question_answer

Which will not go for diazotisation?

A)  \[{{C}_{6}}{{H}_{5}}N{{H}_{2}}\]

B)  \[{{C}_{6}}{{H}_{5}}C{{H}_{2}}N{{H}_{2}}\]

C)  

D)  

Correct Answer: B

Solution :

 Only \[{{1}^{o}}\] aromatic amine (primary aromatic amine) form diazonium salts at low temperature \[({{0}^{o}}-{{5}^{o}}C)\]. A reaction in which \[-N{{H}_{2}}\] group is converted into diazo group \[(-\overset{+}{\mathop{N}}\,\equiv N)\]is called diazotisation. Diazotised salts are stable in cold aqueous solution. \[{{C}_{6}}{{H}_{5}}N{{H}_{2}}+HCl\xrightarrow{{{0}^{o}}-{{5}^{o}}C}{{C}_{6}}{{H}_{5}}\overset{+}{\mathop{N{{H}_{3}}}}\,C{{l}^{-}}\] \[NaN{{O}_{2}}+HCl\xrightarrow{{{0}^{o}}-{{5}^{o}}C}HN{{O}_{2}}+NaCl\] \[{{C}_{6}}{{H}_{5}}\overset{+}{\mathop{N{{H}_{3}}}}\,C{{l}^{-}}+HN{{O}_{2}}\xrightarrow{{{0}^{o}}-{{5}^{o}}C}\] \[{{C}_{6}}{{H}_{5}}\overset{+}{\mathop{{{N}_{2}}C{{l}^{-}}}}\,+2{{H}_{2}}O\] aromatic primary amines,  so undergo diazotisation but \[{{C}_{6}}{{H}_{5}}C{{H}_{2}}N{{H}_{2}}\] (aliphatic amine) will not undergo diazotisation.