What will be 'A' in the following reaction?

\(Sn/ dil. HCl\)

The correct answer is option 3. \(Sn/ dil. HCl\).

The reaction will be as follow:

The process of converting nitrobenzene to aniline involves reducing the nitro group (–NO₂) to an amino group (–NH₂). This is a classic example of a reduction reaction in organic chemistry.

Reagent Options

1. \(C_2H_5^-Na^+ / C_2H_5OH\) (Sodium Ethoxide/Ethanol)

Sodium ethoxide in ethanol is a base used in various organic reactions, such as the Wurtz reaction or deprotonation. It is not used for the reduction of nitrobenzene. This reagent primarily facilitates nucleophilic substitutions or eliminations, not reductions.

2. \(H^+ / H_2O\) (Acidic Conditions)

Acidic conditions (like dilute sulfuric acid or hydrochloric acid) are generally not used alone for reducing nitrobenzene. Although acids can sometimes participate in reduction reactions, they are not typically the primary agents for converting nitrobenzene to aniline.

3. \(Sn / dil. HCl\) (Tin and Dilute Hydrochloric Acid)

Tin (Sn) in the presence of dilute hydrochloric acid (HCl) is a well-known and effective reagent for the reduction of nitrobenzene to aniline. In this reaction, tin acts as a reducing agent and the dilute HCl provides an acidic environment. The nitro group (–NO₂) is reduced to an amino group (–NH₂) through a series of intermediate steps, where tin donates electrons to the nitro group, and hydrochloric acid helps in protonating intermediates and stabilizing the final product.

Reaction:
  

This reaction typically involves the formation of an intermediate nitroso or hydroxylamine derivative before ultimately yielding aniline.

4. \(OH^- / KOH\) (Sodium or Potassium Hydroxide)

Strong bases like potassium hydroxide (KOH) are generally used for deprotonation reactions or for facilitating reactions such as the aldol condensation or saponification. They are not used for the reduction of nitrobenzene. Strong bases do not reduce nitro groups but are more suited for reactions involving deprotonation or nucleophilic attack.

Conclusion

The correct reagent for reducing nitrobenzene to aniline is: 3. \(Sn / dil. HCl\)

This reagent effectively facilitates the reduction by providing a reducing environment (tin) and an acidic medium (dilute HCl) that helps convert the nitro group to an amino group.