Question

Fluorobenzene $C_6{H}_{5}F$ can be synthesized in the laboratory:

• A. by heating phenol with $HF$ and $KF$
• B. from aniline by diazotization followed by heating the diazonium salt with ${HBF}_4$
• C. by direct fluorination of benzene with $F_2$ gas
• D. by reacting bromobenzene with $NaF$ solution

Answer 1

Answer: (B)

from aniline by diazotization followed by heating the diazonium salt with ${HBF}_4$

In laboratory, fluorobenzene is prepared by the first diazotization of aniline and then replacement by fluorine using $HB{F}_4$ (called fluoroboric acid).

Reactions are as follows :
$C_6{H}_{5}N{H}_2+NaN{O}_2+HCl\to C_6{H}_5{N}_2^{+}C{l}^{-}$

Next, $C_6{H}_5{N}_2^{+}C{l}^{-}$ is treated with fluoroboric acid to give fluorobenzene.

Reaction :
$C_6{H}_5{N}_2^{+}C{l}^{-}+HB{F}_4\to C_6{H}_{5}F$

So, Option $B$ is the correct answer.