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 from cumene. We need to identify the major products P, Q, S, and T, and then determine which of the given statements about them are correct. This question might have multiple correct answers.
Step 2: Key Formula or Approach:
Analyze each reaction step to determine the structures of P, Q, S, and T. Then, evaluate each statement based on the properties of these identified compounds.
Step 3: Detailed Explanation:
Part 1: Analyze the first reaction sequence (Aniline to Q)
1. Aniline \(\xrightarrow{\text{1. (CH}_3\text{CO})_2\text{O, pyridine}\) Intermediate:}
Aniline reacts with acetic anhydride ($(\text{CH}_3\text{CO})_2\text{O}$) in pyridine to form acetanilide. This is an acetylation reaction, protecting the amino group.
Intermediate = Acetanilide (\(\text{C}_6\text{H}_5\text{NHCOCH}_3\)).
2. Acetanilide \(\xrightarrow{\text{2. Conc. HNO}_3\text{, Conc. H}_2\text{SO}_4\text{, 288 K}} \text{P}: \)
Acetanilide undergoes nitration. The -NHCOCH$_3$ group is an ortho/para directing group. Under these conditions (mild temperature, $288K$), nitration occurs preferentially at the para position.
So, P = 4-nitroacetanilide (p-nitroacetanilide).
Therefore, statement (C) "P is a dinitro compound" is Incorrect. P has only one nitro group.
3. P (4-nitroacetanilide) \(\xrightarrow{\text{1. H}_3\text{O}^+}{\text{2. NaNO}_2\text{/HCl, 273 - 278 K}} \text{Q}: \)
- Step 1: Hydrolysis of P: 4-nitroacetanilide undergoes acid-catalyzed hydrolysis to remove the acetyl group, regenerating the amino group.
Intermediate = 4-nitroaniline (p-nitroaniline).
- Step 2: Diazotization of 4-nitroaniline: Primary aromatic amines (like 4-nitroaniline) react with nitrous acid ($NaNO_2/HCl$) at low temperatures (0-5\(^{\circ}\)C or 273-278 K) to form an aryl diazonium salt.
So, Q = 4-nitrobenzene diazonium chloride (\(\text{O}_2\text{N}-\text{C}_6\text{H}_4-\text{N}_2^+\text{Cl}^-\)).
Now evaluate statement (A): "Q on treatment with ethanol generates an aromatic aldehyde."
Aryl diazonium salts (Q) react with ethanol to form aryl halides (replacement of $-N_2^+$ with $-H$) or phenol. It typically doesn't form an aromatic aldehyde unless specific conditions are used (e.g., using $H_3PO_2$ for reduction to benzene, or $Cu_2Cl_2$ for replacement with Cl). So, Q reacting with ethanol to give an aromatic aldehyde is generally Incorrect.
Part 2: Analyze the second reaction sequence (Cumene to T)
1. Cumene \(\xrightarrow{\text{1. O}_2\text{/H}_3\text{O}^+}{\text{2. NaOH/CO}_2}{\text{3. H}_3\text{O}^+} \text{S}: \)
- Step 1: Cumene + O$_2$/H$_3$O$^+$: This is the Cumene process for industrial production of phenol. Cumene (isopropylbenzene) is oxidized by air ($O_2$) to cumene hydroperoxide, which then undergoes acid-catalyzed cleavage ($H_3O^+$) to produce phenol and acetone.
- So, S = Phenol (\(\text{C}_6\text{H}_5\text{OH}\)) and Acetone. (S is the major organic product).
Now evaluate statement (B): "S gives positive phthalein dye test."
Phenol gives a positive phthalein dye test (e.g., phenolphthalein test) where it forms a characteristic colored product.
This statement is Correct.
2. S (Phenol) \(\xrightarrow{\text{aqueous NaOH}} \text{T}: \)
Phenol reacts with aqueous NaOH to form sodium phenoxide (\(\text{C}_6\text{H}_5\text{O}^-\text{Na}^+\)). Phenoxide ions are generally colorless in solution.
So, T = Sodium phenoxide.
Now evaluate statement (D): "T is a coloured compound."
Sodium phenoxide solution is colorless. Therefore, this statement 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 (S is Phenol).
(C) P is a dinitro compound. \(\rightarrow\) Incorrect (P is mononitro).
(D) T is a coloured compound. \(\rightarrow\) Incorrect (T is colorless).
Therefore, only statement (B) is correct.
Step 4: Final Answer:
The correct statement is (B) S gives positive phthalein dye test.