The best method for the conversion of ethanol to ethanal is-

Options

A. By passing ethanol vapours over Cu at 578 K
B. By oxidation with acidic potassium dichromate
C. By oxidation with mangenese dioxide at 300ºC
D. By oxidation with acidic KMnO4

Answer

To convert ethanol (C2H5OH) to ethanal (CH3CHO), we need to perform an oxidation reaction. Here’s a step-by-step solution to identify the best method for this conversion:

### Step 1: Understand the Reaction
Ethanol is a primary alcohol, and to convert it to ethanal, we need to oxidize it. The oxidation of primary alcohols typically results in the formation of aldehydes.

**Hint:** Identify the functional groups involved in the conversion and their oxidation states.

### Step 2: Identify Suitable Oxidizing Agents
When choosing an oxidizing agent, it is important to select one that will oxidize ethanol to ethanal without further oxidizing it to a carboxylic acid.

**Hint:** Consider the strength of the oxidizing agent; strong oxidizers can lead to over-oxidation.

### Step 3: Evaluate Different Methods
1. **Passing Ethanol Vapors Over Copper at 573-578 K:**
- This method involves heating ethanol vapors over copper, which acts as a catalyst. At this temperature, ethanol is selectively oxidized to ethanal.
- **Product:** Ethanal (CH3CHO)

2. **Oxidation with Potassium Dichromate (K2Cr2O7):**
- This is a strong oxidizing agent that would oxidize ethanol all the way to acetic acid (a carboxylic acid).
- **Product:** Acetic acid (CH3COOH), not ethanal.

3. **Oxidation with Manganese Dioxide (MnO2):**
- While MnO2 is a mild oxidizing agent, the reaction mechanism can be complex, and it may not be the most efficient for this conversion.
- **Product:** Aldehyde, but the process is not straightforward.

4. **Oxidation with Potassium Permanganate (KMnO4):**
- KMnO4 is also a strong oxidizing agent and would lead to the formation of carboxylic acids.
- **Product:** Acetic acid, not ethanal.

**Hint:** Compare the products formed from each method to determine which one yields ethanal directly.

### Step 4: Conclusion
The best method for the conversion of ethanol to ethanal is by passing ethanol vapors over copper at a temperature of 573-578 K. This method selectively oxidizes ethanol to ethanal without further oxidation to acetic acid.

**Final Answer:** The best method for the conversion of ethanol to ethanal is passing ethanol vapors over copper at 573-578 K.