Which of the following reagents cannot be used for the oxidation
of `1^(@)` alcohol to aldehyde?

Options

A. PCC
B. Collin's reagent
C. `MnO_(2)`
D. `KMnO_(4)`

Explanation

To determine which reagent cannot be used for the oxidation of a primary alcohol to an aldehyde, we will analyze the given reagents one by one.

### Step-by-Step Solution:

1. **Identify the Reagents**: The reagents mentioned in the question are PCC, Collins reagent, MnO2, and KMnO4.

2. **PCC (Pyridinium Chlorochromate)**:
- PCC is known for its ability to oxidize primary alcohols to aldehydes.
- It works effectively in the presence of CH2Cl2 (dichloromethane).
- **Conclusion**: PCC can be used for the oxidation of primary alcohols to aldehydes.

3. **Collins Reagent**:
- Collins reagent consists of chromium trioxide (CrO3) and pyridine, and it is also effective in oxidizing primary alcohols to aldehydes.
- **Conclusion**: Collins reagent can be used for the oxidation of primary alcohols to aldehydes.

4. **MnO2 (Manganese Dioxide)**:
- MnO2 is another reagent that can oxidize primary alcohols to aldehydes.
- **Conclusion**: MnO2 can be used for the oxidation of primary alcohols to aldehydes.

5. **KMnO4 (Potassium Permanganate)**:
- KMnO4 is a strong oxidizing agent that typically oxidizes primary alcohols to carboxylic acids rather than aldehydes.
- While it can oxidize secondary alcohols to ketones, it does not selectively oxidize primary alcohols to aldehydes.
- **Conclusion**: KMnO4 cannot be used for the oxidation of primary alcohols to aldehydes.

### Final Answer:
The reagent that cannot be used for the oxidation of a primary alcohol to an aldehyde is **KMnO4**.

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