Question

Carbon - oxygen bond in ethers can be cleaved by halogen acids, sulphuric acid, phosphorouspentachloride etc. The cleavage of $C-O$ bond takes place under drastic conditions with excess of hydrogen halide, $R-O-R+2HX\to HX\to 2RX+H_{2}O$.

If hydrogen halide is not taken in excess, then one molecule each of alcohol and alkyl halide are formed, $R-O-R+HI\stackrel{373K}{\to }R-OH+R-I$. The order of reactivity of hydrogen halides towards the above mentioned reaction depends on the bond strength of halogenated acids. Weaker is the $H-X$ bond, greater is its reactivity. In case of unsymmetrical ethers, the site of cleavage is such that the halide is formed from the alkyl group which is tertiary, so that the halide formed is tertiary halide.

Indicate whether the following statements / reactions are true or false.
The order of hydrogen halide reactivity is $HI<HBr<HCl$

• A. True
• B. False

Answer 1

The correct option is B False

$H-I$ bond is weaker than $H-Br$ and $H-Cl$

The order is,
$H-Cl<H-Br<H-I$ - bond strength
This is due to the atomic size increase from $-Cl$ to $-I.$