Question

Which reaction is used to prepare 2-hydroxy benzaldehyde from phenol?

• A. Reimer-Tiemann reaction
• B. Kolbe's reaction
• C. Williamson synthesis
• D. Etard's reaction

Hint:

Remember: Reimer-Tiemann reaction is used for formylation of phenol, while Kolbe's reaction is used for carboxylation of phenol.

Answer 1

The Correct Option is A

Step 1: Understanding the target compound.
2-hydroxy benzaldehyde is commonly known as salicylaldehyde. It contains a benzene ring having both a hydroxyl group \(\mathrm{(-OH)}\) and an aldehyde group \(\mathrm{(-CHO)}\) at the ortho position with respect to each other. Since the starting compound is phenol, we need a reaction that introduces a formyl group \(\mathrm{(-CHO)}\) into the aromatic ring of phenol.
Step 2: Identify the correct named reaction.
The Reimer-Tiemann reaction is the specific reaction used for the formylation of phenol in the presence of chloroform and alkali. In this reaction, phenol gives mainly ortho-hydroxy benzaldehyde, that is, 2-hydroxy benzaldehyde or salicylaldehyde. Therefore, this reaction exactly matches the preparation asked in the question.
Step 3: Comparison with the other options.

• (A) Reimer-Tiemann reaction: Correct. It introduces the \(\mathrm{-CHO}\) group into phenol and gives 2-hydroxy benzaldehyde as the major product.
• (B) Kolbe's reaction: Incorrect. Kolbe's reaction introduces a carboxyl group \(\mathrm{(-COOH)}\) into phenol to form salicylic acid, not an aldehyde.
• (C) Williamson synthesis: Incorrect. Williamson synthesis is used for the preparation of ethers, not aldehydes from phenol.
• (D) Etard's reaction: Incorrect. Etard's reaction is used to convert a side-chain methyl group on an aromatic ring into an aldehyde group, such as toluene to benzaldehyde.

Step 4: Conclusion.
Hence, the reaction used to prepare 2-hydroxy benzaldehyde from phenol is the Reimer-Tiemann reaction.
Final Answer:Reimer-Tiemann reaction.