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Reformatsky reaction is one of the most important transformations of organic molecules which involves the synthesis of new carbon-carbon bonds. In general, the Reformatsky reaction produces a -hydroxyl ester by treating alpha-halo ester with a carbonyl molecule such as ester, ketone, or aldehyde in the presence of metallic zinc. The Reformatsky reaction is named after Sergey Nikolaevich Reformatsky, a Russian chemist, who discovered it in the year 1887. Mostly this reaction takes place in the presence of zinc. Extended reactions between carbonyl compounds and a dialkylzinc or an alkyl zinc halide are also represented by this Reformatsky reaction. In this article, we will have a look at the mechanism of Reformatsky reactions, the structure of its reagent, and its advantages.
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Keyterms: Organic molecules, Synthesis, varbon, Ester, Varbonyl, Ketone, Aldehyde, Zinc, Carbonyl compounds, Acid, Solvent
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What is Reformatsky Reaction?
The Reformatsky reaction, in its broadest sense, is an organic reaction that uses acid workup and metallic zinc to convert an aldehyde or ketone and ∝-halo ester to β-hydroxy ester. As a reaction solvent, an inert solvent such as THF (tetrahydrofuran) or diethyl ether is frequently used. The most common solvents employed in this process are ether, benzene, or a benzene ether combination.
The Reformatsky reaction is the condensation reaction of a carbonyl molecule with an alpha halo ester in the presence of zinc metal.
Reformatsky Reaction
Reformatsky Reaction Mechanism
- In most cases, the Reformatsky reaction starts with the aerobic addition or insertion of zinc into the carbon-halogen bond of a ∝-haloester.
- The primary goal of using zinc is to allow the synthesis of an enolate while avoiding the use of Bronsted base, which usually condenses with the organic component or the carbonyl compound itself.
- The compounds coordinate with one another after insertion, resulting in the development of a dimer. This molecule also undergoes rearrangement, which results in the formation of two zinc enolates.
- The oxygen of the ketone or aldehyde then coordinates with the zinc, resulting in a new arrangement where the two new reagents already share a carbon-carbon bond.
- The zinc and oxygen bonds are then split by an acid workup, yielding zinc (II) salt and beta-hydroxy organic molecules as the end result.
- The products, in particular, are essential ingredients for the production of natural products and medications.
Mechanism of Reformatsky Reaction
Structure of Reagent of Reformatsky Reaction
Reformatsky reagents ethyl bromozincacetate and tert-butyl bromozincacetate have crystal structures determined using THF complexes. In the solid state, they both form cyclic 8-membered dimers, although their stereochemistry differs. The ethyl derivative's 8-membered ring has a tub-shaped conformation and contains cis THF ligands and cis Bromo groups. The ring is in a chair shape in the derivative of tert-butyl, and the THF ligands and Bromo groups are trans.
Structure of Reagent of Reformatsky Reaction
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Advantages of Reformatsky Reaction
- Highly hindered ketones are used in the Reformatsky reaction. This reaction also makes it easier for nucleophiles to attach to the ketone's delta positive carbon atom.
- The intramolecular aldol reactions can simply be applied to the Reformatsky mechanism.
- The Reformatsky Reaction uses organozinc halide reagents, which are regarded as moderately stable and widely available.
- The beta-hydroxy ester is isolated as a result of the Reformatsky reaction.
- Another advantage of the Reformatsky reaction is its convenience, as it is an alternative to the reaction of a ketone or aldehyde with the ester's lithium enolate.
- Freshly manufactured zinc powder, a heated column of zinc dust, acid-washed zinc, trimethylchlorosilane, and the copper-zinc pair all enhanced Reformatsky yields.
Things to Remember
- The Reformatsky reaction happens when an alpha-haloester reacts with a carbonyl molecule that can be a ketone, aldehyde, or ester.
- In the presence of zinc, the reaction happens most of the time. Extended reactions between carbonyl compounds and a dialkylzinc or an alkyl zinc halide are also represented by this reaction.
- One advantage of Reformatsky reaction is that the organozinc product does not need to be isolated.
- A new carbon–carbon linkage is formed throughout the reaction process, along with the creation of an organozinc halide and breakdown due to the presence of dilute acids.
- The product ∝-hydroxy esters, in particular, are key ingredients in the production of natural products and medications.
Read More: Werner’s theory of coordination compounds
Sample Questions
Ques. Define Reformatsky reaction. What is the nature of the reaction? (3 marks)
Ans. The Reformatsky reaction is an organic reaction that uses metallic zinc to condense aldehydes or ketones with ∝-halo esters to create β-hydroxy-esters: An alpha-halo ester is treated with zinc dust to produce the organozinc reagent, also known as a 'Reformatsky enolate’.
The Reformatsky reaction is a coupling reaction, which refers to a group of reactions in which two fragments are united by a metal catalyst.
Ques. Why does Zn have a role in the reformatsky reaction? (2 marks)
Ans. The oxidative addition or insertion of zinc into the carbon-halogen link of the ∝-haloester generally starts the Reformatsky reaction. The primary benefit of zinc is that it facilitates the formation of an enolate without the use of a Bronsted base, which ordinarily condenses with the ketone or aldehyde.
Ques. Is Magnesium suitable for the Reformatsky reaction? (2 marks)
Ans. In the presence of low valent iron or copper, which were generated in-situ using a bimetal redox method by reducing Fe(III) or Cu(II) salts with magnesium, an operationally easy and very effective Reformatsky reaction of aldehydes was carried out in THF.
Ques. What distinguishes the Reformatsky reaction from the Grignard reaction? (2 marks)
Ans. One of the most important transformations of organic molecules is the reformatsky reaction, which involves the synthesis of new carbon–carbon bonds. This reaction varies from the Grignard reaction in that the beginning organic reagents contain carbonyl groups.
Ques. In the Reformatsky reaction, how is an organozinc reagent prepared? (2 marks)
Ans. An alpha-halo ester is treated with zinc dust to produce the organozinc reagent, also known as a 'Reformatsky enolate.' Because reformatsky enolates are less reactive than lithium enolates or Grignard reagents, there is no nucleophilic addition to the ester group.
Ques. Describe the mechanism behind the Reformatsky Reaction. (3 marks)
Ans. Organozinc compounds are made in the same way that Grignard Reagents are made from ∝-halogenesters. The stability of esters against organozinc allows for this reaction. There is little competition from proton transfer since zinc enolates have a low basicity, and the range of carbonyl addition partners is relatively broad. Organozinc compounds react as the nucleophilic partner in an addition to create β-hydroxy esters in the presence of ketones or aldehydes.
Ques. How do zinc enolates form in the Reformatsky reaction? (2 marks)
Ans. The addition of zinc enolates to aldehydes or ketones to generate β-hydroxyesters is known as the Reformatsky reaction. Zinc enolates are formed when ∝-haloesters react with activated zinc species, which are often found in zinc powder or zinc–metal combinations.
Ques. Is it possible to use a ketone in the Reformatsky reaction? (3 marks)
Ans. Highly hindered ketones can be used in the Reformatsky reaction. The reaction allows the addition of nucleophiles to a ketone's delta positive carbon atom. For intramolecular aldol reactions, the Reformatsky mechanism can be simply adapted. The Reformatsky Reaction uses organozinc halide reagents that are relatively stable.
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