Which of the following with aqueous KOH will give acetaldehyde ?

Options

A. 1,2 -dichloroethane
B. 1,1- dichloroethane
C. Chloroacetic acid
D. Ethyl chloride

Answer

To determine which compound will yield acetaldehyde when treated with aqueous KOH, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- Aqueous KOH provides hydroxide ions (OH⁻) that can act as nucleophiles. This means they can replace halogen atoms (like Cl) in haloalkanes through a nucleophilic substitution reaction.

2. **Analyzing Each Option**:
- **Option A: 1,2-Dichloroethane (Cl-CH2-CH2-Cl)**:
- When treated with aqueous KOH, both Cl atoms can be replaced by OH⁻ ions.
- The reaction would yield 1,2-ethanediol (a diol), not acetaldehyde.
- **Conclusion**: This option does not produce acetaldehyde.

- **Option B: 1,1-Dichloroethane (CH3-CH(Cl)-Cl)**:
- When treated with aqueous KOH, the two Cl atoms can be replaced by OH⁻ ions.
- The intermediate formed is a geminal diol (CH3-CH(OH)2), which is unstable and can lose a water molecule.
- The elimination of water leads to the formation of acetaldehyde (CH3CHO).
- **Conclusion**: This option produces acetaldehyde.

- **Option C: Chloroacetic Acid (Cl-CH2-COOH)**:
- When treated with aqueous KOH, the Cl atom is replaced by OH⁻, resulting in hydroxyacetic acid (HO-CH2-COOH).
- This does not lead to the formation of acetaldehyde.
- **Conclusion**: This option does not produce acetaldehyde.

- **Option D: Ethyl Chloride (CH3-CH2-Cl)**:
- When treated with aqueous KOH, the Cl atom is replaced by OH⁻, yielding ethanol (CH3-CH2-OH).
- This does not lead to the formation of acetaldehyde.
- **Conclusion**: This option does not produce acetaldehyde.

3. **Final Answer**:
- Among the given options, only **Option B: 1,1-Dichloroethane** will yield acetaldehyde when treated with aqueous KOH.

### Summary:
The correct answer is **Option B: 1,1-Dichloroethane**.