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

The product is (c) \( \mathrm{C}_6\mathrm{H}_6 \).

Step 1: Identify the Reactants

The reactants in this exercise are phenol and zinc dust. Phenol is an aromatic compound with the formula \( \mathrm{C}_6\mathrm{H}_5\mathrm{OH} \). Zinc dust is used to remove the oxygen from phenol.

Step 2: Understand the Reaction Type

The distillation of phenol with zinc dust involves the removal of the hydroxyl (-OH) group from phenol. Zinc dust acts as a deoxygenating agent, which helps remove oxygen atoms, leading to the formation of a new compound.

Step 3: Predict the Product Formation

When phenol \( (\mathrm{C}_6\mathrm{H}_5\mathrm{OH}) \) is treated with zinc dust, the \( \mathrm{OH} \) group is removed, yielding benzene \((\mathrm{C}_6\mathrm{H}_6)\). This is because zinc reduces the phenol by eliminating the oxygen atom as an oxide.

Step 4: Identify the Correct Product

The expected product of the reaction, following the deoxygenation process with zinc dust, is benzene, \( \mathrm{C}_6\mathrm{H}_6 \). This matches option (c) in the given choices.

Key Concepts

Zinc Dust as a Deoxygenating Agent

Zinc dust plays a crucial role in the chemical transformation of phenol by acting as a deoxygenating agent. This means it helps in the removal of oxygen from other chemical compounds. In our reaction, the zinc dust facilitates the removal of the hydroxyl group (\(-OH\)) from phenol. This process is achieved through a chemical reduction, which is a reaction where a compound loses oxygen or gains electrons.

In the case of phenol, zinc effectively "strips" the oxygen atom, forming zinc oxide as a byproduct. The original phenol, which is an aromatic compound, becomes benzene after losing its hydroxyl group. The simplicity and high reactivity of zinc make it an ideal choice for such deoxygenation reactions.

• Zinc acts as a reducing agent.
• The reaction forms zinc oxide as a byproduct.
• This process allows the conversion of \(\mathrm{C}_6\mathrm{H}_5\mathrm{OH}\) to \(\mathrm{C}_6\mathrm{H}_6\).

Aromatic Compounds

Aromatic compounds are fascinating due to their ring-like structure, which offers unique chemical properties. The term "aromatic" initially described compounds with a distinct smell, but now it refers to their stable ring structures. Phenol, used in this exercise, is an aromatic compound featuring a six-membered carbon ring with alternating double bonds, known as a benzene ring, along with a hydroxyl group attached to it.

The resonance of electrons in the benzene ring makes aromatics particularly stable. This stability is due to the delocalized electrons shared over the carbon atoms in the ring structure. This delocalization provides extra electronic cloud stability, which is a hallmark of aromaticity.

• Aromatic compounds contain a benzene ring.
• They have a unique stability due to electron delocalization.
• A common feature is their alternating double bonds.

Benzene Formation

Forming benzene is a fascinating aspect of this reaction. Benzene is produced when the hydroxyl group of phenol is removed, thanks to the deoxygenating power of zinc dust. The reaction essentially restores the phenol to a pure benzene state by shedding its \(-OH\) group and forming a complete benzene ring.

In this single-step conversion, the aromatic structure remains intact, highlighting the resilience and stability of aromatic compounds even amidst structural changes. This transformation to benzene, \(\mathrm{C}_6\mathrm{H}_6\), is both practical and efficient, frequently employed in synthetic chemistry due to its straightforwardness.

• The \(-OH\) group is removed to form a complete benzene ring.
• The process involves electron sharing in the aromatic ring.
• This transformation preserves the aromatic nature of the original compound.