Phenol is treated separately with the reagents given in List-I. Match each reagent with the main product in List-II.
| List-I (Reagent) | List-II (Main product) |
|---|---|
| (A) NaOH, then CO2 and H+ | (I) Phenol-2,4-disulphonic acid |
| (B) CHCl3 and aqueous NaOH, then H+ | (II) Salicylaldehyde |
| (C) Concentrated HNO3 | (III) 2,4,6-Trinitrophenol |
| (D) Concentrated H2SO4 | (IV) 2-Hydroxybenzoic acid |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-IV, B-II, C-III, D-I
The –OH group activates the ring of phenol, and each of these reagents puts a new group on the ring at the ortho and para positions. They differ in the group that enters.
(A) NaOH, then CO2 and H+ — This matches (IV) 2-Hydroxybenzoic acid. This is Kolbe’s reaction: the phenoxide ion is so reactive that even the weak electrophile CO2 substitutes at the ortho position, giving a –COOH group (salicylic acid).
(B) CHCl3 and aqueous NaOH, then H+ — This matches (II) Salicylaldehyde. In the Reimer-Tiemann reaction a –CHO group is introduced at the ortho position; the substituted benzal chloride formed first is hydrolysed by the alkali.
(C) Concentrated HNO3 — This matches (III) 2,4,6-Trinitrophenol. With the concentrated acid, three –NO2 groups enter, at both ortho positions and the para position (picric acid, formed in poor yield).
(D) Concentrated H2SO4 — This matches (I) Phenol-2,4-disulphonic acid. Sulphonation puts two –SO3H groups on the ring; this compound is then nitrated to make picric acid today.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “With concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol. The product is commonly known as picric acid. The yield of the reaction product is poor. Nowadays picric acid is prepared by treating phenol first with concentrated sulphuric acid which converts it to phenol-2,4-disulphonic acid, and then with concentrated nitric acid to get 2,4,6-trinitrophenol.”
“2. Kolbe’s reaction … Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product.”
“3. Reimer-Tiemann reaction … On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. … The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde.”