Q25E - Organic Chemistry (Mcmurry)

Question

Reaction of acetone with ${\mathbf{D}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$ yields hexadeuterioacetone. That is, all the hydrogens in acetone are exchanged for deuterium. Review the mechanism of mercuric-ion-catalyzed alkyne hydration, and then propose a mechanism for this deuterium incorporation.

Step-by-Step Solution

Answer

Mechanism of mercuric-ion-catalyzed alkyne hydration

An interconversion between two forms occurs in this mechanism, one of which is ketone, and another of which is enol. The hydrogen atom takes part in the interconversion by exchanging with the solvent atom.

Mechanism for conversion of acetone into hexadeuterioacetone

In the first step, Addition of ${\mathrm{D}}^{+}$ to the acetone results into a formation of enol   and the one from the methyl group displace and one deuterium atom gets attached.

Similarly removal of the hydrogen atom and addition of the deuterium atom takes place and at last there is a formation of an hexadeuterioacetone takes place.

General mechanism: