JEE Advanced 2022 — Paper 1 — CHEM-I solution

JEE Advanced2022Paper 1CHEM-I

The weight percentage of hydrogen in Q, formed in the following reaction sequence, is ________.

[Given: Atomic mass of H = 1, C = 12, N = 14, O = 16, S = 32, Cl = 35]

Your answer

Solution

Step 1 (Dow process): chlorobenzene + NaOH (623 K, 300 atm) gives sodium phenoxide, which on acid work-up gives phenol.

Step 2: phenol is first sulphonated by conc. H $_{2}$ SO $_{4}$ at the ortho and para positions (the SO $_{3}$ H groups act as blocking and activating positions, also help control product distribution), then nitrated by conc. HNO $_{3}$ . The sulphonic groups are displaced during nitration, yielding 2,4,6-trinitrophenol (picric acid) as the major product Q.

Composition of picric acid C $_{6}$ H $_{3}$ N $_{3}$ O $_{7}$ :

Molar mass = $6 (12) + 3 (1) + 3 (14) + 7 (16) = 72 + 3 + 42 + 112 = 229$ g/mol.

Weight percent of H = $\frac{3}{229} \times 100 = 1.31%$ .

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