`CH_(3)CHO+H_(2)NOH to CH_(3)-CH=N-OH`
the above reaction occurs at

Options

A. `pH=1-2`
B. `pH=3-4`
C. `any range of pH
D. pH=12-14

Answer

To determine the pH at which the reaction between acetaldehyde (CH₃CHO) and hydroxylamine (H₂NOH) occurs to form the product CH₃-CH=N-OH, we can analyze the reaction mechanism and the role of pH in this context.

### Step-by-Step Solution:

1. **Identify Reactants and Products**:
- The reactants are acetaldehyde (CH₃CHO) and hydroxylamine (H₂NOH).
- The product formed is CH₃-CH=N-OH.

2. **Understand the Reaction Mechanism**:
- The reaction involves the nucleophilic attack of the nitrogen atom in hydroxylamine on the carbonyl carbon of acetaldehyde.
- The lone pair of electrons on the nitrogen atom attacks the electrophilic carbon atom of the carbonyl group (C=O).

3. **Formation of the Intermediate**:
- After the nucleophilic attack, an intermediate is formed where the nitrogen is bonded to the carbon, and the oxygen is protonated, leading to a positive charge on the nitrogen.

4. **Proton Transfer**:
- An intermolecular proton transfer occurs, where a proton from the hydroxyl group (OH) is transferred to the nitrogen, stabilizing the intermediate.

5. **Elimination of Water**:
- The intermediate then loses a water molecule (H₂O) through a condensation reaction, resulting in the formation of the double bond between carbon and nitrogen, yielding the final product CH₃-CH=N-OH.

6. **Effect of pH on the Reaction**:
- At low pH (acidic conditions), the nucleophile (hydroxylamine) can become protonated, which reduces its nucleophilicity and inhibits the reaction.
- At high pH (basic conditions), there may not be enough acidic protons available to facilitate the reaction, as the hydroxylamine can also lose a proton.
- Therefore, the optimal pH for this reaction is around neutral to slightly acidic (pH 3 to 4), where the nucleophile is not protonated and can effectively attack the carbonyl carbon.

### Conclusion:
The reaction occurs best at a pH range of approximately 3 to 4.