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When propyne is treated with aqueous ${H_2}S{O_4}$ in presence of $HgS{O_4}$ the major product is:
(A) Propanal.
(B) Propyl hydrogen sulphate.
(C) Acetone.
(D) Propanol.

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Last updated date: 09th Apr 2024
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MVSAT 2024
Answer
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Hint: The chemical breakdown of compound due to reaction of water is called hydrolysis. Hydro meaning water and lysis meaning branching.

Complete step by step answer:
Reaction of propyne with dil. Sulphuric acid, in presence of $HgS{O_4}$ is hydrolysis reaction.
In this reaction first enol is formed which contains a double bond (ene) and alcoholic group (ol). But enol formed is unstable in acidic condition. So it isomerizes to keto form by rearrangement into stable keto form.

 Therefore, in this reaction acetone is formed.

Hence, the correct answer is option (C) .
Additional information:
Addition of water molecule takes place according to markovnikov rule.
When asymmetrical alkyne reacts with asymmetrical reagent. Then the negative part of alternating molecules ionize with a carbon atom which carries a smaller number of hydrogen atoms while the positive part goes to carbon atom with more hydrogen atom.

When rearrangement of the H-atom takes place within a molecule, then the phenomenon is called tautomerism.
Tautomers are isomers of a compound which differ only in the position of proton and electron.
Keto-enol tautomerism is a very common process and is acid or base catalysis. Generally, the keto form of a compound is more stable. Isomers have the same molecular formula but different structures. They also differ in physical properties.

Note:
The equilibrium arrows above do not show the position of equilibrium; it only shows that an equilibrium exists between two forms.