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

Question

Philoid · Accepted Answer

In the presence of sulphuric acid (H₂SO₄), KI produces HI as follows : -

2KI + H₂SO₄ → 2KHSO₄ + 2KI

Since H₂SO₄ is an oxidizing agent, it oxidizes HI (produced in the reaction to I₂) as follows: -

2HI + H₂SO₄ _→ I₂ + SO₂ + H₂O

As a result, the reaction between an 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 H3PO4 is used in the reaction to get the desired product.