Q.CH3-CH2-Cl + NaI --(acetone, heat)--> CH3-CH2-I + NaCl. The reaction is
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The Finkelstein Reaction: Why Iodine Wins in Acetone
Imagine you have a key that almost fits a lock — it goes in, but it's too tight. You'd swap it for a slightly thinner key. That's the intuition behind the Finkelstein reaction. You have an alkyl chloride or bromide (the thick key), and you want to replace the halogen with iodine (the thinner key). The reagent is sodium iodide (NaI), and the solvent is dry acetone.
Why does this work? Iodide ion (I−) is a good nucleophile — it's large, polarizable, and happy to attack an alkyl halide. But the real trick is solubility. Sodium chloride (NaCl) and sodium bromide (NaBr) are practically insoluble in acetone. Sodium iodide, however, dissolves well in acetone. So when you mix an alkyl chloride or bromide with NaI in dry acetone, the iodide displaces the chloride or bromide, and the salt that forms (NaCl or NaBr) simply precipitates out of solution. That precipitation pulls the equilibrium forward — Le Chatelier's principle in action.
The reaction is an SN2 nucleophilic substitution. It works best with primary alkyl halides. Secondary halides react slowly; tertiary halides tend to give elimination instead.
The general equation:
R-Cl+NaIdry acetoneR-I+NaCl↓
R-Br+NaIdry acetoneR-I+NaBr↓
The downward arrow indicates the precipitate that forms — the driving force of the reaction.
Why "Dry" Acetone Matters
Water would dissolve the NaI and also dissolve the NaCl or NaBr that forms. If the salt stays dissolved, the equilibrium doesn't shift, and the reaction stalls. Dry acetone ensures the byproduct salt crashes out, pushing the reaction to completion. Also, water can compete as a nucleophile, giving you an alcohol instead of the desired alkyl iodide.
The Practical Payoff
Alkyl iodides are more reactive than chlorides or bromides — the C-I bond is weaker and iodide is a better leaving group. So the Finkelstein reaction is a way to make a more reactive alkyl halide from a less reactive one. It's used in organic synthesis when you need a good alkylating agent or a substrate for further reactions like the Williamson ether synthesis or Grignard reagent formation. …
Heating an alkyl halide with sodium iodide in dry acetone to exchange the halogen for iodine is a specific named reaction. …
Heating an alkyl halide with NaI in dry acetone replaces the halogen with iodine, precipitating NaCl (or NaBr) out of the acetone solution - this halide-exchange reaction is called the Finkelstein reaction.
CH3-CH2-Cl + NaI --(dry acetone, heat)--> CH3-CH2-I + NaCl.
This works because NaI is soluble in acetone while NaCl (and NaBr) are not, so the precipitation of NaCl continuously drives the equilibrium (Le Chatelier's principle) towards the iodide product. This general method - converting an alkyl chloride or bromide into the corresponding iodide using NaI/dry acetone - is known as the Finkelstein reaction, and is a standard laborat …
- CBSE 2025Set ANNUAL1 markMCQQ.In which medium does Finkelstein reaction take place?(a) Concentrated HCl(b) Concentrated H2SO4(c) Dry acetone(d) Water
›Reveal solutionSolution
The Finkelstein reaction converts alkyl chlorides/bromides to alkyl iodides using NaI, and it must be run in dry acetone so that NaCl/NaBr precipitates out and drives the reaction forward.
R-X (X = Cl, Br)+NaIdry acetoneR-I+NaX↓
…
- CBSE 2023Set A1 markMCQQ.Alkyl iodides are often prepared by the reaction of alkyl chloride/bromides with NaI in dry acetone. This reaction is known as -(a) Finkelstein reaction(b) Sandmeyer's reaction(c) Coupling reaction(d) Kolbe's reaction
›Reveal solutionSolution
The Finkelstein reaction converts alkyl chlorides/bromides to alkyl iodides using NaI in dry acetone.
R-Cl/R-Br + NaI dry acetone R-I + NaCl/NaBr↓
The reaction works because NaI is soluble in dry acetone while NaCl and NaBr are not — the precipitation of NaCl/NaBr drives the equilibrium (Le Chatelier's principle) toward the iodide product. This distinguishes it from Sandmeyer's reaction (diazonium salt → ary …
- CBSE 2023Set ANNUAL1 markMCQQ.CH3CH2Cl + NaI --(Acetone)--> CH3CH2I + NaCl. The reaction is(a) Wurtz reaction(b) Finkelstein reaction(c) Sandmeyer reaction(d) Swarts reaction
›Reveal solutionSolution
The Finkelstein reaction is the specific name for halide exchange using NaI in acetone, driven by NaCl's insolubility in acetone.
CH3CH2Cl + NaI --(acetone)--> CH3CH2I + NaCl
This is the Finkelstein reaction: NaI is soluble in dry acetone while the NaCl (or NaBr) byproduct is not, so it precipitates out, driving the equilibrium (Le Chatelier) towards the iodide product. (Wurtz reaction couples two alkyl halides with Na metal to form a larger alkane; Sandmeyer reaction …
- CBSE 2023Set ANNUAL1 markQ.CH3-CH2-Br + NaI --(Acetone)--> CH3-CH2-I + NaBr The name of this reaction is ________.
›Reveal solutionSolution
The exchange of Br in an alkyl bromide for I using NaI in dry acetone is the Finkelstein reaction, a method for preparing alkyl iodides.
CH3–CH2–Br + NaI --(dry acetone)--> CH3–CH2–I + NaBr
This halogen-exchange reaction is called the Finkelstein reaction. It is used to prepare alkyl iodides from the corresponding alkyl chlorides or bromides. The reaction works because NaI is soluble in dry acetone while the NaCl/NaBr formed is not — it precipitates out, driving the equilibrium (by Le Chatelier's principle) towards …
- CBSE 2022Set ANNUAL1 markMCQQ.The reaction of ethylbromide with NaI in dry acetone to give ethyliodide is called(a) Finkelstein reaction(b) Swarts reaction(c) Wurtz reaction(d) Wurtz-Fittig reaction
›Reveal solutionSolution
Halogen exchange of an alkyl chloride/bromide with NaI in dry acetone to give the corresponding alkyl iodide is the textbook definition of the Finkelstein reaction — option (a).
The reaction
CH3−CH2−Br+NaIdry acetoneCH3−CH2−I+NaBr↓
This is an SN2 halide-exchange reaction. It is driven forward because NaBr (and NaCl) are insoluble in dry acetone and precipitate out, removing them from the equilibrium (Le Chatelier's principle), while NaI is soluble in acetone — the selective precipitation pulls the reaction to completion.
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- CBSE 2022Set ANNUAL1 markQ.CH3CH2Br+NaI→ ............ +NaBr.
›Reveal solutionSolution
Finkelstein reaction: CH3CH2Br+NaIdry acetoneCH3CH2I+NaBr. The missing product is ethyl iodide.
The Finkelstein reaction converts an alkyl chloride/bromide into an alkyl iodide by treatment with sodium iodide in dry acetone:
CH3CH2Br+NaIdry acetoneCH3CH2I+NaBr
…
- CBSE 2019Set ANNUAL1 markQ.Write the general equation for Wurtz reaction.
›Reveal solutionSolution
Two molecules of an alkyl halide react with sodium in dry ether to form a symmetrical alkane with double the number of carbons: 2R−X+2Na→R−R+2NaX.
Concept: In the Wurtz reaction, sodium abstracts the halogen from the alkyl halide, and the two alkyl groups couple to form a new C–C bond, lengthening the carbon chain.
General equation: …
- CBSE 2018Set ANNUAL1 markMCQQ.CH3-CH2-Cl + NaI --(acetone, heat)--> CH3-CH2-I + NaCl. The reaction is(a) Wurtz reaction(b) Fittig reaction(c) Finkelstein reaction(d) none of these
›Reveal solutionSolution
Heating an alkyl halide with NaI in dry acetone replaces the halogen with iodine, precipitating NaCl (or NaBr) out of the acetone solution - this halide-exchange reaction is called the Finkelstein reaction.
CH3-CH2-Cl + NaI --(dry acetone, heat)--> CH3-CH2-I + NaCl.
This works because NaI is soluble in acetone while NaCl (and NaBr) are not, so the precipitation of NaCl continuously drives the equilibrium (Le Chatelier's principle) towards the iodide product. This general method - converting an alkyl chloride or bromide into the corresponding iodide using NaI/dry acetone - is known as the Finkelstein reaction, and is a standard laborat …
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