Question

Ethers like ROR can be cleaved by concentrated HI but not by HCl because:
A. ${I^ - }$ is a weaker nucleophile than $C{l^ - }$
B. ${I^ - }$ is stronger nucleophile than $C{l^ - }$
C. ${S_N}1$ mechanism carried out in this reaction is rapidly in presence of HI.
D. None of these

Answer 1

Hydrogen iodide is a stronger acid than hydrogen chloride due to the large size of iodine ion than chlorine as the atomic radius increases down in the group. Due to the large size the bond between the hydrogen and iodide ion is weaker as compared to the bond between hydrogen ion and chlorine ion. So the hydrogen iodide will dissociate more readily in the solvent as compared to hydrogen chloride.

Complete answer: The ethers like ROR can be cleaved by treating in a strong acidic medium in the presence of nucleophiles. This reaction occurs through the ${S_N}2$ mechanism. In nucleophilic substitution reactions the two indicate the bimolecular reaction. In the ${S_N}2$ mechanism the nucleophilic substitution of the leaving group takes place by the nucleophile group usually (halide ion).
In this reaction, the reaction rate depends on both the nucleophile and the organic compound.
The iodide ion is more nucleophilic than the chlorine atom due to its larger size, the bond length between the hydrogen ion and iodide ion are weaker. Therefore, the iodide ion can be removed more easily than the chloride ion in hydrogen chloride.
Thus, ethers like ROR can be cleaved by concentrated HI but not by HCl because ${I^ - }$ is a stronger nucleophile than $C{l^ - }$.
Therefore, the correct option is A.

Note: The ethers on treating with acid in the presence of nucleophile break down to form alcohol and alkyl halide. Apart from hydrogen iodide, sulphuric acid can also be used in the presence of water to execute this reaction.