Swarts Reaction - Mechanism, Application, Examples, FAQs

What is Swarts Reaction?

Swarts reaction is a process of converting alkyl chloride or alkyl bromide to form alkyl fluoride. It is an organic reaction. The reaction got its name after Frederic Jean Edmond Swarts who reported and explained this reaction for the first time in 1892.

In this article, we cover the swarts reaction which is the topic of class 12 of chapter haloalkanes and haloarenes. Which is very important for boards and JEE Mains Exam, NEET Exam and many others.

Swart's Reaction

The best method for the preparation of alkyl fluorides is the Swarts reaction. This reaction is done by heating Alkyl chloride or alkyl bromide in the presence of heavy metal fluorides. We can use mercurous fluoride or silver fluoride in the form of heavy metal fluorides. If we use light metal fluorides then, the reaction will continue in the forward direction but the product formed will be much less. This is simply a fluorination reaction.

Example of Swarts reaction

1. C₂H₅Cl + AgF→ C₂H₅F + AgCl

2. CH₃Br + AgF → CH₃F + AgBr ( in the presence of fluoride of heavy metals and swarts reagent)

Swarts reaction is the best reaction for the formation of alkyl fluorides with the help of Swarts reagent i..e... (SbF₃ + Cl₂) and heavy metals fluorides such as AgF, F₂Hg₂, CoF_2, or SbF₃.

In general, if we have to prepare metal fluorides we use swarts reaction or swarts fluorination reaction.

What happens in this reaction?

There will be a small answer based on a concept ( higher electronegative elements replace lower electronegative elements).

According to this concept, we all can well notice that chlorine is generally replaced by fluorine in this reaction. In the presence of antimony trifluoride with antimony salts swarts reaction will smoothly move forward due to the +5 oxidation state of antimony salt.

Swarts Reaction Mechanism

This reaction is based on bond breakdown and formation of new bonds i.e. the bond between metal and fluorine will break down and a new bond will be formed between carbon and fluorine. This is generally a displacement reaction in which the displaced bromine or chlorine atom forms a bond with the metal. For the swarts reaction, the reagent we used was a mixture of antimony trifluoride and chlorine. The fluoride formed after swarts reaction will have a low boiling point as compared to the corresponding fluoride according to the role of swarts.

We can also use chlorinated hydrocarbons with metallic fluorides to get hydrocarbons containing both chlorine and fluorine.

We use, Swarts reaction or Swarts fluorination for displacement of chlorine or bromine containing alkyl group with fluorine, and forms alkyl fluoride itself.

A variant of swarts reaction is very in the formation of freons. The main activity of this variation is that fluorination is executed in the presence of hydrogen fluoride and antimony salt in which the oxidation state of antimony salt is +3 & +5.

Applications of Swarts Reaction

• For the production or formation of alkyl fluoride.
• Used in the formation of freons.
• Swarts Reaction is used for chemical anlysis.

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Finkelstein Reaction

This is also a halogen exchange method and its post-reaction product is alkyl iodide.

Finkelstein reaction occurs through Substitution Nucleophilic Bimolecular reaction i.e. Sn2 reaction. This is also a type of organic reaction. In this reaction, primary alkyl halide or pseudohalide reacts with alkali metal halide to form alkyl iodide ( this reaction is based on halogen exchange ).

Commonly used reagents in this reaction are:-

• Sodium iodide – acts as a nucleophile in this reaction
• Ethyl chloride – an alkyl halide to complete this reaction.
• And product is Ethyl iodide i..e.. formed due to the exchange between the iodine and chlorine groups. So it is called the halogen exchange process.

Examples of Finkelstein reactions are:-

• CH₃Br +NaI→ CH₃I + NaBr (reaction will happen in the presence of acetone)
• CH₃Cl + NaI→CH₃I +NaCl (reaction will happen in the presence of acetone)
• C₂H₅Cl+KI→C₂H₅I+KCl (this reaction will happen in the presence of acetone)

Related Topics,

• Sn2 Reaction Mechanism
• Gattermann Reaction
• Stephen Reaction Mechanism
• Diazotization Reaction Mechanism
• Hoffmann Bromamide Reaction Mechanism

Some Solved Examples

Q. Which reagents are used in the swarts reaction?

Ans: The reagents used in swarts reaction are chlorine or many times antimony pentachloride also used with antimony trifluoride. The combination of both these reagents (..e..chlorine and antimony trifluoride) is known as a swarts reagent.

Swarts reagent = SbF₃ + Cl₂

Q. What is the product of Finkelstein's reaction?

Ans: Finkelstein's reaction is named after a German chemist. i.e. Hans Finkelstein.

The product of the Finkelstein reaction is alkyl iodide which is formed due to halogen exchange. Finkelstein reaction follows the sn2 ( Nucleophilic Substitution, Second Order ) pathway to form the product.

Q. Similarity between swarts reaction and finkelstein reaction?

Ans: These both given reaction is halogen exchange reaction. Both of these reactions follow the sn2 (second-order Nucleophilic substitution) pathway to form a product. In the Swarts reaction product is alkyl fluoride and in the Finkelstein reaction product will be alkyl iodide.

Q. Difference between swarts reaction and finkelstein reaction?

Ans: In swarts reaction, reagents are heavy metal fluorides that can easily fluorinate alkyl components. This reaction is used to form alkyl fluoride with good yield. The reagents of the Swarts reaction are SbF₃ + Cl₂ Whereas in the Finkelstein reaction, we get alkyl iodide, not fluoride.

The Reactant of this reaction is sodium iodide in acetone ( NaI + C₃H₆O ) Both of these are organic reactions and widely play an important role in many organic reactions, analysis, etc.

Q. Best method for the preparation of alkyl fluoride?

Ans: Swarts reaction is the best method to form alkyl fluoride by substituting chlorine or bromine. It is a halogen exchange method that completes in the presence of swarts reagent i..e. (SbF₃ + Cl₂)

Here

• SbF₃ = antimony trifluoride
• Cl₂ = molecular chlorine

Q. What are freons?

Ans: It is fluorinated aliphatic organic compounds, which are very useful in commerce and industries.

Constituents of freons:- fluorine + carbon ( must contain these two elements)

Freons can also contain elements like hydrogen, chlorine, or bromine.

There are many types of freons including chlorofluorocarbons ( CFCs), hydrochlorofluorocarbons ( HCFCs), etc.

Freons have been used as refrigerants since the 1930s because of some special properties including colorlessness, odorlessness, inflammability, and less corrosive and toxic gas. Freons can occur in two stages depending on environmental temperature i..e.. liquid or gases. They also have low boiling points, low viscosity, and low surface tension that helps them to be a refrigerant of great value.

Examples of freons:-

• Dichlorodifluoromethane (R-12)
• Tetrafluoroethane (R-134a)

Q. How to convert methyl chloride to methyl fluoride?

Ans: The answer will be through Swarts reaction we can convert it.

CH₃−Cl⟶ SbF₅^???? CH₃−F

When we react methyl chloride with swarts reagents like F₂Hg₂, SbF₅ then methyl chloride undergoes a halogen exchange reaction in which methyl chloride loses its chlorine and gains fluorine.

And by this process, methyl chloride will be converted to methyl fluoride.

Q. Is F₂Hg₂ a reagent of the swarts reaction?

Ans: Yes, it is a very good fluorinating agent and also a reagent for swarts reaction.

F₂Hg₂ – Compound name is “ Mercury(I) fluoride “

Q. What is Swarts reaction?

Ans: It is a process by which chlorine-containing organic compounds are changed to fluorides through a halogen exchange process with the help of swarts reagent i..e.. in the presence of antimony trioxide and chlorine. This reaction follows sn2 i..e. Nucleophilic substitution pathway.

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