Reimer Tiemann Reaction — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Reimer-Tiemann Reaction The Reimer-Tiemann reaction is an organic chemical reaction used for the ortho-formylation of phenols. The reaction involves treating a phenol with chloroform in the presence of a strong base to introduce an aldehyde group, typically ortho to the hydroxyl group. Initial clear solution of phenol and base. The reaction mixture is typically heated, and upon workup, the product salicylaldehyde can be identified by its characteristic 'wintergreen' odor. No immediate color change or precipitation is typically observed during the reaction unless impurities are present or side reactions occur. The Reimer-Tiemann reaction is mildly exothermic. The formation of the salicylaldehyde product is thermodynamically favorable due to intramolecular hydrogen bonding. The dichlorocarbene intermediate (:CCl₂) is highly reactive and short-lived. 1. Deprotonation of chloroform by strong base to generate trichloromethyl anion (CCl3-). 2. Elimination of a chloride ion from CCl3- to form dichlorocarbene (:CCl2), the key electrophilic intermediate. 3. Deprotonation of phenol by strong base to form the phenoxide ion. 4. Nucleophilic attack of the activated phenoxide ring (specifically at the ortho-position due to resonance and chelation with the positively charged sodium ion) on the electrophilic dichlorocarbene. 5. Rearomatization of the ring, followed by protonation to form an intermediate dichloromethyl phenol. 6. Hydrolysis of the dichloromethyl group (-CHCl2) under alkaline conditions to form the aldehyde group (-CHO). Forgetting the generation of dichlorocarbene as the active electrophile. Not understanding the role of the phenoxide ion (activated aromatic ring) in the reaction. Incorrectly predicting para-formylation as the major product; ortho-formylation is kinetically favored due to chelation with the sodium ion and steric hindrance from the hydroxyl group. Confusing the Reimer-Tiemann reaction with other formylation reactions like the Gattermann-Koch reaction. Not accounting for the hydrolysis step of the intermediate dichloromethyl group to the aldehyde.