What is the Difference Between Finkelstein and Swarts Reaction

Finkelstein reaction and Swarts reaction are two examples of halogen exchange reactions. Halogen exchange reactions involve replacing one halogen atom in an organic compound with another. This transformation is often used to prepare different alkyl halides with desired properties.

What is the difference between Finkelstein and Swarts reaction? In Finkelstein reaction, chlorine or bromine is replaced with iodine whereas in Swarts reaction chlorine or bromine is replaced with fluorine.

Key Areas Covered

1. What is Finkelstein Reaction
      – Definition, Features 
2. What is Swarts Reaction
      – Definition, Features 
3. Similarities Between Finkelstein and Swarts Reaction
      – Outline of Common Features
4. Difference Between Finkelstein and Swarts Reaction
      – Comparison of Key Differences
5. FAQ: Finkelstein and Swarts Reaction
      – Answers to Frequently Asked Questions

Key Terms

Finkelstein Reaction, Swarts Reaction, Halogen Reaction

What is Finkelstein Reaction

Finkelstein reaction is an organic reaction belonging to the halogen exchange reaction group.  It involves the substitution of one halogen atom for another within an alkyl halide molecule. Here, chlorine or bromine atom is replaced by iodine atom. The reagent used in this reaction is NaI (sodium iodide). This reaction takes place in polar aprotic solvents such as acetone. This is because sodium iodide readily dissolves in it, unlike sodium chloride or sodium bromide. Hence, the equilibrium of the reaction shifts towards product formation.

The mechanism of the Finkelstein reaction is an SN2 (nucleophilic substitution bimolecular) reaction. The iodide ion (I-) acts as a nucleophile, attacking the carbon atom bonded to the halogen (chlorine or bromine) from the backside. Then, a new carbon-iodine bond forms, simultaneously, breaking the carbon halogen bond.

There are many applications of Finkelstein reactions in chemistry. They are useful in the synthesis of alkyl iodides, in the analysis of alkyl halides, in qualitative analysis, and in making certain other organic compounds.

What is Swarts Reaction

The Swarts reaction is an organic chemical reaction that helps to prepare alkyl fluorides from their corresponding alkyl chlorides or bromides. This change occurs due to heating the alkyl halide in the presence of a heavy metal fluoride, such as silver fluoride (AgF) or mercurous fluoride (Hg₂F₂).

The mechanism of Swarts reaction involves a simple halogen exchange process. The metal-fluorine bond in the heavy metal fluoride breaks and forms a new carbon-fluorine bond.  At the same time, the displaced chlorine or bromine atom forms a bond with the metal.

Alkyl fluorides thus produced has many applications such as in pharmaceutical industry, material science industry, and agrochemical industry.

Similarities Between Finkelstein and Swarts Reaction

1. Both involve the substitution of one halogen atom with another within an alkyl halide molecule. 
2. The starting materials for both reactions are alkyl halides.
3. Both reactions proceed through a nucleophilic substitution mechanism.

Difference Between Finkelstein and Swarts Reaction

Definition

• Finkelstein reaction is a nucleophilic substitution reaction where a halogen atom (usually chlorine or bromine) in an alkyl halide is replaced by an iodide ion, while Swarts reaction is a chemical process that involves the exchange of a halogen atom in an organic compound, typically a fluorine atom replacing a chlorine or bromine atom.

Replacement

• In the Finkelstein reaction, chlorine or bromine is replaced with iodine, while in the Swarts reaction, chlorine or bromine is replaced with fluorine.

Reagent

• In Finkelstein reaction, sodium iodide (NaI) is used as the reagent, whereas in Swarts reaction, silver fluoride (AgF) or antimony trifluoride (SbF₃) is used as the reagent.

Solvent

• In Finkelstein reaction, acetone is commonly used as a solvent while in Swarts reaction, no solvent is required.

Temperature

• Finkelstein reaction occurs under milder conditions, while Swarts reactions require higher temperatures.

Yield

• Swarts reactions often have lower yields compared to Finkelstein reactions.

Conclusion

Finkelstein reaction and Swarts reaction are two halogen exchange reactions. Both involve the substitution of one halogen atom with another within an alkyl halide molecule. However, there is a difference between Finkelstein and Swarts reaction. In Finkelstein reaction, chlorine or bromine is replaced with iodine whereas in Swarts reaction chlorine or bromine is replaced with fluorine.

FAQ: Finkelstein and Swarts Reaction

1. What is the Swarts reaction?

• The Swarts reaction is a chemical process used to convert alkyl chlorides or bromides into alkyl fluorides. It involves heating the alkyl halide with a metallic fluoride like silver fluoride or mercurous fluoride.

2. Is Swartz reaction SN1?

• No, the Swartz reaction is not an SN1 reaction. It’s a halogen exchange reaction where an alkyl halide is converted into an alkyl fluoride using a metal fluoride.

3. Why is iodine not used in Swarts reactions?

• Iodine is not used in Swarts reactions because it forms higher metal halides. The core principle of the Swarts reaction is to exchange a higher alkyl halide with a lower metal halide to produce a lower alkyl halide.

4. Why is fluorine not used in Finkelstein’s reaction?

• Fluorine is not used in the Finkelstein reaction primarily due to the poor nucleophilicity of fluoride ions. This makes them less reactive in nucleophilic substitution reactions. Additionally, the strong bond between carbon and fluorine in organic compounds makes the substitution process unfavorable.

5. What are the limitations of the Finkelstein reaction?

• The Finkelstein reaction is limited to primary alkyl halides. Secondary halides react slowly, while tertiary halides and aryl halides are unreactive.

Reference:

1. “Finkelstein Reaction.” Science Direct. 
2. “Swarts Fluorination.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “Finkelstein reaction mechanism V1” By $береста$ – Own work (CC0) via Commons Wikimedia
2. “Swarts-Reaktion Reaktionsmechanismus V2” By Tamina212 – Own work (Public Domain) via Commons Wikimedia