Question

Aniline and Benzyl amine cannot be distinguished by azo dye test.
(A) True
(B) False

Answer 1

The azo-dye test is performed to test the presence of the amine group in the aromatic amines and for this the amines are treated with a cold acidic solution of sodium nitrate which results in the formation of the azo dye.

Complete step by step solution
Aniline consists of the amine group attached to the benzene ring and has the formula ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{N}{{\text{H}}_{\text{2}}}$ while the benzyl amine has the formula ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{C}{{\text{H}}_{\text{2}}}\text{N}{{\text{H}}_{\text{2}}}$ . From the formulae it can be seen that both the amines have the aryl groups present in their structure and thus both will react with the cold dilute solution of sodium nitrite to form the azo dyes. These azo dyes are very unstable in nature and cannot remain stable beyond $\text{0 - }{{\text{5}}^{\text{0}}}\text{C}$ . The azo dye that is formed due to the reaction between the benzyl amine and the acidic solution of sodium nitrite is not stable and decomposes to form benzyl alcohol and nitrogen gas.
But the reaction of aniline with the cold dilute solution of sodium nitrite gives the azo dye that is stable in the cold temperature range.
Hence, Aniline and Benzylamine can be distinguished by azo dye test and so the correct option is B, False. The reactions involved in the process can be mentioned as follows:
${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{N}{{\text{H}}_{\text{2}}}\xrightarrow{\text{NaN}{{\text{O}}_{\text{2}}}\text{+HCl }{{\left( )-5 \right)}^{0}}\text{C}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{{\text{N}}_{\text{2}}}\text{C}{{\text{l}}^{\text{-}}}\text{+NaCl + 2}{{\text{H}}_{\text{2}}}\text{O}$ (Test for aniline)
${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{C}{{\text{H}}_{\text{2}}}\text{N}{{\text{H}}_{\text{2}}}\xrightarrow{\text{NaN}{{\text{O}}_{\text{2}}}\text{+HCl }{{\left( )-5 \right)}^{0}}\text{C}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{C}{{\text{H}}_{\text{2}}}{{\text{N}}^{\text{+}}}_{\text{2}}\text{C}{{\text{l}}^{\text{-}}}\xrightarrow{\text{Unstable}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}\text{C}{{\text{H}}_{\text{2}}}\text{OH +}{{\text{N}}_{\text{2}}}\text{ +HCl }$ (Test for Benzyl amine).

Hence, option B is correct.

Note
Azo dyes are the organic dyes with the functional group $\text{R-N=N-}{{\text{R}}^{\text{,}}}$ in which the ‘R’ group is an aryl group. They are commercially important compounds and are used as a colouring agent in the textile industry, leather industry, and as a food colour.