Cyanohydrin of which of the following forms lactic acid

Options

A. `CH_3CH_2CHO`
B. `CH_3CHO`
C. HCHO
D. `CH_3COCH_3`

Answer

To determine which cyanohydrin forms lactic acid, we will analyze the given options step by step.

### Step 1: Identify the Cyanohydrins
We have the following options:
1. Propanaldehyde (CH3CH2CHO)
2. Acetaldehyde (CH3CHO)
3. Formaldehyde (HCHO)
4. Acetone (CH3COCH3)

### Step 2: Understand Cyanohydrin Formation
Cyanohydrins are formed when a carbonyl compound (aldehyde or ketone) reacts with hydrogen cyanide (HCN). The reaction adds a cyanide group (-CN) and a hydroxyl group (-OH) to the carbonyl carbon.

### Step 3: Analyze Each Compound
1. **Propanaldehyde (CH3CH2CHO)**:
- Forms a cyanohydrin: CH3CH2C(CN)(OH).
- Hydrolysis does not yield lactic acid.

2. **Acetaldehyde (CH3CHO)**:
- Forms a cyanohydrin: CH3C(CN)(OH).
- Upon hydrolysis, this cyanohydrin can convert to lactic acid (CH3C(OH)COOH).

3. **Formaldehyde (HCHO)**:
- Forms a cyanohydrin: H2C(CN)(OH).
- Hydrolysis does not yield lactic acid.

4. **Acetone (CH3COCH3)**:
- Forms a cyanohydrin: CH3C(CN)(OH)CH3.
- Hydrolysis does not yield lactic acid.

### Step 4: Conclusion
The only compound that, upon formation of its cyanohydrin and subsequent hydrolysis, yields lactic acid is **Acetaldehyde (CH3CHO)**.

Thus, the correct answer is **Option B: CH3CHO (Acetaldehyde)**.

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