Swarts Reaction - Mechanism, Application, Examples, FAQs

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 Swart's reaction

1. $\mathrm{C}_2 \mathrm{H}_5 \mathrm{Cl}+\mathrm{AgF} \rightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{~F}+\mathrm{AgCl}$

2. $\mathrm{CH}_3 \mathrm{Br}+\mathrm{AgF} \rightarrow \mathrm{CH}_3 \mathrm{~F}+\mathrm{AgBr}$ ( in the presence of fluoride of heavy metals and swarts reagent)

Swart's reaction is the best reaction for the formation of alkyl fluorides with the help of Swarts reagent, i.e., $\left(\mathrm{SbF}_3+\mathrm{Cl}_2\right)$ and heavy metals fluorides such as $\mathrm{AgF}, \mathrm{F}_2 \mathrm{Hg}_2, \mathrm{CoF}_2$, or $\mathrm{SbF}_3$.

In general, if we have to prepare metal fluorides, we use the Swarts reaction or the 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 can all well notice that chlorine is generally replaced by fluorine in this reaction. In the presence of antimony trifluoride with antimony salts, the Swart reaction will smoothly move forward due to the +5 oxidation state of the antimony salt.

Swarts Reaction Mechanism

$\text{Step 1: } \text{R}-\underset{\displaystyle|}{\text{X}} + \text{Ag}^+ \rightarrow [\text{R}-\text{X}\cdots\text{Ag}]^+ \text{ (coordination complex)}$

$\text{Step 2: } \text{F}^- \text{ attacks carbon as } \text{Ag}^+ \text{ weakens the C-X bond}$

$\text{R-X} + \text{AgF} \rightarrow \text{R-F} + \text{AgX}\downarrow$

$\text{Driving force: } K_{sp}(\text{AgX}) \ll 1 \Rightarrow \text{AgX precipitates, pushing equilibrium forward}$

$\text{Overall: } \underset{\text{alkyl halide}}{\text{R-X}} + \underset{\text{silver fluoride}}{\text{AgF}} \xrightarrow{\Delta} \underset{\text{alkyl fluoride}}{\text{R-F}} + \underset{\text{silver halide (ppt.)}}{\text{AgX}\downarrow}$

$\text{Where X} = \text{Cl, Br, or I}$

• Swarts' reaction converts alkyl chlorides/bromides/iodides into alkyl fluorides
• The mechanism proceeds via an S_N²-like pathway with AgF as the fluorinating agent
• $\mathrm{Ag}^{+}$ acts as a Lewis acid, coordinating with the halogen to weaken the C−X bond
• Precipitation of insoluble $\mathrm{AgX}(\mathrm{AgCl}, \mathrm{AgBr}, \mathrm{AgI})$ is the thermodynamic driving force
• Reactivity order: $\mathrm{R}-\mathrm{I}>\mathrm{R}-\mathrm{Br}>\mathrm{R}-\mathrm{Cl}$

Applications of the Swarts Reaction

• For the production or formation of alkyl fluoride.
• Used in the formation of freons.
• Swarts ' reaction is used for chemical analysis.

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Finkelstein Reaction

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

Finkelstein reaction occurs through a nucleophilic bimolecular substitution reaction, i.e., S_N² reaction. This is also a type of organic reaction. In this reaction, a primary alkyl halide or pseudohalide reacts with an alkali metal halide to form an 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.

Examples of Finkelstein reactions are:-

• $\mathrm{CH}_3 \mathrm{Br}+\mathrm{NaI} \rightarrow \mathrm{CH}_3 \mathrm{I}+\mathrm{NaBr}$ (reaction will happen in the presence of acetone)
• $\mathrm{CH}_3 \mathrm{Cl}+\mathrm{NaI} \rightarrow \mathrm{CH}_3 \mathrm{I}+\mathrm{NaCl}$ (reaction will happen in the presence of acetone)
• $\mathrm{C}_2 \mathrm{H}_5 \mathrm{Cl}+\mathrm{KI} \rightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{I}+\mathrm{KCl}$ (this reaction will happen in the presence of acetone)

Related Topics,

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

Some Solved Examples

Question 1. 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 (chlorine and antimony trifluoride) is known as a Swarts reagent.

Swarts reagent $=\mathrm{SbF}_3+\mathrm{Cl}_2$

Question 2. 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 an alkyl iodide, which is formed due to halogen exchange. The Finkelstein reaction follows the S_N² ( Nucleophilic Substitution, Second Order ) pathway to form the product.

Question 3. Similarity between Swart's reaction and Finkelstein's reaction?

Ans: Both given reactions are halogen exchange reactions. Both of these reactions follow the S_N² (second-order Nucleophilic substitution) pathway to form a product. In the Swarts reaction, the product is alkyl fluoride, and in the Finkelstein reaction, the product will be alkyl iodide.

Question 4. Difference between the Swarts reaction and the Finkelstein reaction?

Ans: In Swart's reaction, reagents are heavy metal fluorides that can easily fluorinate alkyl components. This reaction is used to form alkyl fluoride with a good yield. The reagents of the Swarts reaction are SbF₃ + Cl_2, 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 play an important role in many organic reactions, analysis, etc.

Question 5: Swarts' reaction is used for the preparation of:

A. Fluoroalkanes
B. Chloroalkanes
C. Bromoalkanes
D. Iodoalkanes

Solution: Swarts' reaction involves the replacement of halogen (usually $\mathrm{Cl} / \mathrm{Br}$ ) by fluorine using metal fluorides like $\mathrm{AgF}_1 \mathrm{SbF}_3 \rightarrow$ formation of fluoroalkanes.

Hence, the correct answer is option (A)

Question 6: In Swart's reaction, the halide most commonly replaced is:

A. F
B. Cl
C. Br
D. I

Solution: Chloroalkanes are generally converted into fluoroalkanes using metal fluorides.

Hence, the correct answer is option (B)

Question 7. The Finkelstein reaction is mainly carried out in:

A. Aqueous medium
B. Acetone
C. Benzene
D. Water–ethanol mixture

Solution: Finkelstein reaction: $\mathrm{R}-\mathrm{Cl} / \mathrm{R}-\mathrm{Br}+\mathrm{NaI} \rightarrow \mathrm{R}-\mathrm{I}+\mathrm{NaCl} / \mathrm{NaBr}$ (in acetone).
$\mathrm{NaCl} / \mathrm{NaBr}$ precipitates out → reaction driven forward.

Hence, the correct answer is option (B)

Question 8. Is F₂Hg₂ a reagent of the Swarts reaction?

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

$\mathrm{F}_2 \mathrm{Hg}_2$ – Compound name is “ Mercury(I) fluoride “

Question 9. What is Swart's 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 the S_N^2, i.e., Nucleophilic substitution pathway.

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