An aliphatic carboxylic acid of moleuclar formula `C_(2)H_(4)O_(2)` on reaction with `PCl_(5)` gives a compound Y. Y when heated with sodium salt of the acid produces-

Options

A. Ethyl acetate
B. Ethyl acetoacetate
C. Methyl methanoate
D. Ethanoic anhydride

Answer

To solve the problem step by step, we will identify the aliphatic carboxylic acid, its reaction with PCl5, and the subsequent reaction with the sodium salt of the acid.

### Step 1: Identify the Aliphatic Carboxylic Acid
The molecular formula given is C2H4O2. The simplest aliphatic carboxylic acid with this formula is acetic acid (ethanoic acid), which has the structure CH3COOH.

### Step 2: Reaction with PCl5
When acetic acid (CH3COOH) reacts with phosphorus pentachloride (PCl5), it undergoes chlorination to form acetyl chloride (compound Y). The reaction can be represented as follows:

\[ \text{CH}_3\text{COOH} + \text{PCl}_5 \rightarrow \text{CH}_3\text{COCl} + \text{POCl}_3 + \text{HCl} \]

Here, CH3COCl is the compound Y.

### Step 3: Reaction of Compound Y with Sodium Salt of the Acid
The sodium salt of acetic acid is sodium acetate, which can be represented as CH3COO^- Na^+. When acetyl chloride (CH3COCl) reacts with sodium acetate, a nucleophilic substitution occurs. The acetate ion (CH3COO^-) acts as a nucleophile and attacks the electrophilic carbon in acetyl chloride, leading to the formation of ethanoic anhydride.

The reaction can be represented as follows:

\[ \text{CH}_3\text{COCl} + \text{CH}_3\text{COO}^- \text{Na}^+ \rightarrow \text{CH}_3\text{COO}-\text{C}(=O)-\text{CH}_3 + \text{NaCl} \]

### Step 4: Identify the Product
The product formed from the reaction of acetyl chloride with sodium acetate is ethanoic anhydride, which has the structure:

\[ \text{(CH}_3\text{CO)}_2\text{O} \]

### Final Answer
The compound produced when Y (acetyl chloride) is heated with the sodium salt of the acid (sodium acetate) is ethanoic anhydride.

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