# Why is sulphuric acid not used during the reaction of alcohols with KI?

Question:

Why is sulphuric acid not used during the reaction of alcohols with KI?

Solution:

In the presence of sulphuric acid (H2SO4), KI produces HI

$2 \mathrm{KI}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow 2 \mathrm{KHSO}_{4}+2 \mathrm{HI}$

Since $\mathrm{H}_{2} \mathrm{SO}_{4}$ is an oxidizing agent, it oxidizes $\mathrm{HI}$ (produced in the reaction to $\mathrm{I}_{2}$ ).

$2 \mathrm{HI}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{I}_{2}+\mathrm{SO}_{2}+\mathrm{H}_{2} \mathrm{O}$

As a result, the reaction between alcohol and HI to produce alkyl iodide cannot occur. Therefore, sulphuric acid is not used during the reaction of alcohols with KI. Instead, a non-oxidizing acid such as H3POis used.