Describe two methods of preparing chlorobenzene, with equations and conditions.

1. 1 · Name the two methods. Electrophilic substitution of benzene, and Sandmeyer's reaction of a diazonium salt.
2. 2 · Method 1. C₆H₆ + Cl₂ → C₆H₅Cl + HCl, with anhydrous FeCl₃ in the dark.
3. 3 · Method 2: make the diazonium salt. C₆H₅NH₂ + NaNO₂ + 2HCl → C₆H₅N₂⁺Cl⁻ + NaCl + 2H₂O at 273 to 278 K.
4. 4 · Method 2: Sandmeyer step. C₆H₅N₂⁺Cl⁻ with Cu₂Cl₂ in HCl → C₆H₅Cl + N₂.
5. 5 · Close in one line. So chlorobenzene comes either straight from benzene or from aniline through its diazonium salt.

Scoring tip: Write the temperature of diazotisation; it is the most often missed mark.