of electrons on the oxygen atom. Therefore, they form salts with strong acids. The oxonium salts are soluble in acid solution. We can facilitate the regeneration of ether by hydrolysis of these salts.

Ethers also form coordination complexes with Lewis acids like BF₃, AICI₃, RMgX etc. Therefore, we can derive the fact that ethers are very good solvents for Grignard reagents.

3) Formation of Peroxides

Ethers form peroxide linkage with oxygen when we expose them to air or ozonized oxygen in presence of sunlight or ultraviolet light. These peroxides are highly poisonous in nature. They are oily liquids and decompose violently even at low concentrations. Therefore, we must ensure never to evaporate esters to dryness. It might lead to explosive reactions.

Besides this, we must also check the purity of ether before its use as an anaesthetic agent. An impure ether (having peroxide linkage) gives red colour when shaken with ferrous ammonium sulphate and potassium thiocyanate. This could prove to be lethal for the patients on whom we try anaesthesia.

On mixing with KI solution, it liberates I₂ which turns starch paper blue.

We can make these ethers free from peroxide linkages by distilling them with highly concentrated sulphuric acid, H₂SO₄. Also, we can check for the peroxide formation by adding a little amount of Cu₂O to the ether.

4) Reactions of Ether Involving Cleavage of Carbon-Oxygen Bond

• Action of dil. H₂SO₄ : Ethers, on heating with dilute H₂SO₄ , under high pressure, hydrolyse to corresponding alcohols.
• Action of Conc. H₂SO₄ : Ethers, on warming with conc. H₂SO₄ , give alkyl hydrogen sulphate.

R-OR  +  conc. H₂SO₄   →    2R HSO₄

R-OR’  +  conc. H₂SO₄  →  RHSO₄  +  R’HSO₄

• Action of HI:

The products that we get during the action of HI on ethers depend mainly upon the temperature in which we carry out the reaction.

R-OR + HI   R-OH + RI

R-OR’ + HI   R’-OH + RI

Note: In case of a mixed ether, halogen atom attaches itself to the simpler alkyl group.

CH₃OC₂H₅ + HI → CH₃I + C₂H₅OH

R-R + HI   2RI + H₂O

We would observe similar reactions with HCI, HBr & the reactivity order is HI > HBr > HCI.

• Action of PCI₅ : In the presence of heat, we get the following reaction:

R-O-R + PCI₅    2RCI + POCI₃

• Action of Acetyl chloride or Acetic anhydride :

• Dehydration of Ethers:

C₂H₅OC₂H₅  2CH₂=CH₂ + H₂O

• Action of Carbon Monoxide :

C₂H₅OC₂H₅, + CO   C₂H₅COOC₂H₅

ROR   +   CO   →   RCOOR

You can download Alcohols, Phenols and Ethers Cheat Sheet by clicking on the download button below

Solved Example for You

Q: Write down a few uses of ethers.

Ans: We commonly use ethers as:

• General anaesthetic agent.
• As a refrigerant. This is because it produces cooling on evaporation.
• A solvent for oils, fats, resins, Grignard reagent etc.
• For providing inert & moisture free medium for reactions e.g. Wurtz reaction.