Question

Complete the following reactions: (i) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{CHCl}_{3}+\) alc. \(\mathrm{KOH} \rightarrow\) (ii) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl}+\mathrm{H}_{3} \mathrm{PO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (iii) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4}(\) conc. \() \rightarrow\) (iv) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \rightarrow\) (v) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{Br}_{2}(\mathrm{aq}) \rightarrow\) (vi) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O} \rightarrow\)

Short answer

(i) C₆H₅NC; (ii) C₆H₆; (iii) C₆H₅NH₃⁺ HSO₄⁻; (iv) C₆H₅OH; (v) C₆H₂Br₃NH₂; (vi) C₆H₅NHCOCH₃.

Step-by-step solution

Reaction with Chloroform and Alc. KOH

The reaction of aniline (C₆H₅NH₂) with chloroform and alcoholic KOH typically leads to the formation of an isocyanide or isonitrile.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} + \mathrm{CHCl}_{3} + 3\mathrm{KOH} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NC} + 3\mathrm{KCl} + 3\mathrm{H}_{2}\mathrm{O}\]

Diazotization and Reduction

Benzene diazonium chloride (C₆H₅N₂Cl) reacts with hypophosphorous acid (H₃PO₂) in the presence of water to give benzene as the main product.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl} + \mathrm{H}_{3} \mathrm{PO}_{2} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{6} + \mathrm{N}_{2} + \mathrm{H}_{3} \mathrm{PO}_{3} + \mathrm{HCl}\]

Reaction with Concentrated Sulfuric Acid

Aniline reacts with concentrated sulfuric acid to form anilinium hydrogen sulfate.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+} \mathrm{HSO}_{4}^{-}\]

Reaction with Alcohol and Diazotized Amine

Benzene diazonium chloride reacts with ethanol to produce phenol, along with nitrogen gas and acetaldehyde.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl} + \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH} + \mathrm{N}_{2} + \mathrm{CH}_{3} \mathrm{CHO} + \mathrm{HCl}\]

Bromination of Aniline

Aniline reacts with bromine water to form 2,4,6-tribromoaniline.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} + 3\mathrm{Br}_{2} \rightarrow \mathrm{C}_{6} \mathrm{H}_{2} \mathrm{Br}_{3} \mathrm{NH}_{2} + 3\mathrm{HBr}\]

Acetylation Reaction

Aniline reacts with acetic anhydride to form acetanilide.\[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} + \left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NHCOCH}_{3} + \mathrm{CH}_{3} \mathrm{COOH}\]

Key concepts

Aniline Reactions

Aniline, known by its chemical formula \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NH}_{2}\), is an aromatic amine with many fascinating reactions.
It is a precursor in various organic synthesis processes.
Its electron-rich phenyl ring attached to the amino group makes it susceptible to electrophilic substitution.
A common feature in many organic reactions is that the amino group strongly activates the aromatic ring
This increases the reactivity compared to benzene.Aniline's reactions are diverse:

• It can react with acids to form ammonium salts.
• It undergoes halogenation, resulting in products like 2,4,6-tribromoaniline, as seen with bromine water.
• It also takes part in acetylation and other electrophilic substitution reactions.

To better understand aniline reactions, we focus on specific types like substitution, bromination, and acetylation.
These are important for synthesis in both educational and industrial settings.

Substitution Reactions

Substitution reactions are essential in organic chemistry, especially with aromatic compounds like aniline.
A substitution reaction involves replacing an atom or a group in a molecule with another atom or group.
In aniline, this often occurs with the hydrogen atoms on the phenyl ring.
The amino group directs incoming electrophiles to the ortho and para positions, due to its electron-donating nature.
As a result, aniline can undergo a variety of transformations in controlled conditions:

• Halogen substitution with reagents like bromine leads to products like tribromoaniline.
• Nitration gives nitroaniline derivatives.
• Friedel-Crafts reactions are possible but require specific conditions to avoid side reactions.

Understanding substitution reactions with aniline is key for synthesizing more complex aromatic compounds in the lab.

Diazonium Salts

Diazonium salts are pivotal intermediates in organic synthesis, derived from aromatic amines like aniline.
By reacting aniline with nitrous acid, diazonium salts (\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{N}_{2}^+\mathrm{Cl}^-\)) are formed.
These salts are known for their versatility in transformation into various other compounds.
let's explore some essential features and reactions of diazonium salts:

• They can be reduced to form hydrocarbons, e.g., benzene from benzene diazonium chloride.
• They can be transformed into phenols through a reaction with water.
• They serve as intermediates for Sandmeyer reactions, providing a pathway to aryl halides.

These attributes make diazonium salts invaluable in synthetic pathways, allowing chemists to design functionalized aromatic compounds efficiently.

Bromination

Bromination is the process of adding bromine atoms to a compound, highly relevant in modifying aniline.
Aniline is particularly reactive towards bromination due to its activating amino group.
Aniline reacts with bromine water, leading to tribromoaniline formation.
Let’s delve into the specifics of bromination in the context of aniline:

• In the presence of bromine water, the rapid reaction results in a white precipitate of 2,4,6-tribromoaniline.
• The reaction is a classic example of electrophilic substitution.
• This transformation illustrates the high activity of the ortho and para positions.

Bromination of aniline showcases how functional group interactions influence reaction pathways, essential knowledge for mastering organic synthesis.

Acetylation

Acetylation is a type of reaction where an acetyl group is introduced into a molecule.
For aniline, acetylation involves transforming it into acetanilide by reacting it with acetic anhydride.
This reaction is important for multiple reasons:

• It protects the amino group by reducing its reactivity during subsequent reactions.
• Acetylated anilines display reduced solubility, aiding purification processes.
• These derivatives offer different biological properties, enhancing their application scope.

Moreover, acetylation of aniline serves as a useful strategy in laboratory settings
It prepares the molecule for further synthetic applications while minimizing reaction hurdles.