Phenol can be converted to o-hydroxy-benzaldehyde by :

Options

A. Kolbe reaction
B. Reimer - Tiemann reaction
C. Wurta reaction
D. Sandmeyer's reaction

Explanation

To convert phenol to ortho-hydroxy-benzaldehyde, we can follow these steps:

### Step 1: Identify the Reactants
We start with phenol, which is a benzene ring with a hydroxyl group (-OH) attached. We need to convert this into ortho-hydroxy-benzaldehyde, which has an aldehyde group (-CHO) at the ortho position relative to the hydroxyl group.

### Step 2: Choose the Correct Reaction
The reaction that facilitates this conversion is the Riemann-Tiemann reaction. This reaction involves treating phenol with chloroform (CHCl3) in the presence of a strong base, such as aqueous sodium hydroxide (NaOH) or potassium hydroxide (KOH).

### Step 3: Set Up the Reaction Conditions
The reaction is typically carried out at around 70 degrees Celsius. Under these conditions, phenol reacts with chloroform and the base.

### Step 4: Mechanism of the Reaction
1. **Formation of Intermediates**: The base deprotonates phenol, generating a phenoxide ion, which then reacts with chloroform to form an intermediate.
2. **Elimination of By-products**: During the reaction, sodium chloride (NaCl) and water (H2O) are eliminated as by-products.
3. **Formation of the Aldehyde**: After further reactions and hydrolysis, the aldehyde group is introduced at the ortho position of the benzene ring.

### Step 5: Final Product
The final product of this reaction is ortho-hydroxy-benzaldehyde, also known as salicylaldehyde.

### Conclusion
Thus, the conversion of phenol to ortho-hydroxy-benzaldehyde is achieved through the Riemann-Tiemann reaction.