Question

Give a reason for the following:

Ethoxy ethane with conc. HI at 373 K gives C₂H₅OH and CH₃I but not CH₃OH and C₂H₅I.

Answer 1

At 373 K enthoxy ethane reacts with concentrated HI to produce C₂H₅OH and CH₃I. This is due to the fact that this reaction uses a S_N² mechanism, with the nucleophilic substitution taking place at the carbon linked to the ethoxy group. The iodide ion (I^-) from HI functions as a nucleophile, attacking the carbon atom in ethoxyethane and displacing the ethoxy group. This substitution process produces ethanol and methyl iodide.

\[\ce{\underset{Ethoxy ethane}{C2H5OH5} + 2HI -> \underset{Ethanol}{C2H5OH} + \underset{Methyl iodide}{CH3I}}\]

The absence of methanol (CH₃OH) and ethyl iodide (C₂H₅I) is most likely due to the instability of the methoxide ion (CH₃O⁻) and the formation of ethyl carbocation (C₂H₅⁺) as reaction intermediates.