Name: Hunsdiecker Reaction
Uploaded: 2019-07-19
Duration: 2 min 54 s
Description: The Hunsdiecker reaction is a name reaction in organic chemistry whereby silver salts of carboxylic acids react with a halogen to produce an organic halide.

Question

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

KI

?

Accepted Answer

In the presence of sulphuric acid $(H_{2} {SO}_{4})$ , $KI$ produces $HI$ .
$\underset{Potassium iodide}{2 KI (s)} + \underset{Sulphuric acid}{H_{2} {SO}_{4} (l)} \to \underset{Potassium hydrogen sulphate}{2 {KHSO}_{4} (s)} + \underset{Hydrogen iodide}{2 HI (g)}$

Since $H_{2} {SO}_{4}$ is an oxidising agent, it oxidises $HI$ (produced in the reaction to $I_{2}$ ).
$\underset{Hydrogen iodide}{2 HI (g)} + \underset{Sulphuric acid}{H_{2} {SO}_{4} (l)} \to \underset{Sulphur dioxide}{{SO}_{2} (g)} + \underset{Iodine}{I_{2} (s)} + \underset{Water}{H_{2} O (l)}$

Thus, the reaction between alcohol and $HI$ to form an alkyl iodide cannot occur. Hence, sulphuric acid is not used during the reaction of alcohols with $KI$ . Instead, a non-oxidising acid such as $H_{3} {PO}_{4}$ is used.

$\underset{Methanol}{{CH}_{3} OH (l)} + \underset{Potassium iodide}{KI (s)} + \underset{Phosphoric acid}{H_{3} {PO}_{4} (l)} \overset{∆}{\to} \underset{Iodomethane}{{CH}_{3} - I (l)} + \underset{Potassium dihydrogen phosphate}{{KH}_{2} {PO}_{4} (s)} + \underset{Water}{H_{2} O (l)}$

Telangana Board Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 2: Intext Questions

Telangana Board Chemistry Solutions for Exercise - Telangana Board Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 2: Intext Questions

Questions from Telangana Board Solutions for Chapter: Haloalkanes and Haloarenes, Exercise 2: Intext Questions with Hints & Solutions

Learn and Prepare for any exam you want !