The reaction of an ether with hydrogen iodide (HI) involves the cleavage of the C-O bond.
- Mechanism (First Cleavage): The ether contains a primary propyl group and a tertiary butyl group. When one of the alkyl groups is tertiary, the reaction proceeds via an SN1 mechanism due to the stability of the tertiary carbocation .
Protonation of the oxygen is followed by the cleavage of the bond between oxygen and the tertiary carbon, forming the stable tert-butyl carbocation and propyl alcohol. The iodide ion attacks the carbocation to form tert-butyl iodide (I−C(CH3)3).
- Effect of Excess HI: The reaction mixture contains Excess HI. The alcohol formed in the first step (propyl alcohol, H3C−CH2−CH2−OH) reacts further with HI.
The hydroxyl group is replaced by iodine via nucleophilic substitution : R−OH+HI→R−I+H2O. This converts propyl alcohol to propyl iodide (H3C−CH2−CH2−I).
- Conclusion: Both alkyl groups are converted to their corresponding iodides.
Products: H3C−CH2−CH2−I + I−C(CH3)3