CBSE Class 12 · 2001 · Delhi; also Delhi Compartment · Compounds Containing NitrogenVery Short Answer

Write the chemical reactions occurring in the preparation of fluorobenzene from aniline.

Answer: Diazotise, then Balz–Schiemann: C₆H₅N₂⁺Cl⁻ + HBF₄ → C₆H₅N₂⁺BF₄⁻ →Δ→ C₆H₅F + BF₃ + N₂.

Solution

Step 1 — diazotisation (273–278 K):

C_{6} H_{5} N H_{2} + NaN O_{2} + 2HCl \to C_{6} H_{5} N_{2}^{+} C l^{-} + NaCl + 2 H_{2} O

Step 2 — Balz–Schiemann:

C_{6} H_{5} N_{2}^{+} C l^{-} HB F_{4} C_{6} H_{5} N_{2}^{+} B F_{4}^{-} Δ C_{6} H_{5} F + B F_{3} + N_{2} ↑

CBSE Class 12 Board · 2001 · Delhi; also Delhi Compartment · Subjective