Oxymercuration of Alkenes to form Ethers using Hg(OAc)2

by James

Description: When an alkene is treated with an alcohol in the presence of mercuric acetate [Hg(OAc)2] it will add to the more substituted position of the alkene (Markovnikoff) to give an ether. The mercury can then be removed using NaBH4.

Notes: The alcohol is generally used as the solvent here.

Examples: 

Notes: Note that in the second reaction, no rearrangement occurs (this would have happened for the acid-catalyzed reaction).

The last example is an intramolecular reaction – often gives students a hard time.

The byproducts in all cases are NaOAc, HOAc, BH3 and Hg(s)

Mechanism: The alkene attacks Hg(OAc)2, displacing acetate and forming a mercuronium ion (Step 1, arrows A and B). Next, the more substituted carbon is attacked by the solvent alcohol (Step 2, arrows C and D). The resulting protonated ether is then deprotonated by acetate (Step 3, arrows E and F). Removal of mercury is done with NaBH4. The mechanism of this step is not generally considered to be “important” for Org 1/ Org 2. However it is shown separately below.

Mechanism for removal of mercury:


Notes: Attack of alcohol (Step 2) occurs trans to the mercury, although that is not depicted here. Removal of mercury proceeds through formation of a free radical, so the reaction is not stereoselective.

{ 3 comments… read them below or add one }

Andrialene Anticuando

okay lang. add more example.

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Raj

In the last example why wasn’t ROH used along with Hg(OAc)2

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Diana Lee

For the removal of mercuric acetate why must sodium borohydride be added in a basic condition?

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