What are the products formed when phenol and nitrobenzene are treated separately with a mixture of concentrated sulfuric acid and concentrated nitric acid?

When phenol and nitrobenzene are treated with a mixture of concentrated sulfuric acid and concentrated nitric acid, they undergo different reactions due to their distinct chemical properties. Let's break down what happens to each compound when exposed to this nitrating mixture.

Nitration of Phenol

Phenol (C6H5OH) is a relatively reactive aromatic compound due to the presence of the hydroxyl (-OH) group, which is an activating group for electrophilic aromatic substitution reactions. When phenol is treated with concentrated sulfuric acid and nitric acid, it undergoes nitration, leading to the formation of nitrophenols.

Products of Phenol Nitration

The primary products formed from the nitration of phenol are:

• 2-Nitrophenol: Formed when the nitro group (-NO2) is introduced at the ortho position relative to the hydroxyl group.
• 4-Nitrophenol: Formed when the nitro group is introduced at the para position relative to the hydroxyl group.

The ortho and para positions are favored due to the electron-donating effect of the hydroxyl group, which stabilizes the positive charge on the intermediate carbocation formed during the reaction. The reaction can be represented as follows:

C6H5OH + HNO3 → C6H4(NO2)OH (ortho and para products)

Nitration of Nitrobenzene

Nitrobenzene (C6H5NO2), on the other hand, is a much less reactive aromatic compound because the nitro group is a deactivating group. This means that it reduces the electron density of the aromatic ring, making it less susceptible to electrophilic attack. When nitrobenzene is treated with the same nitrating mixture, the reaction proceeds differently.

Products of Nitrobenzene Nitration

The primary product formed from the nitration of nitrobenzene is:

• 1,3-Dinitrobenzene: This compound is formed when a second nitro group is introduced at the meta position relative to the existing nitro group.

Due to the electron-withdrawing nature of the nitro group, the nitration occurs predominantly at the meta position, as the ortho and para positions are less favorable for further substitution. The reaction can be summarized as follows:

C6H5NO2 + HNO3 → C6H4(NO2)2 (meta product)

Summary of Reactions

To summarize, the nitration of phenol leads to the formation of 2-nitrophenol and 4-nitrophenol, while the nitration of nitrobenzene primarily yields 1,3-dinitrobenzene. The differences in the products arise from the varying reactivity of the compounds due to the presence of activating or deactivating groups on the aromatic ring.

This distinction highlights the importance of functional groups in determining the outcomes of electrophilic aromatic substitution reactions. Understanding these principles can help predict the behavior of various aromatic compounds under similar conditions.