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Alkoxymercuration vs. Oxymercuration

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Ethers and alcohols are used for a variety of purposes, and there are several different methods to form ethers and alcohols. In this lesson we will learn about alkoxymercuration and oxymercuration.

Alcohols and Ethers

Alcohols include many more compounds than the alcohol you can find in your local bar, and they all have a multitude of purposes. Alcohols can be used as an energy source, a solvent for perfumes and medical drugs, and as a cleaning agent.

A similar compound, ethers, play an important role as one of the earliest anesthetics and today are used in diesel engines to help them start.

  • Alcohols are any carbon chain containing an OH group attached to one of the carbon atoms.
  • Ethers are a carbon chain containing an OR group (an oxygen attached to another carbon chain) attached to one of the carbon atoms.

These compounds can be produced in two fairly similar methods: oxymercuration uses mercury to form alcohols, while alkoxymercuration uses mercury to form ethers.

Oxymercuration

Oxymercuration occurs when a mercury species and water react with an alkene (a carbon-carbon double bond). Then sodium borohydride is added to hydrate the other carbon.

This reaction is regioselective but not stereoselective. Regioselective means that the OH will always be added to the most highly substituted carbon (the carbon with the most non-hydrogen attachments). Non-stereospecific means that the OH may be added to either the front or the back, and both occur in equal proportions.

So, in other words we can predict which carbon the OH will be added to, but not what the final 3D orientation will be.


The blue hydrogen comes from the sodium borohydride and the green OH comes from the water
Oxymercuration reaction


In this reaction you can see that the OH comes from the water (as indicated in green) and that the hydrogen comes from the sodium borohydride (as indicated in blue). You can also see that the OH ended up on the carbon that had 1 hydrogen and 1 chloride attached, while the hydrogen ended up on the carbon with 2 hydrogen atoms attached.


The oxymercuration reaction has a cyclic mercurinium ion intermediate
Cyclic mercurinium ion


This reaction occurs with a cyclic mercurinium ion intermediate. Both carbon atoms that were participating in the double bond bind to the mercury, forming a little triangle with three partial positive charges. With the help of THF (tetrahydrofuran, a solvent) the water attacks the more substituted carbon because it will have the largest partial positive charge, since the non-hydrogen substituent draws electrons away more than hydrogen.

When sodium borohydride is added we see a demercuration, where the mercury is removed and replaced with a hydrogen, forming the alcohol.

Alkoxymercuration

Alkoxymercuration occurs in almost the exact same method as oxymercuration. Alkoxymercuration:

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