Problem 56 - A Complete Resource Book in Chemistry for JEE Main

Question

The reaction of \(\mathrm{CO}_{2}\) with sodium phenoxide at \(400 \mathrm{~K}\) results in the formation of (a) salicyaldehdye (b) sodium benzoate (c) benzoic acid (d) sodium salicylate

Step-by-Step Solution

Answer

The reaction forms sodium salicylate.

Step 1: Understand the Reactants

The reaction involves carbon dioxide \( (\mathrm{CO}_2) \) and sodium phenoxide. Sodium phenoxide is the sodium salt of phenol \( (\mathrm{C_6H_5ONa}) \).

Step 2: Review the Reaction

The reaction described is known as the Kolbe-Schmitt reaction, where \( \mathrm{CO}_2 \) reacts with sodium phenoxide at high temperatures (around 400 K) and under pressure to form a specific type of carboxylated aromatic compound.

Step 3: Determine the Reaction Product

In the Kolbe-Schmitt reaction, when \( \mathrm{CO}_2 \) reacts with sodium phenoxide, it specifically forms sodium salicylate as the main product. The \( \mathrm{CO}_2 \) adds to the ortho position relative to the phenoxide group on the benzene ring.

Key Concepts

Sodium Phenoxide

Sodium phenoxide is an important compound in organic chemistry. It is essentially the sodium salt of phenol, with the chemical formula \( \mathrm{C_6H_5ONa} \). In this compound, the sodium ion (\(\mathrm{Na^+}\)) is bonded to the oxygen of the phenoxide ion \((\mathrm{C_6H_5O^-})\). Sodium phenoxide is a white crystalline solid and, typically, is very reactive.

This reactivity is due to the electron-rich nature of the phenoxide ion, which is stabilized by the resonance within the aromatic benzene ring. This stabilization enhances the nucleophilic properties of the oxygen atom, making sodium phenoxide particularly suitable for electrophilic substitution reactions.

In the Kolbe-Schmitt reaction, sodium phenoxide acts as a nucleophile. It reacts with \(\mathrm{CO_2}\) to form carboxylated products. This reaction is crucial for producing various aromatic compounds with carboxylic acid groups, a functional group integral to many pharmaceuticals and dyes.

Sodium Salicylate

Sodium salicylate is a pivotal product in the Kolbe-Schmitt reaction. Formed when sodium phenoxide reacts with carbon dioxide, sodium salicylate is the sodium salt of salicylic acid. Its chemical formula is \(\mathrm{C_7H_5O_3Na} \).

Here's what happens in the reaction: carbon dioxide attaches to the ortho position (the adjacent carbon atom) on the benzene ring relative to the phenoxide group. This addition results in the formation of an aromatic carboxylate. Sodium salicylate is highly relevant in the pharmaceutical industry as it is a precursor for the production of aspirin (acetylsalicylic acid), a widely used medication for pain and inflammation relief.

As a compound, sodium salicylate also has anti-inflammatory and analgesic properties. It works by inhibiting certain enzymes in the body, reducing inflammation and pain. This makes its production through the Kolbe-Schmitt reaction not only chemically intriguing but also practically important.

Carbon Dioxide

Carbon dioxide (\( \mathrm{CO_2} \)) is a well-known gas in the atmosphere, but it also plays a crucial role in organic chemistry, especially in the Kolbe-Schmitt reaction. In this reaction, carbon dioxide acts as a carbon source to introduce carboxyl groups into aromatic compounds such as the benzene ring.

During the Kolbe-Schmitt reaction with sodium phenoxide, carbon dioxide is introduced at high temperatures and under pressure. The conditions allow \( \mathrm{CO_2} \) to add to the aromatic ring at the ortho position relative to the phenoxide group. This results in the formation of sodium salicylate, a compound with significant pharmaceutical relevance.

Beyond the scope of the Kolbe-Schmitt reaction, \( \mathrm{CO_2} \) is also fundamental in many biological and environmental systems. It is a key player in processes such as photosynthesis and respiration. Furthermore, understanding the behavior of carbon dioxide in chemical reactions aids in developing carbon capture and sequestration technologies, which are vital for mitigating climate change.