Question

Predict the products of the reaction of benzene and nitric acid with a sulfuric acid catalyst.

Short answer

The products of the reaction between benzene, nitric acid, and sulfuric acid catalyst is nitrobenzene.

Step-by-step solution

Identify the type of reaction

The reaction between benzene, nitric acid, and sulfuric acid is a type of electrophilic aromatic substitution called nitration. Sulfuric acid acts as a catalyst to generate the electrophile.

Form the electrophile

Nitric acid reacts with sulfuric acid to form the nitronium ion \(\mathrm{NO_2^+}\), which is the active electrophile in the reaction.

Electrophilic attack on benzene

The nitronium ion attacks the electron-rich benzene ring to form an intermediate arenium ion (also known as a sigma complex).

Deprotonation

The arenium ion is deprotonated by the loss of a hydrogen ion, which restores the aromaticity of the benzene ring, resulting in nitrobenzene as the product.

Key concepts

Nitration of Benzene

The fascinating process of nitration of benzene is a prime example of electrophilic aromatic substitution, where a nitro group ((NO_2)) takes the place of a hydrogen atom on the benzene ring. This reaction is not only essential for creating various chemicals in the industry but also serves as a fundamental teaching concept in organic chemistry. The substitution proceeds through the generation of an electrophile, which in this case is the nitronium ion, and the subsequent attack of this electrophile on the electron-rich aromatic ring of benzene. Understanding this reaction helps to unlock the synthesis of many complex molecules and grasp the underlying principles of organic reaction mechanisms.

Sulfuric Acid Catalyst

In the nitration process, sulfuric acid is not merely a spectator but a powerful catalyst. It plays a crucial role by reacting with nitric acid to produce the nitronium ion, the actual attacking species in the reaction mechanism. Its ability to protonate nitric acid and facilitate the loss of a water molecule is pivotal in forming the highly reactive nitronium ion. This catalyst's use showcases the importance of understanding acid-base reactions and how they intersect with organic synthesis routes.

Nitronium Ion

Understanding the nitronium ion ((NO_2^+)) is essential in mastering the nitration reaction. This positively charged entity is exceptionally electrophilic, meaning it's attracted to electron-rich areas, such as the pi-electron cloud of benzene. The formation of this electrophile is the heart of the nitration process, and grasping its generation and reactivity provides insights into the nature of electrophiles and their role in organic chemistry reactions.

Sigma Complex

A key intermediate in the nitration of benzene is the sigma complex, or arenium ion, which forms when the nitronium ion attacks the benzene ring. This intermediate is a temporary, non-aromatic species that forms as the benzene ring donates electron density to stabilize the electrophile. Its formation and stabilization are central concepts in understanding how the aromatic ring can temporarily sacrifice its aromaticity to form new chemical bonds, an idea that is fundamental in the study of reaction intermediates and mechanisms in organic chemistry.

Aromaticity

Aromaticity refers to the unique stability possessed by aromatic compounds like benzene, which results from a ring of continuous overlapping p-orbitals and the associated delocalized pi-electron cloud. This property is not just a theoretical concept but a practical one, influencing the reactivity and properties of molecules. The restoration of aromaticity following the formation of the sigma complex explains why certain steps in the reaction are favorable. In essence, the molecule regains its aromatic character, driving the reaction forward to its final product, often a hallmark of electrophilic aromatic substitution reactions like nitration.