Question

Nitrobenzene gives n-phenylhydroxyl-amine by (a) \(\mathrm{H}_{2} / \mathrm{Pd}-\mathrm{C}\) (b) \(\mathrm{Sn} / \mathrm{HCl}\) (c) \(\mathrm{Zn} / \mathrm{NH}_{4} \mathrm{Cl}\) (d) \(\mathrm{Zn} / \mathrm{NaOH}\)

Short answer

Option (c) ( / ) is correct for producing n-phenylhydroxylamine from nitrobenzene.

Step-by-step solution

Understand the Reaction

We are dealing with the reduction of nitrobenzene to produce n-phenylhydroxylamine. The goal is to identify which reagent from the list effectively performs this transformation.

Evaluate Option (a) ( )

The reagent ( / -) typically reduces nitro groups to amines. Using this reagent, nitrobenzene would be reduced to aniline, skipping the n-phenylhydroxylamine stage.

Evaluate Option (b) ( / )

The ( / ) reagent is a reducing agent that usually converts nitro compounds to amines, bypassing the intermediate hydroxylamine stage entirely.

Evaluate Option (c) ( / )

The combination ( / ) is known to partially reduce nitro compounds to their corresponding n-phenylhydroxylamine derivatives via a controlled reduction process.

Evaluate Option (d) ( / )

Similar to option (b), ( / ) reduces nitro groups but typically leads to the full reduction to aniline, not stopping at n-phenylhydroxylamine.

Choose the Correct Option

From the above evaluations, it’s clear that option (c) ( / ) effectively reduces nitrobenzene to n-phenylhydroxylamine, making it the correct choice.

Key concepts

Nitrobenzene Reduction

Nitrobenzene is an organic compound and a derivative of benzene. It contains a nitro group (-NO₂) attached to the aromatic ring. The reduction of nitrobenzene involves transforming this nitro group into another functional group, and in many cases, you aim to produce intermediates like n-phenylhydroxylamine. This specific reduction is an important reaction in organic chemistry because it provides a route to convert nitro compounds into useful intermediates for creating other compounds. During this transformation, the nitro group loses oxygen and gains hydrogen atoms, altering its chemical structure. To achieve selective reduction to n-phenylhydroxylamine, specific reagents must be applied under controlled conditions. A precise approach is crucial to prevent further reduction, which would lead to a different product.

Organic Chemistry Reagents

In the context of nitrobenzene reduction, several organic chemistry reagents can be employed to facilitate this transformation.

• **Pd-C with Hydrogen ( \(\mathrm{H}_{2}/\mathrm{Pd}-\mathrm{C}\))**: Palladium on carbon with hydrogen gas is a common choice for hydrogenation reactions. However, it typically reduces nitro groups all the way to amines such as aniline, without stopping at intermediates such as n-phenylhydroxylamine.
• **Tin and Hydrochloric Acid ( \(\mathrm{Sn}/\mathrm{HCl}\))**: This reagent is also effective for fully reducing nitro groups to amines. It operates via a more complex pathway and may not produce the desired intermediate product.
• **Zinc with Ammonium Chloride ( \(\mathrm{Zn}/\mathrm{NH}_{4}\mathrm{Cl}\))**: This specific reagent is known for its ability to perform controlled reductions. In this scenario, it can efficiently reduce nitrobenzene to n-phenylhydroxylamine, without proceeding further to full amine reduction.
• **Zinc with Sodium Hydroxide ( \(\mathrm{Zn}/\mathrm{NaOH}\))**: Similar to other strong reducers, this choice typically does not halt at the hydroxylamine stage and moves towards full reduction.

Controlled Reduction Process

Controlled reduction is crucial when the goal is to obtain a specific intermediate product rather than fully reducing a molecule to its base form. For nitrobenzene, achieving n-phenylhydroxylamine as an intermediate requires careful selection of conditions and reagents. When using \(\mathrm{Zn}/\mathrm{NH}_{4}\mathrm{Cl}\), its ability to control the degree of reduction allows it to convert nitrobenzene to n-phenylhydroxylamine effectively.This controlled reduction process benefits from the milder nature of the reaction environment compared to stronger reducers. It avoids over-reduction, which would otherwise result in further conversion of n-phenylhydroxylamine into aniline. This careful balance in the reaction conditions exemplifies how controlled reduction processes can allow chemists to target specific products without excess byproducts or additional reaction steps. Understanding the mechanics of these reactions aids in their careful application in practical synthetic chemistry.