Ethane can be prepared from ethanal in one step by the use of

Options

A. zinc amalgam and conc. HCl
B. amalgamated zinc and hydrochloric acid (or red P and Hl)
C. lithium aluminium hydride in ether
D. none of the above

Answer

To prepare ethane from ethanal in one step, we can use specific reagents that facilitate the reduction of the carbonyl group in ethanal (acetaldehyde) to a methylene group, resulting in ethane. Here’s how we can approach the solution step by step:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant we have is ethanal (CH₃CHO), which is an aldehyde.
- The product we want to prepare is ethane (C₂H₆).

2. **Understand the Reaction Type**:
- To convert an aldehyde to an alkane, we need to perform a reduction reaction. This involves the addition of hydrogen or the removal of the oxygen.

3. **Select the Reagents**:
- The question provides options for reagents that can achieve this transformation.
- The two effective reagents for this conversion are:
- **Zinc amalgam (Zn/Hg) with concentrated hydrochloric acid (HCl)**: This combination is known for reducing carbonyl compounds to alkanes.
- **Amalgamated zinc and hydrochloric acid**: This is essentially the same as the first option and also facilitates the reduction.

4. **Write the Reaction**:
- When ethanal reacts with zinc amalgam and concentrated HCl, the carbonyl group (C=O) is reduced to a methylene group (–CH₂–), resulting in ethane:
\[ \text{CH}_3\text{CHO} + \text{Zn/Hg} + \text{HCl} \rightarrow \text{C}_2\text{H}_6 \]

5. **Evaluate Other Options**:
- **Lithium aluminium hydride (LiAlH₄) in ether**: This reagent reduces aldehydes to alcohols, not to alkanes, so it is not suitable for this reaction.
- **Red phosphorus and HI**: This combination can also reduce carbonyl compounds to alkanes, similar to zinc amalgam and HCl.

6. **Conclusion**:
- The correct reagents that can convert ethanal to ethane in one step are:
- Zinc amalgam and concentrated HCl
- Amalgamated zinc and hydrochloric acid
- Therefore, the answer is that ethane can be prepared from ethanal using either of these reagents.

### Final Answer:
Ethane can be prepared from ethanal in one step by the use of:
- Zinc amalgam and concentrated HCl
- Amalgamated zinc and hydrochloric acid