Question

The mercury-catalyzed hydration of alkynes involves the formation of an organomercury enol intermediate. Draw the electron-pushing mechanism to show how each of the following intermediates is formed.

Short answer

a).

b).

c).

Step-by-step solution

General mechanism of mercury-catalyzed hydration

Alkyne acts as a source of electrons in this reaction. When the alkyne donates its pi electron to the mercury cation, a carbocation is formed. Water acts as a nucleophile. It attacks the carbocation to form the organomercury-enol intermediate.

Addition reaction of alkynes

Alkyne act as nucleophile and it attacks on the mercury metal (${\mathrm{Hg}}^{+}$) atom and carbocation forms on the other carbon atom. ${\mathrm{H}}_2\mathrm{O}$acts as nucleophile and attacks on the carbocation which lead to the formation of organomercury- enol intermediate.

Addition reaction of alkynes

Alkyne act as nucleophile and it attacks on the mercury metal ( ${\mathrm{Hg}}^{+}$) atom and carbocation forms on the other carbon atom. ${\mathrm{H}}_2\mathrm{O}$acts as nucleophile and attacks on the carbocation which lead to the formation of organomercury- enol intermediate.