Mercury(II) Acetate

Mercury(II) acetate, Hg(OAc)2, is the mercury reagent used in oxymercuration to hydrate an alkene and make a Markovnikov alcohol. It gives a cleaner addition than acid-catalyzed hydration because it avoids carbocation rearrangements.

What is Mercury(II) Acetate?

Mercury(II) acetate is the electrophilic mercury reagent used in the oxymercuration step of alkene hydration. In Organic Chemistry, you usually see it written as Hg(OAc)2 or Hg(CH3COO)2, and it reacts with a double bond to start the conversion of an alkene into an alcohol.

The main job of Hg(OAc)2 is to activate the alkene without letting a free carbocation form. Instead of the double bond just “taking on water” directly, the alkene attacks mercury and forms a bridged mercurinium ion. That bridge spreads out the positive charge, which is why the reaction is much less likely to rearrange than acid-catalyzed hydration.

After that first step, water attacks the more substituted carbon of the mercurinium ion, so the OH group ends up in the Markovnikov position. Then demercuration removes the mercury group and leaves the alcohol behind. If your class is comparing hydration methods, this is the clean, two-step route that gives you Markovnikov addition without the usual rearrangement problems.

A useful way to think about mercury(II) acetate is that it is not the final product-forming reagent by itself. It is the setup reagent. It creates the reactive intermediate that controls regiochemistry and stereochemistry, then gets replaced in the second step of oxymercuration-demercuration.

Because mercury compounds are toxic, the reagent also comes with a safety warning in lab settings. You may see oxymercuration discussed in synthesis problems, mechanism questions, or reaction comparisons, but in real lab work the handling and waste disposal matter just as much as the mechanism.

Why Mercury(II) Acetate matters in Organic Chemistry

Mercury(II) acetate matters because it is the reagent that makes oxymercuration work as a clean alkene-to-alcohol method. In Organic Chemistry, that means you can predict where the OH group goes, how the intermediate behaves, and why the product comes out Markovnikov without rearrangements.

This term also shows up when you compare hydration methods. If you know Hg(OAc)2, you can tell the difference between oxymercuration and acid-catalyzed hydration, especially on questions where a rearranged product would be wrong. That comparison is a big part of reaction-selection problems, where the real skill is choosing the method that gives the desired regiochemistry.

It also connects mechanism to product structure. The mercury reagent forms a bridged intermediate, so you do not get a free carbocation, and that changes what products are possible. That idea carries into other synthesis questions where intermediate stability controls the outcome.

How Mercury(II) Acetate connects across the course

Oxymercuration

Mercury(II) acetate is the reagent that starts oxymercuration. If you see Hg(OAc)2 in a mechanism, you are usually looking at the step where the alkene is activated and a mercurinium ion forms. The follow-up demercuration step is what finishes the conversion to the alcohol.

Hydration of Alkenes

This is the broader reaction category that mercury(II) acetate helps carry out. Hydration means adding H and OH across a double bond, and oxymercuration is one of the most reliable ways to do it. It is especially useful when you want Markovnikov addition without rearrangements.

Acid-Catalyzed Hydration

Both methods make alcohols from alkenes, but they do not behave the same way. Acid-catalyzed hydration can rearrange because it goes through a free carbocation, while mercury(II) acetate keeps the charge in a bridged intermediate. That difference often decides which product you should expect.

Alcohols

The whole point of using mercury(II) acetate in this context is to help build an alcohol from an alkene. In synthesis problems, the reagent is usually a clue that the final product will be an alcohol with the OH group on the more substituted carbon. It connects directly to product naming and structure drawing.

Is Mercury(II) Acetate on the Organic Chemistry exam?

A reaction-mechanism question will often give you an alkene and ask for the product after Hg(OAc)2, H2O, then reduction. Your job is to trace the oxymercuration-demercuration sequence and place the OH group in the Markovnikov position without drawing a rearranged carbocation product. If the prompt compares methods, mercury(II) acetate is the clue that the alkene is being hydrated cleanly, not through acid-catalyzed conditions.

On a problem set or quiz, you may also need to name the intermediate or explain why the product forms with the observed regiochemistry. If a mechanism sketch is required, show the bridged mercurinium ion first, then water attack, then removal of mercury. That is the logic instructors look for when they want more than just the final alcohol structure.

Mercury(II) Acetate vs Acid-Catalyzed Hydration

These are easy to mix up because both convert alkenes to alcohols. Mercury(II) acetate is used in oxymercuration, which avoids carbocation rearrangements by forming a bridged intermediate. Acid-catalyzed hydration goes through a free carbocation, so rearranged products can appear.

Key things to remember about Mercury(II) Acetate

• Mercury(II) acetate, Hg(OAc)2, is the electrophilic reagent that starts oxymercuration of an alkene.

• In this reaction, the alkene forms a bridged mercurinium ion instead of a free carbocation, so rearrangements are avoided.

• Water attacks the more substituted carbon, which gives Markovnikov placement of the OH group.

• Hg(OAc)2 is not the final alcohol-forming step by itself, because demercuration removes the mercury group afterward.

• If you see this reagent in a synthesis problem, think clean alkene hydration, Markovnikov alcohol, and no rearranged carbocation product.

Frequently asked questions about Mercury(II) Acetate

What is Mercury(II) Acetate in Organic Chemistry?

Mercury(II) acetate is the Hg(OAc)2 reagent used to begin oxymercuration of alkenes. It helps convert a double bond into a Markovnikov alcohol by forming a bridged mercurinium ion instead of a free carbocation.

Why is mercury(II) acetate used in oxymercuration?

It activates the alkene in a controlled way. That lets water add across the double bond without rearrangements, which is why oxymercuration is often preferred over acid-catalyzed hydration when the product needs to be predictable.

Does mercury(II) acetate make anti-Markovnikov alcohols?

No. In oxymercuration, the OH group ends up on the more substituted carbon, so the reaction is Markovnikov. Anti-Markovnikov alcohol formation is the pattern you associate with hydroboration-oxidation instead.

What do you draw after mercury(II) acetate in a mechanism?

First draw the mercurinium ion intermediate, then show water attacking the more substituted carbon. After that, demercuration removes the mercury group and leaves the alcohol. That sequence is the core of the mechanism.