Question

What are X and Y in the following set of reactions?
(dry acetone)

• A. NaI / dry acetone; SbF$_3$
• B. NaI / H$_2$O; NaF
• C. NaI / H$_2$O; SbF$_3$
• D. NaI / dry acetone; NaF

Hint:

Remember that Finkelstein reactions (halide exchange) require dry acetone to precipitate NaBr. SbF$_3$ is often used to replace fluorine atoms due to its ability to form stable complexes with F.

Answer 1

The Correct Option is A

Step 1 (Y):

The first transformation is the conversion of \(\ce{CH3-CH2-CH(Br)-CH2-F}\) to \(\ce{CH3-CH2-CH(Br)-CH3}\). This indicates the fluorine atom is replaced by a methyl group, suggesting a nucleophilic substitution where F is replaced. Since fluoride is a poor leaving group, a reagent like SbF₃ is used to facilitate this by forming a complex.

Step 2 (X):

The next transformation is from bromoalkane to iodoalkane, which is a typical Finkelstein reaction:

\[ \ce{R-Br + NaI -> R-I + NaBr} \]

This reaction occurs in dry acetone to drive the equilibrium toward product formation because NaBr precipitates out.

Thus:

• Y = SbF₃
• X = NaI / dry acetone