Which of the following reagents converts `C_(6)H_(5)COCHO` to `C_(6)H_(5)CHOHCOOH`?

Options

A. Aq. NaOH
B. Acidic `Na_(2)SO_(3)`
C. `Na_(2)CrO_(4)//H_(2)SO_(4)`
D. `NaNO_(2)//HCl`.

Explanation

To convert `C6H5COCHO` (benzaldehyde) to `C6H5CHOHCOOH` (hydroxybenzoic acid), we can utilize the Canizzaro reaction, which requires a strong base as a reagent. Here’s a step-by-step solution:

### Step 1: Identify the Reactants and Products
- **Reactant:** C6H5COCHO (Benzaldehyde)
- **Product:** C6H5CHOHCOOH (Hydroxybenzoic acid)

### Step 2: Understand the Reaction Type
This transformation can be classified under the Canizzaro reaction, which involves the disproportionation of aldehydes in the presence of a strong base.

### Step 3: Choose the Appropriate Reagent
The reagent required for the Canizzaro reaction is a strong base. The suitable choice here is **aqueous NaOH**.

### Step 4: Mechanism of the Reaction
1. **Nucleophilic Attack:** The hydroxide ion (OH-) from NaOH attacks the carbonyl carbon of the aldehyde (C=O), resulting in the formation of a tetrahedral intermediate.
2. **Hydride Shift:** A hydride ion (H-) is transferred from one aldehyde molecule to another, leading to the formation of an alcohol and a carboxylic acid.
3. **Protonation:** The alkoxide ion formed is then protonated to yield the final product, hydroxybenzoic acid.

### Step 5: Final Product Formation
After the reaction with HCl (to protonate the alkoxide), the final product `C6H5CHOHCOOH` is obtained.

### Conclusion
The reagent that converts `C6H5COCHO` to `C6H5CHOHCOOH` is **aqueous NaOH**.