Question

${C_2}{H_5} - O - {C_2}{H_5} + HI \to {C_2}{H_5} - OH + {C_2}{H_5} - I$
Identify the reaction condition in which reaction occurs.
(A) High temperature
(B) HIgh vacuum
(C) Cold
(D) None of the above

Answer 1

Ether is very less reactive amongst other functional groups. This reaction will require protonation of the oxygen atom followed by the attack of the nucleophile iodide ion to break the strong C-O single bond.

Complete step by step solution:
This reaction involves the cleavage of C-O bond in ethers but ethers are least reactive functional groups. We require to react hydrogen halides under drastic conditions to make te reaction occur.
- Drastic conditions means harsh conditions that involves high concentration of reagents and high temperatures as well.
- In this reaction also only if we give high temperature then only this reaction will give products. In lower temperatures, activation energy is not enough to make products.
So, correct answer is (A) High temperature

Additional Information:
- If Alkyl aryl ethers are allowed to react with hydrogen halides at drastic conditions, then C-O bond between alkyl carbon and oxygen will break because bond between aryl carbon and oxygen will be more stable in comparison.
- In these type of reactions, reactivity of hydrogen halides is as follows:
HI > HBr > HCl
- The mechanism of this reaction involves protonation of the ether oxygen and then the nucleophilic attack of halide breaks the bond by ${S_N}2$ mechanism.
- If asymmetric ether is reacted with hydrogen halides, then the alkyl group that has least steric hindrance will form halide. Means tendency to form halide of alkyl groups will be Primary > Secondary > Tertiary.

Note: Do not think that as protonation of the ether can be done with HI, it will react to give product at lower temperatures. The nucleophilic attack to break the C-O bond of ether always requires drastic conditions.