Question

Explain the Finkelstein reaction.

Hint:

Heat an alkyl chloride or bromide with NaI in dry acetone. The alkyl iodide forms and NaCl or NaBr precipitates.

Answer 1

Step 1: Name the reaction type:
The Finkelstein reaction is a halide exchange reaction. It is used to prepare alkyl iodides from alkyl chlorides or alkyl bromides.

Step 2: Write the reaction:
The alkyl chloride or bromide is heated with sodium iodide in dry acetone.
\[ \mathrm{R-X + NaI \xrightarrow{\text{dry acetone}} R-I + NaX\downarrow} \quad (\mathrm{X = Cl, Br}) \]
For example:
\[ \mathrm{CH_3CH_2Br + NaI \xrightarrow{\text{dry acetone}} CH_3CH_2I + NaBr\downarrow} \]

Step 3: Explain why it goes forward:
Sodium iodide dissolves in dry acetone, but sodium chloride and sodium bromide do not.
The NaCl or NaBr separates out as a precipitate.
Removing the product from the solution pushes the equilibrium to the right, by the Le Chatelier principle.
The reaction is an \(\mathrm{S_N2}\) substitution, and the iodide ion is the attacking nucleophile.

Final Answer:
Finkelstein reaction: alkyl chloride or bromide with NaI in dry acetone gives alkyl iodide, and NaCl or NaBr precipitates. \[ \boxed{\mathrm{R-X + NaI \rightarrow R-I + NaX\downarrow}} \]