Fluorobenzene $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~F}\right)$ can be synthesized in the laboratory

(A) by heating phenol with HF and KF

(C) by direct fluorination of benzene with $\mathrm{F}_{2}$ gas

(D) by reacting bromobenzene with NaF solution

JEE Main · 2006 · 30 Apr 2006 · Offline · Compounds Containing Nitrogen

Fluorobenzene

(C_{6} H_{5} F)

can be synthesized in the laboratory

(A)by heating phenol with HF and KF
(B)from aniline by diazotisation followed by heating the diazonium salt with $HBF_{4}$ ✓ Correct
(C)by direct fluorination of benzene with $F_{2}$ gas
(D)by reacting bromobenzene with NaF solution

Answer: (B)

Fluorobenzene is made by the Balz-Schiemann route rather than by direct fluorination, which is far too violent, or by displacing a halide with

NaF

, which aryl halides resist. Aniline is first diazotised with nitrous acid at

0

5^{\circ} C

to the benzenediazonium salt, which is converted with

HB F_{4}

to the diazonium tetrafluoroborate; gentle heating of this solid then decomposes it to fluorobenzene, nitrogen and

B F_{3}

. The preparation thus proceeds from aniline by diazotisation followed by heating the diazonium salt with

HB F_{4}

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option