Write, with equations and conditions: (i) Kolbe's reaction, (ii) the Reimer-Tiemann reaction, (iii) bromination of phenol in water and in CS₂.

1. 1 · State the principle. -OH is activating and ortho-para directing: its lone pair raises the electron density at the ortho and para positions.
2. 2 · Kolbe's reaction. C₆H₅ONa + CO₂ (heat, pressure), then H⁺ → salicylic acid (2-hydroxybenzoic acid).
3. 3 · Reimer-Tiemann reaction. Phenol + CHCl₃ + aqueous NaOH (warm), then H⁺ → salicylaldehyde (2-hydroxybenzaldehyde).
4. 4 · Bromination.
   • Br₂ in CS₂, 273 K → 4-bromophenol (major) + 2-bromophenol
   • Bromine water → 2,4,6-tribromophenol, white precipitate
5. 5 · Link to real life. Salicylic acid goes into anti-dandruff and acne products and into aspirin.
6. 6 · Close in one line. So the activated ring of phenol reacts even with weak electrophiles such as CO₂.

Scoring tip: Give both the common and IUPAC names of each product: salicylic acid (2-hydroxybenzoic acid), salicylaldehyde (2-hydroxybenzaldehyde).