Question

Liebermann’s nitroso reaction is used for testing.
$\left( A \right)$ Primary amines
$\left( B \right)$ Secondary amines
$\left( C \right)$ Tertiary amines
$\left( D \right)$All the above

Answer 1

Liebermann’s nitroso reaction is given by phenol, secondary amine (both aliphatic and aromatic) and containing nitroso group. Secondary amines show a distinguished test, Known as Liebermann’s nitroso reaction.

Complete step by step answer:
Because $2$ degree amine is converted into nitrosamine by treating the amine with $HN{O_2}$. On warming the phenol and conc.${H_2}S{O_4}$ Brown red color is formed at first, which changes to blue then green. Color changes to red on dilution and further to greenish blue or violet on treatment with alkali.
Secondary amines (aliphatic or aromatic) react with nitrous acid to form $N$-nitroso amines. The reaction is given below
${\left( {C{H_3}} \right)_2}N - N = O + HONO \to {\left( {C{H_3}} \right)_2}N - N = O + {H_2}O$
Where ${\left( {C{H_3}} \right)_2}N - N = O$ is $N -$Nitrosodimethylamine.
Nitrosamines are water soluble yellow oils and when warmed with phenol and few drops of conc.${H_2}S{O_4}$ Produce a green color solution which turns blue on adding alkali. This reaction is called Liebermann’s nitroso reaction. Tertiary amine do not react with nitrous acid.
Hence, the Option $\left( B \right)$ is correct.

Additional information: The Liebermann reagent named after Hungarian chemist Leo Liebermann $\left( {1852 - 1926} \right)$ is used as a simple as well as other compounds. It is composed of a mixture of potassium nitrite and concentration sulfuric acid. $1$ g of potassium nitrite is used for every $10$ mL of sulfuric acid.

Note:
The test is performed by scraping off a small amount of the substance and adding a drop of the reagent(which is initially clear and colorless). The results are analyzed by viewing the color of the resulting mixture, and by the time taken for the change in color to become apparent.