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.


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