Match List-I with List-II
|
List-I Reaction |
List-II Preparation |
|
(A) Kolbe's Reaction |
(I) Salicylaldehyde |
|
(B) Reimer-Tiemann Reaction |
(II) Salicylic acid |
|
(C) Williamson synthesis |
(III) Ethyl methyl ether |
|
(D) Cumene Process |
(IV) Phenol |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(II), (B)-(I), (C)-(III), (D)-(IV)
The four reactions are standard preparations from the chemistry of phenols and ethers. Two of them put a new group ortho to the –OH of phenol: carbon dioxide gives a –COOH group (Kolbe) and chloroform in alkali gives a –CHO group (Reimer-Tiemann). Williamson synthesis joins an alkoxide and an alkyl halide into an ether, and the cumene process makes phenol itself on an industrial scale.
(A) Kolbe’s Reaction — This matches (II) Salicylic acid. Sodium phenoxide, more reactive than phenol towards electrophiles, is attacked by the weak electrophile \( \ce{CO2} \) at the ortho position; acidification gives 2-hydroxybenzoic acid.
\( \displaystyle \ce{C6H5OH} \xrightarrow{\ce{NaOH}} \ce{C6H5ONa} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CO2}} o\text{-}\ce{HOC6H4COOH} \)
(B) Reimer-Tiemann Reaction — This matches (I) Salicylaldehyde. Phenol is heated with chloroform and aqueous sodium hydroxide; a –\( \ce{CHCl2} \) group enters the ortho position and is hydrolysed to –CHO, and acidification gives 2-hydroxybenzaldehyde.
\( \displaystyle \ce{C6H5OH} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CHCl3},\ \text{aq. }\ce{NaOH}} o\text{-}\ce{HOC6H4CHO} \)
(C) Williamson synthesis — This matches (III) Ethyl methyl ether. A sodium alkoxide displaces the halide of a primary alkyl halide by \(S_N2\) attack, so sodium ethoxide and methyl bromide give ethyl methyl ether.
\( \displaystyle \ce{C2H5ONa + CH3Br -> C2H5-O-CH3 + NaBr} \)
(D) Cumene Process — This matches (IV) Phenol. Cumene (isopropylbenzene) is oxidised by air to cumene hydroperoxide, which dilute acid splits into phenol and acetone.
\( \displaystyle \ce{C6H5CH(CH3)2} \xrightarrow{\ce{O2}} \ce{C6H5C(CH3)2OOH} \xrightarrow{\ce{H+}/\ce{H2O}} \ce{C6H5OH + CH3COCH3} \)
Shortcut: (A)-(II) appears only in Option (2).