Finkelstein Reaction

The Finkelstein reaction is a Substitution Nucleophilic Bimolecular reaction ( \(S_{N}2\) Reaction) involves the exchange of halogen atom. It is named after the Hans Finkelstein, a German chemist.

It is an organic reaction that uses an alkyl halide exchange into another alkyl halide through a reaction wherein the metal halide salt is used. This reaction takes place at an equilibrium process by taking the advantage of poor acetone solubility in metal halide salt that is newly formed. The mechanism of the Finkelstein reaction is single-step \(S_{N}2\) reaction with stereochemistry inversion.

The classic Finkelstein reaction involves the process of an alkyl bromide or an alkyl chloride into an alkyl iodide which is treated with a sodium iodide solution in acetone. As the sodium iodide is soluble in the acetone, but the sodium bromide and sodium chloride are not soluble in the acetone. The reaction works good with the primary halides but better with α-carbonyl halides and allyl benzyl.

For instance: The bromoethane can be converted to iodoethane:

\(CH_{3} CH_{2}Br \ _{(acetone)} + Nal \ _{(acetone)} \rightarrow CH_{3} CH_{2} I \ _{(acetone)} + NaBr \ \ _{(s)}\)

The success of this reaction depends on the below conditions.

  • Nucleophilicity
  • Nature of group
  • Carbon-halogen bond
  • Alkyl Halide reactivity

In the modern usage of Finkelstein reaction, it has expanded including in the process of changing alcohols to alkyl halides by converting the alcohol to a sulfonate ester in the first stage, and then the substitution changes.

For Example: Synthesis of chrysochlamic acid.