Question

The total number of reagents from those given below, that can convert nitrobenzene into aniline is ___________. (Integer answer) 
I. \( Sn - HCl \) 
II. \( Sn - NH_4OH \) 
III. \( Fe - HCl \) 
IV. \( Zn - HCl \) 
V. \( H_2 - Pd \) 
VI. \( H_2 - Raney \ Nickel \)} 
 

Hint:

While many metals reduce nitro groups, the final product depends on the pH. Acidic medium results in aniline, whereas neutral or basic media lead to bimolecular reduction products.

Answer 1

Correct Answer: 5

Step 1: Understanding the Concept:
The conversion of nitrobenzene to aniline is a reduction process where the \( -NO_2 \) group is converted to an \( -NH_2 \) group. This can be achieved using metal-acid combinations or catalytic hydrogenation.
Step 2: Detailed Explanation:
1. Metal + Acid (I, III, IV): Reduction with metals like Sn, Fe, or Zn in the presence of concentrated \( HCl \) is the standard laboratory and industrial method. Specifically, \( Fe/HCl \) is preferred industrially as it produces \( FeCl_2 \) which hydrolyzes to release more \( HCl \).
2. Catalytic Hydrogenation (V, VI): Hydrogen gas in the presence of finely divided catalysts like Palladium (Pd) or Raney Nickel (Ni) reduces nitro groups to amines efficiently.
3. Sn + \( NH_4OH \) (II): This is a reduction in a basic/neutral medium. In such conditions, the reduction of nitrobenzene often stops at intermediate stages like phenylhydroxylamine or involves coupling to form azoxybenzene, depending on exact conditions. It is not the standard reagent to produce aniline.
Step 3: Final Answer:
Reagents I, III, IV, V, and VI are successful. The total count is 5.