Finkelstein reaction

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The Finkelstein reaction is an SN2 reaction that involves the exchange of one halogen atom for another. Halide exchange is an equilibrium reaction, but the reaction can be driven to completion by taking advantage of differential solubility of halide salts.

R-X + X'^- ⇌ R-X' + X^-

The classic Finkelstein reaction involves the conversion of an alkyl chloride or an alkyl bromide to an alkyl iodide by the addition of sodium iodide in acetone. Since sodium iodide is soluble in acetone and sodium chloride and sodium bromide are not, the equilibrium is shifted by the precipitation of the insoluble salt. For example, bromoethane can be converted to iodoethane:

CH₃CH₂Br + NaI → CH₃CH₂I + NaBr