`RCOOH to RCH_(2)COOH`. This conversion is known as reaction:

Options

A. Arndt-Eistert reaction
B. Hundsicker reaction
C. HVZ reaction
D. Cannizaro reaction

Answer

To convert a carboxylic acid (RCOOH) into a β-hydroxy carboxylic acid (RCH₂COOH), we employ a specific reaction known as the **Iron Ester Reaction**. Here’s a step-by-step breakdown of the process:

### Step-by-Step Solution:

1. **Starting Material**: Begin with a carboxylic acid (RCOOH). This compound contains a carbonyl group (C=O) and a hydroxyl group (–OH).

**Hint**: Identify the functional groups present in the starting material.

2. **Formation of Diazoketone**: Treat the carboxylic acid with diazomethane. This results in the formation of a diazoketone intermediate. The diazomethane reacts with the carbonyl carbon of the carboxylic acid, leading to the formation of a new compound.

**Hint**: Recall the role of diazomethane in organic reactions, particularly in forming intermediates.

3. **Rearrangement**: The diazoketone undergoes rearrangement upon exposure to moist silver oxide or silver benzoate and trimethylamine. This rearrangement is crucial as it facilitates the addition of an extra carbon atom to the structure.

**Hint**: Understand the significance of the reagents used in this step and how they promote rearrangement.

4. **Formation of Acyl Carbene**: In the presence of heat, the diazoketone loses nitrogen gas (N₂), forming an acyl carbene intermediate. This intermediate is highly reactive and can undergo further transformations.

**Hint**: Consider the stability and reactivity of carbenes and how they can lead to new products.

5. **Hydrolysis**: Finally, the acyl carbene is hydrolyzed in the presence of water (H₂O), resulting in the formation of the desired β-hydroxy carboxylic acid (RCH₂COOH), which now contains an additional carbon atom compared to the starting carboxylic acid.

**Hint**: Remember the role of hydrolysis in converting reactive intermediates into stable products.

### Conclusion:
The conversion of RCOOH to RCH₂COOH is known as the **Iron Ester Reaction**. This reaction effectively adds a carbon atom to the carboxylic acid, transforming it into a β-hydroxy carboxylic acid.