Question

What will be product in given reaction

A.
B.
C.
D.

Answer 1

Aldehydes and ketones can be prepared by the hydration of alkynes in the presence of mercuric salts as catalyst, Hydration of alkynes other than acetylene gives ketone and also Formaldehyde cannot be prepared by the hydration of alkynes method.
Aliphatic aldehydes and ketones are the functional isomers of each other because they have the same molecular formula but different functional groups.

Complete answer:
The addition of water to alkynes forms unstable enol (intermediate in organic chemistry that is represented as an alkene with a hydroxyl group attached to one end of alkene double bond) which rearranges to form a more stable keto tautomer. The mechanism of the reaction is as follows,
At the first step, the $\pi$ electron of the triple bond behaves as a Lewis base and attacks the proton, protonating the carbon with hydrogen substituents, and then there is an attack of a nucleophilic water molecule on electrophilic carbocation, this creates an Oxonium ion.
Then the base is deprotonated giving rise to alcohol called enol then occurs tautomerism i.e. concurrent proton and double bond shift, which goes from enol form to keto isomer form.
According to the question prop-1-enyl benzene in the presence of $HgS{O_4}$ forms 1-phenylprop-1-en-1-ol which on further tautomerization forms propiophenone.

Therefore the correct answer is option C.

Note:
Hydroboration-oxidation method is complementary to the direct $H{g^{2 + }}$ catalysed hydration reaction of terminal alkynes because different products are obtained.
Hydration of terminal alkyne with $H{g^{2 + }}$ salt and water gives methyl ketone whereas hydroboration-oxidation of the same terminal alkyne gives aldehyde.