An organic compound ‘A’ on treatment with KCN gave B which on hydrolysis with dil. HCl gave acetic acid. Identify A.

Answer

To solve the problem, we need to identify the organic compound 'A' based on the reactions described. Let's break down the steps:

### Step 1: Understanding the Reaction
The compound 'A' reacts with KCN (potassium cyanide), which provides a cyanide ion (CN⁻) that acts as a nucleophile. This suggests that 'A' is likely a haloalkane, where a halogen atom (X) is replaced by the cyanide group.

### Step 2: Identifying Product B
When 'A' reacts with KCN, it forms product 'B'. The reaction can be represented as:
\[ R-X + KCN \rightarrow R-CN + KX \]
Here, R represents the alkyl group, and X is the halogen (which could be Cl, Br, or I).

### Step 3: Hydrolysis of Product B
Product 'B' (R-CN) undergoes hydrolysis in the presence of dilute HCl to yield acetic acid (CH₃COOH). The hydrolysis of a nitrile (R-CN) typically produces a carboxylic acid (RCOOH):
\[ R-CN + H_2O \xrightarrow{HCl} RCOOH + NH₃ \]

### Step 4: Determining the Structure of A
Since the final product after hydrolysis is acetic acid (CH₃COOH), we can deduce that R must be CH₃ (methyl group). Therefore, the structure of 'B' is CH₃CN (methyl cyanide).

To find 'A', we consider the nucleophilic substitution reaction:
\[ CH₃X + KCN \rightarrow CH₃CN + KX \]
If 'B' is CH₃CN, then 'A' must be CH₃Cl (methyl chloride), since the chlorine atom is the leaving group.

### Conclusion
The organic compound 'A' is identified as:
\[ \text{A} = \text{CH}_3\text{Cl} \]

### Summary of Steps:
1. Identify that 'A' is a haloalkane reacting with KCN.
2. Recognize that product 'B' is a nitrile formed from 'A'.
3. Understand that hydrolysis of 'B' yields acetic acid.
4. Conclude that 'A' is CH₃Cl based on the final product.