Question

Ethers when dissolved in cold concentrated sulphuric acid forms

• A. Alkanoic acids
• B. Oxonium salts
• C. Alkanols
• D. Alkyl hydrogen sulphate

Hint:

Remember that oxygen atoms in organic molecules with lone pairs can readily behave as weak bases. Protonation of an neutral oxygen atom always creates a positively charged oxonium ion.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the product formed when an ether is dissolved in cold, concentrated sulfuric acid ($\text{H}_2\text{SO}_4$).

Step 2: Key Formula or Approach:
Ethers act as Lewis bases because the oxygen atom carries two unshared pairs of electrons (lone pairs). When treated with a strong mineral acid like cold concentrated $\text{H}_2\text{SO}_4$, the ether undergoes protonation.

Step 3: Detailed Explanation:
The reaction involves the transfer of a proton ($\text{H}^+$) from sulfuric acid to the ethereal oxygen atom: $$\text{R-O-R} + \text{H}_2\text{SO}_4 \rightarrow [\text{R-}\xrightarrow{\text{+}}{\text{O}}\text{H-R}]\text{HSO}_4^-$$ Due to this protonation, a stable, water-soluble ionic species known as a dialkyl oxonium salt is formed. This property is often used to distinguish ethers from non-polar compounds like alkanes.

Step 4: Final Answer:
Ethers dissolve in cold concentrated sulfuric acid to form oxonium salts, which corresponds to option (B).