Reaction intermediate formed in the formation of salicylaldehyde from phenol (Reimer-Tiemann reaction) is

Options

A. Carbocation
B. Free radical
C. Carbanion
D. Carbene

Answer

To determine the reaction intermediate formed in the formation of salicylaldehyde from phenol through the Reimer-Tiemann reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**: The Reimer-Tiemann reaction involves the ortho-formylation of phenols using chloroform and a strong base, typically sodium hydroxide (NaOH).

2. **Formation of Carbene**: In the first step, chloroform (CHCl3) reacts with the base (NaOH) to generate a dichlorocarbene intermediate. This occurs through an alpha elimination process where one of the chlorine atoms is removed, resulting in the formation of the carbene.

\[ \text{CHCl}_3 + \text{NaOH} \rightarrow \text{CCl}_2 + \text{NaCl} + \text{H}_2\text{O} \]

3. **Attack on Phenoxide Ion**: The generated dichlorocarbene acts as an electrophile and attacks the phenoxide ion (the deprotonated form of phenol). The electron density of the phenoxide ion is concentrated at the ortho position, facilitating the attack.

4. **Formation of the Intermediate**: The attack of the dichlorocarbene on the ortho position of the phenoxide ion leads to the formation of a more stable intermediate, which is a chlorinated phenol.

5. **Intramolecular Proton Exchange**: Following this, an intramolecular proton exchange occurs, where a hydrogen atom from the phenol is transferred to the carbene, leading to the formation of the final intermediate.

6. **Hydrolysis and Final Product**: In the presence of water, the chlorine atom is hydrolyzed, resulting in the formation of the aldehyde group. The final product of this reaction is salicylaldehyde.

### Conclusion:
The reaction intermediate formed in the Reimer-Tiemann reaction is **dichlorocarbene**.