The Reimer–Tiemann reaction is used to introduce a –CHO (aldehyde) group into a phenol ring, usually at the ortho position (forming salicylaldehyde).

Overall reaction

Phenol + CHCl₃ + NaOH → o-hydroxybenzaldehyde (major) + p-hydroxybenzaldehyde (minor)

Key Points to Remember

• Reagent: CHCl₃ + NaOH
• Reactive intermediate: dichlorocarbene (:CCl₂)
• Directing group: –O⁻ (phenoxide) → ortho/para directing
• Major product: ortho-hydroxybenzaldehyde
• Para product is minor due to intramolecular H-bonding stabilizing ortho product