Salicylaldehyde is synthesized from phenol, when reacted with

Step 1: Identify the target product — Salicylaldehyde

Salicylaldehyde = 2-hydroxybenzaldehyde ($\ce{o-HO-C6H4-CHO}$). The synthesis from phenol involves introducing a $\ce{-CHO}$ group ortho to the -OH.

Step 2: Match reaction to product

• (a) HCl, NaOH: Sodium phenoxide + HCl would just regenerate phenol. No synthesis.

• (b) CO2, NaOH: This is the Kolbe reaction → gives salicylic acid (2-hydroxybenzoic acid), NOT the aldehyde.

• (c) CCl4, NaOH: Carbon tetrachloride does not react with phenol under these conditions to give salicylaldehyde. $\ce{CCl4}$ does not form dichlorocarbene easily.

• (d) HCCl3 (chloroform), NaOH: This is the Reimer-Tiemann reaction:

  • $\ce{CHCl3 + NaOH -> :CCl2}$ (dichlorocarbene)
  • Carbene attacks ortho position of phenoxide
  • Hydrolysis of -CHCl2 → -CHO
  • Product: salicylaldehyde ✓

Answer: HCCl3, NaOH (Reimer-Tiemann reaction)

Key Points to Remember:

• $\ce{CHCl3}$ (chloroform) + phenol/NaOH = Reimer-Tiemann → aldehyde (salicylaldehyde).
• $\ce{CO2}$ + phenol/NaOH = Kolbe reaction → carboxylic acid (salicylic acid).
• The key distinction: CHCl3 gives -CHO; CO2 gives -COOH.