Question 1 of 26intermediate💡 UnderstandShort Answer2 marks

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

Correct Answer

Sulphuric acid is not used during the reaction of alcohols with KI because it interferes with the formation of alkyl iodide.

When H₂SO₄ is mixed with KI, it converts KI to the corresponding acid, HI (hydroiodic acid). The sulphuric acid then acts as an oxidizing agent and oxidises HI to I₂.

This oxidation reaction prevents the formation of the desired alkyl iodide product. Therefore, H₂SO₄ cannot be used for the conversion of alcohols to alkyl iodides using KI. Instead, orthophosphoric acid is preferred for preparing alkyl iodides from alcohols.

Exercise: Intext Questions | Q: 6.2 | (Page 9)
For More Understanding

Explanation

The textbook explicitly states in the answers section (6.2) that H₂SO₄ cannot be used along with KI because it converts KI to HI, which is then oxidised to I₂. The context also mentions that good yields of R-I may be obtained by heating alcohols with sodium or potassium iodide in 95% orthophosphoric acid, indicating that H₃PO₄ is the suitable acid for this reaction, not H₂SO₄.

Solution Steps

  1. Step 1: Identify that H₂SO₄ reacts with KI to form HI

  2. Step 2: Explain that H₂SO₄ oxidises HI to I₂

  3. Step 3: Conclude that this prevents alkyl iodide formation

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