Reactions of Substituted Benzenoid Derivatives to Form Products P Q R S

To determine the correct statement(s), let us analyze the step-by-step chemical transformations to identify the major products P, Q, R, and S.

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1. Formation of Product P

• Reactant: 1-ethyl-4-tert-butylbenzene.
• Reagents:
  1. $\text{KMnO}_4, \text{KOH}, \Delta$
  2. $\text{H}_3\text{O}^+$
• Mechanism:
  • The ethyl group ($-\text{CH}_2\text{CH}_3$) has benzylic hydrogens ($\alpha$-hydrogens) and is vigorously oxidized by alkaline $\text{KMnO}_4$ upon heating to form a carboxylate group ($-\text{COO}^-$), which gives a carboxylic acid group ($-\text{COOH}$) after acidic workup.
  • The tert-butyl group ($-\text{C(CH}_3)_3$) lacks benzylic hydrogens and therefore remains unreacted during oxidation.
• Product P: 4-tert-butylbenzoic acid (a monocarboxylic acid).

$\text{P} = \text{4-tert-butylbenzoic acid}$

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2. Formation of Product Q

• Reactant: Methyl 3-(chlorocarbonyl)benzoate (a 1,3-disubstituted benzene containing $-\text{COCl}$ and $-\text{COOMe}$).
• Reagents:
  1. $\text{NaOH}, \text{H}_2\text{O}$
  2. $\text{H}_3\text{O}^+$
• Mechanism:
  • Base-catalyzed hydrolysis converts both the acid chloride ($-\text{COCl}$) and the methyl ester ($-\text{COOMe}$) groups into carboxylate anions ($-\text{COO}^-$).
  • Acidification with $\text{H}_3\text{O}^+$ protonates these groups to yield dicarboxylic acid.
• Product Q: Benzene-1,3-dicarboxylic acid (isophthalic acid).

$\text{Q} = \text{benzene-1,3-dicarboxylic acid}$

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3. Formation of Product R

• Reactant: 3-(3-methoxy-3-oxopropanoyl)benzonitrile (a 1,3-disubstituted benzene containing $-\text{CN}$ and $-\text{COCH}_2\text{COOMe}$).
• Reagents:
  1. $\text{H}_3\text{O}^+, \Delta$
  2. $\text{H}_2\text{CrO}_4$
• Mechanism:
  • Step (i): Acidic hydrolysis converts the nitrile group ($-\text{CN}$) into a carboxylic acid group ($-\text{COOH}$) and the methyl ester ($-\text{COOMe}$) into a carboxylic acid group ($-\text{COOH}$), forming $3\text{-(2-carboxyacetyl)benzoic acid}$.
  • Upon heating ($\Delta$), the resulting $\beta$-keto acid moiety undergoes decarboxylation to release $\text{CO}_2$, yielding 3-acetylbenzoic acid ($3\text{-HOOC-C}_6\text{H}_4\text{-COCH}_3$).
  • Step (ii): Treatment with chromic acid ($\text{H}_2\text{CrO}_4$) oxidizes the acetyl group ($-\text{COCH}_3$) to a carboxylic acid group ($-\text{COOH}$).
• Product R: Benzene-1,3-dicarboxylic acid (isophthalic acid).

$\text{R} = \text{benzene-1,3-dicarboxylic acid}$

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4. Formation of Product S

• Reactant: 2-(4-bromophenyl)-1,3-dioxolane.
• Reagents:
  1. $\text{Mg}$, dry ether
  2. $\text{CO}_2$, then $\text{H}_3\text{O}^+$
  3. Ammoniacal $\text{AgNO}_3$, $\text{H}_3\text{O}^+$
• Mechanism:
  • Step (i): Reaction with $\text{Mg}$ in dry ether forms the Grignard reagent at the aryl bromide position ($-\text{MgBr}$).
  • Step (ii): Nucleophilic addition of the Grignard reagent to $\text{CO}_2$ followed by acidic workup introduces a carboxylic acid group ($-\text{COOH}$) at the 4-position. Concurrently, the acidic conditions deprotect the 1,3-dioxolane acetal group back to an aldehyde group ($-\text{CHO}$), forming 4-formylbenzoic acid.
  • Step (iii): Ammoniacal $\text{AgNO}_3$ (Tollens' reagent) selectively oxidizes the aldehyde group ($-\text{CHO}$) to a carboxylate anion, which upon acidification yields a carboxylic acid group ($-\text{COOH}$).
• Product S: Benzene-1,4-dicarboxylic acid (terephthalic acid).

$\text{S} = \text{benzene-1,4-dicarboxylic acid}$

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Evaluation of Options:

• (A) Incorrect:

  • The monomer of Dacron is terephthalic acid (benzene-1,4-dicarboxylic acid), whereas P is 4-tert-butylbenzoic acid.
  • The monomer of Glyptal is phthalic acid (benzene-1,2-dicarboxylic acid), whereas Q is isophthalic acid (benzene-1,3-dicarboxylic acid).

• (B) Incorrect:

  • P is a monocarboxylic acid (4-tert-butylbenzoic acid), not a dicarboxylic acid.

• (C) Correct:

  • Both Q and R are benzene-1,3-dicarboxylic acid (isophthalic acid).

• (D) Correct:

  • R is a dicarboxylic acid and does not contain carbonyl compounds with $\alpha$-hydrogens, so it does not undergo aldol condensation.
  • S is a dicarboxylic acid (terephthalic acid) and is not an aldehyde, so it does not undergo the Cannizzaro reaction.

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Conclusion:

The correct statements are C and D.