For the following reaction sequence, choose the correct option. Benzene (i) CH₃COCl, AlCl₃ (ii) NaOCl P+Q
- A.If P is the sodium salt of a carboxylic acid, Q is a primary alcohol
- B.P and Q are aromatic compounds
- C.If P gives a carboxylic acid on acidification, Q gives a poisonous gas on exposure to air and light✓
- D.Both P and Q are carbonyl compounds
Correct Answer
(C) If P gives a carboxylic acid on acidification, Q gives a poisonous gas on exposure to air and light
Solution & Explanation
Step 1 — Friedel–Crafts acylation. Benzene + CH₃COCl in the presence of anhydrous AlCl₃ gives acetophenone, C₆H₅COCH₃ (an aryl methyl ketone). Step 2 — Haloform (here "chloroform") reaction. Acetophenone has a CH₃CO– group attached to carbon, so it answers the haloform test. NaOCl supplies the hypohalite (Cl⁺/OCl⁻); the three α-hydrogens are successively replaced and the C–C bond is then cleaved. Products: P = sodium benzoate, C₆H₅COONa, and Q = chloroform, CHCl₃. Step 3 — Test the options. On acidification, sodium benzoate (P) gives benzoic acid, C₆H₅COOH — a carboxylic acid. This matches the first half of option (C). Step 4 — Fate of CHCl₃ (Q). Chloroform, on exposure to air and light, is slowly oxidised to phosgene: 2 CHCl₃ + O₂ → 2 COCl₂ + 2 HCl. Phosgene (COCl₂) is a poisonous gas. This matches the second half of option (C). Why the others fail: Q is CHCl₃, not a primary alcohol (A wrong); CHCl₃ is not aromatic (B wrong); neither final product P nor Q is a carbonyl compound — the ketone has already been consumed (D wrong). Hence the correct answer is option C.
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