The conversion of phenol to aspirin is carried out by

The correct answer is Option (3) → Kolbe’s reaction followed by acetylation.

Aspirin is acetylsalicylic acid: a benzene ring carrying a –COOH group and, next to it, an acetylated –OH group (–\( \ce{OCOCH3} \)). Making it from phenol needs two changes: a –COOH group must be introduced at the ortho position, and the –OH group must be acetylated.

Kolbe’s reaction introduces the –COOH group. Sodium phenoxide reacts with carbon dioxide under pressure (4–7 atm, about 400 K), and acidification gives salicylic acid (2-hydroxybenzoic acid):

    \( \displaystyle \ce{C6H5OH + NaOH -> C6H5ONa + H2O} \)

    \( \displaystyle \ce{C6H5ONa + CO2} \xrightarrow{\text{4-7 atm, 400 K}} \ce{HOC6H4COONa} \)

    \( \displaystyle \ce{HOC6H4COONa + HCl -> HOC6H4COOH + NaCl} \)

Acetylation of the phenolic –OH group with acetic anhydride then gives aspirin:

    \( \displaystyle \ce{HOC6H4COOH + (CH3CO)2O} \xrightarrow{\ce{H+}} \underset{\text{aspirin}}{\ce{CH3COOC6H4COOH}} + \ce{CH3COOH} \)

So phenol is converted to aspirin by Kolbe’s reaction followed by acetylation.

Why the other options are incorrect

• Option (1) Reimer-Tiemann reaction followed by acetylation — Incorrect. The Reimer-Tiemann reaction (\( \ce{CHCl3} \) + NaOH) introduces a –CHO group, giving salicylaldehyde, not salicylic acid.

      \( \displaystyle \ce{C6H5OH} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CHCl3}\text{ + aq. }\ce{NaOH}} \underset{\text{salicylaldehyde}}{\ce{HOC6H4CHO}} \)

• Option (2) acetylation followed by Reimer-Tiemann reaction — Incorrect. Acetylation first blocks the –OH group, and Reimer-Tiemann would still give an aldehyde, not an acid.

• Option (4) acetylation followed by Kolbe’s reaction — Incorrect. Kolbe’s reaction needs the phenoxide ion; once the –OH is acetylated there is no phenoxide to react with \( \ce{CO2} \). The order of the two steps matters.

NCERT (2026-27 edition):
Esterification – “… The introduction of acetyl (CH₃CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin.”

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.”