Finkelstein reaction

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The Finkelstein reaction (often referred to as halogen exchange or halex reaction) is an SN2 reaction that involves the exchange of one halogen atom for another. It is an equilibrium reaction, but the reaction can be driven to completion by exploiting the differential solubility of halide salts, or by using a large excess of the halide salt.

R-X + X′ ⇌ R-X′ + X

Description

The classic Finkelstein reaction entails the conversion of an alkyl chloride or bromide to an alkyl iodide by treatment with a solution of sodium iodide in acetone. Sodium iodide is soluble in acetone, while NaCl and NaBr are not. The reaction is driven toward products by mass action due to the precipitation of the poorly NaCl or NaBr.[1]

Alkyl halides differ greatly in the ease with which they undergo the Finkelstein reaction. The reaction works well for primary (except for neopentyl) halides, and exceptionally well for allyl, benzyl, and α-carbonyl halides. Secondary halides are far less reactive. Vinyl, aryl and tertiary alkyl halides are unreactive

The aromatic chlorides and bromides are not easily substituted by iodide, though they may occur when a catalyst is used, such as copper(I) iodide in combination with diamine ligands, nickel bromide, tri-n-butylphosphine, etc.

Projects

  • Make nitriles
  • Qualitative test for alkyl halides

References

  1. https://www.youtube.com/watch?v=15ZkhhJcXXk

Relevant Sciencemadness threads