Halogen Exchange Reactions
Preparation of iodoalkanes (Finkelstein reaction) and fluoroalkanes (Swarts reaction) using halogen exchange.
What is Halogen Exchange Reactions?
A chemical reaction in which one halogen atom in a molecule is replaced by another halogen atom.
Key formula / rule: Finkelstein Reaction
Key points
- Understand the principle of halogen exchange reactions.
- Identify and describe the Finkelstein reaction.
- Identify and describe the Swarts reaction.
- Predict the products of these reactions.
Common exam trap
Using aqueous acetone in Finkelstein reaction, which would dissolve the precipitated NaCl/NaBr.
Definitions
- Term
Halogen Exchange Reaction
- Meaning
A chemical reaction in which one halogen atom in a molecule is replaced by another halogen atom.
- Term
Finkelstein Reaction
- Meaning
A specific halogen exchange reaction used to synthesize alkyl iodides from alkyl chlorides or bromides using sodium iodide in dry acetone.
- Term
Swarts Reaction
- Meaning
A halogen exchange reaction used to synthesize alkyl fluorides from alkyl chlorides or bromides using metal fluorides, such as antimony trifluoride.
Learning objectives
Understand the principle of halogen exchange reactions.
Identify and describe the Finkelstein reaction.
Identify and describe the Swarts reaction.
Predict the products of these reactions.
Explain the role of solvents and catalysts.
Formulae
- Name
Finkelstein Reaction
- Note
The precipitation of NaX in dry acetone drives the reaction forward.
- Expression
R-X + NaI $\xrightarrow{\text{dry acetone}}$ R-I + NaX↓ (where X = Cl, Br)
- Name
Swarts Reaction
- Note
Often catalyzed by SbCl5.
- Expression
R-X + SbF3 $\xrightarrow{\text{catalyst}}$ R-F + SbX3 (where X = Cl, Br)
Prerequisites
Alkyl halides
Nucleophilic substitution reactions (SN1 and SN2)
Solubility and precipitation concepts
Reactivity of halogens
Common mistakes
Using aqueous acetone in Finkelstein reaction, which would dissolve the precipitated NaCl/NaBr.
Confusing the reagents or conditions for Finkelstein and Swarts reactions.
Assuming direct synthesis of iodoalkanes or fluoroalkanes from alcohols is always efficient without these methods.
Keywords
Halogen Exchange
Finkelstein Reaction
Swarts Reaction
Alkyl Iodide
Alkyl Fluoride
Nucleophilic Substitution
SN2 Reaction
Sodium Iodide
Antimony Trifluoride
Dry Acetone
Practice preview
In the Finkelstein reaction, which of the following is used as a reagent?…
easy
Which of the following reactions is known as the Finkelstein reaction?…
easy
The Swarts reaction is used for the preparation of:…
easy