Problem 7 - Chemistry in 30 days

Question

When phenol is heated with zinc dust, the major product formed is (a) benzaldehyde (b) phenolphthalein (c) benzene (d) biphenyl

Step-by-Step Solution

Answer

The major product formed is benzene.

Step 1: Identify the Reactants and Reagents

The reaction involves phenol as the starting material, and it is reacted with zinc dust.

Step 2: Determine the Typical Reaction Involving Phenol and Zinc Dust

In organic chemistry, heating phenol with zinc dust is a common process used to reduce the phenolic group to form benzene.

Step 3: Understand the Mechanism

When zinc dust is heated with phenol, the hydroxyl group (-OH) of the phenol is reduced to hydrogen, essentially eliminating the hydroxyl group and resulting in a benzene ring.

Step 4: Predict the Major Product

The major product is benzene, as the hydroxyl group is removed, leaving behind the benzene ring.

Step 5: Check the Options Provided

Compare the possible major products: (a) benzaldehyde, (b) phenolphthalein, (c) benzene, and (d) biphenyl. From our steps, benzene is the correct product formed.

Key Concepts

Phenol

Phenol is a simple aromatic compound with the chemical formula \( C_6H_5OH \). It consists of a benzene ring bonded to a hydroxyl group \((-OH)\).
Phenol is known for its acidic properties, as the presence of the hydroxyl group increases the electron affinity of the benzene ring, making it more likely to release a hydrogen ion. In organic chemistry, phenol is often a starting material for various reactions due to its reactivity.

• It can undergo electrophilic substitution reactions, where the hydrogen atom of the hydroxyl group is replaced by other functional groups.
• Due to the hydroxyl group, phenol is more reactive than benzene.

Understanding phenol is crucial for predicting the outcomes of reactions, such as those involved in the conversion to benzene when reacted with zinc dust.

Zinc Dust

Zinc dust is a fine powder form of zinc metal, which is often used as a reducing agent in chemical reactions. The role of zinc dust in organic chemistry is pivotal because it can donate electrons, aiding in reduction processes.
When applied to phenol and heated, zinc dust facilitates the removal of oxygen from the hydroxyl group \((-OH)\) on the phenol molecule.

• Zinc dust initiates electron transfer, leading to the reduction reaction.
• It is a safe and effective reducing agent for laboratory and industrial processes.

In the specific reaction involving phenol, zinc dust is instrumental in removing the hydroxyl group, leaving behind the simpler structure of benzene.

Benzene Formation

The transformation of phenol into benzene is an essential reaction in organic chemistry. This process eliminates the hydroxyl group from the phenol molecule, resulting in the formation of benzene, a simpler aromatic compound.
This reaction showcases a classic example of reduction, where the phenol loses oxygen and potentially gains hydrogen, hence forming a benzene ring.

• The process involves a direct reduction where the hydroxyl group is removed.
• This type of reaction highlights the difference between phenol and benzene structures, emphasizing the loss of the \(-OH\) group.

The formation of benzene from phenol through the use of zinc dust is a clear demonstration of how modification of functional groups can lead to entirely new compounds.

Reduction Reaction

Reduction reactions play a vital role in organic chemistry and involve the gain of electrons or the decrease in oxidation state of a molecule.For phenol undergoing reduction with zinc dust, the focus is on the removal of the hydroxyl group \((-OH)\), converting it into benzene.
Reduction reactions like this one are not merely about gaining hydrogen, but also about the strategic removal of functional groups.

• Zinc dust acts as the reducing agent, effectively aiding in the removal of oxygen from the \(-OH\) group.
• This reduction showcases the importance of selecting appropriate reagents to achieve desired transformation.

The reaction exemplifies how specific reagents and conditions can effectively alter molecular structures, demonstrating the versatility and utility of reduction in organic transformations.