Question

Identify $A$ in the following reaction.
$A$ + Acetic anhydride $\xrightarrow{H^+}$ Aspirin + Acetic acid

• A. Acrylic acid
• B. Oxalic acid
• C. Salicylic acid
• D. Phthalic acid

Hint:

Chemistry Tip: The synthesis of Aspirin is a classic laboratory experiment. Always remember the pairing: Salicylic Acid + Acetic Anhydride = Aspirin + Acetic Acid.

Answer 1

The Correct Option is C

Concept: Chemistry (Organic Chemistry) - Synthesis of Aspirin (Acetylation of Phenols).

Step 1: Identify the target product. The target product is Aspirin. The chemical name for Aspirin is acetylsalicylic acid. Its structure consists of a benzene ring with a carboxylic acid group ($-COOH$) and an ester/acetyl group ($-OCOCH_3$) at the ortho position relative to each other.

Step 2: Analyze the reagents used. The reagent used is acetic anhydride in the presence of an acid catalyst ($H^{+}$). Acetic anhydride is a common acetylating agent used to introduce an acetyl group ($-COCH_3$) onto an oxygen or nitrogen atom, typically reacting with alcohols, phenols, or amines.

Step 3: Determine the functional group required in the starting material '$A$'. Since acetic anhydride introduces an acetyl group to form an ester linkage in Aspirin (acetylsalicylic acid), the starting material '$A$' must contain a hydroxyl group ($-OH$) attached to the benzene ring. It must also already contain the carboxylic acid group ($-COOH$).

Step 4: Identify the structure and name of '$A$'. A molecule with a benzene ring containing both a hydroxyl group ($-OH$) and a carboxylic acid group ($-COOH$) at adjacent (ortho) positions is called 2-hydroxybenzoic acid. The common and widely used name for this specific compound is Salicylic acid.

Step 5: Write the complete chemical equation to verify the reaction. The complete reaction is the acetylation of the phenolic hydroxyl group in salicylic acid.
Reaction: $C_6H_4(OH)(COOH) + (CH_3CO)_2O \xrightarrow{H^+} C_6H_4(OCOCH_3)(COOH) + CH_3COOH$. In words: Salicylic acid + Acetic anhydride $\xrightarrow{H^+}$ Acetylsalicylic acid (Aspirin) + Acetic acid. This perfectly matches the given reaction scheme, confirming that '$A$' is indeed Salicylic acid. $$ \therefore \text{The compound 'A' is Salicylic acid.} $$