In the following reaction, what is X ?C₂H₂ —(H₂O, 60°C / HgSO₄, H₂SO₄)→ X ⇌ CH₃CHO 1)CH₃CH₂OH 2)CH₃-O-CH₃ 3)CH₃CH₂CHO 4)H₂C = CHOH

Correct answer :(4)

Keto – enol tautomerism:

It is an equilibrium between an aldehyde or ketone and a  structural isomer called, the enol form. When acetylene reacts with water in presence of mercuric sulphate and Sulphuric acid, it initially converts into Vinyl alcohol which is present in enol form. The scene all form of vinyl alcohol tautomerises into acetaldehyde. (ethanal).

The condition to exhibit tautomerisation is that, the Carbonyl compound must have at least one Alpha hydrogen.

In the above reaction,  acetylene reacts with water in presence of mercuric sulphate and Sulphuric Acid to form Vinyl alcohol which tautomerises into Acetaldehyde. Vinyl alcohol is enol form and acetaldehyde is the keto form. This thought of our temperature dependent. Generally enol form is stable at low temperature while keto form is stable at high temperature.