A solution contains 1g mol. Each of p-toluene diazonium chloride and p-nitrophenyl diazonium cholride. To this 1g mol.of alkaline solution of phenol is added. Predict the major product. Explain your answer.

Explanation

In alkaline medium, phenol forms phenoxide ion which is more electron rich and hence more reactive than phenol. Coupling reactions between diazonium salts is an example of electrophilic aromatic substitution. In this reaction, diazonium salt acts as the electrophile and phenoxide ion as the nucleophile. evidently stronger the electrophile faster is the reaction. Now due to electrowithdrawing effect of the `-NO_(2)` group, p-nitrophenyldiazonium cation is a stronger electrophile than p-toluenediazonium cation (+I-effect of `CH_(3)` grou reduces its electrophilicity) and hence couples preferentially with phenol to form 4-hydroxy-4'-nitroazobenzene as the major product.