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