The Reimer-Tiemann reaction uses a dichlorocarbene precursor molecule such as chloroform, an alkali hydroxide, and a protic solvent to convert a phenol to an ortho-formyl phenol. The base first abstracts the hydrogen from chloroform, creating a trichlorocarbanion, which loses a chloride ion to form dichlorocarbene. Phenol is then deprotonated by the base, delocalizing electrons into the ortho position of the ring, which attack the carbene. An internal proton transfer and release of a chloride ion forms a carbon-carbon double bond, which hydroxide adds to, resulting in the release of the last chloride ion. Tautomerization produces the final product.

• Reagents: CHCl₃, Base (NaOH, KOH, or CsOH), Protic Solvent
• Reactant: Phenol
• Product: Ortho-Formyl Phenol
• Type of Reaction: Electrophilic Aromatic Substitution
• Bond Formation: Ph-CH=O

Lab Tips

• Phenol is typically dissolved in a 10-40% aqueous solution of an alkali hydroxide, to which excess chloroform is added. The resulting biphasic solution should be vigorously stirred at around 60°C for about three hours.
• Ortho-formyl products tend to predominate, but when this position is already substituted, para-formyl phenols are obtained.
• Alkyl-, alkoxy- and halogenated phenols, naphthols, salicylic acid derivatives, heterocyclic phenols such as hydroxyquinolines and hydroxypyrimidines, pyrroles and indoles also undergo formylation under these reaction conditions.

Mechanism

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