Question

Phenol on treating with concentrated ${H_2}S{O_4}$ at $15 - {20^ \circ }C$ mainly produces:
A.phenol-2,4,6-trisulfonic acid
B.2-Hydroxy benzene sulphonic acid
C.Phenol-4-sulphonic acid
D.A $50\% $ mixture of ortho and para phenol sulfonic acid

Answer 1

Hint: Phenol is an aromatic compound with chemical formula ${C_6}{H_6}O$ . It consists of hydroxyl group and phenyl group attached to each other. Moreover it is a white crystalline solid which is soluble in water whereas phenol sodium salt i.e. sodium phenoxide is much more soluble.

Complete step by step answer:
Phenol was discovered in the year 1834 by Ferdinand Runge. These are the organic compounds containing at least one \[O - H\] group which is directly attached to the benzene ring. Now, phenols can be synthesized by two methods:
From sulphonic acids –In this process, sodium benzene sulphonate is fused with sodium hydroxide at 573kto produce sodium phenoxide, which further on acidification yields phenol. The reactions are given below:
 ${C_6}{H_5}S{O_3}Na + 2NaOH\xrightarrow{{573K}}{C_6}{H_5}ONa + N{a_2}S{O_3} + {H_2}O$
 $2{C_6}{H_5}ONa + 2HCl \to 2{C_6}{H_5}OH + 2NaCl$
From diazonium salts-In this process when a diazonium salt solution is steam distilled or is added to boiling dil. Sulphuric acid, it forms phenol. The reaction is given below:
 ${C_6}{H_5}{N_2}Cl + {H_2}O\xrightarrow[{{H_2}S{O_4}}]{\Delta }{C_6}{H_5}OH + {N_2} + HCl$
Now, the product of the reaction of phenol with conc. Sulphuric acid depends upon the temperature of the reaction. So, when phenol is treated with conc. ${H_2}S{O_4}$ at $15 - {20^ \circ }C$ , o-phenol sulphonic acid is formed as the major product. But, when phenol is treated with conc. Sulphuric acid at ${100^ \circ }C$ , then p-phenol sulphonic acid is obtained as the major product. The reactions are given below:
Hence, option B is correct.

Note:Phenol has various applications. It is used as a precursor in drugs, in the production of nylon, as an antiseptic and also to preserve vaccines. Moreover, derivatives of phenol are used in beauty products like hair color and sunscreen.