JEE Advanced 2023 Paper 2 Q07 Chemistry Organic Reactions & Mechanisms Carboxylic Acids & Derivatives Hard

JEE Advanced 2023 Paper 2 · Q07 · Carboxylic Acids & Derivatives

In the following reactions, $P$, $Q$, $R$, and $S$ are the major products. (a) 1-ethyl-4-tert-butylbenzene (an arene bearing a $-$CH$_2$CH$_3$ group and a $-$C(CH$_3$)$_3$ group on a benzene ring in para positions) is treated with (i) KMnO$_4$, KOH, $\Delta$; (ii) H$_3$O$^+$ $\rightarrow P$. (b) Methyl 3-(chlorocarbonyl)benzoate (a benzene ring meta-substituted with $-$COOCH$_3$ and $-$COCl) is treated with (i) NaOH, H$_2$O; (ii) H$_3$O$^+$ $\rightarrow Q$. (c) Methyl 3-(3-cyanobenzoyl)acetate (a benzene ring meta-substituted with $-$CN and $-$COCH$_2$COOCH$_3$ ; that is, a $\beta$-keto ester aryl group with a meta cyano substituent) is treated with (i) H$_3$O$^+$, $\Delta$; (ii) H$_2$CrO$_4$ $\rightarrow R$. (d) 2-(4-bromophenyl)-1,3-dioxolane (a 4-bromophenyl group attached to a cyclic acetal $-$CH(OCH$_2$CH$_2$O$-$)) is treated with (i) Mg, dry ether; (ii) CO$_2$, then H$_3$O$^+$; (iii) ammoniacal AgNO$_3$, H$_3$O$^+$ $\rightarrow S$. The correct statement(s) about $P$, $Q$, $R$, and $S$ is(are)

  1. A. $P$ and $Q$ are monomers of polymers dacron and glyptal, respectively.
  2. B. $P$, $Q$, and $R$ are dicarboxylic acids.
  3. C. Compounds $Q$ and $R$ are the same.
  4. D. $R$ does not undergo aldol condensation and $S$ does not undergo Cannizzaro reaction.
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:C, D

Solution

(a) KMnO$_4$/KOH/$\Delta$ oxidises only the benzylic C-H bearing side chain. The ethyl group is oxidised to $-$COOH, but the $tert$-butyl group has no benzylic hydrogen and is unaffected. So $P = $ 4-$tert$-butylbenzoic acid, a mono-carboxylic acid. (b) NaOH/H$_2$O hydrolyses both the methyl ester ($-$COOMe) and the acid chloride ($-$COCl) to carboxylates; H$_3$O$^+$ protonates to give the diacid. $Q = $ benzene-1,3-dicarboxylic acid (isophthalic acid). (c) Acidic hydrolysis converts $-$CN to $-$COOH and hydrolyses the $\beta$-keto methyl ester $-$COCH$_2$COOMe; the resulting $\beta$-keto acid decarboxylates on heating to give an aryl methyl ketone $-$COCH$_3$. H$_2$CrO$_4$ then oxidises the methyl ketone side chain to $-$COOH (haloform-type oxidation of aryl methyl ketones). The cyano group has already become $-$COOH. Net: a benzene ring meta-substituted with two $-$COOH groups. $R = $ benzene-1,3-dicarboxylic acid (isophthalic acid). Therefore $Q = R$. Option (C) is TRUE. (d) Mg/dry ether on 2-(4-bromophenyl)-1,3-dioxolane gives the aryl Grignard with the acetal intact; CO$_2$/H$_3$O$^+$ installs $-$COOH at the para position. The acidic work-up also hydrolyses the cyc…[truncated]

Want to drill deeper? Open this question inside SolveKar AI and tap "Why?" on any step — the AI Mentor reads your full solution context and explains until it clicks. Download SolveKar AI →