Which hydrocarbon on warming with mercuric sulphate and dilute sulphuric acid forms carbonyl compounds ?

Question

Accepted Answer

Option 3, "Alkyne," is the correct answer because alkynes, specifically terminal alkynes, undergo hydration in the presence of mercuric sulphate (HgSO₄) and dilute sulphuric acid (H₂SO₄) to form carbonyl compounds. This reaction is known as the oxymercuration-demercuration process. In this reaction, the alkyne is converted into an enol, which then tautomerizes to form a ketone or aldehyde, depending on the structure of the alkyne. For example, when acetylene (a simple alkyne) is treated with these reagents, it forms acetaldehyde.

Now, let's explain why the other options are incorrect:

1. **Alkane**: Alkanes are saturated hydrocarbons and are generally unreactive under normal conditions. They do not react with mercuric sulphate and dilute sulphuric acid to form carbonyl compounds. Alkanes require more vigorous conditions, such as combustion or halogenation, to undergo any significant chemical transformation.

2. **Alkene**: Alkenes can undergo hydration reactions, but they do not require mercuric sulphate for this process. Instead, they typically react with dilute sulfuric acid directly or through hydroboration-oxidation to form alcohols, not carbonyl compounds. The presence of mercuric sulphate is specific to the hydration of alkynes.

3. **Benzene**: Benzene is an aromatic hydrocarbon and does not react with mercuric sulphate and dilute sulfuric acid to form carbonyl compounds. Benzene is quite stable due to its aromatic nature and requires specific conditions, such as Friedel-Crafts acylation, to introduce carbonyl groups into its structure.

In summary, the correct answer is Option 3, "Alkyne," because alkynes uniquely react with mercuric sulphate and dilute sulfuric acid to form carbonyl compounds through a specific hydration mechanism. The other options do not undergo this reaction under the given conditions.