Finkelstein reaction

What is Finkelstein reaction?

The Finkelstein reaction, which was first reported by Finkelstein in 1910, is a method for converting alkyl bromides or chlorides into alkyl iodides by reacting them with potassium or sodium iodide in acetone.

The reaction is often referred to as the Finkelstein halide exchange, Finkelstein displacement, or Conant-Finkelstein reaction.

 

Finkelstein reaction - general reaction scheme - Finkelstein halide exchange - Finkelstein displacement - Conant-Finkelstein reaction
Finkelstein reaction

Mechanistically, the Finkelstein reaction involves a simple nucleophilic substitution, typically via SN2, as iodide is a stronger nucleophile than bromide or chloride. The reaction typically yields very high and even quantitative yields, particularly when conducted in DMF. However, the presence of a trifluoromethyl group can retard or accelerate the reaction, depending on its position in the molecule.

Generally, aryl halides do not undergo this type of halide displacement under normal conditions. For dihalides, unsaturated or cyclic compounds may form via carbocation intermediates, which form transient covalent iodides or are reduced directly by iodide to free radicals. However, with the presence of a 10 % CuI catalyst, even aromatic halide exchange can occur smoothly at -40 ºC.

References

Finkelstein, H. (1910), Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden. [Preparation of organic iodides from the corresponding bromides and chlorides.] Ber. Dtsch. Chem. Ges., 43: 1528-1532. https://doi.org/10.1002/cber.19100430257

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