Reimer-Tiemann Reaction:
Mechanism & Examples

By Chemca Editorial Team • Updated Jan 2026 • 9 min read

The Reimer-Tiemann Reaction is a classic electrophilic aromatic substitution reaction used primarily for the formylation of phenols. By treating phenol with chloroform in the presence of an aqueous alkali, we synthesize Salicylaldehyde (2-Hydroxybenzaldehyde).

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1. General Reaction

Phenol reacts with Chloroform ($CHCl_3$) and aqueous Sodium Hydroxide ($NaOH$) at around $340 \text{ K}$, followed by acid hydrolysis, to produce o-hydroxybenzaldehyde as the major product.

$$ \text{Phenol} + CHCl_3 + 3NaOH \xrightarrow{340 K} \text{Salicylaldehyde} + 3NaCl + 2H_2O $$

Note: The para-isomer is also formed as a minor product, but the ortho-isomer is dominant due to the stability provided by intramolecular hydrogen bonding (chelation).

2. Detailed Mechanism

The reaction proceeds via the formation of a highly reactive, neutral electrophile called Dichlorocarbene ($:CCl_2$).

Step 1: Generation of Electrophile

The strong hydroxide ion from the alkali abstracts the highly acidic proton from chloroform to form a trichloromethyl anion. This unstable anion rapidly loses a chloride ion ($\alpha$-elimination) to form Dichlorocarbene.

$$ OH^- + CHCl_3 \rightleftharpoons H_2O + :CCl_3^- $$ $$ :CCl_3^- \xrightarrow{\text{fast}} Cl^- + :CCl_2 \text{ (Dichlorocarbene)} $$

$:CCl_2$ is an electron-deficient species with an incomplete octet (sextet of electrons) and acts as a powerful neutral electrophile.

Step 2: Electrophilic Attack

In the basic medium, phenol is converted to the phenoxide ion, which is far more reactive towards electrophilic aromatic substitution than phenol itself. The electron-rich phenoxide ring attacks the dichlorocarbene primarily at the ortho position.

$$ \text{Phenoxide ion} + :CCl_2 \rightarrow \text{Intermediate Substituted Complex} $$

Step 3: Hydrolysis and Acidification

The resulting intermediate undergoes rapid basic hydrolysis to form an unstable gem-diol, which immediately loses water to form an aldehyde group. Final acidification yields Salicylaldehyde.

3. Important Variation: Synthesis of Salicylic Acid

If Carbon Tetrachloride ($CCl_4$) is used instead of Chloroform ($CHCl_3$), the reaction introduces a carboxyl group ($-COOH$) instead of an aldehyde group, yielding Salicylic Acid (2-Hydroxybenzoic acid).

$$ \text{Phenol} + CCl_4 + 4NaOH \xrightarrow[\text{then } H^+]{\Delta} \text{Salicylic Acid} + 4NaCl $$

4. Key Points for Exams

Electrophile: Dichlorocarbene ($:CCl_2$).
Reaction Type: Electrophilic Aromatic Substitution (EAS).
Intermediate: Dichloromethyl substituted phenoxide complex.
Major Product: Ortho-isomer (Salicylaldehyde).
Driving Force for Major Product: Intramolecular Hydrogen Bonding makes the ortho isomer more stable and easier to isolate (it is steam volatile, while the para isomer is not).

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