Compound 'A' reacts with `PCl_(5)` to given 'B' which on treatment with `KCN` followed by hydrolysis give propanoic acid as the product. What is 'A'?

Options

A. Ethane
B. Propane
C. Ethyl chloride
D. Ethyl alcohol

Answer

To determine compound 'A', let's analyze the information provided step by step.

### Step 1: Understand the Reaction with PCl5
Compound 'A' reacts with PCl5 to form compound 'B'. PCl5 is known to react with alcohols to form alkyl chlorides. Therefore, compound 'A' must be an alcohol.

**Hint:** Remember that PCl5 is commonly used to convert alcohols to alkyl halides.

### Step 2: Identify the Product 'B'
Since 'B' is formed from 'A' and is an alkyl chloride, we can denote it as RCl. The problem states that after treatment with KCN (potassium cyanide), followed by hydrolysis, we obtain propanoic acid.

**Hint:** Consider the structure of propanoic acid (C3H6O2) to deduce the number of carbons in 'B'.

### Step 3: Analyze the Final Product
Propanoic acid has the structure CH3CH2COOH, which indicates it has three carbon atoms. Since 'B' is an alkyl chloride that leads to propanoic acid after reacting with KCN and hydrolysis, it must have two carbon atoms (the third carbon comes from the carboxylic acid group).

**Hint:** Count the number of carbons in propanoic acid to determine how many carbons 'B' should have.

### Step 4: Determine the Structure of 'B'
Given that 'B' must have two carbon atoms, the possible structure for 'B' is ethyl chloride (CH3CH2Cl). This is because when ethyl chloride reacts with KCN, it will replace the chlorine atom with a cyanide group, forming propionitrile (CH3CH2CN).

**Hint:** Think about how alkyl halides react with nucleophiles like KCN.

### Step 5: Reaction of 'B' with KCN
When ethyl chloride (B) reacts with KCN, it forms propionitrile (CH3CH2CN). Upon hydrolysis, propionitrile is converted to propanoic acid (CH3CH2COOH).

**Hint:** Hydrolysis of nitriles typically yields carboxylic acids.

### Step 6: Identify Compound 'A'
Since we established that 'B' is ethyl chloride, we need to find the alcohol 'A' that reacts with PCl5 to yield ethyl chloride. The only alcohol that fits this description and has two carbon atoms is ethanol (CH3CH2OH).

**Hint:** Recall that the alcohol must have the same number of carbon atoms as the alkyl chloride formed.

### Conclusion
Thus, compound 'A' is **ethanol (CH3CH2OH)**.

### Final Answer
**A = Ethanol (C2H5OH)**