Question

Compound \(\mathrm{A}\) on reduction gives \(\mathrm{B}\), which on further reaction with \(\mathrm{CHCl}_{3}\) and alcoholic KOH gives compounds \(\mathrm{C}\), which on further hydrolysis gives aniline. The compound \(\mathrm{A}\) is (a) nitrosobenzene (b) methylamine (c) nitromethane (d) nitrobenzene

Short answer

Compound \( \mathrm{A} \) is nitrobenzene.

Step-by-step solution

Identify the Final Product

The problem states that the final compound after a series of reactions is aniline. Aniline is an aromatic amine with the formula \( \text{C}_6\text{H}_5\text{NH}_2 \), derived from benzene.

Understand the Reactions Given

Compound \( \mathrm{A} \) is reduced to \( \mathrm{B} \). \( \mathrm{B} \) reacts with \( \mathrm{CHCl}_3 \) and alcoholic \( \text{KOH} \) to give \( \mathrm{C} \), which upon hydrolysis yields aniline. This sequence of reactions resembles a well-known organic reaction transformation involving nitro compounds.

Determine the Type of Compounds Involved

The reaction involving \( \mathrm{CHCl}_3 \) and alcoholic \( \text{KOH} \) is characteristic of the Hofmann reaction or the Sandmeyer reaction, often related to aromatic nitro compounds or nitrenes leading to an amine.

Analyze Compound A

Among the options, \( \mathrm{A} \) could be an aromatic nitro compound, because aniline is aromatic. Given the options, the transformation from nitrobenzene (\( \mathrm{A} \)) through reduction aligns with forming phenylamine, which is converted to aniline.

Conclusion Based on Reaction Pathway

In line with organic chemistry, compound \( \mathrm{A} \) is nitrobenzene because it undergoes a reduction process to form aniline. Thus, the reduction to \( \mathrm{B} \) initially forms an intermediate that aligns with known reaction pathways to form aniline.

Key concepts

Nitrobenzene

Nitrobenzene is an organic compound that appears as a yellowish, oily liquid with a distinct almond-like odor. It is identified by its chemical formula, \( \text{C}_6\text{H}_5\text{NO}_2 \). Nitrobenzene plays a crucial role in organic chemistry as it is commonly used as a precursor to aniline through reduction reactions.

The structure of nitrobenzene includes a benzene ring bonded to a nitro group \( (\text{-NO}_2) \), where the nitrogen atom is bonded to two oxygen atoms. One of the key features of the nitro group is that it is electron-withdrawing. This influences the reactivity of the benzene ring, impacting the types of reactions nitrobenzene can undergo.

• Due to the presence of the nitro group, nitrobenzene is relatively stable. It doesn't undergo reactions quite as readily as other benzene derivatives.
• However, nitrobenzene can be converted into more reactive compounds, such as aniline, through reduction processes, which is a typical method in industrial and laboratory settings for producing amines.

Aniline Formation

Aniline formation from nitrobenzene is an important transformation in organic chemistry. It represents the reduction of the nitro group \((-\text{NO}_2)\) to an amino group \((-\text{NH}_2)\). Aniline, a primary aromatic amine, is significant in the production of various industrial chemicals and dyes.

The reduction process typically involves using specific reducing agents such as tin and hydrochloric acid, or catalytic hydrogenation, where hydrogen gas is used in the presence of a catalyst to achieve the reduction. Through these reactions, the oxygen from the nitro group is removed, and hydrogen atoms are introduced, resulting in an amino group.

• Aniline, with its molecular formula \( \text{C}_6\text{H}_5\text{NH}_2 \), plays an influential role as a building block in the production of pharmaceuticals, polymers, and rubber processing chemicals.
• The transformation from nitrobenzene to aniline is a pivotal step in synthetic organic chemistry, illustrating the connectivity between simple aromatic compounds and complex amine derivatives.

Organic Reaction Mechanisms

Organic reaction mechanisms are like the blueprints of chemical reactions. They provide insight into how and why reactions occur, detailing every step of the transformation from reactants to products.

Understanding these mechanisms is essential as it allows chemists to predict the products of reactions and to design new reactions for synthesizing desired compounds. In the transition from nitrobenzene to aniline and further reactions, mechanisms illustrate the breaking and formation of chemical bonds.

• The reduction of nitrobenzene to aniline involves electron transfer and protonation, key steps detailed in mechanisms showing how the nitro group is reduced to an amino group by sequential steps involving intermediate species.
• Knowing specifics about these electron transfers and intermediate species helps chemists control and optimize conditions for better yield and efficiency.

Hofmann and Sandmeyer Reactions

Hofmann and Sandmeyer reactions are named transformations that hold a prominent place in organic chemistry, particularly related to the formation and modification of amines.

The Hofmann reaction primarily involves the conversion of amines to their corresponding isocyanates and further into amines through substitution. It's a method widely employed in modifying amine functional groups.

The Sandmeyer reaction, on the other hand, involves replacing an amino group \((\text{-NH}_2)\) on an aromatic ring with different substituents such as halogens using copper salts. This reaction is an essential tool in synthetic chemistry for manipulating aromatic compounds.

• In the context of transforming nitrobenzene to aniline, these reactions outline typical routes in synthetic protocols for creating or transforming aromatic amines.
• Understanding the nuances of these named reactions provides chemists with versatile methods for functionalizing aromatic compounds, expanding the utility and applicability of simple molecules like nitrobenzene.