Question

The reaction sequence is: Benzene \(\xrightarrow{\text{Conc.HNO}_3, \text{Conc.H}_2\text{SO}_4, 323-333\text{K}}\) A \(\xrightarrow{\text{Fe/HCl}}\) B \(\xrightarrow{\text{NaNO}_2\text{/HCl}, 273\text{K}}\) C \(\xrightarrow{\text{C}_2\text{H}_5\text{OH}}\) Benzene + D + HCl + N\(_2\). Organic compound 'D' is

• A. Phenol (C\(_6\)H\(_5\)OH)
• B. Acetic acid (CH\(_3\)COOH)
• C. Ethanal (CH\(_3\)CHO)
• D. N-ethylaniline (C\(_6\)H\(_5\)NH-C\(_2\)H\(_5\))

Hint:

Reactions of diazonium salts are very important. Remember that with mild reducing agents like ethanol (C\(_2\)H\(_5\)OH) or hypophosphorous acid (H\(_3\)PO\(_2\)), the diazonium group is replaced by -H. In the process, ethanol is oxidized to ethanal.

Answer 1

The Correct Option is C

Step 1: Understanding the reaction sequence.
This is a multi-step synthesis starting from benzene. We need to identify the product at each step to determine the final product 'D'.
Step 2: Identifying compounds A, B, and C.

• Benzene \(\rightarrow\) A: The reaction of benzene with a nitrating mixture (Conc. HNO\(_3\) + Conc. H\(_2\)SO\(_4\)) is electrophilic aromatic substitution (nitration). The product A is Nitrobenzene (C\(_6\)H\(_5\)NO\(_2\)).
  
• A \(\rightarrow\) B: The reaction of nitrobenzene with Fe/HCl is a standard method for the reduction of the nitro group to an amino group. The product B is Aniline (C\(_6\)H\(_5\)NH\(_2\)).
  
• B \(\rightarrow\) C: The reaction of aniline with NaNO\(_2\)/HCl at low temperature (273K or 0\(^\circ\)C) is diazotization. The product C is Benzenediazonium chloride (C\(_6\)H\(_5\)N\(_2\)\(^+\)Cl\(^-\)).
  

Step 3: Identifying the final reaction and product D.
The benzenediazonium chloride (C) is treated with ethanol (C\(_2\)H\(_5\)OH). In this reaction, ethanol acts as a reducing agent, and the diazonium group is replaced by a hydrogen atom, yielding benzene. Ethanol itself gets oxidized.
The reaction is:
\[ \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{CH}_3\text{CH}_2\text{OH} \rightarrow \text{C}_6\text{H}_6 + \text{CH}_3\text{CHO} + \text{N}_2 + \text{HCl} \] Ethanol (an alcohol) is oxidized to Ethanal (an aldehyde). Therefore, the organic compound 'D' is ethanal.
Step 4: Final Answer:
The organic compound 'D' formed in the reaction is Ethanal (CH\(_3\)CHO).