Question

In the following reaction sequence, P, Q, S and T are the major products.

The correct statement(s) about P, Q, S and T is(are)

• A. Q on treatment with ethanol generates an aromatic aldehyde.
• B. S gives positive phthalein dye test.
• C. P is a dinitro compound.
• D. T is a coloured compound.

Hint:

Break down complex reaction sequences into individual steps. Remember key named reactions (e.g., Cumene process, Hofmann bromamide, diazotization) and their typical products. Also, recall common functional group tests (e.g., phthalein dye test for phenols).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question presents two separate multi-step reaction sequences. The first sequence starts from aniline, and the second starts from cumene. We need to identify the major products \(P\), \(Q\), \(S\), and \(T\), and then determine which of the given statements are correct. This question may have multiple correct answers.

Step 2: Key Formula or Approach:
Analyze each reaction step carefully to determine the structures of \(P\), \(Q\), \(S\), and \(T\). Then evaluate each statement using the properties of these compounds.

Step 3: Detailed Explanation:
Part 1: Analyze the first reaction sequence (Aniline to \(Q\))

1. Aniline \(\xrightarrow{\text{1. }(CH_3CO)_2O,\ \text{pyridine}}\) Intermediate
Aniline reacts with acetic anhydride in pyridine to form acetanilide. This is an acetylation reaction used to protect the amino group. Thus, the intermediate formed is: \[ \text{Acetanilide } (C_6H_5NHCOCH_3) \]

2. Acetanilide \(\xrightarrow{\text{Conc. }HNO_3,\ \text{Conc. }H_2SO_4,\ 288\,K} P\)
Acetanilide undergoes nitration. The \(-NHCOCH_3\) group is ortho/para directing, and under mild conditions para substitution predominates. Thus, \[ P = p\text{-nitroacetanilide} \] Therefore, statement (C) “\(P\) is a dinitro compound” is Incorrect.

3. \(P \xrightarrow{\text{1. }H_3O^+} \xrightarrow{\text{2. }NaNO_2/HCl,\ 273\text{-}278\,K} Q\)

Step 1: Hydrolysis of \(P\)
\(p\)-Nitroacetanilide undergoes hydrolysis to form \(p\)-nitroaniline. \[ p\text{-Nitroacetanilide} \rightarrow p\text{-Nitroaniline} \]
Step 2: Diazotization
\(p\)-Nitroaniline reacts with nitrous acid \((NaNO_2/HCl)\) at low temperature to form the diazonium salt. Thus, \[ Q = p\text{-Nitrobenzene diazonium chloride} \]
Now evaluate statement (A): “\(Q\) on treatment with ethanol generates an aromatic aldehyde.” Aryl diazonium salts do not generally produce aromatic aldehydes with ethanol. Ethanol usually reduces the diazonium group to hydrogen. Hence, statement (A) is Incorrect.

Part 2: Analyze the second reaction sequence (Cumene to \(T\))

1. Cumene \(\xrightarrow{\text{1. }O_2/H_3O^+} \xrightarrow{\text{2. }NaOH/CO_2} \xrightarrow{\text{3. }H_3O^+} S\)

Cumene undergoes the cumene process to produce phenol. Thus, \[ S = \text{Phenol} \]
Now evaluate statement (B): “\(S\) gives positive phthalein dye test.” Phenol gives a positive phthalein dye test. Hence, statement (B) is Correct.

2. \(S \xrightarrow{\text{aqueous NaOH}} T\)
Phenol reacts with aqueous NaOH to form sodium phenoxide. Thus, \[ T = \text{Sodium phenoxide} \]
Now evaluate statement (D): “\(T\) is a coloured compound.” Sodium phenoxide is generally colorless. Hence, statement (D) is Incorrect.

Summary of Statements:
(A) \(Q\) on treatment with ethanol generates an aromatic aldehyde \(\rightarrow\) Incorrect
(B) \(S\) gives positive phthalein dye test \(\rightarrow\) Correct
(C) \(P\) is a dinitro compound \(\rightarrow\) Incorrect
(D) \(T\) is a coloured compound \(\rightarrow\) Incorrect

Step 4: Final Answer:
The correct statement is \[ \boxed{(B)} \]