Chemical Properties of Ethers
Reactions involving C-O bond cleavage and Electrophilic Substitution.
By chemca Team • Updated Jan 2026
Ethers are generally inert towards bases, reducing agents, and oxidizing agents due to the absence of active hydrogen. However, they undergo cleavage with strong acids and electrophilic substitution in aromatic ethers.
1. Cleavage of C-O Bond by Acids
Reaction with Hydrogen Halides
Ethers react with $HI$ or $HBr$ to form Alkyl Halides and Alcohols. (Reactivity: $HI > HBr > HCl$).
$$ R-O-R + HI \xrightarrow{373K} R-I + R-OH $$
If $HI$ is in excess, the alcohol also converts to alkyl iodide.
Site of Cleavage (Important Rules):
- Case 1: Primary/Secondary Groups ($S_N2$): The halide ion ($I^-$) attacks the smaller (less hindered) alkyl group.
Example: $CH_3-O-CH_2CH_3 + HI \rightarrow CH_3I + CH_3CH_2OH$ - Case 2: Tertiary Group ($S_N1$): The halide ion attacks the tertiary carbon because the reaction proceeds via stable carbocation.
Example: $(CH_3)_3C-O-CH_3 + HI \rightarrow (CH_3)_3C-I + CH_3OH$ - Case 3: Alkyl Aryl Ethers (Resonance): The $O-Aryl$ bond is strong due to partial double bond character. Cleavage occurs only at the $O-Alkyl$ bond.
Example: $C_6H_5-O-CH_3 + HI \rightarrow C_6H_5OH (\text{Phenol}) + CH_3I$
2. Electrophilic Substitution (Aromatic Ethers)
Reactions of Anisole
The alkoxy group ($-OR$) is activating and ortho-para directing.
A. Halogenation (Bromination)
Bromination occurs in Ethanoic Acid medium.
$$ \underset{\text{Anisole}}{C_6H_5OCH_3} + Br_2 \xrightarrow{CH_3COOH} \underset{\text{p-Bromoanisole (Major)}}{p\text{-Isomer}} + \underset{\text{o-Bromoanisole (Minor)}}{o\text{-Isomer}} $$
B. Nitration
$$ C_6H_5OCH_3 + \underset{\text{Nitrating Mixture}}{HNO_3 / H_2SO_4} \rightarrow p\text{-Nitroanisole (Major)} + o\text{-Nitroanisole} $$
C. Friedel-Crafts Reactions
Alkylation: $$ C_6H_5OCH_3 + CH_3Cl \xrightarrow{Anhyd. AlCl_3} p\text{-Methoxytoluene} + o\text{-Isomer} $$
Acylation: $$ C_6H_5OCH_3 + CH_3COCl \xrightarrow{Anhyd. AlCl_3} p\text{-Methoxyacetophenone} $$
3. Auto-oxidation
Formation of Explosive Peroxides
Ethers react with atmospheric oxygen in the presence of light to form hydroperoxides and peroxides, which are explosive.
$$ R-O-CH_2-R + O_2 \xrightarrow{Light} R-O-CH(OOH)-R $$
Safety Test: Old ether samples are tested with $Fe^{2+}$ salts followed by KSCN. Red color (Fe(SCN)3) indicates presence of peroxides (oxidizing agents).
Knowledge Check
Test your understanding of Ether Reactions
No comments:
Post a Comment