Which method cannot be employed for production of an alkane?

Options

A. Heating sodium salts of carboxylic acids with soda lime
B. Treating alkyl halides with Na in ethereal solution.
C. Electrolysis of aqueous solution of sodium or potassium salt of carboxylic acid
D. Dehydrohalogenation of alkyl halides .

Answer

To determine which method cannot be employed for the production of an alkane, we will analyze the four options provided:

1. **Heating sodium salts of carboxylic acids with soda lime**:
- When sodium salts of carboxylic acids (like sodium acetate) are heated with soda lime (a mixture of NaOH and CaO), they undergo decarboxylation to produce alkanes. For example:
\[ \text{CH}_3\text{COONa} + \text{NaOH} \xrightarrow{\Delta} \text{CH}_4 + \text{Na}_2\text{CO}_3 \]
- This method does produce alkanes, so it cannot be the correct answer.

2. **Treating alkyl halides with sodium in ethereal solution**:
- This method is known as the Wurtz reaction. When alkyl halides (like bromoethane) are treated with sodium in dry ether, they couple to form alkanes:
\[ 2 \text{CH}_3\text{Br} + 2 \text{Na} \xrightarrow{\text{dry ether}} \text{C}_2\text{H}_6 + 2 \text{NaBr} \]
- Since this method produces alkanes, it is also not the correct answer.

3. **Electrolysis of aqueous solution of sodium or potassium salt of carboxylic acid**:
- Electrolysis of sodium acetate, for example, can produce alkanes:
\[ 2 \text{CH}_3\text{COONa} + 2 \text{H}_2\text{O} \xrightarrow{\text{electrolysis}} \text{C}_2\text{H}_6 + 2 \text{CO}_2 + 2 \text{NaOH} + \text{H}_2 \]
- This method also produces alkanes, ruling it out as the correct answer.

4. **Dehydrohalogenation of alkyl halides**:
- In this method, alkyl halides are treated with a strong base (like alcoholic KOH) to eliminate HX (a hydrogen halide) and form alkenes:
\[ \text{CH}_3\text{CH}_2\text{X} + \text{KOH (alc)} \rightarrow \text{CH}_2=\text{CH}_2 + \text{HX} \]
- This reaction results in the formation of alkenes, not alkanes.

**Conclusion**:
The method that cannot be employed for the production of an alkane is **dehydrohalogenation of alkyl halides** (Option 4).

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