Alkoxymercuration

Definition

Alkoxymercuration is a reaction in organic chemistry where an alkene is treated with mercury(II) salts and an alcohol to form an ether product. It is a key method for preparing ethers, as described in the context of Chapter 18.2 Preparing Ethers.

5 Must Know Facts For Your Next Test

1. Alkoxymercuration is a two-step process that first involves the addition of a mercury(II) salt (such as Hg(OAc)2) across the carbon-carbon double bond of an alkene.
2. The mercurinium ion intermediate then reacts with an alcohol to form the desired ether product, with the mercury group being replaced by the alkoxy group.
3. Alkoxymercuration is regioselective, meaning the mercury group preferentially adds to the less substituted carbon of the alkene.
4. The reaction is typically carried out in an aqueous or alcoholic solvent, and the mercury byproduct is reduced and removed in the workup.
5. Alkoxymercuration is a useful method for preparing symmetrical and unsymmetrical ethers, as it allows for the introduction of a variety of alkoxy groups.

Review Questions

• Describe the mechanism of the alkoxymercuration reaction, including the formation of the mercurinium ion intermediate.
  • The alkoxymercuration reaction begins with the addition of a mercury(II) salt, such as Hg(OAc)2, across the carbon-carbon double bond of an alkene. This forms a mercurinium ion intermediate, where the positively charged mercury atom is bonded to the two adjacent carbons. The mercurinium ion is then attacked by the nucleophilic alcohol, displacing the mercury and forming the desired ether product. The mechanism is regioselective, with the mercury preferentially adding to the less substituted carbon of the alkene.
• Explain the role of the alcohol in the alkoxymercuration reaction and how it affects the product formation.
  • The alcohol plays a crucial role in the alkoxymercuration reaction, as it serves as the nucleophile that attacks the mercurinium ion intermediate to form the ether product. The choice of alcohol determines the identity of the alkoxy group that is incorporated into the final ether. Different alcohols can be used to synthesize a variety of symmetrical and unsymmetrical ethers, allowing for the introduction of diverse alkoxy substituents. The reactivity and steric hindrance of the alcohol can also influence the regioselectivity and overall yield of the reaction.
• Discuss the advantages and limitations of the alkoxymercuration reaction in the context of ether synthesis, and compare it to other methods for preparing ethers.
  • The alkoxymercuration reaction is a valuable method for the synthesis of ethers due to its regioselectivity and the ability to introduce a wide range of alkoxy groups. It allows for the preparation of both symmetrical and unsymmetrical ethers, which can be challenging to achieve using other ether synthesis methods. However, the use of mercury-containing reagents and the need for a reduction step in the workup can be considered limitations of the alkoxymercuration approach. Alternative ether synthesis methods, such as Williamson ether synthesis or nucleophilic substitution reactions, may be preferred in certain cases, depending on the specific substrate and functional group compatibility requirements. The choice of ether synthesis method ultimately depends on the desired product, the available starting materials, and the overall reaction conditions.

Related terms

Electrophilic Addition: A type of organic reaction where an electrophile adds across a carbon-carbon double bond, breaking the π bond and forming two new σ bonds.

Mercurinium Ion: An electrophilic mercury-containing species that forms during alkoxymercuration, which then reacts with the alcohol to form the ether product.

Ether: A functional group consisting of an oxygen atom connected to two alkyl or aryl groups, with the general formula R-O-R'.