Chemistry · Haloalkanes And Haloarenes · NEET
It makes an alkyl IODIDE. You start with an alkyl chloride or alkyl bromide (R-Cl or R-Br) and react it with NaI in dry acetone. The equation is R-Cl + NaI -> R-I + NaCl. So the chlorine or bromine leaves and iodine takes its place. Easy way to remember: Finkelste-IN puts Iodine IN.
NaI dissolves well in acetone, but the NaCl or NaBr that forms does NOT dissolve in acetone. So NaCl or NaBr falls out as a solid (precipitate). Once it leaves the solution, it cannot react backward. By Le Chatelier's Principle, removing a product pushes the reaction forward, giving more alkyl iodide. The acetone must be DRY because water would spoil the reaction.
The Swarts reaction makes an alkyl FLUORIDE. You heat an alkyl chloride or bromide with a metal fluoride. The chlorine or bromine is replaced by fluorine. Example: CH3-Br + AgF -> CH3-F + AgBr. It is the standard way to get C-F bonds, which are hard to make directly.
Any of these metal fluorides: AgF (silver fluoride), Hg2F2 (mercurous fluoride), CoF2 (cobalt fluoride) or SbF3 (antimony trifluoride). All four supply fluoride ion to replace the other halogen. NEET often asks you to pick these out of an option list, so memorise the set: Ag, Hg2, Co, Sb fluorides.
Both are halogen exchange, but the product halogen is different. Finkelstein: NaI + dry acetone -> alkyl IODIDE. Swarts: metal fluoride (AgF/Hg2F2/CoF2/SbF3), heat -> alkyl FLUORIDE. Finkelstein needs the special dry acetone trick to work; Swarts just needs heating with the fluoride salt.
You cannot easily make alkyl iodides or fluorides directly and cheaply. Iodide and fluoride are hard leaving positions to set up by normal routes. Halogen exchange is a smart shortcut: first make the easy chloride or bromide, then swap it for the harder-to-add iodine or fluorine. This matters for NEET because these are the standard named methods in the NCERT chapter.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It goes by an SN2 mechanism. Iodide ion is a strong nucleophile and attacks the carbon, kicking out the chloride or bromide in one step. That is why it works best on primary and simple alkyl chlorides or bromides.
No, the whole point is to MAKE the alkyl iodide. Iodide is added, and the driving force is the removal of the insoluble NaCl or NaBr. There is no reason for iodide to leave again in dry acetone.
Yes, the same idea (replacing chlorine with fluorine using metal fluorides such as SbF3) is used industrially to make fluorine-containing compounds like Freons. This links to the polyhalogen compounds part of the chapter.
Water would dissolve the NaCl or NaBr and could interfere with NaI. Dry acetone keeps NaCl/NaBr insoluble so it precipitates and pushes the reaction forward to give the alkyl iodide.
