Reimer-Tiemann Reaction Mechanism: How CHCl3 Becomes CHO on Phenol

Chloroform is an unreactive solvent. So how does it end up as an aldehyde group on phenol? The answer is a short-lived species with only six electrons on carbon: dichlorocarbene.

Follow the Reimer-Tiemann reaction step by step: how NaOH makes phenoxide and the trichloromethyl anion, how dichlorocarbene forms by alpha-elimination, how the ring attacks it, why the product is ortho, and how CHCl2 is hydrolysed to CHO. We finish with carbene trapping, the two-layer reaction, the CCl4 variant and the traps NEET likes to test.

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In this video

• 0:00The puzzle: how does CHCl3 become CHO?
• 1:07The reaction at a glance
• 2:07Step 1: the base works twice (phenoxide and CCl3 minus)
• 3:11Step 2: dichlorocarbene forms (the slow step)
• 4:27Step 3: the ring attacks the carbene
• 5:35Why ortho?
• 6:33Step 4: hydrolysis to CHO
• 7:31Going further: trapping the carbene, two layers, CCl4
• 8:44Exam traps
• 9:40Recap and close