Question

Indicate how you would perform the following syntheses: (1) aniline from benzene, (2) ethyl amine from ethane.

Short answer

To synthesize aniline from benzene, first prepare nitrobenzene by reacting benzene with a mixture of concentrated nitric acid and concentrated sulfuric acid. Then reduce the nitro group to the amine group using tin and hydrochloric acid or catalytic hydrogenation. To synthesize ethylamine from ethane, first, convert ethane into ethene through dehydrogenation. Lastly, convert ethene to ethylamine via hydrogenation in the presence of ammonia, or by treating ethene with ammonia using a metal oxide catalyst.

Step-by-step solution

Preparation of Nitrobenzene from Benzene

To synthesize aniline from benzene, we should first prepare nitrobenzene. To form nitrobenzene, react benzene with a mixture of concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄) at 335-355 K or 60-85 °C. The reaction follows an electrophilic substitution mechanism. The intermediate formed in this reaction is a nitronium ion (NO₂⁺). The overall reaction can be written as: \( C_6H_6 + HNO_3 -> C_6H_5NO_2 + H_2O \)

Reduction of Nitrobenzene to Aniline

To obtain aniline from nitrobenzene, reduce the nitro group (NO₂) of nitrobenzene to an amine group (NH₂). The reduction can be achieved using either tin (Sn) and hydrochloric acid (HCl) or catalytic hydrogenation using a metal catalyst such as palladium on carbon, followed by the addition of an aqueous base. The overall reaction can be represented as: \( C_6H_5NO_2 + 3H_2 -> C_6H_5NH_2 + 2H_2O \) Now, for the synthesis of ethylamine from ethane:

Dehydrogenation of Ethane to Ethene

To synthesize ethylamine from ethane, the first step is to convert ethane into ethene. This can be done by dehydrogenation. Dehydrogenation can be carried out over heterogeneous catalysts such as Cr₂O₃/Al₂O₃ at 600-700 °C. The overall reaction can be written as: \( C_2H_6 -> C_2H_4 + H_2 \)

Synthesis of Ethylamine from Ethene

There are different routes to synthesize ethylamine from ethene. Here are two possible methods: 1. Hydrogenation of Ethene: Ethene can be converted to ethylamine by hydrogenation in the presence of ammonia (NH₃) using a metal catalyst like Raney Nickel (Porous Ni/Al alloy) at a high temperature (130 °C) and high pressure (250 atm). Loss of hydrogen from the ethene and gain of hydrogen from ammonia will occur in this reaction. The overall reaction can be represented as: \( C_2H_4 + NH_3 -> C_2H_5NH_2 \) 2. Treating Ethene with Ammonia: Ethene can also be converted to ethylamine by reacting with ammonia using a metal oxide catalyst such as silica-supported alumina (Al₂O₃/SiO₂) or zeolite at elevated temperature. The overall reaction can be written as: \( C_2H_4 + NH_3 -> C_2H_5NH_2 \)

Key concepts

Aniline Synthesis

Aniline is a crucial compound in the chemical industry, widely used in dyes, pharmaceuticals, and more. The journey to synthesize aniline from benzene involves a two-step transformation.
First, benzene is converted to nitrobenzene through electrophilic substitution, where a nitronium ion attaches to the benzene ring. Once you have nitrobenzene, the reduction process transforms it into aniline.
This reduction can be achieved either by using tin and hydrochloric acid, or via catalytic hydrogenation using palladium on carbon, together with a base to finalize the conversion.

• Conversion of nitro groups to amino groups is the key step.
• Catalysts play a significant role in efficient transformation.

Nitrobenzene Preparation

Creating nitrobenzene from benzene involves a nitration reaction, which is a classic example of electrophilic aromatic substitution. In this reaction, benzene reacts with a mix of concentrated nitric and sulfuric acids.
This mixture forms the potent nitronium ion, which acts as the electrophile, adding to the benzene ring.
Nitration is conducted at moderate temperatures (60-85 °C), ensuring the benzene is efficiently converted to nitrobenzene.

• The mixture of acids is essential to form the nitronium ion.
• Temperature control ensures desired reaction conditions.

Ethylamine Synthesis

Ethylamine is often synthesized from ethene, which is initially derived from ethane through dehydrogenation. Ethylamine has various applications in producing agricultural chemicals and pharmaceuticals.
The conversion of ethene to ethylamine can occur through hydrogenation in the presence of ammonia and a suitable metal catalyst at elevated pressures and temperatures.

• Ammonia is a key reactant that supplies the amino group.
• Raney Nickel is a commonly used catalyst for this transformation.

There are alternative ways to conduct this reaction, involving different catalyst setups, highlighting the flexibility and adaptability of the method.

Electrophilic Substitution

Electrophilic substitution is a fundamental reaction in organic chemistry, particularly for transforming aromatic compounds like benzene.
During nitration, benzene undergoes electrophilic substitution when the nitronium ion (NO₂⁺) attacks the electron-rich benzene ring, replacing a hydrogen atom.
This mechanism is essential in many synthesis pathways, where activating electrophiles react with aromatic compounds.

• The stability of the benzene ring is crucial for the process.
• Electrophiles must be sufficiently reactive to interact with aromatic rings.

Dehydrogenation Process

Dehydrogenation is an industrial method used to transform saturated hydrocarbons like ethane into unsaturated ones like ethene. This process involves the removal of hydrogen atoms, typically requiring high temperatures and catalysts.
For instance, in converting ethane to ethene, catalysts like Cr₂O₃/Al₂O₃ facilitate the reaction at temperatures around 600-700 °C.
Dehydrogenation is vital for forming starting materials used in further synthesis, such as making ethylamine.

• High temperatures drive the endothermic reaction forward.
• Catalysts are essential for enhancing the reaction efficiency.