Question

In the following sequence of reactions, the compound Q formed will be?
${C_6}{H_6}\xrightarrow{{oleum}}P\xrightarrow[{(ii){H^ + }}]{{(i)NaOH}}Q$
A.Aniline
B.Phenol
C.Benzaldehyde
D.Benzene sulphonic acid

Answer 1

It is a preparation method to convert benzene to phenol. Oleum is a dense and corrosive liquid consisting of concentrated sulphuric acid which contains excess sulfur trioxide in solution.

Complete step by step answer: Benzene which is represented as ${C_6}{H_6}$ reacts with oleum to form benzene sulphonic acid. Oleum which is represented as ${H_2}{S_2}{O_7}$ and Benzene sulphonic acid as ${C_6}{H_5}S{O_3}H$ . Then benzene sulphonic acid reacts with sodium hydroxide (NaOH) to form sodium benzene sulphonate (${C_6}{H_5}S{O_3}Na$) . It is a neutralization reaction. It is further getting fuse with excess NaOH to get sodium phenoxide $\left( {{C_6}{H_5}ONa} \right)$ and treat it in the presence of hydrogen ion to get the required product i.e. phenol. Phenol is represented as ${C_6}{H_5}OH$ . Hence, option B is correct.
${C_6}{H_6}\xrightarrow[{{H_2}{S_2}{O_7}(conc.{H_2}S{O_4})}]{{Oleum}}{C_6}{H_5}S{O_3}H\xrightarrow[{(2){H^ + }}]{{(1)NaOH}}{C_6}{H_5}OH$
Phenol is an aromatic compound that consists of one or more OH groups directly attached to the carbon of the benzene ring. Phenol word is derived from the word ‘Phene’ which is an old name of benzene. For –OH Group, (hydroxyl) use as a prefix and (ol) use as a suffix. It is a colorless, crystalline solid with phenolic odor. It is used in washrooms.
Therefore, P = Sodium benzene sulphonate and Q = Phenol.

Additional information:
Some other method for preparation of phenol:
Preparation of phenols from haloarenes
Preparation of phenols from Diazonium salts
Preparation of phenols from Cumene

Note: Aniline is more basic. Phenol loses a proton easily to form the phenolate ion, and therefore is a reasonably strong acid. Aniline only reluctantly accepts a proton to form the anilinium ion, and hence is a weak base.