Question

Identify the product C in the series.
C$_6$H$_5$NO$_2 \xrightarrow{\text{Fe/HCl}} A \xrightarrow{\text{NaNO}_2\text{+HCl, } 273\text{ K}} B \xrightarrow{\text{H}_2\text{O, } 283\text{ K}} C$

• A. C$_6$H$_5$OH
• B. C$_6$H$_5$CH$_2$OH
• C. C$_6$H$_5$CHO
• D. C$_6$H$_5$NH$_2$

Hint:

Key Exam Tip:
Remember the key transformations:
• Nitro group reduction to amine: e.g., R-NO$_2 \xrightarrow{\text{Fe/HCl or Sn/HCl}} R-NH_2$.
• Diazotization of primary aromatic amines: R-NH$_2 \xrightarrow{\text{NaNO}_2\text{+HCl, low temp}} R-N_2^+Cl^-$.
• Hydrolysis of diazonium salts: R-N$_2^+X^- \xrightarrow{\text{H}_2\text{O, heat}} R-OH + N_2 + HX$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This sequence describes the laboratory preparation of phenol from nitrobenzene through reduction and diazotization steps.
Step 2: Detailed Explanation:
Stage 1: Reduction
Nitrobenzene (\( C_6H_5NO_2 \)) is reduced using iron and hydrochloric acid.
\( C_6H_5NO_2 + 6[H] \xrightarrow{Fe/HCl} C_6H_5NH_2 (A) + 2H_2O \)
Compound A is Aniline.
Stage 2: Diazotization
Aniline reacts with ice-cold nitrous acid (formed from \( NaNO_2 + HCl \)) at \( 273 \, K \).
\( C_6H_5NH_2 + HNO_2 + HCl \xrightarrow{273 \, K} C_6H_5N_2^+Cl^- (B) + 2H_2O \)
Compound B is Benzene Diazonium Chloride.
Stage 3: Hydrolysis
When benzene diazonium chloride is warmed with water at \( 283 \, K \), the diazo group is replaced by a hydroxyl group.
\( C_6H_5N_2Cl + H_2O \xrightarrow{\Delta} C_6H_5OH (C) + N_2 \uparrow + HCl \)
Compound C is Phenol.
Step 3: Final Answer:
The final product \( C \) is phenol, which corresponds to the formula \( C_6H_5OH \).