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

<p>In the presence of sulphuric acid (H₂SO₄), KI produces HI as follows : -</p><p>2KI + H₂SO₄ → 2KHSO₄ + 2KI</p><p>Since H₂SO₄ is an oxidising agent, it oxidises HI (produced in the reaction to I₂)</p><p>2HI + H₂SO₄ _→ I₂ + SO₂ +;</p><p>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-oxidising acid such as H3PO4 is used in the reaction to get the desired product.<br><br></p><p dir="ltr">A few things you can remember here, while solving &lt;a href="https://www.shiksha.com/preparation/chemistry-ncert-solutions-class-12th-haloalkanes-and-haloarenes-4511-ns"&gt;NCERT Solutions for Haloalkanes And Haloarenes&lt;/a&gt;.</p><ul><li dir="ltr" aria-level="1"><p dir="ltr" role="presentation">Sulphuric acid is a powerful oxidising agent. We know this because the sulphur atom in sulphuric acid is in its highest possible oxidation state (+6). It can only be reduced. And it can readily accept electrons from other substances.</p></li><li dir="ltr" aria-level="1"><p dir="ltr" role="presentation">It oxidises the necessary intermediate, hydrogen iodide (HI), to iodine (I2). We know this because iodide ions are strong reducing agents, and they can simply give up electrons. So when sulphuric acid accepts electrons, it can convert the iodide to elemental iodine.</p></li><li dir="ltr" aria-level="1"><p dir="ltr" role="presentation">The alcohol cannot be converted to alkyl iodide. The reason for this is that the side reaction consumes the iodide ions necessary to act as a nucleophile and replace the alcohol's -OH group. This is the desired alkyl iodide.</p></li><li dir="ltr" aria-level="1"><p dir="ltr" role="presentation">A non-oxidising acid like phosphoric acid (H3PO4) is used instead to produce the desired alkyl iodide. Phosphoric acid is a weaker oxidising agent than sulphuric acid and does not react with the iodide ions. That allows the intended reaction with the alcohol to proceed.&nbsp;&nbsp;<br><br><br></p></li></ul>

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