Reimer -Tiemann reaction involves a

Options

A. Carbonium ion intermediate
B. Carbene intermediate
C. Carbanion intermediate
D. Free radical intermediate

Answer

### Step-by-Step Solution:

1. **Understanding the Reaction**: The Reimer-Tiemann reaction involves the reaction of phenol with chloroform (CHCl₃) in the presence of a strong base, typically sodium hydroxide (NaOH) or potassium hydroxide (KOH). This reaction leads to the formation of salicylaldehyde.

2. **Initial Setup**: Begin with phenol (C₆H₅OH) and add it to a solution of a strong base (NaOH or KOH) along with chloroform (CHCl₃). The base deprotonates the phenol, forming a phenoxide ion (C₆H₅O⁻).

3. **Formation of Carbene**: The chloroform reacts with the hydroxide ion to produce a carbene intermediate. The chlorine atoms in chloroform are electron-withdrawing, making the carbon atom more electrophilic. The hydroxide ion attacks the carbon of chloroform, leading to the release of chloride ions and the formation of a carbene (C=CH₂).

4. **Nucleophilic Attack**: The phenoxide ion, which is now negatively charged, acts as a nucleophile and attacks the carbene. This results in the formation of a new carbon-carbon bond.

5. **Formation of Salicylaldehyde**: After the nucleophilic attack, rearrangements occur, and water is eliminated from the intermediate. This leads to the formation of salicylaldehyde (C₇H₆O₂), which contains both a hydroxyl group (OH) and an aldehyde group (CHO) on adjacent carbon atoms.

6. **Conclusion**: The Reimer-Tiemann reaction involves the formation of a carbene intermediate, which is crucial for the reaction mechanism.

### Final Answer:
The Reimer-Tiemann reaction involves a **carbene intermediate**.

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