Halogen exchange

Alkyl iodides are conveniently prepared by treating an alkyl chloride or bromide with sodium iodide dissolved in methanol or acetone (R-Cl + NaI in acetone -> R-I + NaCl-down-arrow); because sodium chloride or sodium bromide is insoluble in acetone, it precipitates out of the solution and can simply be filtered off, which also pulls the equilibrium towards the iodide product. This exchange is called the Finkelstein reaction. Alkyl fluorides, which cannot be made well from HF directly, are instead prepared by heating an alkyl chloride or bromide with a metal fluoride such as AgF, Hg2F2, AsF3 or SbF3 (R-Cl + AgF -> R-F + AgCl-down-arrow); this exchange …