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 (d) sodium salicylate.

Step 1: Identify the Reaction

The reaction involves carbon dioxide \(\mathrm{CO}_2\) and sodium phenoxide. This reaction is a well-known process called Kolbe-Schmitt reaction.

Step 2: Recall the Kolbe-Schmitt Reaction

The Kolbe-Schmitt reaction is a chemical process that converts phenols to hydroxy acids. In this reaction, sodium phenoxide reacts with \(\mathrm{CO}_2\) at high temperatures, typically around 400 K.

Step 3: Predict the Product

The product of the Kolbe-Schmitt reaction involving sodium phenoxide and \(\mathrm{CO}_2\) is sodium salicylate, due to carboxylation at the ortho position of the phenoxide ion.

Step 4: Verify the Options

Among the given options, (d) sodium salicylate is the product obtained from the reaction between \(\mathrm{CO}_2\) and sodium phenoxide at 400 K, which matches our prediction from the Kolbe-Schmitt reaction.

Key Concepts

Sodium Phenoxide

Sodium phenoxide is an important compound in organic chemistry, particularly known as a nucleophilic form of phenol. It is created when phenol is deprotonated in the presence of sodium hydroxide, resulting in the phenoxide ion. This ion carries a negative charge, making it more reactive than phenol itself.
In the context of the Kolbe-Schmitt reaction, sodium phenoxide serves as the starting material. The ion's nucleophilic oxygen can react with carbon dioxide, setting the stage for the creation of new carbon-carbon bonds. This ability to participate in such transformations highlights its significance in synthetic chemistry.
Key properties of sodium phenoxide:

• Highly reactive due to its negative charge.
• Primarily acts as a nucleophile.
• Used extensively in organic synthesis, specifically for carboxylation reactions.

Sodium phenoxide's role in reactions like the Kolbe-Schmitt is crucial, enabling the transformation of simple phenols into more complex aromatic compounds, such as sodium salicylate.

Carboxylation

Carboxylation is a chemical process where a carboxyl group \((-COOH)\) is introduced into a substrate. In the Kolbe-Schmitt reaction, this process occurs when sodium phenoxide reacts with carbon dioxide \((\mathrm{CO}_2)\). The presence of elevated temperatures around 400 K facilitates this transformation.
This reaction introduces a carboxylic acid group ortho to the hydroxyl group on the aromatic ring, giving rise to salicylic acid's sodium salt. This conversion is what makes carboxylation so important in organic chemistry, allowing the transformation of relatively simple compounds into functionalized derivatives.
Important aspects of carboxylation in the Kolbe-Schmitt reaction include:

• Temperature control, which is crucial for successful reactions.
• The nucleophilic attack of the phenoxide ion on \(\mathrm{CO}_2\), facilitating the formation of a new carbon-carbon bond.
• The formation of intermediates that quickly rearrange to yield the carboxylated product, sodium salicylate.

This kind of transformation has broader applications, especially in pharmaceuticals and the synthesis of various organic compounds.

Sodium Salicylate

Sodium salicylate is the final product of the Kolbe-Schmitt reaction involving sodium phenoxide and carbon dioxide. It is the sodium salt form of salicylic acid, sharing many of the therapeutic properties of its parent compound.
This compound is notable for its use in the pharmaceutical industry, particularly for its analgesic and anti-inflammatory properties. Sodium salicylate's formation in the Kolbe-Schmitt reaction illustrates the practical application of this synthetic method.
Here are some focal points about sodium salicylate:

• Soluble in water, thanks to the presence of the sodium ion.
• Frequent use as an analgesic and antipyretic, particularly before the advent of aspirin.
• Valuable as a precursor in the synthesis of more complex molecules.

The Kolbe-Schmitt reaction's ability to produce sodium salicylate demonstrates how strategic chemical transformations can yield compounds of high pharmaceutical value. This underscores the importance of chemical synthesis in real-world applications.