Water can be added across a triple bond in the presence of

Concept:

Hydration of alkynes:

• Alkynes when treated with dilute sulfuric acid H2SO4 containing a small amount of mercuric sulfate give carbonyl compounds.
• The ultimate is the addition of a molecule of water to the triple bond.
• The addition follows the Markownikov rule.
• Hydration of symmetrical non-terminal alkynes yields single ketones.
• Unsymmetrical non-terminal alkynes yield a mixture of two or more ketones.

 Markownikov rule:

• During the addition of a polar molecule to an unsymmetrical alkene or alkyne, the negative part of the addendum is added to the more substituted Carbon atom.
• The positive part of the addendum gets added to the less substituted carbon part of the alkyne.

Explanation:

• A molecule of water will be added to the triple bond following the Markownikovs rule.
• The first step is the addition of Hg ⁺⁺ to the triple bond giving a cyclic intermediate.
• The next step is the attack of water to the more substituted carbon atom.
• Loss of Hg⁺⁺ ion takes place in the next step and hydrogen is added to the less substituted carbon atom.
• The final step involves keto-enol tautomerization to give the final product ketone or aldehyde.
• The detailed mechanism of the reaction is given below:

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Hence, water can be added across a triple bond in the presence of acid and HgSO4.