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

The given reaction is a coupling reaction between phenol and diazonium salts. Coupling reactions between diazonium salts and a phenol or an amine are electrophilic substitution reactions. In alkaline medium, phenol forms phenoxide ion which is more electron rich than phenol and hence more reactive for electrophilic attack. The electrophile in this reaction is aryldiazonium cation. Evidently, stronger the electrophile faster is the reaction. New due to the electronwithdrawing effect of the -`NO_2` group, p-nitrophenyldiazonium cation is a stronger electrophile than p-toluenediazonium cation because + I effect of `CH_3` group reduces the electrophilicity of the p-toluenediazonium cation. Hence, p-nitrodiazonium cation couples preferentially with phenol to form 4-hydroxy-4-nitroazobenzene as the major product.