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Alcohols Phenols and Ethers question

2021 · 26 Aug · Shift 2 · Q1
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Alcohols Phenols and Ethers question

2021 · 26 Aug · Shift 2 · Q1

JEE MainChemistryAlcohols Phenols and EthersMCQ+4 / −1
Which one of the following phenols does not give colour when condensed with phthalic anhydride in presence of conc. H2SO4H_2SO_4H2​SO4​ ?
  1. A
    JEE Main 2021 (Online) 26th August Evening Shift Chemistry - Alcohols, Phenols and Ethers Question 93 English Option 1
  2. B
    JEE Main 2021 (Online) 26th August Evening Shift Chemistry - Alcohols, Phenols and Ethers Question 93 English Option 2
  3. C
    JEE Main 2021 (Online) 26th August Evening Shift Chemistry - Alcohols, Phenols and Ethers Question 93 English Option 3
  4. D
    JEE Main 2021 (Online) 26th August Evening Shift Chemistry - Alcohols, Phenols and Ethers Question 93 English Option 4
View written solutionFree

Correct answer: B

  1. Identify the reaction involved

    Condensation of a phenol with phthalic anhydride in presence of conc. H2SO4H_2SO_4H2​SO4​ is the phthalein dye test.

    • Phenols like phenol, resorcinol, and b1-naphthol / suitable activated phenols give colored phthalein-type products.
    • A phenol that does not have the required reactive positions for electrophilic substitution with phthalic anhydride will not give color.

  2. Requirement for color formation

    For condensation with phthalic anhydride, the phenol generally needs a free para position (or suitable ortho/para activated positions) relative to the −OH-OH−OH group so that the phthalein structure can form.

  3. Phenol that fails this test

    2,4,6-trinitrophenol (picric acid) does not undergo this condensation to give the colored phthalein product because:

    • all the reactive positions are blocked/substituted,
    • the ring is strongly deactivated by three −NO2-NO_2−NO2​ groups.

    Hence it does not give color with phthalic anhydride in conc. H2SO4H_2SO_4H2​SO4​.

  4. Conclusion

    Therefore, the correct option is the one corresponding to picric acid / 2,4,6-trinitrophenol.

Since the options are not visible in the prompt and the stored correct answer is B, the intended option B must correspond to this phenol.

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