Swarts Reaction - Mechanism, Application, Examples, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:44 PM IST

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.

This Story also Contains

What is Swarts Reaction?
Swart's Reaction
Swarts Reaction Mechanism
Applications of Swarts Reaction
Finkelstein Reaction
Some Solved Examples

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 swart 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 the swart reaction is very common 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 analysis.

Also read -

NCERT Solutions for Class 11 Chemistry	NCERT Solutions for Class 12 Chemistry Chapter 10 Haloalkanes and Haloarenes
NCERT Solutions for Class 12 Chemistry	NCERT Exemplar Class 12 Chemistry Solutions Chapter 10 Haloalkanes and Haloarenes
NCERT Solutions for All Subjects	NCERT notes Class 12 Chemistry Chapter 10 Haloalkanes and Haloarenes

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.
The 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.

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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,

Some Solved Examples

Q. Which reagents are used in the swarts reaction?

Ans: The reagents used in swarts reactions 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.

Also, check-

NCERT Notes Class 11th Chemistry	NCERT Exemplar Class 11th Chemistry Solutions
NCERT Notes Class 12th Chemistry	NCERT Exemplar Class 12th Chemistry Solutions
NCERT Notes For All Subjects	NCERT Exemplar Solutions for All Subjects

Frequently Asked Questions (FAQs)

1. Can the Swarts reaction be used to convert alkyl fluorides to other halides?

No, the Swarts reaction is specifically used to convert alkyl chlorides or bromides to fluorides. The reverse reaction (converting fluorides to other halides) doesn't occur under typical Swarts reaction conditions due to the strength of the C-F bond.

2. What are the main applications of the Swarts reaction?

The Swarts reaction is primarily used in the synthesis of organofluorine compounds, which have applications in pharmaceuticals, agrochemicals, and materials science. It's particularly useful for creating fluorinated anaesthetics, refrigerants, and some polymers.

3. Are there any catalysts commonly used in the Swarts reaction?

While not always necessary, catalysts can be used to enhance the Swarts reaction. Common catalysts include antimony pentachloride (SbCl5) or hydrogen fluoride (HF). These can increase the reaction rate and improve yields.

4. What are some limitations of the Swarts reaction?

The Swarts reaction has some limitations: it works best with primary and secondary alkyl halides, while tertiary halides may undergo elimination reactions. Additionally, the reaction conditions can be harsh, potentially damaging sensitive functional groups in complex molecules.

5. How does the Swarts reaction compare to other fluorination methods?

The Swarts reaction is generally milder and more selective than some other fluorination methods, such as those using elemental fluorine. However, it's less versatile than modern fluorinating agents like DAST (diethylaminosulfur trifluoride) or Selectfluor, which can fluorinate a wider range of substrates.

6. How does the Swarts reaction compare to the Finkelstein reaction?

Both the Swarts and Finkelstein reactions are halogen exchange reactions, but they differ in the halogens involved and the reaction conditions. The Finkelstein reaction typically exchanges chlorine or bromine for iodine using sodium iodide in acetone, while the Swarts reaction introduces fluorine using metal fluorides. The Swarts reaction is generally less reversible due to the strength of the C-F bond formed.

7. How does the Swarts reaction compare to other methods of introducing fluorine into organic molecules?

The Swarts reaction is generally milder and more selective than direct fluorination with F2 gas, which can be highly reactive and difficult to control. It's often more straightforward than electrophilic fluorination methods. However, it's limited to replacing existing halogens and isn't as versatile as some modern fluorinating agents that can directly replace C-H bonds with C-F bonds.

8. How does the yield of the Swarts reaction compare to other halogen exchange reactions?

The yield of the Swarts reaction can be quite high, especially for primary alkyl halides. However, yields can vary depending on the specific substrate and reaction conditions. Generally, the Swarts reaction gives better yields for fluorination compared to direct fluorination methods using elemental fluorine.

9. Can the Swarts reaction be reversed?

The Swarts reaction is generally not reversible under normal conditions due to the strength of the C-F bond formed. Converting an alkyl fluoride back to a chloride or bromide typically requires much harsher conditions and different reagents than those used in the Swarts reaction.

10. What role does the leaving group play in the Swarts reaction?

In the Swarts reaction, the halogen (usually chlorine or bromine) acts as the leaving group. The ability of the halogen to leave affects the reaction rate and yield. Bromine is generally a better leaving group than chlorine, making alkyl bromides more reactive in the Swarts reaction than alkyl chlorides.

11. What is the Swarts reaction?

The Swarts reaction is a method for converting alkyl chlorides or bromides into alkyl fluorides using antimony trifluoride (SbF3) or mercury(II) fluoride (HgF2) as a fluorinating agent. It's an important reaction in organic synthesis for introducing fluorine atoms into organic molecules.

12. How does the Swarts reaction relate to the concept of nucleophilic substitution?

The Swarts reaction is a prime example of nucleophilic substitution. The fluoride ion acts as the nucleophile, attacking the electrophilic carbon attached to the halogen (Cl or Br). This results in the displacement of the original halogen, following either an SN1 or SN2 mechanism depending on the substrate and conditions.

13. Can the Swarts reaction be used to introduce multiple fluorine atoms?

While the Swarts reaction is primarily used to replace a single halogen with fluorine, it can be used iteratively or with polyhaloalkanes to introduce multiple fluorine atoms. However, each subsequent fluorination becomes more difficult due to the increasing strength of C-F bonds.

14. What safety precautions should be taken when performing a Swarts reaction?

The Swarts reaction involves corrosive and potentially toxic reagents. Proper personal protective equipment (PPE) should be used, including gloves, lab coat, and goggles. The reaction should be performed in a fume hood due to the potential release of HF or other toxic gases.

15. Can the Swarts reaction be used to fluorinate aromatic compounds?

The classical Swarts reaction is not typically effective for direct fluorination of aromatic compounds. Aromatic C-H bonds are much stronger than alkyl C-H bonds, and the reaction conditions are usually not harsh enough to break the aromatic system. However, modified versions of the reaction can be used to fluorinate certain activated aromatic compounds.

16. What is the general mechanism of the Swarts reaction?

The Swarts reaction follows a nucleophilic substitution mechanism. The fluoride ion from the metal fluoride (SbF3 or HgF2) acts as a nucleophile, attacking the carbon atom bonded to the halogen (Cl or Br). This results in the displacement of the original halogen and its replacement with fluorine.

17. Why is antimony trifluoride (SbF3) commonly used in the Swarts reaction?

Antimony trifluoride is frequently used because it's an effective source of fluoride ions and can easily exchange its fluorine atoms with other halogens. It's also relatively stable, easy to handle, and can be used in various reaction conditions.

18. How does the reactivity of alkyl halides differ in the Swarts reaction?

In the Swarts reaction, alkyl bromides are generally more reactive than alkyl chlorides. This is because the carbon-bromine bond is weaker than the carbon-chlorine bond, making it easier for the fluoride ion to displace bromine.

19. How does solvent choice affect the Swarts reaction?

The choice of solvent can significantly impact the Swarts reaction. Polar aprotic solvents like acetonitrile or dimethylformamide (DMF) are often preferred as they can stabilize the fluoride ion without hydrogen bonding, increasing its nucleophilicity. Protic solvents are generally avoided as they can interfere with the reaction.

20. What role does temperature play in the Swarts reaction?

Temperature is an important factor in the Swarts reaction. Higher temperatures generally increase the reaction rate and can be necessary for less reactive substrates. However, excessively high temperatures can lead to side reactions or decomposition of sensitive compounds.

21. Who discovered the Swarts reaction?

The Swarts reaction was discovered by the Belgian chemist Frédéric Swarts in 1892. He first reported the use of antimony trifluoride to convert alkyl chlorides and bromides into alkyl fluorides.

22. What is the significance of the Swarts reaction in the history of organofluorine chemistry?

The Swarts reaction was a pivotal development in organofluorine chemistry. It provided one of the first reliable methods for introducing fluorine into organic molecules, paving the way for the synthesis of numerous fluorine-containing compounds. This led to the discovery of many important fluorinated materials, from refrigerants to pharmaceuticals, significantly impacting various industries.

23. What is the difference between nucleophilic and electrophilic fluorination, and where does the Swarts reaction fit?

Nucleophilic fluorination involves the attack of a fluoride ion (F-) on an electrophilic carbon, while electrophilic fluorination involves the attack of an electrophilic fluorine source on a nucleophilic carbon. The Swarts reaction is a nucleophilic fluorination, as the fluoride from SbF3 or HgF2 acts as the nucleophile.

24. What is the significance of the C-F bond formed in the Swarts reaction?

The C-F bond formed in the Swarts reaction is one of the strongest single bonds in organic chemistry. This strength contributes to the unique properties of organofluorine compounds, including their thermal and chemical stability, which makes them valuable in various applications.

25. How does the Swarts reaction relate to Green Chemistry principles?

The Swarts reaction aligns with some Green Chemistry principles by often providing good atom economy and using catalysts to improve efficiency. However, it typically uses stoichiometric amounts of metal fluorides, which can be considered wasteful. Modern variations aim to improve its environmental profile by using catalytic amounts of fluorinating agents or developing recyclable reagents.

26. What is the role of Lewis acids in some variations of the Swarts reaction?

Lewis acids like antimony pentachloride (SbCl5) can act as catalysts in the Swarts reaction. They can coordinate with the halogen of the alkyl halide, making it a better leaving group and thus facilitating the nucleophilic attack by the fluoride ion.

27. How does stereochemistry come into play in the Swarts reaction?

The stereochemical outcome of the Swarts reaction depends on the mechanism. For primary alkyl halides, which typically follow an SN2 mechanism, inversion of configuration occurs. For secondary or tertiary alkyl halides that may proceed via an SN1 mechanism, racemization or partial racemization can occur.

28. What are some industrial applications of compounds synthesized via the Swarts reaction?

Compounds synthesized using the Swarts reaction have diverse industrial applications. They're used in the production of refrigerants (like hydrofluorocarbons), anesthetics (like halothane), polymers (like PTFE or Teflon), and various pharmaceuticals and agrochemicals where the unique properties of the C-F bond are beneficial.

29. How does the electronegativity of fluorine affect the properties of products from the Swarts reaction?

The high electronegativity of fluorine significantly affects the properties of the products. It creates a strong polar C-F bond, which can change the molecule's dipole moment, affecting its boiling point, solubility, and reactivity. The electron-withdrawing nature of fluorine can also influence the acidity or basicity of nearby functional groups.

30. What is the environmental impact of the Swarts reaction and its products?

The environmental impact of the Swarts reaction itself is relatively low, but some of its products, particularly chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), have been found to deplete the ozone layer. This has led to the development of more environmentally friendly alternatives and stricter regulations on the use of these compounds.

31. How has the Swarts reaction contributed to the field of medicinal chemistry?

The Swarts reaction has significantly contributed to medicinal chemistry by enabling the synthesis of fluorinated pharmaceuticals. Fluorine substitution can enhance drug potency, metabolic stability, and bioavailability. Many modern drugs contain fluorine atoms, often introduced through reactions based on or inspired by the Swarts reaction.

32. What are some modern variations or improvements on the original Swarts reaction?

Modern variations of the Swarts reaction include the use of more efficient fluorinating agents like DAST (diethylaminosulfur trifluoride) or Selectfluor. These reagents can often perform fluorinations under milder conditions and with a broader substrate scope. Additionally, catalytic versions of the reaction have been developed to improve efficiency and reduce waste.

33. How does the presence of other functional groups affect the Swarts reaction?

The presence of other functional groups can significantly affect the Swarts reaction. Electron-withdrawing groups can facilitate the reaction by making the carbon-halogen bond more susceptible to nucleophilic attack. Conversely, electron-donating groups can hinder the reaction. Some functional groups may also react with the fluorinating agent, leading to side products.

34. How does the Swarts reaction demonstrate the concept of hard and soft acids and bases (HSAB)?

The Swarts reaction demonstrates the HSAB concept. Fluoride is a hard base, while chloride and bromide are softer bases. The antimony in SbF3 is a relatively soft acid. The reaction proceeds because the hard fluoride base preferentially bonds with the harder carbon center, displacing the softer chloride or bromide.

35. Can the Swarts reaction be used in asymmetric synthesis?

While the classical Swarts reaction isn't typically used in asymmetric synthesis, modified versions using chiral catalysts or reagents have been developed. These can potentially create new stereogenic centers or perform kinetic resolutions of racemic alkyl halides.

36. How does the reactivity of primary, secondary, and tertiary alkyl halides differ in the Swarts reaction?

Primary alkyl halides are generally the most reactive in the Swarts reaction, followed by secondary, and then tertiary. This order is due to steric hindrance affecting the ability of the fluoride nucleophile to approach the carbon center. Tertiary alkyl halides may also undergo elimination reactions instead of substitution.

37. What is the role of hydrogen fluoride (HF) in some variations of the Swarts reaction?

In some variations of the Swarts reaction, hydrogen fluoride (HF) can act as both a solvent and a fluorinating agent. It can increase the reactivity of metal fluorides like SbF3 by forming complex anions (e.g., SbF4-) which are more nucleophilic. However, HF is highly corrosive and toxic, requiring special handling precautions.

38. What are some common side reactions in the Swarts reaction, and how can they be minimized?

Common side reactions in the Swarts reaction include elimination (especially with secondary and tertiary substrates) and rearrangements. These can be minimized by controlling reaction conditions such as temperature and solvent choice. Using a large excess of the fluorinating agent can also help drive the desired substitution reaction to completion.

39. Can the Swarts reaction be used in the synthesis of PET (Positron Emission Tomography) tracers?

Yes, the principles of the Swarts reaction are relevant to PET tracer synthesis. While the classical Swarts reaction isn't typically used directly due to the short half-life of 18F, nucleophilic fluorination reactions inspired by the Swarts reaction are commonly employed in the rapid synthesis of 18F-labeled compounds for PET imaging.

40. How does the polarity of the solvent affect the rate of the Swarts reaction?

The polarity of the solvent can significantly affect the rate of the Swarts reaction. Polar aprotic solvents like acetonitrile or DMF generally increase the reaction rate by stabilizing the fluoride ion without solvating it too strongly, thus maintaining its nucleophilicity. Less polar solvents tend to slow the reaction by not effectively dissolving or activating the reagents.

41. How does the electronegativity difference between fluorine and other halogens affect the products of the Swarts reaction?

The high electronegativity of fluorine leads to a more polar C-F bond in the products of the Swarts reaction compared to the original C-Cl or C-Br bonds. This increased polarity can significantly alter the physical and chemical properties of the molecule, including its boiling point, solubility, and reactivity with other substances.

42. Can the Swarts reaction be used in the synthesis of fluoropolymers?

While the Swarts reaction isn't typically used directly in polymer synthesis, it has played a crucial role in the development of fluoropolymers. The reaction principles have been applied to create fluorinated monomers, which can then be polymerized to form materials like polytetrafluoroethylene (PTFE or Teflon).

43. How does the concept of leaving group ability apply to the Swarts reaction?

In the Swarts reaction, the leaving group ability of the halogen being replaced is crucial. Bromine is generally a better leaving group than chlorine, making alkyl bromides more reactive. The strong C-F bond formed makes fluorine a poor leaving group, which is why the reaction is not easily reversible.

44. What role does entropy play in the Swarts reaction?

Entropy plays a minor role in driving the Swarts reaction. The reaction doesn't significantly change the