Problem 91 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Nitrobenzene and hydrogen in presence of zinc combines to form: |BHU 1999] (a) azobenzene (b) bertene (c) azoxybenzene (d) aniline

Step-by-Step Solution

Answer

The reaction forms aniline.

Step 1: Understanding the Reaction

We need to figure out the chemical reaction between nitrobenzene and hydrogen in the presence of zinc. Typically, nitro compounds when reduced in the presence of a metal like zinc and an acid, will reduce completely to amines.

Step 2: Deducing the Product

When nitrobenzene is reduced, the nitrogen-oxygen groups are replaced with hydrogen, forming an aniline group. Therefore, nitrobenzene ( C_6H_5NO_2) can be reduced to aniline ( C_6H_5NH_2) using a reducing agent like zinc and acid.

Step 3: Conclusion

From the reaction pathway of reduction of nitrobenzene with hydrogen and zinc, we can conclude that it yields aniline. The correct option describing the products is (d) aniline.

Key Concepts

Nitrobenzene Reduction

Nitrobenzene is a common organic compound with the structure \( C_6H_5NO_2 \). In chemical conversions, it is often used as a starting material that undergoes reduction. Reduction involves adding hydrogen to a molecule, typically resulting in the loss of oxygen.To understand this process in nitrobenzene – zinc acts as a catalyst, assisting in the chemical transformation. Zinc catalysis aids in the reduction of nitro groups, (-NO_2), into amino groups (-NH_2). This makes it pivotal in converting nitrobenzene into aniline by replacing the oxygen atoms with hydrogen.The use of acids alongside zinc creates a favorable environment for this hydrogen transfer. Together, they facilitate the breakdown of the strong bonds in nitrobenzene, allowing it to be reduced successfully. Typically, a typical reaction will follow this general path:

• Nitrobenzene (\( C_6H_5NO_2 \))
• Reduction using hydrogen (in the presence of zinc and an acid)
• Formation of Aniline (\( C_6H_5NH_2 \))

Understanding and applying the concept of nitrobenzene reduction is essential for producing aniline efficiently.

Aniline Synthesis

Aniline is an aromatic amine that plays a vital role in pharmaceuticals, dyes, and polymers. It consists of a benzene ring attached to an amino group (\( -NH_2 \)). Synthesizing aniline, particularly from nitrobenzene, is crucial for many industrial and chemical applications.The process typically involves reducing nitrobenzene (\( C_6H_5NO_2 \)) using hydrogen. Zinc serves as the reducing agent alongside acids to facilitate an effective reduction process.The reaction involves the following basic steps:

• Nitrobenzene initially possesses a nitro group which needs to be reduced.
• By utilizing hydrogen and zinc, the reduction can occur, removing oxygen atoms.
• The resultant product is aniline, characterized by the amino group replacing the nitro group.

Obtaining aniline is pivotal due to its extensive use in various chemical syntheses and formulations.The transformation from nitrobenzene to aniline exemplifies a fundamental process in organic chemistry, showcasing how the manipulation of molecular structures can produce significant and diverse end products.

Zinc Catalysis

Zinc catalysis is a process where zinc is used to accelerate chemical reactions without being consumed in the process. In the context of nitrobenzene reduction to aniline, zinc serves as a powerful catalyst. Catalysts play a crucial role in lowering the activation energy, allowing reactions to proceed faster or under milder conditions. Here's how zinc catalysis assists in the reduction reaction:

• Activation: Zinc helps activate the nitrobenzene molecule, making it ready for the transformation.
• Hydrogenation: Zinc allows for the effective transfer of hydrogen atoms to the nitro group, leading to its reduction.
• Efficiency: Provides a robust environment for efficient and complete conversion of nitrobenzene.

Using zinc as a catalyst is beneficial because it is relatively inexpensive and widely available. In addition, it avoids potential side reactions, yielding aniline predominantly, which is ideal for large-scale production. Zinc catalysis, therefore, is integral in simplifying complex reduction processes, proving invaluable in various industrial applications where specific chemical transformations are necessary.