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 solve the question regarding the reaction intermediate formed in the formation of salicylaldehyde from phenol (Reimer-Tiemann reaction), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Reaction Context**:
The Reimer-Tiemann reaction involves the conversion of phenol to salicylaldehyde using chloroform (CHCl3) in a basic medium (usually KOH).

**Hint**: Familiarize yourself with the Reimer-Tiemann reaction and its purpose in organic synthesis.

2. **Identify the Reactants**:
The main reactants in this reaction are phenol (C6H5OH) and chloroform (CHCl3).

**Hint**: Recognize the structure of phenol and chloroform to understand how they interact.

3. **Mechanism Overview**:
In the presence of a strong base (KOH), the hydroxide ion (OH-) abstracts an acidic hydrogen from chloroform, leading to the formation of a carbanion intermediate (CCl3-).

**Hint**: Recall the role of strong bases in deprotonation reactions.

4. **Formation of the Reaction Intermediate**:
The carbanion intermediate (CCl3-) then undergoes a rearrangement, losing one chlorine atom to form a dichlorocarbene (CCl2). This intermediate is crucial as it is highly reactive and can attack the aromatic ring of phenol.

**Hint**: Understand how carbanions can rearrange to form more stable intermediates.

5. **Attack on Phenol**:
The dichlorocarbene (CCl2) acts as an electrophile and attacks the ortho or para position of the phenol, leading to the formation of salicylaldehyde.

**Hint**: Consider the electrophilic aromatic substitution mechanism when thinking about how the carbene interacts with phenol.

6. **Conclusion**:
The reaction intermediate formed during the Reimer-Tiemann reaction is a dichlorocarbene (CCl2).

**Hint**: Remember that the nature of the intermediate is key to understanding the overall reaction mechanism.

### Final Answer:
The reaction intermediate formed in the formation of salicylaldehyde from phenol in the Reimer-Tiemann reaction is **dichlorocarbene (CCl2)**.