Finkelstein reaction

Method

The classic Finkelstein reaction entails the conversion of an alkyl chloride or an alkyl bromide to an alkyl iodide by treatment with a solution of sodium iodide in acetone. Sodium iodide is soluble in acetone while sodium chloride and sodium bromide are not; therefore, the reaction is driven toward products by mass action due to the precipitation of the poorly soluble NaCl or NaBr. An example involves the conversion of the ethyl ester of 5-bromovaleric acid to the iodide:{{cite journal|title=Copper-catalyzed Conjugate Addition of Functionalized Organozinc Reagents to α,β-Unsaturated Ketones: Ethyl 5-(3-oxocyclohexyl)pentanoate|author1=B. H. Lipshutz |author2=M. R. Wood |author3=R. Tirado :EtO2C(CH2)4Br + NaI → EtO2C(CH2)4I + NaBr

Potassium fluoride is used for the conversion of chlorocarbons into fluorocarbons. Such reactions usually employ polar solvents such as dimethyl formamide, ethylene glycol, and dimethyl sulfoxide.

Use for analysis

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; as a result, the reaction of NaI in acetone can be used as a qualitative test to determine which of the aforementioned classes an unknown alkyl halide belongs to, with the exception of alkyl iodides, as they yield the same product upon substitution. Below some relative rates of reaction (NaI in acetone at 60 °C):

Aromatic Finkelstein reaction

The aromatic chlorides and bromides are not easily substituted by iodide, though they may occur when appropriately catalyzed. The so-called "aromatic Finkelstein reaction" is catalyzed by copper(I) iodide in combination with diamine ligands. Nickel bromide and tri-n-butylphosphine have been found to be suitable catalysts as well.

References

References

1. Finkelstein, Hans. (1910). "Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden". [[Ber. Dtsch. Chem. Ges.]].
2. {{March6th
3. Ervithayasuporn, V.. (2013). "One-pot synthesis of halogen exchanged silsesquioxanes: octakis(3-bromopropyl)octasilsesquioxane and octakis(3-iodopropyl)octasilsesquioxane". [[Dalton Trans.]].
4. (1956). "n-Hexyl Fluoride".
5. Han, Q.; Li, H-Y. "Potassium Fluoride" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons, New York. {{doi. 10.1002/047084289X.rp214
6. Streitwieser, A.. (1956). "Solvolytic Displacement Reactions at Saturated Carbon Atoms". [[Chem. Rev.]].
7. (1964). "The Effect of the Carbonyl and Related Groups on the Reactivity of Halides in S_N2 Reactions". [[J. Am. Chem. Soc.]].
8. (2002). "Copper-Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein Reaction". [[J. Am. Chem. Soc.]].
9. (2012). "Nickel-catalysed aromatic Finkelstein reaction of aryl and heteroaryl bromides". [[Chem. Commun.]].