The electophile involved in Reimer-Tiemann reaction is :

Question

Accepted Answer

The Reimer-Tiemann reaction is a chemical reaction used to convert phenols into ortho-formyl phenols using chloroform and a strong base, typically sodium hydroxide. The key to understanding this reaction lies in identifying the electrophile that facilitates the transformation.

1. **Explanation for Option 2 (:CCl₂) as the Correct Answer:**

In the Reimer-Tiemann reaction, the electrophile involved is dichlorocarbene (:CCl₂). This electrophile is generated in situ from chloroform (CHCl₃) in the presence of a strong base like NaOH. The base deprotonates chloroform, leading to the formation of the trichloromethide anion (CCl₃⁻), which then loses a chloride ion to form the neutral, highly reactive dichlorocarbene (:CCl₂). This carbene acts as the electrophile that attacks the phenol, leading to the formation of the ortho-formylated product. Thus, Option 2 is correct because :CCl₂ is the electrophile responsible for the reaction.

2. **Explanation for Why the Other Options are Incorrect:**

- **Option 1 ($CH_{3}^{+}$):** The methyl cation ($CH_{3}^{+}$) is a carbocation and not involved in the Reimer-Tiemann reaction. This reaction specifically requires the formation of a carbene, not a carbocation, to proceed. Therefore, $CH_{3}^{+}$ is not the electrophile in this context.

- **Option 3 ($Cl^{-}$):** The chloride ion ($Cl^{-}$) is a nucleophile, not an electrophile. In the Reimer-Tiemann reaction, the role of the electrophile is crucial, and $Cl^{-}$ does not fulfill this role. Instead, it is involved in the generation of the dichlorocarbene but does not act as the electrophile itself.

- **Option 4 ($OH^{-}$):** The hydroxide ion ($OH^{-}$) is a strong base and acts as a nucleophile in many reactions. In the Reimer-Tiemann reaction, it is used to deprotonate chloroform to generate the dichlorocarbene, but it is not the electrophile. Its role is to facilitate the formation of the actual electrophile, :CCl₂.

In conclusion, the correct electrophile in the Reimer-Tiemann reaction is :CCl₂, making Option 2 the correct choice. The other options do not fit the role of the electrophile in this specific reaction mechanism.