Chemical Cleavage Reactions of Ethers

Cleavage of C--O bond using Hydrohalic Acids ($$\text{HX} = \text{HI}$$ or $$\text{HBr}$$):

$$\text{R--O--R'} + \text{HX} \to \text{R--X} + \text{R'--OH}$$

Mechanism Rules for Unsymmetrical Ethers ($$\text{R--O--R'}$$):

1. Primary/Secondary Alkyl Groups: Reaction goes via $$S_N2$$. Halide ($$\text{X}^-$$) attacks the less sterically hindered (smaller) alkyl group:
2. $$\text{CH}_3\text{--O--CH}_2\text{CH}_3 + \text{HI} \to \text{CH}_3\text{I} + \text{CH}_3\text{CH}_2\text{OH}$$
3. Tertiary Alkyl Group Present: Reaction goes via $$S_N1$$. Halide ($$\text{X}^-$$) attaches to the tertiary carbon to form the more stable $$3^\circ$$ carbocation:
4. $$\text{(CH}_3)_3\text{C--O--CH}_3 + \text{HI} \to \text{(CH}_3)_3\text{C--I} + \text{CH}_3\text{OH}$$
5. Alkyl Aryl Ethers (Anisole): Cleavage occurs at the alkyl-oxygen bond (due to partial double bond character of the $$sp^2$$ aryl-oxygen bond):
6. $$\text{C}_6\text{H}_5\text{--O--CH}_3 + \text{HI} \to \text{Phenol } (\text{C}_6\text{H}_5\text{OH}) + \text{CH}_3\text{I}$$