Problem 57 - A Complete Resource Book in Chemistry for JEE Main

Question

The distillation of phenol with zinc dust gives (a) \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{C}_{6} \mathrm{H}_{5}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OC}_{6} \mathrm{H}_{5}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{12}\)

Step-by-Step Solution

Answer

Option (c) \( \mathrm{C}_{6} \mathrm{H}_{6} \) is formed.

Step 1: Understand the Reaction

When phenol (C_6H_5OH) is distilled with zinc dust, the zinc serves as a reducing agent. Phenol is the compound undergoing the change, and the goal of this process is to reduce phenol.

Step 2: Identify the Desired Product

In this context, during the reduction of phenol with zinc dust, a common reaction involves the removal of the oxygen group from the phenol to form benzene (C_6H_6).

Step 3: Choose the Correct Product

Based on the identified reaction products from the reduction of phenol with zinc dust, match the expected product with the given options. The expected product is benzene (C_6H_6), which corresponds to option (c).

Key Concepts

Phenol Distillation

Phenol distillation is a process used to purify or transform phenolic compounds. Phenol, chemically known as hydroxybenzene (\( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH} \)), is a common starting material. During distillation, the goal is often to modify the compound through the application of heat, leading to evaporation and subsequent condensation. This method separates compounds based on differences in boiling points.

In the case of phenol, it undergoes a special type of distillation known as "dry distillation". This involves heating the solid compound in the absence of air. However, the twist in this method is the addition of zinc dust, which plays a critical role. By incorporating zinc dust, the distillation process takes a turn towards a chemical reaction that reduces phenol into benzene.

• Phenol itself is a volatile and somewhat corrosive compound.
• Distillation effectively leverages the different boiling points of phenol and its reduction product, benzene.
• The process results in the transformation of phenol by removing its hydroxyl group, simplifying the structure to form benzene.

Zinc Dust Reaction

Zinc dust reaction is a cornerstone of transforming phenol into benzene through reduction. Zinc acts as a strong reducing agent, meaning it donates electrons to other chemicals during the reaction.

When phenol is treated with zinc dust, the role of zinc is to aid in the removal of the oxygen atom bound to the aromatic ring of phenol. The process involves breaking the O-H bond in phenol and replacing it with a hydrogen atom, which results in benzene (\( \mathrm{C}_{6} \mathrm{H}_{6} \)).

• Zinc dust is finely powdered zinc, providing more surface area for the reaction.
• This type of reaction is known for effectively stripping the oxygen group from phenol.
• Zinc's ability to reduce phenol makes it indispensable in many organic synthesis processes.

This reaction highlights how a simple metal, through careful application, can transform complex organic compounds.

Benzene Formation

Benzene formation from phenol involves the transformation from a hydroxyl functional group to a fully hydrogenated aromatic compound. Benzene is a central compound in organic chemistry due to its stability and simple structure, represented by the formula \( \mathrm{C}_{6} \mathrm{H}_{6} \).

During the reduction of phenol, benzene is formed when its hydroxyl group is replaced by a hydrogen atom. This results in a cyclic, conjugated structure that emphasizes the planar nature of benzene. The transformation to benzene not only simplifies phenol's chemical structure but also converts it into a highly significant industrial compound.

• Benzene is a building block for many other complex chemicals.
• Understanding benzene's stable structure helps chemists predict reactions and interactions.
• This process is a great example of the interplay between different chemical elements and how they can modify complex structures.

Through controlled reactions like the reduction of phenol, benzene becomes accessible for further scientific and industrial applications.