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)

Correct Option: S gives positive phthalein dye test.

Let us analyze the given chemical reaction sequences step-by-step to identify the major products P, Q, S, and T.

Reaction Sequence 1: Formation of P and Q

1. Aniline to P:

Aniline is reacted with acetic anhydride ((CH₃CO)₂O) in pyridine. The -NH₂ group is acetylated to form acetanilide (-NHCOCH₃), protecting the amino group and reducing its activating effect.

Next, nitration using concentrated HNO₃ and H₂SO₄ at 288 K leads to para-nitration as the major product because the acetamido group (-NHCOCH₃) is bulky and ortho/para-directing.

Thus, P is 4-nitroacetanilide (a mononitro compound, not a dinitro compound).

2. P to Q:

Hydrolysis of P (4-nitroacetanilide) with H₃O⁺ removes the acetyl group to give 4-nitroaniline.

Subsequent diazotization of 4-nitroaniline using NaNO₂/HCl at 273–278 K yields 4-nitrobenzenediazonium chloride as product Q.

Reaction Sequence 2: Formation of S and T

1. Cumene to S:

Cumene (isopropylbenzene) undergoes oxidation with O₂ followed by acid hydrolysis (H₃O⁺) to form phenol and acetone (Cumene process).

Phenol then reacts with NaOH and CO₂ followed by acidic workup (Kolbe-Schmitt reaction) to yield salicylic acid (2-hydroxybenzoic acid) as product S.

2. Properties of S (Salicylic Acid / Phenolic derivative):

Phenolic compounds with an unblocked ortho or para position, such as salicylic acid or phenol, react with phthalic anhydride in the presence of concentrated H₂SO₄ to form phthalein dyes (such as phenolphthalein derivative). Therefore, S gives a positive phthalein dye test.

Evaluating the given options:

1. "Q on treatment with ethanol generates an aromatic aldehyde." – Incorrect (Diazonium salts treated with ethanol undergo reduction to give nitrobenzene, not an aromatic aldehyde).

2. "S gives positive phthalein dye test." – Correct (Salicylic acid contains a phenolic -OH group and reacts with phthalic anhydride to yield a phthalein dye).

3. "P is a dinitro compound." – Incorrect (P is a mononitro compound: 4-nitroacetanilide).

4. "T is a coloured compound." – (Evaluation shows that the dye formation or azo coupling gives an azo dye; however, among the given single/multiple choice options provided in the correct answer key, the primary correct statement is that S gives a positive phthalein dye test).