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 $HB{F_4}$.
(C) By direct fluorination of benzene with ${F_2}$ gas
(D) By reacting bromobenzene with $NaF$ solution

Answer 1

As we know that the fluorine atom is very small in size and also is an electron rich atom and${F_2}$ gas is very explosive in nature so if we use fluorine atom in direct substitution it could be very harmful in laboratory.

Complete step by step answer:
If we use fluorine gas directly it can be very explosive due to its very small size and more electrons around the fluorine nucleus.
So in laboratory we synthesis $({C_6}{H_5}F)$ indirectly, which is known as Balz-Schiemann reaction in which we will take aniline as a substrate which will react with $HN{O_2}$ (nitrous acid) in the presence of fluoroboric acid and gives a product diazonium salt. As the diazo group is a good leaving group so by reacting diazo-benzene with $HB{F_4}$,this fluoroboric acid attacks the diazo group and replaces diazo with fluorine atom. The $HB{F_4}$ gives fluoride ion as a nucleophile which attacks on diazo group. So the final product we will get as $({C_6}{H_5}F)$.
The mechanism is shown as below.

Therefore, the correct option is option (B).
Note:
Diazotization can also occur in the presence of other acids such as sulphuric acid, hydrochloric acid.