Question

Ortho hydroxy benzoic acid + Ac2O/pyridine

Answer 1

Acetylsalicylic acid

Answer 2

The reaction involves the acetylation of ortho-hydroxybenzoic acid (salicylic acid) with acetic anhydride in the presence of pyridine.

1. Reactants:

   • Ortho-hydroxybenzoic acid (Salicylic acid): It contains a phenolic hydroxyl group (-OH) and a carboxylic acid group (-COOH).

   • Acetic anhydride ($\text{Ac}_2\text{O}$): An acetylating agent.

   • Pyridine: Acts as a base catalyst, facilitating the reaction by activating the anhydride and deprotonating the hydroxyl group.

2. Reaction Type:

   This is an esterification reaction, specifically an acetylation. The phenolic hydroxyl group is more reactive towards acetylation than the carboxylic acid group under these conditions.

3. Mechanism (Simplified):

   The phenolic -OH group of salicylic acid acts as a nucleophile and attacks the carbonyl carbon of acetic anhydride. The pyridine helps in deprotonating the phenolic -OH, making it a stronger nucleophile, and also activates the acetic anhydride. An acetate group ($\text{CH}_3\text{COO}^-$) is eliminated, and an ester linkage is formed. The carboxylic acid group remains unaffected.

4. Product:

   The product formed is acetylsalicylic acid, commonly known as Aspirin.

Chemical Equation:

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Ortho-hydroxybenzoic acid (Salicylic acid) + Acetic anhydride $\xrightarrow{\text{Pyridine}}$ Acetylsalicylic acid (Aspirin) + Acetic acid

Structures:

• Ortho-hydroxybenzoic acid (Salicylic acid):

• Acetic anhydride:

• Acetylsalicylic acid (Aspirin):

The product is Acetylsalicylic acid (Aspirin).

Explanation of the solution:

Ortho-hydroxybenzoic acid (salicylic acid) has a phenolic -OH group and a carboxylic -COOH group. Acetic anhydride is an acetylating agent. In the presence of pyridine, the phenolic -OH group undergoes acetylation to form an ester, while the carboxylic acid group remains unreacted. This yields acetylsalicylic acid (Aspirin).