Question

why is sulphuric acid not used during the reaction of alcohol with kI.

Answer 1

In the presence of sulphuric acid (H2SO4), KI produces HI....Since is an oxidizing agent, it oxidizes HI (produced in the reaction to I2). 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 H3PO4 is used.

Answer 2

Sulphuric acid is a strong oxidizing agent (specially conc.H2SO4) so it oxidizes the HI produced to Iodine vapours...thus the alkyl iodide cannot be prepared...thus the purpose of our reaction is defeated.