Show how each of the following compounds can be synthesized from benzene:
d. p-chloroaniline

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Step 1: Begin with benzene as the starting material. The first step is to introduce a chlorine atom onto the benzene ring. This can be achieved through an electrophilic aromatic substitution reaction called chlorination. React benzene with chlorine (Cl₂) in the presence of a catalyst such as FeCl₃ to form chlorobenzene. The reaction is:

C 6_{6} H 6_{6} + {Cl}_{2} → C_{6} H_{5} Cl

Step 2: Next, introduce the amino group (-NH₂) onto the benzene ring. To achieve this, perform a nitration reaction on chlorobenzene. React chlorobenzene with a mixture of concentrated nitric acid (HNO₃) and sulfuric acid (H₂SO₄) to form p-nitrochlorobenzene. This reaction introduces a nitro group (-NO₂) at the para position relative to the chlorine atom due to the electron-withdrawing nature of the chlorine substituent.

Step 3: Reduce the nitro group (-NO₂) in p-nitrochlorobenzene to an amino group (-NH₂). This can be done using a reducing agent such as tin (Sn) and hydrochloric acid (HCl), followed by neutralization with a base. The product of this step is p-chloroaniline.

Step 4: Purify the p-chloroaniline product to ensure it is free of any by-products or impurities. This can be done through recrystallization or other purification techniques.

Step 5: Verify the structure of the synthesized p-chloroaniline using spectroscopic methods such as IR, NMR, or mass spectrometry to confirm the presence of the desired functional groups and the correct substitution pattern on the benzene ring.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process is crucial for synthesizing various derivatives of benzene, including p-chloroaniline. Understanding the mechanism of EAS helps in predicting the positions where substituents will attach to the aromatic ring based on the directing effects of existing groups.

Nitration of Benzene

Nitration is a specific type of electrophilic aromatic substitution where a nitro group (NO2) is introduced to the benzene ring. This reaction typically involves the use of concentrated nitric acid and sulfuric acid. The resulting nitrobenzene can then be further transformed into p-chloroaniline through subsequent reactions, highlighting the importance of nitration in the synthesis pathway.

Reduction of Nitro Compounds

The reduction of nitro compounds is a key step in converting nitrobenzene to an amine, such as p-chloroaniline. This process can be achieved using various reducing agents, such as iron and hydrochloric acid or catalytic hydrogenation. Understanding the reduction mechanism is essential for successfully synthesizing amines from their corresponding nitro derivatives, which is a critical step in the overall synthesis from benzene.

Show how each of the following compounds can be synthesized from benzene:d. p-chloroaniline