Question

Which one of the following is not the correct reaction of aryl diazonium salts?
(A) \[{C_6}{H_5}N_2^ + C{l^ - } + C{u_2}C{l_2} \to {C_6}{H_5}Cl\]
(B) \[{C_6}{H_5}N_2^ + C{l^ - } + HB{F_4} \to {C_6}{H_5}F\]
(C) \[{C_6}{H_5}N_2^ + C{l^ - } + {H_3}P{O_2} \to {C_6}{H_5}P{O_4}\]
(D) \[{C_6}{H_5}N_2^ + C{l^ - } + SnC{l_2}/HCl \to {C_6}{H_5}NHN{H_2}\]

Answer 1

Hint: To answer this question, we must first know what aryl diazonium salts are. They are basically chloride salts of di-nitro substituted benzene rings which form important intermediates.

Complete step by step solution:
We should know that aryl diazonium salts usually react with nucleophiles with a loss of nitrogen from its structure. Since, this leaving group of Nitrogen is very stable, these reactions are favored energetically.
The most widely practiced reaction of diazonium salts is azo coupling. In this process, the diazonium compound is attacked by, i.e., coupled to, electron-rich substrates. When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution:
Let us now look at the options provided to us:
The first reaction given here is actually a Sandmeyer reaction catalyzed by a cuprous salt.
The second reaction is called Schiemann reaction by which fluoride substitution occurs.
But the third reaction given here is incorrect because reaction with hypophosphorous acid simply produces benzene by reductive removal of nitro groups. Unlike the nucleophilic substitution reactions, this reduction probably proceeds by a radical mechanism. The correct reaction should have been:
\[{C_6}{H_5}N_2^ + C{l^ - } + {H_3}P{O_2} \to {C_6}{H_6} + {N_2} + {H_3}P{O_3} + HCl\]

Hence, the answer is Option (C) \[{C_6}{H_5}N_2^ + C{l^ - } + {H_3}P{O_2} \to {C_6}{H_5}P{O_4}\]

Note: Diazonium compounds are standard reagents used in synthesis of organic compounds, especially aryl derivatives. But the first use of diazonium salts was to produce water-fast dyed fabrics by immersing that fabric in an aqueous solution of the diazonium compound, followed by immersion of the same in a solution of the electron-rich ring that undergoes electrophilic substitution. The major applications of diazonium compounds are in the dye and pigment industry.