Problem 7 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Phenol on treatment with \(\mathrm{CO}_{2}\) in the presence of \(\mathrm{NaOH}\) followed by acidification produces compound \(X\) as the major product. \(X\) on treatment with \(\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}\) in the presence of catalytic amount of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) produces :

Step-by-Step Solution

Answer

Aspirin is formed.

Step 1: Understanding the Initial Reaction

The initial reaction involves phenol reacting with carbon dioxide \((\mathrm{CO}_{2})\) and sodium hydroxide \((\mathrm{NaOH})\). This setup is known as the Kolbe-Schmitt reaction, which synthesizes salicylic acid from phenol. In this process, phenol deprotonates to form phenoxide ion, which then undergoes carboxylation with \(\mathrm{CO}_{2}\) to form the sodium salt of salicylic acid. Acidification converts this salt to salicylic acid, which we will refer to as compound \(X\).

Step 2: Identifying the Major Product of Initial Reaction

After realizing that the Kolbe-Schmitt reaction is involved, we identify that the major product \(X\) from treating phenol with \(\mathrm{CO}_{2}\) and \(\mathrm{NaOH}\) followed by acidification is salicylic acid (2-hydroxybenzoic acid).

Step 3: Reacting Compound X with Acetic Anhydride

Next, compound \(X\) (salicylic acid) is treated with acetic anhydride \((\mathrm{(CH_{3}CO)_{2}O})\) in the presence of sulfuric acid \((\mathrm{H}_{2} \mathrm{SO}_{4})\) as a catalyst. This reaction is an acetylation where the hydroxyl group \((-OH)\) of salicylic acid reacts with acetic anhydride to form acetylsalicylic acid, commonly known as aspirin.

Step 4: Identifying the Final Product

The treatment of salicylic acid with acetic anhydride and a catalytic amount of sulfuric acid will lead to the formation of aspirin. This process acetylates the hydroxyl group of salicylic acid.

Key Concepts

Phenol

Phenol, a simple aromatic organic compound, is known for its slightly sweet odor and is colorless to white in its pure form. It is a crucial starting material in various chemical reactions due to its reactive hydroxyl group (-OH). Phenol has a structure consisting of a hydroxyl group bonded to a benzene ring, making it part of the alcohol family.

In the Kolbe-Schmitt reaction, phenol is used to produce salicylic acid. Initially, phenol undergoes deprotonation in the presence of a strong base such as sodium hydroxide ( ext{NaOH} ), which transforms it into a phenoxide ion. This ion is more reactive and can easily react with carbon dioxide ( ext{CO}_{2} ).

• The phenoxide ion reacts with ext{CO}_{2} to form an intermediate carboxylate.
• Upon acidification, this intermediate is converted to salicylic acid, demonstrating phenol's ability to form complex products through simple reactions.

Salicylic Acid

Salicylic acid, also known as 2-hydroxybenzoic acid, is a vital compound in pharmaceutical chemistry for its role in synthesizing aspirin and other drugs. It is characterized by both a carboxyl group (-COOH) and a hydroxyl group (-OH) attached to a benzene ring.

In the chemical process known as the Kolbe-Schmitt reaction, salicylic acid is synthesized from phenol. The sodium salt form of salicylic acid is produced when phenol reacts with ext{CO}_{2} in the presence of ext{NaOH} .

• This sodium salt is then acidified to yield salicylic acid, marking the completion of the carboxylation of phenol.
• The central importance of salicylic acid in these reactions highlights its key position in forming more complex aromatic compounds.

Acetylation

Acetylation is a crucial chemical reaction where an acetyl group ( ext{CH}_3 ext{CO}- ) is introduced into an organic compound. This process is fundamental in modifying the properties and functionality of various molecules.

In the context of salicylic acid, acetylation is the reaction where acetic anhydride ( ext{CH}_3 ext{CO})_2 ext{O} oxygen) is used, often with a catalyst such as sulfuric acid ( ext{H}_2 ext{SO}_4 ).

• During acetylation, the hydroxyl group (-OH) in salicylic acid reacts with the acetyl group from acetic anhydride.
• This reaction produces acetylsalicylic acid, commonly known as aspirin, a widely used analgesic and anti-inflammatory drug.
• The presence of a catalyst, like ext{H}_2 ext{SO}_4 , speeds up the reaction, ensuring that the hydroxyl group is efficiently acetylated to form the desired product.

Acetylation not only changes the chemical structure but also alters the biological properties and pharmaceutical profile of such compounds, demonstrating its importance in pharmaceutical chemistry.