JEE Advanced 2024 Paper 1, Chemistry Section 2 Q2: Properties and Important Reactions of Aldehydes & Ketones

JEE Advanced2024Paper 1Chemistry Section 2

Reaction of iso-propylbenzene with $O_{2}$ followed by the treatment with $H_{3} O^{+}$ forms phenol and a by-product P. Reaction of P with 3 equivalents of $C l_{2}$ gives compound Q. Treatment of Q with $Ca (OH)_{2}$ produces compound R and calcium salt S.

The correct statement(s) regarding P, Q, R and S is(are)

A
Reaction of P with R in the presence of KOH followed by acidification gives
B
Reaction of R with $O_{2}$ in the presence of light gives phosgene gas
C
Q reacts with aqueous NaOH to produce $C l_{3} CC H_{2} OH$ and $C l_{3} CCOONa$
D
S on heating gives P

Solution

The Hock (cumene) process: cumene + O $_{2}$ then H $_{3}$ O $^{+}$ gives phenol and acetone (P = $C H_{3} COC H_{3}$ ).

Treatment of acetone with 3 equivalents of Cl $_{2}$ chlorinates only the methyl groups on one side completely, giving 1,1,1-trichloroacetone (Q = $C H_{3} COCC l_{3}$ ).

With Ca(OH) $_{2}$ , the haloform-type cleavage occurs: $C H_{3} COCC l_{3}$ splits to give R = CHCl $_{3}$ (chloroform) and the calcium salt of acetate, S = $(C H_{3} COO)_{2} Ca$ .

(A) Acetone + CHCl $_{3}$ with KOH (base-catalysed addition of the trichloromethyl carbanion to the carbonyl) gives, after acidification, 1,1,1-trichloro-2-methyl-2-propanol $(C H_{3})_{2} C (OH) CC l_{3}$ — known as chloretone. Correct.

(B) Chloroform is oxidised by atmospheric O $_{2}$ in the presence of light to give phosgene COCl $_{2}$ . Correct.

(C) Q is $C H_{3} COCC l_{3}$ . Aqueous NaOH cleaves it via haloform reaction to give CHCl $_{3}$ and $C H_{3} COONa$ (sodium acetate), not $C l_{3} CC H_{2} OH$ and $C l_{3} CCOONa$ . Incorrect.

(D) Dry distillation of calcium acetate (S) yields acetone (P). Correct.

$∴$ Correct: (A), (B), (D).

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JEE Advanced 2024 Paper 1, Chemistry Section 2 Q2: Properties and Important Reactions of Aldehydes & Ketones

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