Question

Which of the following reacts with chloroform and base to form phenyl isocyanide? (a) nitrobenzene (b) phenol (c) chlorobenzene (d) aniline

Short answer

Aniline (option d) reacts with chloroform and base to form phenyl isocyanide.

Step-by-step solution

Identify the Reaction

The reaction in question involves the formation of phenyl isocyanide. The key reaction to form an isocyanide (or carbylamine) is the carbylamine reaction, which requires a primary amine, chloroform, and a base.

Analyze Each Option

We need to determine which of the provided compounds contains a primary amine group, as this group is necessary for the carbylamine reaction to occur. (a) Nitrobenzene does not have an amine group. (b) Phenol is an alcohol, not an amine. (c) Chlorobenzene is a chlorinated aromatic compound without an amine group. (d) Aniline contains a primary amine group, characterized by the NH2 group attached directly to the benzene ring.

Confirm the Reaction with Aniline

Aniline, which is a primary amine, can indeed react with chloroform in the presence of a base (such as NaOH) to form phenyl isocyanide. The reaction proceeds as:\[C_6H_5NH_2 + CHCl_3 + 3KOH \rightarrow C_6H_5NC + 3KCl + 3H_2O\]This confirms that aniline is the compound that fits the reaction criteria.

Key concepts

Primary Amines

Primary amines are a fundamental class of organic compounds. They are characterized by the presence of an amino group (-NH\(_2\)) attached to a carbon atom. In these compounds, the nitrogen atom is connected to only one carbon-containing group, while the other two positions at nitrogen are occupied by hydrogen atoms.

Here are some key points about primary amines:

• They serve as important building blocks in organic chemistry, participating in key reactions.
• The simplest example of a primary amine is methylamine, where a methyl group is attached to the nitrogen.
• Primary amines are known for their ability to engage in hydrogen bonding, impacting their boiling points and solubility in water.

In the context of the carbylamine reaction, primary amines play a crucial role. Only primary amines can undergo this reaction to form isocyanides. Secondary and tertiary amines do not have the same reactivity in this type of reaction because they lack sufficient hydrogen atoms at the nitrogen.

Phenyl Isocyanide Formation

The formation of phenyl isocyanide is a specific variation of the carbylamine reaction. It demonstrates how aniline, a primary aromatic amine, can transform through the reaction with chloroform and a strong base like KOH.

Here’s a simple breakdown of the process:

• Reagents: The main substances needed are aniline (C\(_6H_5NH_2\)), chloroform (CHCl\(_3\)), and potassium hydroxide (KOH).
• Reaction: When these reactants are heated together, the chloroform loses hydrogen chloride, and the amine attacks the resulting dichlorocarbene intermediate, leading to the phenyl isocyanide.
• The overall chemical equation for this transformation is: \[C_6H_5NH_2 + CHCl_3 + 3KOH \rightarrow C_6H_5NC + 3KCl + 3H_2O\]

This transformation is notable because it proceeds through distinct steps involving intermediate species. The ability of an aromatic primary amine, such as aniline, to access this route highlights its unique structural properties.

Organic Reaction Mechanisms

Understanding organic reactions involves deciphering the series of steps, known as the reaction mechanism, that lead from reactants to products. For the carbylamine reaction, this is particularly interesting, given the formation of phenyl isocyanide from aniline, chloroform, and a base like KOH.

Here's the process in action:

• Step 1: Chloroform reacts with the base to generate dichlorocarbene, a potent reactive intermediate.
• Step 2: The amino group in aniline acts as a nucleophile, attacking the electron-deficient dichlorocarbene to form a new C-N bond.
• Step 3: The result is the expulsion of halide ions and water, leading to the formation of the isocyanide.

The reaction mechanism is essential to appreciate because it highlights the energetic changes and intermediates that occur during the reaction process. The carbylamine reaction is a classic example of organic chemistry transformations, providing a deeper look into how reactants are transformed through a series of well-defined steps.