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ChemistrySingle correct+4 / -1Question 70 of 75

JEE Main 2026 · 4 Apr · Shift 1, Chemistry question 70

Identify the colour of compound 'X' in the sequence of the reaction.

Two phenol + phthalic anhydride (conc. H₂SO₄) give phenolphthalein (the lactone). NaOH opens it to the pink quinonoid dianion (one phenoxide, one quinone ring, a carboxylate). Excess NaOH gives X: the carbinol trianion, with C bearing OH, two phenoxide rings and the benzoate ring.
Choose one option
Answer and worked solution

Official answer: D

Phenolphthalein (from phenol and phthalic anhydride) is colourless; base gives the pink quinonoid dianion.

Excess NaOH adds OH⁻ at the central carbon, giving the carbinol trianion X. Its conjugation is broken, so X is colourless.

(D)

Topics:Indicators and titrationsPhenols
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